EGU General Assembly 2022  

Many sectors of society are vulnerable to decadal changes in climate, which impact food security, freshwater availability, spread of pests and diseases, heat waves, droughts, floods, cyclones, wildfires, energy supply and demand, transport, migration, and conflict. On decadal timescales climate is influenced by both internal variability and changes in radiative forcing. Climate predictions that are initialised with observations are needed to account for all of these factors and will be reviewed in this talk.

Understanding the drivers of decadal climate is crucial for gaining confidence in forecasts. One hypothesis, namely that Arctic sea ice loss weakens mid-latitude westerly winds, promoting more severe cold winters, has sparked more than a decade of scientific debate. The Polar Amplification Model Intercomparison Project was developed to address this issue and results from coordinated multi-model experiments will be presented that support the above hypothesis and suggest that this effect is underestimated by current models. However, even when accounting for this underestimation, the response to Arctic sea ice is small compared to yearly variations in mid-latitude winters.

For predictions to be useful they must be skilful and reliable. There is mounting evidence that models may underestimate the strength of predictable signals, especially for atmospheric circulation in the North Atlantic. This error has been termed the “signal-to-noise paradox” since it leads to the unexpected situation that models can predict the real world better than one of their own ensemble members. Skilful predictions can be achieved using a very large ensemble, but the model output cannot be taken at face value and needs calibrating to obtain skilful and reliable forecasts. Given the potential impacts of changes in atmospheric circulation, understanding why the signal-to-noise ratio is too small in current climate models, and assessing the extent to which correcting this model error would reduce uncertainties in regional climate change projections of the coming decades, are high priority areas for future research.

How to cite: Smith, D.: Decadal climate predictions, impacts of Arctic sea ice loss, and the signal-to-noise paradox, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2912, https://doi.org/10.5194/egusphere-egu22-2912, 2022.

  The Milankovitch Theory of orbital climate change postulates that changes in the caloric summer half-year insolation (or Northern Hemisphere summer insolation (NHSI) at ~65°N latitude) drive changes in the ice-sheets extent (i.e., global ice-volume) at Earth’s orbital periods (i.e., the sensu-stricto theory). These insolation-driven changes in turn, incite ancillary changes in other parts of the global climate systems via various forcing and feedback mechanisms (the sensu-lato hypothesis). In this theoretical framework the high-latitude glaciation processes took the center stage while the low-latitude global monsoon was essentially excluded. In the last two decades, large numbers of cave d¹⁸O records with precise radiometric chronologies have propelled speleothems to the forefront of paleoclimatology. Of particular interest are the speleothem records from North America that reveal a persistent orbital pacing of the North American climate at the precession band, which is nearly in phase with changes in the global ice-volume and atmospheric CO₂ but lags June insolation at 65°N by ~5000 years, in accordance with the sensu-stricto Milankovitch theory. Contrastingly, the low-latitude tropical speleothem records manifest an orbital-scale pattern of global monsoon, which is dominated by precession cycles with a nearly anti-phased relation between the two hemispheres. Importantly, the monsoon variations track summer (July/January) insolation without significant lags at the precession band. We thus suggest that precession-induced changes in summer insolation produce distinct climate variability in the ice-sheet proximal and tropical regions predominantly via the (delayed) ice-volume/CO₂ forcing/feedbacks and nearly-in-phase monsoon/CH₄ responses/feedbacks.

  As for global-scale millennial events that were superimposed on orbital-scale climate variations, the essence of these events—i.e., conventional ice age terminations and other smaller events (the so-called ‘low-amplitude versions of terminations’), is virtually similar. The time-series of millennial-scale variations after removing orbital insolation signals from the speleothem monsoon record and long-term trend in the Antarctic ice core temperature (δD) record characterize the millennial climate variances of both ice age termination and low-amplitude versions of termination events. Remarkably, the millennial-scale variations show significant obliquity and precession cycles that are in-phase with North Hemisphere June insolation, implying a critical role of changes in orbital insolation in triggering the ice age terminations. These observations, in turn, provide new insights into the classic ‘100 ka problem’.

  Indeed, a more comprehensive picture of orbital theory of climate is steadily emerging with the growth of new geological proxy data, particularly the low-latitude speleothem data from the vast global monsoon regime, providing critical complements to marine and ice-core data.

How to cite: Cheng, H.: Milankovitch Theory and Global Monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1422, https://doi.org/10.5194/egusphere-egu22-1422, 2022.

Due to their relevance for regional weather and climate, teleconnections are an extremely active area of research. One key task is to quantify the contribution of a teleconnection to regional anomalies in both models and observations. This is, for instance, important to improve forecasts on time scales ranging from subseasonal to multidecadal, or to attribute ensemble spreads to changes in large-scale drivers. However, robustly estimating the effects of a teleconnection remains challenging due to the often simultaneous influences of multiple climate modes. While physical knowledge about the involved mechanisms is often available, how to extract a particular causal pathway from data are usually unclear.

In this talk I argue for adopting a causal inference-based framework in the statistical analysis of teleconnections to overcome this challenge. A causal approach requires explicitly including expert knowledge in the statistical analysis, which allows one to draw quantitative conclusions. I illustrate some of the key concepts of this theory with simple examples of well-known atmospheric teleconnections. Moreover, I show how the deductive nature of a causal approach can help to assess the plausible influence of Arctic sea ice loss on mid-latitude winter weather, thereby helping to reconcile differences between models and observations. I finally discuss the particular challenges and advantages a causal inference-based approach implies for climate science.

References

Kretschmer, M., Adams, S. V., Arribas, A., Prudden, R., Robinson, N., Saggioro, E., & Shepherd, T. G. (2021). Quantifying Causal Pathways of Teleconnections, Bulletin of the American Meteorological Society, 102(12), E2247-E2263. Retrieved Jan 13, 2022, from https://journals.ametsoc.org/view/journals/bams/102/12/BAMS-D-20-0117.1.xml

Kretschmer, M., Zappa, G., and Shepherd, T. G. (2020), The role of Barents–Kara sea ice loss in projected polar vortex changes, Weather and Climate Dynamics, doi: 10.5194/wcd-1-715-2020

How to cite: Kretschmer, M.: Quantifying Causal Pathways of Teleconnections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8246, https://doi.org/10.5194/egusphere-egu22-8246, 2022.

The representation of the South American Monsoon System (SAMS) by global climate models (GCMs) is of key relevance for a better comprehension of the physical mechanisms behind the recent and future climate changes over South Tropical South America (STSA) in a global warming scenario. During the last four decades STSA experimented a lengthening of the dry season related to diverse forcings, leading to an increase in fire activity and severe socio-environmental impacts. In the present study, a set of 16 GCMs simulations from the CMIP6 experiment were evaluated during the historical period 1979-2014 in terms of how well they reproduced the atmospheric circulation over STSA through a weather-typing (WTs) approach. 9 WTs were first identified based on low-level wind anomalies from the ERA5 reanalysis, which summarized the atmospheric variations over STSA throughout the year. Focus was put on the representation of WTs during the SAMS initiation and the dry-to-wet transition season (from July to October). Model performance depended on the seasonal cycle and spatial structure of the WTs. Some of the GCMs adequately reproduced the different WTs and their spatio-temporal configurations, with lower skills in the transition seasons. Furthermore, GCMs tended to go from dry to wet conditions too quickly, evidencing deficiencies in the representation of the SAMS onset. This was particularly associated with a poor representation of the southerly wind intrusions to STSA and the intra-seasonal variability of the South American low-level jet. In terms of the relationship between WTs and rainfall on interannual time-scales, a selection of GCMs was able to associate the occurrence of anomalous wet and dry years with specific WTs, indicating well-represented physical processes modulating precipitation variability. Overall, this study could identify few GCMs that managed to simulate the main atmospheric circulation features in STSA (among them, the CESM2, CMCC-CM2-HR4 and MPI-ESM1-2-HR models), which is particularly important for driving high-resolution modelling experiments as well as for the analysis of future projections.

How to cite: Olmo, M., Espinoza, J. C., Bettolli, M. L., Sierra, J. P., Junquas, C., and Arias, P.: Process-based GCMs evaluation over South Tropical South America during the dry-to-wet transition season following a weather typing approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-133, https://doi.org/10.5194/egusphere-egu22-133, 2022.

Rising sea levels in the 21^st century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming.

Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.

How to cite: Creel, R., Austermann, J., Kopp, R., Khan, N., Ashe, E., Kingslake, J., and Albrecht, T.: Probabilistic Estimation of mid-Holocene global mean sea level, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1953, https://doi.org/10.5194/egusphere-egu22-1953, 2022.

The beachrock formations represent a significant paleo-environmental proxy because they can record both the vertical and the horizontal evolution of the coastline. They have been used to assess Holocene coastline evolution and crustally induced relative sea level (RSL) change, notably in the Sea of Marmara. In this study, we report existence of the less known submerged beachrocks in the nearshore coastal area of Tekirdag city (Altinova), the northern Sea of Marmara. The beachrocks found in the Tekirdag coastline are locally spread, parallel to the coastline with an extend of about 5 km and at depths ranging from -2 to 0m below present sea level. The beachrock is defined by a calcite-cemented shoreline sandstone. The cement mineralogy and morphology of the beachrocks are indicative of the diagenetic environment, and therefore the examination of the cement characteristics and microstratigraphy can allow identify the type of cement and spatial relationship between the past shoreline and beachrock formation zone.

The Tekirdag coastal area is located in the western Marmara Region. The western coasts of the Marmara Region include a number of natural features inherited from their coastal evolution. Besides, relative sea level change during late Quaternary in this region and its vicinity are generally not homogeneous as a result of the tectonic activity controlled by the North Anatolian Fault Zone (NAFZ) which played a crucial role in the coastline evolution at different periods of the region.

The aim of our study to reconstruct the shoreline modification using beachrocks in the study area. For this purpose, we coupled a series of methodologies for the paleo-environmental and geomorphological study of the coastal zone and the shallow submarine area, which included: a) coring from submerged beachrocks, b) petrographic and microstratigraphic analyses of cementation, c) monitoring of underwater beachrocks and coastal zone by drone and e) dating the formation of beachrocks. Through our analyses we aim to better contribute the use of beachrocks as accurate proxies for the RSL variation in the study area.

How to cite: Tarı, U., Sunal, G., Özcan, O., and Yaltırak, C.: Submerged beachrock: A tool for reconstructing relative sea level change example from Tekirdag coastline, Sea of Marmara, Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5004, https://doi.org/10.5194/egusphere-egu22-5004, 2022.

We present new proxy-based sea-level reconstructions for southern New Zealand spanning the last millennium. These palaeo sea-level records usefully complement sparse Southern Hemisphere proxy and tide-gauge sea-level datasets and, in combination with instrumental observations, can test hypotheses about the drivers of 20^th century global sea-level change, including land-based ice melt and regional sterodynamics. We develop sea-level transfer functions from regional datasets of salt-marsh foraminifera to establish a new proxy-based sea-level record at Mokomoko Inlet, at the southern tip of the South Island, and to improve the previously published sea-level reconstruction at Pounawea, located about 110 km to the east. Chronologies are based on radiocarbon, radiocaesium, stable lead isotope and pollen analyses. Both records are in good agreement and show sea level several decimetres below present over the last millennium, before a rapid sea-level rise in the first half of the 20^th century that reached maximum rates in the 1940s. Previously reported discrepancies between proxy-based sea-level records and tide-gauge records are partially reconciled by accounting for barystatic and sterodynamic components of regional sea-level rise. We conclude that the rapid sea-level rise during the middle 20^th century along the coast of southern New Zealand was primarily driven by regional thermal expansion and ocean dynamics.

How to cite: Garrett, E., Gehrels, R., Hayward, B., Newnham, R., Gehrels, M., Morey, C., and Dangendorf, S.: Late Holocene sea-level change in southern New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5675, https://doi.org/10.5194/egusphere-egu22-5675, 2022.

Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ¹⁸O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT is also an important tool for forecasting effects of anthropogenic climate change.

Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (K-feldspar only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), the combination with in-situ Sr-isotope fingerprinting and ⁸⁷Rb/⁸⁷Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, recovered from the Weddell Sea, ca. 750 km from the continental rise in 4671 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14.09 to 14.26 Ma.

Our findings are consistent with predictions made by recent palaeo-ice sheet models (eg., Gasson et al. 2016), which predict the development of sizeable and discrete embayments around the continent, including the Weddell Sea. We argue that the IRD derived from the unstable sector associated with this embayment formation at the time.

Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).

Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.

Gasson, E, et al., 2016, Proceedings of the National Academy of Sciences, v. 113, (13), p. 3459-3464, doi: www.pnas.org/cgi/doi/10.1073/pnas.1516130113.

Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.

How to cite: Neofitu, R., Mark, C., O'Connell, S., Kelley, S., Rösel, D., Zack, T., Flowerdew, M., and Daly, J. S.: Tracking ice-sheet dynamics by detrital feldspar Pb-isotope and 87Rb/87Sr dating during the Middle Miocene Climatic Transition, Weddell Sea, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6484, https://doi.org/10.5194/egusphere-egu22-6484, 2022.

Tillandsia landbeckii is a bromeliad that inhabits the hyperarid coast of the Atacama Desert where it survives solely on moisture and nutrients from fog. It does so by constituting a unique dune ecosystem that maximizes its fog capture potential as well as preserving layers of buried tillandsia plants. These buried layers can survive over multiple millennia and here we present data based on stratigraphic, radiocarbon, stable isotopes, and leaf wax analyses that we are applying to these ancient leaves and stems to reconstruct past variations in fog moisture and nutrient cycling. Some of the oldest buried layers date back to >10,000 14C yrs BP and our results show that both d15N and leaf waxes are capable of tracking variations in moisture changes although we observed significant variation in d15N values across living plants which may be due to the plants' age. Past variations in fog likely track variations in large-scale synoptic climate features such as the height of the Marine Boundary Layer and the strength of the Southern Pacific Anticyclone.

How to cite: Latorre, C., Contreras, S., Jaeschke, A., Garcia, J. L., and del Río, C.: Ancient Tillandsia landbeckii dune ecosystems and their potential to reveal past variations in coastal fog moisture during the Holocene in the Atacama Desert, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7988, https://doi.org/10.5194/egusphere-egu22-7988, 2022.

Proglacial sediments hold continuous and high-resolution records of past glacier dynamics. In this study, we examine the sediments of Eyre Fjord (Chilean Patagonia, 49°S), which is fed by Pio XI Glacier, to gain a better understanding of how the surging phase of a growing glacier is recorded in marine sediments. Pio XI Glacier has experienced a net advance of >10 km since 1945 and has had several surging phases that each last 2 – 3 years and occur every ~14 years. The last reported surging phases happened between 1976 – 1979, 1997 – 1998, and 2014 – 2018. Thirty CTD profiles taken in the fjord along one longitudinal and three transverse transects in February 2019 show that sediment transfer through the fjord during a quiescent (i.e., non-surging) phase in summer primarily happens by means of widespread (unchannelised) hyperpycnal flows that are 20 – 100 m thick. To assess spatiotemporal variability in sedimentation throughout the fjord, nine sediment cores were collected in 2019. Concentrations of short-lived radionuclides suggest a sedimentation rate of 3 – 20 cm/year. Sediment grain size and magnetic susceptibility, (CT) density, and inorganic geochemistry (Fe, Ti, K, Mn, Zr, Zn, Rb, Sr), which were obtained at higher resolution, were used as proxies for hydrodynamic conditions in the fjord. The longest sediment record holds fine glacial mud and low density sediments between 135 – 70 cm and in the upper 10 cm, which indicate relatively low hydrodynamic activity, likely corresponding to the quiescent phases before 2014 after 2018. Between 70 cm and 10 cm, the overall denser and coarser sediments intercalated with cm-thick sandy layers indicate higher hydrodynamic activity and flood events, most likely representing the most recent (2014 – 2018) surging phase of the glacier. Interestingly, the thickest and coarsest flood deposits seem to be concentrated at the top of the sediment unit that represents the surging phase suggesting that the floods are the most intense towards the end of the surging phase. Overall, these results show that quiescent and surging phases of surge-type glaciers leave distinct sedimentary signatures in fjord sediments, offering the possibility to use longer sediment records to identify former surging phases.

How to cite: Piret, L., Bertrand, S., and Moffat, C.: Fjord sedimentary signature of the last surging phase of Pio XI Glacier (Chilean Patagonia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10055, https://doi.org/10.5194/egusphere-egu22-10055, 2022.

Marine sediment cores containing a unique Pliocene paleoenvironmental record were collected from the East Antarctic Wilkes Land continental rise by the IODP Expedition 318 at Site U1361 (Escutia et al., 2011). Site U1361 is located in front of the Wilkes Subglacial Basin (WSB) were, today, the East Antarctic Ice Sheet (EAIS) is grounded below sea level (marine-based) and therefore more vulnerable to climate changes.

We have conducted a facies analysis using shipboard measurements taken during Expedition 318 (i.e., physical properties data such as density (GRA) and magnetic susceptibility (MST) and high-resolution digital images), complemented with continuous elemental geochemical analyses. In addition, we have conducted high-resolution siliceous microfossil analyses to characterize past “warmer-than-present” intervals during the Pliocene warm period (~ 3-5 Ma) and their terminations recorded in site U1361 between ~ 73 to 123 mbsf. Our study is complemented by a pilot high-resolution detailed work on siliceous microfossils conducted from 3.69 to y 3.56 Ma that captures changes in sea ice cover and oceanic conditions (Armbrecht et al., 2018).

Preliminary analyses show that sediments consist of alternating intervals of interglacial diatom-rich/bearing silty clay with dispersed clasts that are ~ 0.5 to 8 m thick, and glacial sparsely laminated bioturbated clays with occasionally dispersed clasts.  In general, interglacial sediments is characterized by lower density, higher MST values, lower Mn/Ti and Fe/Ti ratios, and high Ca/Al, Si/Al, and Ba/Al ratios. Bioturbated clay with any dispersed clasts has a marked opposite trend (i.e., higher density, lower MST values, lower Ca/Al, Si/Al, and Ba/Al ratios and higher Mn/Ti and Fe/Ti ratios). This changes in lithology, physical properties and geochemical composition record significant changes in paleoenvironmental conditions. However, each glacial/interglacial (and vice versa) period exhibit specific characteristics and diatom associations pointing to different sea ice conditions during the selected Pliocene intervalsthat can be indirectly linked to ice-sheet dynamics in the Wilkes Subglacial Basin. The results of this study are relevant in order to understand the response of the EAIS dynamics and marine biota to an increase of the ocean surface temperatures during the transition from atmospheric CO₂ concentrations similar to pre-industrial to concentrations close to present values (410 ppm).

This work has been conducted in the frame of projects H2020-MSCA-IF-2018-ANTICE-841980/CTM2017-89711-C2-1-P and is a contribution to the SCAR INSTANT Program.

Escutia, C. et al., 2011 doi:10.2204/​iodp.proc.318.105.2011

Armbrecht et al., 2018. doi:10.1016/j.marmicro.2017.10.008

How to cite: Gutiérrez-Pastor, J., Escutia, C., Jiménez-Espejo, F. J., Rigual-Hernández, A. S., Bárcena, M. Á., McKay, R., and Morales, C.: Sedimentological facies characterization of Pliocene key interglacial-glacial intervals, IODP site 1361A, East Antarctic Wilkes Land margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10174, https://doi.org/10.5194/egusphere-egu22-10174, 2022.

Thwaites Glacier (TG) is thinning and accelerating while sitting on a landward-dipping bed, with an ice shelf that is rapidly disintegrating and losing its ability to buttress ice flow from upstream, and is in deep water that allows warm Circumpolar Deep Water (CDW) to reach its grounding zone.  Significant retreat of TG would trigger loss of ice across the region.  In recent decades, the mass balance of TG has become increasingly negative, suggesting that unstable retreat may have already begun.  The Thwaites Offshore Research (THOR) group has just completed four field deployments aimed at understanding the recent history of TG and neighboring ice, including Pine Island Glacier (PIG).  Three cruises on the RVIB N.B. Palmer, combined with sub-ice-shelf sediment coring, provide a suite of new data along the TG and PIG margins.  Data include multibeam surveys, 3.5 kHz subbottom profiler, over 100 new sediment cores, and high-resolution seismic profiles.  Break-up of floating ice cover in front of TG in 2019 allowed surveying of previously unmapped seafloor.  Major calving of PIG in 2020 allowed marine surveying over the locations where sub-ice-shelf cores were collected in the past, allowing direct ties between ice-based and marine work.  As of this writing in January 2022, we are entering into the Amundsen Sea for our third marine field season. 

Sediment cores record the history of grounding-zone retreat and ice interaction with the ocean over timescales from decades to several thousand years.  Proxies used to reconstruct ice and ocean histories include sedimentary facies analysis, diatom and foraminiferal assemblage data, and geochemical analyses.  Sedimentological analyses show a diverse array of lithofacies attributed to different environmental conditions.  Many cores across the region contain laminated mud with sparse gravel and sand, suggesting deposition of meltwater deposits. Downcore ²¹⁰Pb measurements are used to create age models of the past ~100 years.  Combination of ages with facies models, including CT scans, reveals that the progressive detachment of Thwaites from pinning points began in the mid twentieth century, coincident with retreat of PIG (Smith et al., 2017) and with increasing advection of warm water onto the Amundsen shelf (Hillenbrand et al., 2017).  Conversely, Cranton Bay, to the northeast of PIG and separated from Pine Island Bay by a shallow sill, appears to be characterized by cold deep water and high productivity, allowing it to serve as an endmember different from the records obtained proximal to the large glacial outlets where CDW is impinging.

The satellite record of glacial retreat is inherently short.  Observations are accumulating about forcing mechanisms that can impact the stability of ice, such as increased CDW on the Amundsen Sea shelf.  However, without the time to observe the response of the ice, discovery of the forcing mechanisms is just half the story.  The other half of the story is completed by using the paleo record to see how ice has responded to drivers in the past.

How to cite: Wellner, J., Clark, R., Lehrmann, A., Lepp, A., Hillenbrand, C.-D., Totten, R., Simkins, L., Comas, M., Mawbey, E., Hopkins, R., Smith, J., Anderson, J., Hogan, K., Nitsche, F., Graham, A., and Larter, R.: Pre-satellite retreat of Thwaites and Pine Island glaciers: Recent results from sediment cores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10609, https://doi.org/10.5194/egusphere-egu22-10609, 2022.

Climate Change has increased the intensity, duration, and frequency of extreme weather events such as heatwaves (HW), which have impacts on ecosystems, economics, and human populations, including adverse health effects and the increase in the number of deaths due to the heat stress. However, there are still few studies evaluating the occurrence of adverse health due to HW in South America. Particularly in Brazil, regional differences in the effects of heatwaves are expected due to their continental dimensions, which makes it necessary to carry out local studies. This work presents a long term analysis of the occurrence of HW in the 14 major metropolitan regions (MRs) in Brazil, namely: Manaus, Belém, Salvador, Recife, Fortaleza, Goiânia, Brasília, Cuiabá, São Paulo, Rio de Janeiro, Belo Horizonte, Porto Alegre, Curitiba and Florianópolis. Observational temperature data (1970-2020) provided by the National Institute of Meteorology (INMET) were used to compute the Extreme Heat Factor (EHF) index, which was used to identify and classify HW in terms of severity.  Significant and positive trends in the frequency of HW were observed over decades in all MRs, particularly in the north (Manaus and Belém) and central west region (Goiania and Brasilia). Particularly, from 2014 to 2019, all the MRs presented HW regime every year, including severe and/or extreme events. In general, the longest and the most intense HW in Brazilian MRs occurred in the last decade (2010-2020), with the exception of the 1997–1998 El Niño-related events. Daily mortality and hospital admission data from the Brazilian Public Health System (SUS) were used to assess the relationships between HW and health. Results indicate excess mortality (observed to expected ratio) during HW events in the MRs studied, with the elderly being the most vulnerable age group, in agreement with previous studies. The cause of death and the gender susceptibility to HW were also analyzed, and the results vary among the different MRs. This work provides an extensive characterization of the occurrence of HW in Brazil and valuable insights for the implementation of public mitigation and adaptation strategies in some of the most populated regions of South America.

This work was supported by FIOCRUZ [grant VPPCB-003-FIO-19] and FAPERJ [grant E26/202.714/2019]. D.M.S. was supported by FIOCRUZ [grant VPPCB-003-FIO-19].

How to cite: Monteiro dos Santos, D., N. Garcia, B., L. Geirinhas, J., Russo, A., F. Peres, L., and Libonati, R.: Long term characterization of heat waves in Brazil and their impacts on mortality rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10721, https://doi.org/10.5194/egusphere-egu22-10721, 2022.

Most relative sea level (RSL) curves in Norway have been solidly constructed using sea-level index points (SLIPs) from isolation basins. Many of these curves show RSL falling at a slow and steady rate to modern sea level during the late Holocene, despite a lack of SLIPs younger than ca. 2000 years. Tide gauge records from southern and western Norway indicate that RSL may have been rising since they were installed (ca. 100 years ago), while the few RSL curves with one or two SLIPs younger than 2000 years BP hint that rates of sea-level fall accelerated during this period. This study aims to close the gap between palaeo and instrumental data by generating late Holocene SLIPs from low-elevation and intertidal basins in southwestern Norway. Geochemical analyses of the sediment cores from all the studied areas thus far suggests that marine influence has been increasing in recent centuries, possibly due to rates of eustatic sea level rise overtaking residual glacioisostatic adjustment (ca. 1-2 mm/yr) from the Last Glacial Maximum. Anecdotal evidence from local residents of Egersund, with family histories and records of past storm levels going back to the 1800s, confirm this. Discrete storm layers consisting of shell fragments in one salt marsh at the back of a sheltered intertidal basin, however, may be overprinting any subtle trends in recent RSL rise. Full results of multi-proxy analyses of 8 cores from four salt marshes and protected, intertidal basins with bedrock sills will be presented from the southwestern corner of Norway.

How to cite: Holthuis, M., Nixon, F. C., Kylander, M., van der Bilt, W., Martin, J., and Lakeman, T.: Late Holocene sea-level change and storms in southwestern Norway based on new data from intertidal basins and salt marshes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12297, https://doi.org/10.5194/egusphere-egu22-12297, 2022.

Our team has previously built a ~7500 year tsunami history for the northern patch of the Sunda Megathrust. However, the paleo-tsunami history south of Aceh province and the 2004 rupture patch remains poorly understood. We conducted geological investigation to better define the boundaries of rupture patches along the Megathrust.

We utilized satellite imagery to pinpoint potential sites likely to archive evidence of paleo tsunami inundations and co-seismic land-level change. Due to the continuing Covid-19 pandemic and restrictions, our researchers from Singapore, and USA could not travel to Indonesia. However, because of the longstanding close collaboration between the Earth Observatory of Singapore and Syiah Kuala University, Banda Aceh, Indonesia, the project continued to progress. The Syiah Kuala University team investigated nearly 20 sites between Banda Aceh in the northern patch of the of Sumatra Megathrust and Padang in the south. Several sites preserved probable paleo-tsunami sediments. The paleo-tsunami sediments were identified from anomalous layers of sand in low energy environments where they would not normally occur, such as mangroves, coastal lowlands, and/or swales.

 
Here we present results of litho-, bio- and chronostratigraphical analysis from Susoh as well as preliminary information from sites along the coastline between Meulaboh and Padang. From Susoh we described stratigraphy from a series of cores to a depth of 4.75 m. The top 2.5 meters was dominated by muds typical of estuarine or tidal flat settings, but it is interrupted by three pulses of sandy muds. At 2.55 m we encountered a 0.2 m thick layer of course sand, underlain by a 0.5 m thick mangrove peat with a gradual transition into organic sandy muds and sands. Pollen analysis from the fine-grained organic layers indicate they were formed in a mangrove environment. Radiocarbon dating of the organic macrofossils from the mangrove peat indicate the tsunami event occurred post 1850 cal. yrs BP. Our research continues to improve our understanding of the Sumatran Megathrust.

How to cite: Majewski, J., Richards, G., Daly, P., Switzer, A., Ismail, N., Afrizal, T., Christie, M., and Horton, B.: Extending paleo-tsunami records south of the 2004 Indian Ocean Tsunami patch, Sumatra, Indonesia: 2022 update, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12629, https://doi.org/10.5194/egusphere-egu22-12629, 2022.

Predicted future climate scenarios share similar characteristics with the Eocene ‘greenhouse’ period. However, short-term Early Eocene terrestrial climate variability is still poorly constrained mainly due to the rarity of adequately resolved climate archives. This lack of information restricts not only the evaluation of past continental climate conditions but additionally limits regional climate modelling efforts but also the validation of model outputs. Here, we present highly-resolved biomarker-based (bacterial membrane lipid and leaf wax) paleoclimate data from the UNESCO World Heritage Site Messel Fossil Pit (Germany) that cover an interval of ca. 640 ka. The drilled Messel paleolake succession, characterized by finely laminated and frequently varved black pelites (referred to as ‘oil shale’) represent a regional climate and environmental archive from the latest Early to Middle Eocene (~48.0-47.4 Ma) of western Central Europe. Downcore mean annual air temperature (MAAT) reconstructions inferred from bacterial-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs) show a long-term cooling trend and range from 14 to 22°C. High-resolution sampling within the basal and middle core interval reveal several short-term negative temperature excursions of 4-5°C, respectively. Moreover, we measured compound-specific δ²H and δ¹³C of excellently preserved odd carbon numbered mid- and long-chain leaf wax n-alkanes in order to estimate past regional hydroclimatic conditions. δ²H values of terrestrial long- and aquatic mid-chain n-alkanes show exceptional variations of up to 45‰ and 60‰, respectively. In contrast, δ¹³C values of long-chain n-alkanes are within 5‰ (-28‰ to -33‰) while mid-chain δ¹³C values vary by 11‰, ranging between -26‰ and -37‰. Our results indicate that the Early to Middle Eocene temperature history of central western Europe, particularly on short geological timescales was much more variable than previously assumed. We recognize two abrupt shifts in MAAT that coincide with lower δ²H values and therefore may point to either wetter climate conditions or changed atmospheric moisture trajectories. We emphasize that the long-term decline in estimated MAAT towards the top of the Messel section has to our best knowledge not been quantified from any time-equivalent terrestrial archive in Central Europe, but resembles Early Eocene cooling patterns well-documented from the global oceans.

How to cite: Schmitt, C., Vasiliev, I., Martínez-García, A., and Mulch, A.: Variable Early Eocene continental hydroclimate in Central Europe?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1701, https://doi.org/10.5194/egusphere-egu22-1701, 2022.

The intensification of the Northern Hemisphere glaciations at the end of the Pliocene epoch represents one of the most substantial climatic shifts during Cenozoic. Paradoxically, sea surface temperatures in the high latitude North Atlantic Ocean increased between 2.9–2.7 Ma, against a background of global cooling and declining atmospheric pCO₂. To investigate the origin of this high latitude warming, we obtained sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. In fact, we find evidence for enhanced production of Mediterranean Outflow Water during the mid-Pliocene to late Pliocene. We argue that the injection of this warm water on intermediate levels drove a sub-surface heat channel into the high-latitude North Atlantic where it warmed the sea surface. We further used Earth System Models to numerically constrain the impact of enhanced Mediterranean Outflow Water production on the northward heat transport within the North Atlantic. In accord with the proxy evidence, the numerical model results show the formation of a sub-surface channel that funneled heat from the subtropics into the high latitude North Atlantic. We further suggest that warming of the North Atlantic realm by this mechanism might have substantially delayed ice sheet growth at the end of the Pliocene.

How to cite: Bahr, A., Kaboth-Bahr, S., Stepanek, C., Amorim Catunda, M. C., Karas, C., Ziegler, M., García-Gallardo, Á., and Grunert, P.: Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2042, https://doi.org/10.5194/egusphere-egu22-2042, 2022.

Cenozoic evolution of South Asian Monsoon and mechanisms driving changes recorded in the geological record remain highly debated. An intensification of monsoonal rainfall recorded in sediment archives from the earliest Miocene (23-20 million years ago, Ma) is generally attributed to Himalayan uplift. However, Indian Ocean paleorecords place the onset of strong monsoons around 13 Ma, linked to strengthening of the Somali Jet that forces Arabian Sea upwelling.  In this contribution we reconcile these divergent records using Ocean-Atmosphere and ocean biogeochemistry models. Our results show that factors forcing monsoon circulation versus rainfall are decoupled and diachronous : Asian topography predominantly controlled early Miocene rainfall patterns, with limited impact on ocean-atmosphere circulation. Yet the uplift of East African and Middle Eastern topography played a pivotal role in the establishment of modern Somali Jet structure above the western Indian Ocean, while strong upwelling initiate in response to the emergence of the Arabian Peninsula. Our results emphasize a polygenetic history of the South Asian Monsoon with multiple paleogeographic controls: although elevated rainfall seasonality was likely a persistent feature since the India-Asia collision in the Paleogene, the modern-like monsoonal atmospheric circulation was only reached recently, in the late Neogene.

How to cite: Sarr, A.-C., Donnadieu, Y., Bolton, C., Ladant, J.-B., Licht, A., Fluteau, F., Laugié, M., Tardif, D., and Dupont-Nivet, G.: Reconciling South Asian Monsoon Rainfall and Wind Histories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2399, https://doi.org/10.5194/egusphere-egu22-2399, 2022.

The Northern Annular Mode (NAM) is the leading mode of atmospheric climate variability in the middle and high Northern latitudes in the present-day climate. Its most prominent regional expression is the North Atlantic Oscillation (NAO), a mode of variability that is well-known and has a strong influence on North Atlantic weather patterns. According to the IPCC AR6 WGI report, the current generation of climate models are ‘skillful’ in simulating the spatial features and variance of the historical and present-day NAM/NAO. However, what kind of NAM or NAO patterns can we expect in a warm future climate?

To answer this question, we have performed equilibrium climate simulations of a warm ‘future’ as well as a warm past climate. Specifically, we have simulated the mid-Pliocene climate, a warm (~400 ppm CO₂) geological period approximately 3Ma ago, using a global coupled climate model (CESM1.0.5). Our simulations compare well to higher latitude sea-surface temperature reconstructions. We have performed sensitivity studies using a pre-industrial and a mid-Pliocene geography, as well as two levels of radiative forcing, as a part of intercomparison project PlioMIP2. But the question remains, to what extent can we treat the mid-Pliocene as an ‘analog’ for a future warm climate?

Looking at Northern hemisphere winter (DJF) sea-level pressure data, we find that the annular ‘belts of action’ move poleward partially due to increase in CO₂, but mainly due to the mid-Pliocene boundary conditions. Over the North Pacific Ocean, sea-level pressure variability slightly increases with CO₂, but greatly reduces due to the mid-Pliocene geography. The NAM seems to behave more ‘annular’ and less ‘sectoral’ or regional due to the mid-Pliocene climate boundary conditions. We will focus on the mechanisms that explain the differences between the past and future simulations.

How to cite: Oldeman, A., Baatsen, M., von der Heydt, A., van Delden, A., and Dijkstra, H.: Atmospheric variability in the Northern Hemisphere winter in a warm past and a future climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2957, https://doi.org/10.5194/egusphere-egu22-2957, 2022.

The evolution of central Asian drylands during the Cenozoic is a hot topic in paleoclimate research, but the underlying mechanism remains unclear. Here, we investigate this topic with climate modeling based on six key geological periods. Our results indicate that central Asian drylands have existed since the early Eocene, after which they move northward and become narrower. Although changed land–sea distribution and decreased atmospheric CO2 concentration promote the aridification of drylands, they only slightly affect the latitudinal distribution of drylands. By comparison, the growth of Asian high-topography areas, especially the Tibetan Plateau (TP), makes central Asian drylands move northward, concentrate in narrow latitudinal bands, and increase in intensity. Good model-data qualitative agreement is obtained for stepwise aridification in midlatitude inland Asia north of ~40°N, and the uplifted main and northern TP by the early Miocene likely forced drylands to change in this region.

How to cite: Zhang, R., Zhang, Z., Jiang, D., Ramstein, G., Dupont-Nivet, G., and Li, X.: Modeling the evolution of central Asian drylands during the Cenozoic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3321, https://doi.org/10.5194/egusphere-egu22-3321, 2022.

Coals and evaporates are the most commonly used paleoclimate indicators, regarded as representatives of humid and arid climate conditions in the geological record, respectively. However, the quantitative and systematic climate significance of coals and evaporates in the Earth history still unknown. Here, we perform a series of simulations to simulate global climate conditions of Phanerozoic, using an Earth system model CESM 1.2.2 and reconstructed paleotopographies (Scotese, 2018). Combining with a global-scale complication of coals and evaporate from the present back to Devonian (Boucot et al., 2013), climate variables of annual average surface temperature (AAST), annual average precipitation (AAP) and annual average net precipitation (AANP) of the area where coals and evaporates formed are extracted for analysing quantitative climate conditions of coals and evaporates. The preliminary results show that (1) AAST of evaporate areas vary with global mean temperature, while the variation of coals areas’ AAST reflect a stage change,which are consistent with the stage evolution of land plant and lignin-degrading fungi; (2) AAP and AANP of coals and evaporates areas are relatively stable through the Earth history. Coals areas have general more AAP and AANP than evaporates in 25%-75% quantiles but have similar range with evaporites areas in 5%-95% quantiles.

Key words: coals, evaporates, plant evolution, deep-time climate, numerical simulation

References

Scotese C R, 2018. PALEOMAP PaleoAtlas Rasters[J].

Boucot A J, Chen X, Scotese C R, 2013. Lithology Data Tables[J].

How to cite: Bao, X. and Hu, Y.: Climate conditions of coals and evaporates in the Earth history, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4335, https://doi.org/10.5194/egusphere-egu22-4335, 2022.

Dust, as one of the most common types of atmospheric aerosol, affects climate in many different ways. Atmospheric dust scatters and absorbs sunlight and reduces solar radiation received at the surface; it absorbs and emits longwave radiation, having a greenhouse effect; it has a complex indirect effect on climate by serving as cloud nuclei; when deposited on snow or ice, it reduces the surface albedo and warms the surface. Despite its importance in the climate system, how the dust emission and atmospheric dust loading varied during the Earth history is unclear. Here I will give a summary of the atmospheric dust loading as well as its climatic impact for a few typical periods of the Earth. All the results are from numerical simulations and are still premature due to uncertainties in vegetation cover and soil erodibility, and biases and inability of the climate model used.

In present day, the atmospheric dust loading is slightly more than 20 Tg, and has a small impact on the global climate. Such dust loading was diminished during the mid-Holocene (~6 thousand years ago; 6 ka) and the reduced dust induced a very slight global warming (~0.1 °C) but a cooling of the Northern Hemisphere by weakening the Atlantic meridional ocean circulation (AMOC). During the cold last glacial maximum (~21 ka), the atmospheric dust loading was ~2-3 times that of present day. Had not been this dust, the LGM climate would have been colder by ~2 °C and AMOC weaker by ~30%. Clearly, the snow-darkening effect of dust was dominative during this cold time period. For earlier periods with different continental configurations, the atmospheric dust loading also varied significantly. For 80 million years ago (Ma), the continents were dispersive and the total area of the continents was small, the atmospheric dust loading was only ~1.4 Tg. For 240 Ma, the continents clustered into a supercontinent and centered around the equator, the atmospheric dust loading ~21 Tg. For a continental configuration (130 Ma) that had an area in between 80 Ma and 240 Ma, the atmospheric dust loading was ~6.1 Tg. The dust had a cooling effect of <1 °C in all these three periods. For time periods earlier than 400 Ma when land vegetation had not evolved yet, the atmospheric dust loading could have been ~10 times of present day and cooled the climate by ~10 °C. However, such cooling effect disappeared and became a warming effect when the climate was entering a snowball Earth state, due to stronger and stronger snow-darkening effect.

Overall, there was more dust during a cold time period due to stronger winds, weaker hydrological cycle and more dust sources, and the dust had a warming effect to the climate. During the warm time periods, dust tended to have a cooling effect because there was too little snow and ice for the snow darkening by dust to be effective. There was also more dust during periods when the area of continents was larger and more clustered, due to drier land surface.

How to cite: Liu, Y., Lin, Q., Zhang, M., Liu, P., Zhang, J., and Liu, Z.: Evolution of Dust and Its Climatic Impact during Earth’s History, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4906, https://doi.org/10.5194/egusphere-egu22-4906, 2022.

Snowball Earth is a hypothesized state in the deep past of Earth in which the ocean was completely or nearly completely covered by sea ice, resulting from a runaway ice-albedo feedback. Here, we address how the treatment of sea-ice thermodynamics affects the initiation of a Snowball Earth in the global climate model ICON-A run in an idealized slab-ocean aquaplanet setup. Specifically, we study the impact of vertical resolution and brine pockets of ice by comparing the 3-layer Winton and a 0-layer Semtner scheme, and we investigate the impact of limiting ice thickness to 5m.

The internal heat storage of ice is increased by higher vertical resolution and brine pockets, which weakens surface melting and increases global albedo by allowing snow and ice to persist longer into the summer season. The internal heat storage weakens the melt-ratchet effect, as is confirmed with offline simulations with the two ice schemes. The result is a substantially easier Snowball Earth initiation and an increase in the critical CO₂ for Snowball initiation by 50%. Limiting ice thickness impedes Snowball initiation as the removal of excess ice leads to an artificial heat source. Yet, the impact is minor and critical is decreased by 5% only.

The results show that while the sea-ice thickness limit plays only a minor role, the internal heat storage of ice represents an important factor for Snowball initiation and needs to be taken into account when modeling Snowball Earth initiation.

How to cite: Hörner, J., Voigt, A., and Braun, C.: Snowball Earth initiation and the thermodynamics of sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5167, https://doi.org/10.5194/egusphere-egu22-5167, 2022.

The North American Southwest (SW NA) has recently experienced periods of extreme drought, largely due to an increased intensity in evaporation. Yet, there remains large uncertainty in the predicted future changes of precipitation over this region. As a result, the future of SW NA hydroclimate remains uncertain.  The North American Monsoon (NAM) is an atmospheric circulation feature of SW NA hydroclimate that is generated by interactions between topography and moisture surge from the Gulf of California and the Gulf of Mexico.  Previous research has shown a weakened NAM in response to elevated levels of atmospheric CO₂.  However, when analyzing proxy paleoclimate reconstructions during the Pliocene, various records suggest wetter conditions during that time.  We use the mid-Pliocene (3.3 – 3.0 Millions of years ago) as an analog for ongoing climate change because this interval featured topography, geography, and biome assemblages similar to today, but a warmer global mean temperature by 2 - 4 °C compared to pre-industrial, and a sustained 400 ppm CO₂.  Here we are testing whether a high resolution simulation (25 km) can better capture the NAM and provide different sensitivity to boundary conditions compared to low resolution (100 km) simulations, using the same Community Earth System Model.  Increased resolution has been shown to improve the representation of features within the NAM for simulations of the present.   Our pre-industrial simulations display a more extensive monsoon region with high spatial resolution, which indicates a dependency of simulated NAM on resolving topographic features such as the Rockies, Basin and Range, and Gulf of California, all of which can only be captured at high spatial resolutions.  Simulations of the mid-Pliocene displayed weakened NAM precipitation along the west coast of the southwestern North America at a low resolution when compared to the pre-industrial run.  Yet, this weakening signal is limited to the Pacific side of the orographic slopes in the high resolution simulation, with the rest of the monsoon region featuring increased precipitation.  Ongoing work will explore the sources for this resolution dependency, and will quantify contributions of mesoscale systems, such as tropical and extratropical cyclones, to precipitation in the monsoon region.

How to cite: Albright, M. G., Feng, R., Zhu, J., Otto-Bliesner, B., Li, H., and Bhattacharya, T.: Mid-Pliocene North American Monsoon in Weather Resolving Coupled Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5586, https://doi.org/10.5194/egusphere-egu22-5586, 2022.

The late Miocene and early Pliocene is marked by a major
oceanographic and geological event called the Late Miocene Biogenic
Bloom (LMBB). This event is characterized by high accumulation rates of
opals from diatoms and high calcite accumulation rates from calcareous
nannofossils and planktic foraminifera. The LMBB extends over several
million years and is present in the Pacific, Atlantic and Indian Oceans. Two
hypotheses have emerged from the literature to explain this event: a
global increase in the supply of nutrients to ocean basins through chemical
alteration of the continents and/or a major redistribution of nutrients in the
oceans. The objective of this study is to provide a more comprehensive
look at the temporal and geographical aspects of the LMBB. We have
compiled ocean drilling data (ODP-IODP) covering the late Miocene and
early Pliocene. This compilation contains sedimentation rates as well as
CaCO3, opal and terrigenous accumulation rates. After a careful screening
of the database, checking that all data are on the same time scale, we first
work on global trends of sedimentation and biogenic production before
going into more details. For instance, we show that the magnitude of the
Biogenic Bloom strongly varied between the three oceanic basins.
Normalization to a post-LMBB state allows comparison of rates of increase
in CaCO3 accumulation in different geographical areas (grouping several
sites). A very strong LMBB signature is present in oceanic area bordering
the western side of Australia. In the Atlantic Ocean, it is mainly present
near the equator and over South Africa. The LMBB signature is less
pronounced in the Indian Ocean but remains trackable near the northern
coasts of the basin. Moreover, it is also heterogeneous in terms of the
mineralogy produced and deposited in the deep ocean between regions.
For example, in the equatorial eastern Pacific, the LMBB signature is
present in the silica accumulation term but not in carbonates accumulation
one. Outputs from coupled ocean/atmosphere models (IPSL-CM5A2) using
late Miocene paleogeography and integrating a marine biogeochemistry
module (PISCES) have been gathered and will be discussed in regard to
our database.

How to cite: Pillot, Q., Suchéras-Marx, B., Sarr, A.-C., Bolton, C., Ladant, J.-B., and Donnadieu, Y.: Spatial heterogeneity of the Late Miocene Biogenic Bloom, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5621, https://doi.org/10.5194/egusphere-egu22-5621, 2022.

The mid-Pliocene warm period (mPWP, ~3.3 – 3 Ma) is the most recent geological period with a CO₂ concentration similar to the present day (~400 ppm). The Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) focuses on the KM5c time slice (3.205 Ma), giving insight into the climate dynamics of this period. Sea surface temperature (SST) proxies indicate amplified warming over the North Atlantic in the mPWP with respect to the pre-industrial period, which may be linked to an intensified Atlantic Meridional Overturning Circulation (AMOC). Zhang et al. (2021) reported a stronger mPWP AMOC in all the PlioMIP2 simulations but found no consistent relation to either the Atlantic northward ocean heat transport (OHT) or average North Atlantic SSTs. We therefore look further into the drivers and consequences of a stronger AMOC in the mPWP compared to pre-industrial simulations.

Within the PlioMIP2 ensemble, we find that all model simulations with a closed Bering Strait and Canadian Archipelago show strongly reduced freshwater transport from the Arctic Ocean into the North Atlantic. The resulting increase in sea surface salinity in the subpolar North Atlantic and Labrador Sea stimulates deepwater formation in these areas. The stronger AMOC is therefore primarily a response to the closure of the Arctic gateways. We also look at the different components of the Atlantic OHT, associated with either the overturning circulation or the wind-driven gyre circulation. While the ensemble mean of the overturning component is increased significantly in magnitude in the mPWP, it is partly compensated by a reduced gyre component. Our results point towards a complex interplay between atmospheric and oceanic processes and indicate that considering these components separately allows for a better understanding of the climatic response to the AMOC strength.

How to cite: Weiffenbach, J., Baatsen, M., and von der Heydt, A.: Drivers and consequences of a stronger mid-Pliocene Atlantic Meridional Overturning Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6006, https://doi.org/10.5194/egusphere-egu22-6006, 2022.

The physiological evolution of vegetation affects the interaction between vegetation and climate. Angiosperms have higher leaf vein density than all other plants throughout evolutionary history, contributing to higher transpiration capacities. However, the climatic response to changes in physiological functions of angiosperms has remained to be determined. Here, Community Earth System Model (CESM) version 1.2.2 and BIOME4 vegetation model are applied to simulate the world without angiosperms by reducing the maximum carboxylation rate (Vmax) to 1/4 (Boyce et al, 2009), in conditions of both fixed and non-fixed vegetation distribution. First, we maintain the pre-industrial vegetation distribution, the results illustrate that the world without angiosperms would have less productivity, higher global mean temperature, consisting with the results of Boyce and Lee (Boyce and Lee, 2010). In addition, the warmer southern hemisphere and colder northern hemisphere are identified, which are caused by the decrease of the strength of Atlantic Meridional Overturning Circulation (AMOC). Second, we consider changes of vegetation structure, the results show that temperature and precipitation would vary significantly locally, and the area of tropical forest would decline sharply in the world without angiosperms, which may affect biodiversity. The evolution of physiological functions of angiosperms influences climate and provides potential competitive advantages for angiosperms to dominate modern vegetation.

How to cite: Guo, J., Hu, Y., and Liu, Y.: The Impact of Angiosperms Physiological Evolution on Earth Systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6721, https://doi.org/10.5194/egusphere-egu22-6721, 2022.

The Late Permian climate is the background state for the climate perturbations which lead to the
Permian-Triassic Boundary (~252 Ma). The Permian-Triassic Boundary mass extinction is well established as
the largest of Earth’s mass extinctions with an estimated 90% loss of species. Climate perturbations linked to
carbon emissions from Siberian Trap volcanism are attributed as the drivers of the mass extinction through
extreme temperature increases and changes in ocean circulation and biogeochemistry. Fully-coupled Earth
System Models are required to investigate the sensitivities and feedbacks of the system to these widespread
climate perturbations. The Late Permian climate is simulated with a modified version of the Max Planck
Earth System Model v1.2 similar to that used in the 6^th -phase of the Coupled Model Intercomparison Project.
Geochemical and palaeobiological proxy data are used to constrain the boundary conditions of the modelled
climate state.
The simulated Late Permian climate state is characterised by a 100 year global mean 2 m surface air
temperature of 19.7°C, rising up to 37.7°C in the low-latitude continental interior. Prevailing 100 year global
mean total precipitation patterns indicate that the continental interior was largely arid from ~50°N to ~50°S and
a rainfall maximum of up to 6.5 mm day^-1 is present at the equatorial boundary of the Tethys and Panthalassic
Oceans. Dynamic terrestrial vegetation in the model is dominated by woody single-stemmed evergreens and
soft-stemmed plant functional groups. The 100 year global mean surface ocean of the Late Permian illustrates
a warm-pool across the equatorial boundary between the Tethys and Panthalassic Oceans with a maximum
temperature of 31.7°C decreasing to temperatures as low as -1.9°C near the poles. Surface salinities vary
broadly across the global oceans with 100 year global mean values ranging from 21.9, in well flushed regions
of strong freshwater flux, to 49.2, in low-latitude regions of restricted exchange. Large-scale seasonal mixing
below 60°S in the Panthalassic Ocean dominates the global meridional overturning circulation. These model
data fit within the bounds represented by the available proxy data for the Late Permian. Additionally, I will
present first results of the ocean biogeochemical state in the Hamburg Ocean Carbon Cycle model with an
extended Nitrogen-cycle. I will also illustrate the results of our investigation into the influence of the Late
Permian monsoon variability on the terrestrial vegetation and ocean carbon cycles.

How to cite: Burt, D., Ilyina, T., and Kleinen, T.: Dynamics and variability of the Late Permian climate-carbon state in an Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6804, https://doi.org/10.5194/egusphere-egu22-6804, 2022.

Dust in the atmosphere affects climate by directly absorbing and scattering solar radiation. In present days, most of dust is emitted from dry regions over North Africa and Arabian Peninsula. It has been shown that it impact on global mean surface temperature, African monsoon, the number of tropical cyclones over the Atlantic Ocean, ENSO variability and the strength of Atlantic meridional ocean circulation (AMOC). The climate of late Paleozoic ice age bears some similarity to late Cenozoic climate. However, late Paleozoic ice age was a period of continental convergence and supercontinents formation. On different continental configurations, the area of dry regions may vary considerably, so that dust emissions and atmospheric dust loading changed accordingly. As  expected, the impact of dust on climate during this period was also very different from that of present days. In this work, we use the fully coupled global climate model CESM1.2.2 to examine the influence of dust on climate during late Palaeozoic ice age. Dust aerosols simulated by bulk aerosol model alter atmospheric radiation through scattering and absorbing both shortwave and longwave radiation. Results show that during late Palaeozoic ice age, sources of dust were mainly distributed on the western continent in the subtropics. The total amount of the atmospheric dust loading was less than that of present days due to the smaller subtropical continental area. Such dust induced a significant cooling of surface temperature at low latitudes by altering radiation. Dust falling on southern hemisphere continents covered by ice and snow caused a rising of surface temperature.

How to cite: Lin, Q. and Liu, Y.: Influence of Dust on Climate during the late Palaeozoic ice age, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6918, https://doi.org/10.5194/egusphere-egu22-6918, 2022.

In this study, we investigate the meridional temperature gradients during the past 250 million years. We compare the differences between proxy data of oxygen isotopes and lithologic indicators and globally coupled atmosphere-ocean climate system model simulation results. Two climate models are employed, CESM1.2.2 and HadleyCM3. There are several significant differences between the model results and Scotese’s reconstruction and proxy data: 1) the tropical surface temperatures are usually higher in the model simulations than both Scotese’s reconstruction (Scotese 2016; Scotese et al. 2021) and proxy data (e.g., Huber and Caballero 2012, Song et al. 2019; Zhu et al. 2019), whereas the surface temperatures in high latitudes are usually lower; 2) the meridional temperature gradients in the model simulations are smaller in low latitudes but larger in the middle latitudes than Scotese’s reconstruction. These comparisons are helpful for paleoclimatology understanding and for future paleo-temperature reconstructions.

How to cite: Wei, M., Yang, J., Hu, Y., Liu, Y., Li, X., Bao, X., Guo, J., Lan, J., Li, Z., Lin, Q., Man, K., yin, Z., and Yuan, S.: Meridional temperature gradients during the past 250 million years: Proxies versus Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7520, https://doi.org/10.5194/egusphere-egu22-7520, 2022.

Over million-year timescale the carbon cycle evolution is driven by mantle CO₂ degassing (source) and by continental weathering that drawdowns atmospheric CO₂ through silicate weathering reactions (sink). Based on a novel geochemical proxy of chemical weathering intensity (i.e. using measurements of Hf and Nd isotope ratios in clay-size fractions of sediments) and clay mineralogy, we discuss the links between tectonic, continental weathering and climate evolution during the late Cretaceous. That period records the very first step of the last greenhouse to icehouse transition and is concomitant to major uplift phases affecting the African and South-American margins.

Two sites along the South American Atlantic margin (ODP 356 and 1259) were targeted based on their relatively complete record of upper Cretaceous sediments. At Site 356, our results indicate the occurrence of enhanced chemical weathering during the Campanian and Maastrichtian following the uplift of the Southeastern Brazilian margin that promoted the establishment of more hydrolysing conditions.

At Demerara Rise (Site 1259), our data suggest a coupling between physical erosion and chemical weathering, which may be explained in this area by the presence of persistent hydrolysing conditions typical of equatorial climate and reduced tectonic activity. From the Turonian to the early Campanian, i.e. a period of relative tectonic quiescence, our data suggest that climate was likely the main driver controlling the evolution of chemical weathering intensity. By contrast, from the middle Campanian to Maastrichtian, we propose that mountain uplift, although moderate, induced a marked increase in chemical weathering intensity.

Together, this new data acquired at two 2 sites that encountered different regional climatic, geologic and tectonic conditions suggest that chemical weathering markedly intensified during the late Cretaceous and likely acted as a major sink for atmospheric CO₂. While the onset of weathering increase at both sites appear to postdate the initiation of global temperature decrease, we suggest here that this process could have participated to accelerating or maintaining colder climate conditions at that time.

Key Words: late Cretaceous – paleoclimate – weathering – uplift - clay mineralogy – Hf-Nd isotope

How to cite: Corentin, P., Pucéat, E., Pellenard, P., Guiraud, M., Blondet, J., Freslon, N., Bayon, G., and Adatte, T.: Hafnium-neodymium isotope evidence for enhanced weathering and tectonic-climate interactions during the Late Cretaceous, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7744, https://doi.org/10.5194/egusphere-egu22-7744, 2022.

Earth has undergone dramatic temperature fluctuations and the tectonic process of continental breaking up and reassembling in the past 540 million years. How these caused changes in the global hydrological cycle is an interesting question. To study the evolution of the global hydrological cycle since the Cambrian, we carried out 55 equilibrium simulations to simulate climate evolution in the past 540 million years, using CESM1.2.2. It is found that the global mean precipitation is closely correlated with the global mean surface temperature (GMST), especially oceanic precipitation has high correlation with GMST, with a coefficient of 0.92. Land precipitation also has statistically significant correlation with GMST. However, the correlation coefficient is much lower. Further analysis shows that land precipitation is also determined by continental fragmentation, mean latitudes, and total area, and that the semi-arid area is most sensitive to GMST changes.

How to cite: Hu, Y., Li, X., and Li, Z.: The hydrological cycle in the past 540 million years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8237, https://doi.org/10.5194/egusphere-egu22-8237, 2022.

Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Early Eocene by 2150 CE, suggesting that we are effectively reversing a more than 50-million-year cooling trend in less than two centuries. Terrestrial records of rivers and floodplains from Paleogene sedimentary basins in the US Western interior and Europe indicate an increase in flash floods and droughts at paleo-mid latitudes, indicating increased precipitation intensity and intermittency. In the Uinta Basin, Utah magnetostratigraphic analyses, absolute age dates, and biostratigraphy allow the reconstruction of changes in hydroclimate from the Early Paleocene, to the Paleocene-Eocene Thermal Maximum (PETM), and through the Early Eocene Climatic Optimum (EECO). Here we observe that the largest shifts in hydroclimate are not linked to the PETM but rather occur during the warm Late Paleocene and then at the end of the EECO. This is indicated by the river sedimentary record that shows a shift from normal rivers, such as are characteristic at mid-latitudes today, to flood-prone rivers in late Paleocene. The rivers shifted back to normal at the end of the EECO. Coeval changes are observed in floodplain paleosols where the late Paleocene and early Eocene paleosols indicate sustained droughts and intermittent seasonal rains. At the PETM there is no change in the state of hydroclimate, but rather a further intensification of floods and droughts. Comparison to other terrestrial basins at mid-latitudes shows similar patterns. These results show that the most dramatic shifts in hydroclimate were not linked to the largest amplitude of atmospheric drivers at the PETM, but rather suggest a threshold-driven relationship between the atmospheric drivers and hydroclimate. This may suggest that significant changes in hydroclimate are to be expected already before 2150 CE. 

How to cite: Slawson, J. and Plink-Bjorklund, P.: Long-term increase in precipitation intermittency and intensity at Paleogene mid latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10287, https://doi.org/10.5194/egusphere-egu22-10287, 2022.

The meridional heat transport is primarily governed by the geometry between the Earth and the Sun and it has been shown in previous studies that it is nearly invariant in different climates. Nevertheless, the processes, which contribute to the whole transport, do not stay invariable, but their changes compensate each other. Thus, the changes in the various transport processes give an insight into the climate system and its changes in different conditions, such as the high CO₂ concentrations of the Early Eocene Climatic Optimum (EECO).

In our work we investigate the meridional heat transport and its elements in climate model simulations from DeepMIP focusing on the EECO. The meridional heat transport is divided into atmospheric and ocean heat transport. The atmospheric heat transport is further divided into moist and dry energy transport and also into transport by the meridional overturning circulation, transient eddies and stationary eddies. Annual and seasonal changes are compared in the preindustrial control simulation, in the 1xCO₂ simulation and in simulations with high CO₂ concentration values (3xCO₂, 4xCO₂, 6xCO₂). We found that in a warmer climate, where the hydrological cycle is expected to be stronger, the transport of the meridional overturning circulation at the tropics, so the circulation of the Hadley cell, is more intense. Also, at the subtropics the energy transport of monsoon systems and at the mid-latitudes the energy transport of cyclones and anticyclones is different than in the control climate.

How to cite: Kelemen, F. D. and Ahrens, B.: Partitioning meridional heat transport in Early Eocene Climatic Optimum model simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10380, https://doi.org/10.5194/egusphere-egu22-10380, 2022.

Global climates have undergone tremendous fluctuations during the past 250 million years, primarily driven by variations in tectonic dynamics, atmospheric greenhouse gases, and solar irradiance. Paleoclimate modeling has offered a feasible approach to investigating secular climate change for such a long span of time deep in the past. Nevertheless, global mean surface temperatures (GMSTs) simulated by previous studies scarcely depict the trend of past climate change. In this study, using the Community Earth System Model version 1.2.2 (CESM1.2.2), we present an ensemble of snapshot simulations during the past 250 million years based on the reconstructed GMSTs. An energy balance analysis is carried out to explore and quantitatively describe the causes of temperature change for the past 250 million years. We find that different levels of global mean warming for the past 250 million years compared with the pre-industrial period predominantly results from relative increase in greenhouse gas emissivity (12.2 °C), with the changing paleogeography (5.6 °C) and solar constant (3.0 °C) playing secondary roles. It is highlighted that the individual effect of heat transport convergence varies inconspicuously in spite of considerable changes of paleogeography and mean climate states during this time. The simulations are potentially valuable resources for extensive studies including climate dynamics analysis in geological timescales and paleoclimate-proxy intercomparison.

How to cite: Li, X., Guo, J., Lan, J., Lin, Q., Yuan, S., Yang, J., Liu, Y., and Hu, Y.: Climate evolution during the past 250 million years simulated by the Community Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10701, https://doi.org/10.5194/egusphere-egu22-10701, 2022.

The high frequency oscillations between wet and dry conditions plus the warmer temperatures when the Earth comes closest to the sun, might suggest weathering and hence accumulation rates should be highest during times of maximum eccentricity and maximum precessional variability in the tropics. But time series analysis of 20 Myr of continuous cores of tropical, lacustrine Late Triassic-age strata of the Newark Rift Basin (202–222 Ma) surprisingly show that that is not the case because accumulation rates are highest during the times of lowest precessional variance at the modes of the Mars–Earth (g₄-g₃) orbital cycle, when eccentricity is at a minimum.

            Three different methods of analysis reveal an accumulation pattern at variance with this intuitive model. 1) Tuning the depth-domain depth rank, color, and natural gamma data series to the 405 kyr, Venus–Jupiter (g₂-g₅) eccentricity metronome reveals oscillations in accumulation rates of ~20m to ~100m/Myr/cycle (within a total range of 70m – 250m/Myr). Spectral analysis reveals these oscillations occur with the same period (~1.8Myr) as the Mars–Earth modulation of precession for that time, with highs in accumulation rate occurring during lows in eccentricity. A weaker signal of the Mars–Earth (s₄-s₃) inclination cycle is also present at about 1/2 the period of the eccentricity cycle. 2) Application of the eTimeOpt method of sedimentation rate analysis reveals the same pattern and magnitudes of sedimentation rate variations in depth rank and color. 3) Spectral analyses of gamma and XRF elemental data from intervals of low- vs high-precessional variance show that significantly lower accumulation rated occurred during extended times of high- vs low-precessional variation.

            Accumulation rate oscillations in the Newark Rift Basin should be tracking weathering rates to supply the immense volumes of sediment involved in the accumulation rate variations. Such volumes could not be somehow stored in the highlands for hundreds of thousands of years, otherwise potentially shifting weathering and accumulation rates out of phase.

            The implication of these empirical data is that because pCO₂ should be drawn down under higher weathering rates, and the phase of eccentricity modulation of precession is global, pCO₂ should be oscillating in phase with the Mars–Earth eccentricity cycle. On the short-term, low-pCO₂ should characterize times of low-precessional variability, evidently associated with high-accumulation rates, based on these empirical data, and not vice-versa as might be intuitively modeled. In turn, the oscillations in pCO₂ would be expected to cause global temperature oscillations at the g₄-g₃ frequency. These non-intuitive results, suggesting a hitherto unanticipated relationship between orbital pacing of climate and pCO₂, can be tested and further explored by continuous XRF elemental scanning of these cores, currently underway, and by collection of more densely sampled soil carbonate and leaf stomatal pCO₂ proxy data, from proposed new cores. The mechanisms driving the relationships between these reproducible empirical data are, however, not obvious, but would seem to be related to the precession-scale variability of climate, not just the magnitude of greenhouse gas concentrations or temperatures.

How to cite: Olsen, P., Kinney, S., Chang, C., Schaller, M., Whiteside, J., and Kent, D.: Eccentricity modulation of weathering and accumulation rates: non-intuitive, empirical relationship suggests links between orbital pacing and pCO2    , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10720, https://doi.org/10.5194/egusphere-egu22-10720, 2022.

Reconstructing deep ocean temperature is important to infer deep water mass structure and hence ocean circulation patterns in the past. The late Paleocene-early Eocene experienced the warmest climates of the Cenozoic, with highly elevated CO₂ levels and no ice sheets on the continents [1,2]. Benthic foraminiferal δ¹⁸O records suggest relatively stable deep ocean conditions on long time scales (>100 kyr) in this hothouse [2–4]. However, interpretations from benthic δ¹⁸O records are complicated by influences of factors other than temperature, such as the isotope composition of the seawater (δ¹⁸O_sw), pH, and species-specific physiological effects [5,6]. Carbonate clumped isotope thermometry (Δ₄₇) has the major advantage that it is independent of the isotope composition of the fluid source, and is not measurably affected by other non-thermal influences [7–10]. Early Cenozoic clumped isotope reconstructions from the North Atlantic have revealed surprisingly large deep-sea temperature swings under hothouse conditions [11]. Extreme warming is recorded at the onset of the Early Eocene Climatic Optimum (EECO) [11]. To explore the spatial extent of these deep-sea temperature changes, we reconstructed early Eocene Δ₄₇-based deep-sea temperatures from the South Atlantic Ocean, a location that is considered to capture a global signal [2–4]. We find similar deep-sea temperatures as those from the North Atlantic. Cooler temperatures of ~12 °C stand out in the interval (54–52 Ma) before the peak warmth of the EECO (52–50 Ma) of ~20 °C. This result overthrows the classic view of a gradual early Eocene warming trend based on benthic δ¹⁸O records, at least for the deep Atlantic Ocean. Our findings raise new questions on the regions of deep water formation, changes in deep ocean circulation, and the driving mechanisms in the early Cenozoic hothouse.

References
[1] Anagnostou, E. et al. (2016). Nature, 533(7603), 380-384.
[2] Zachos, J. et al. (2001). Science, 292(5517), 686-693.
[3] Lauretano, V. et al. (2018). Paleoceanography and Paleoclimatology, 33(10), 1050-1065.
[4] Westerhold, T. et al. (2020). Science, 369(6509), 1383-1387.
[5] Ravelo, A. C., & Hillaire-Marcel, C. (2007). Developments in marine geology, 1, 735-764.
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[10] Meinicke, N. et al. (2020). Geochimica et Cosmochimica Acta, 270, 160-183.
[11] Meckler, A. N. et al. (in revision).

How to cite: Agterhuis, T., Ziegler, M., Koene, B. L. P., de Vries, L., Roozendaal, A., and Lourens, L. J.: South Atlantic deep-sea temperatures across the onset of the Early Eocene Climatic Optimum based on clumped isotope thermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10815, https://doi.org/10.5194/egusphere-egu22-10815, 2022.

The reconstruction of deep-ocean temperatures is key in the study of the different climate states in the geological past. Reconstructions covering the Pliocene-Pleistocene transition shed light on the global climatic change that followed the mid-Pliocene warm period and culminated in full glaciation of the Northern Hemisphere.

Global δ18O records measured on seafloor dwelling foraminifera constitute the backbone of our understanding of the climatic trends and transitions of the last 65 million years [1,2]. These records suggest that the glacial intensification over the last 2.8 Ma experienced the onset of Quaternary-style ice age cycles and the progression towards a more deterministic climate system increasingly sensitive to orbital forcings. Deep-sea temperature variability across this time is thought to have stayed in a 4ºC range with near-freezing temperatures occurring at every glacial maximum, especially after the Mid-Pleistocene transition [2,3]. However, temperature signals based on carbonate δ18O data are built upon uncertain assumptions of non-thermal factors such as those regarding the isotopic composition of the ancient seawater.

Carbonate clumped thermometry (𝛥47) is based on thermodynamic principles that determine the ordering of isotopes within the carbonate crystal lattice [4]. It is independent of the fluid composition. 𝛥47 thermometry has recently been used to anchor Mg/Ca records of the Miocene while revealing a comparatively warm deep ocean [5].

Here we present 𝛥47-based deep-sea temperature constraints across the Pliocene-Pleistocene transition obtained from benthic foraminifera of ODP Site 1264 in the South Atlantic Ocean. In combination with benthic δ18O analyses, we furthermore interpret our measurements into global ice volume and ocean circulation changes in the Atlantic Basin across the major onset of the Northern Hemisphere Glaciation.

[1] Zachos, J., et al. (2001), Science 292, 686-693.

[2] Westerhold, T., et al. (2020), Science, 369, 1383–1387,

[3] Elderfield, H., et al. (2012) Science, 337(6095), 704-709.

[4] Eiler, J.M. (2007), Earth Planet. Sci. Lett. 262, 309-327.

[5] Modestou, S. E., et al. (2020) Paleoceanography and Paleoclimatology 35, e2020PA003927.

How to cite: Domínguez Valdés, E., Kocken, I., Agterhuis, T., Müller, I., Bode, N., Kroon, D., Lourens, L., and Ziegler, M.: South Atlantic deep-sea temperature evolution across the Pliocene-Pleistocene transition from clumped isotope thermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11222, https://doi.org/10.5194/egusphere-egu22-11222, 2022.

Oceanic Anoxic Events (OAEs) were geologically short-lived events of widespread ocean deoxygenation and marine organic carbon burial and occurred mostly during the Cretaceous period. The development of OAEs is largely attributed to the impact of massive volcanism on climate and marine biogeochemistry; however, the lack of similar events during other carbon-cycle perturbations suggests additional mechanisms. We use the IPSL-CM5A2 Earth System Model to assess the role of changing paleogeography in priming the Cretaceous Ocean for large-scale decrease in intermediate and deep oxygen concentrations. We focus on three time-slices that present differences in potential gateway (e.g. the Central American Seaway) depth and basin configuration (e.g. the North Atlantic): the Aptian age (~120 Ma), the Cenomanian-Turonian boundary (~94 Ma) and the Maastrichtian age (~70 Ma). This set of simulations illustrates the impact of paleogeography on global circulation and its consequences for intermediate and deep water oxygenation. We also show results for two different atmospheric CO2 concentrations (2x and 4x pre-industrial) to study the additional influence of differing climatic states on oxygenation and primary productivity, and their importance relative to ocean dynamics.

How to cite: Donnadieu, Y., Papadomanolaki, N., Laugie, M., Sarr, A., and Ladant, J.-B.: Modeling the Impact of Paleogeography on Cretaceous Ocean Deoxygenation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11663, https://doi.org/10.5194/egusphere-egu22-11663, 2022.

The Nordic Seas are a key region for global ocean circulation, crucial in water mass exchange between the North Atlantic and the Arctic oceans, and deepwater formation. The advection of Atlantic Water (AW) to the Nordic Seas is decisive for the oceanography and climate of the region and beyond. Here, we present a set of sedimentary records, including two new cores from the western Nordic Seas to reconstruct the history of AW routing in the Nordic Seas over the Holocene. Our results show that the early Holocene (11.7 - 8 ka BP) thermal maximum, caused by an “overshoot” of overturning circulation and high insolation, was limited to the eastern Nordic Seas, while the western part remained cold due to the meltwater blocking the spreading of AW. After 8 ka BP, the retreat of the freshwater lid allowed AW to reach the central Greenland Sea, where deep convection developed. The weakening of the overturning circulation during the 8.2 ka BP event could have played an important role in this circulation shift. After 5 ka BP, the increase in sea-ice export from the Arctic strengthened deep convection, which intensified the westward AW flow. A disruption of convectional activity around 2.7 ka BP, triggered by a minimum in solar activity, caused cooling and expansion of sea ice in the Nordic Seas and might have contributed to a global climatic deterioration. The overturning circulation in the Nordic Seas did not recover to its previous state until the present. We demonstrate that the rate of AW advection into the Nordic Seas alone is not enough to understand the oceanographic evolution of this area and its influence on regional or even global ocean and climate changes. The shifts in AW routing within the Nordic Seas and the rate of deep convection are also important.

How to cite: Telesiński, M. M., Łącka, M., Kujawa, A., and Zajączkowski, M.: The significance of Atlantic Water routing in the Nordic Seas during the present interglacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1312, https://doi.org/10.5194/egusphere-egu22-1312, 2022.

Examination of the palaeoclimate record of the last 800 kyr has revealed a large diversity among interglacials in terms of their duration, structure and intensity.  Interglacials may be classified as either short (mean duration 13 kyr) or long (mean duration 28 kyr).  The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks: the longest interglacials are characterized by the obliquity peak lagging the first precession minimum by 10±2 kyr and leading the second precession minimum by a similar amount; thus the first boreal summer insolation minimum occurs at the time of maximum obliquity, which overrides the increase in precession and prevents glacial inception associated with a decline in summer insolation.  The phasing of precession and obliquity also determines the structure of an interglacial, leading to two main categories: (1) shorter interglacials characterized by rapid deglaciation and an early temperature optimum, usually followed by a decline; and (2) longer interglacials characterized by protracted deglaciation and the persistence of interglacial values over two insolation peaks, with the interglacial peak occurring in the second insolation maximum.  With respect to intensity, a broad feature is that interglacials before the Mid-Brunhes Event (MBE; 430 ka) appear weaker (cooler, higher δ¹⁸O_benthic, atmospheric CO₂ lower than pre-industrial concentrations).  The strongest interglacials occurred after the MBE, although MIS7e and MIS7c-a are closer in intensity to pre-MBE interglacials.  Of particular interest is MIS 11c, one of the most unusual Quaternary interglacials.  Its features include: (i) a high sea-level highstand attained under modest insolation forcing; (ii) a long duration extending over two insolation peaks; (iii) persistence of relatively stable atmospheric CO₂ concentrations, remaining in the range 270-282 ppm for a 24 kyr period; and (iv) a decoupling between high CO₂ and high sea level in the early part of the interglacial that is unique in the last 800 kyr.  Although some of these features are also encountered in other interglacials, their combination with strong interglacial intensity is unique to MIS 11c and appears to be a function of the high CO₂concentrations from the beginning of the interglacial.

How to cite: Tzedakis, C., Hodell, D., Nehrbass-Ahles, C., and Wolff, E.: All interglacials are different, but some are more different than others, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2443, https://doi.org/10.5194/egusphere-egu22-2443, 2022.

Marine Isotope Stage (MIS) 5, between about 130 and 70 ka BP, is a relatively long warm period characterized by climate oscillations consisting of three interstadials and two stadials. In this study, two sets of snapshot simulations by a step of 2 ka covering the whole MIS-5 period are performed with the model HadCM3 to investigate the relative impacts of insolation, CO₂ and Northern Hemisphere ice sheets on the internal variations within MIS-5 and spatial variations of the East Asian climate, including the East Asian summer monsoon (EASM) intensity. The first set of experiments are forced by varying insolation and GHGs (OrbGHG) and the second ones are forced by varying insolation, GHGs and ice sheets (OrbGHGIce). Results show that a similar trend with precession can be found in the simulated summer precipitation, temperature and EASM index in both OrbGHG and OrbGHGIce, indicating the dominant role of precession on the EASM. Within the range of CO₂ variability during MIS-5, the change of CO₂ causes similar degree of warming effect, but much lower degree of humidifying effect compared to insolation. Insolation and CO₂ change the precipitation through different dynamic and thermodynamic processes. Our results also show that the influence of ice sheets on temperature and precipitation is less important than the effect of insolation and it varies from regions and in time. The effect of ice sheets depends on background insolation and also the location, height and area of ice sheets. The simulated spatial-temporal variations of the EASM climate are compared with proxy records and the mechanisms involved are investigated. 

How to cite: Lyu, A. and Yin, Q.: The spatial-temporal patterns of East Asian climate in response to insolation, CO2 and ice sheets during MIS-5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2635, https://doi.org/10.5194/egusphere-egu22-2635, 2022.

Different IPCC-CMIP6 climate models give diverse results when run under common interglacial forcing. The mid-Holocene and the Last Interglacial are the two time periods from which we have the most results. The diversity is particularly true for the Arctic, where sea ice physics plays a key role. Whilst scientists have known for more than twenty years that summer temperatures in the Arctic during the Last Interglacial – the warm period around 127,000-128,000 years ago - were around 4°C above those of today (from lake, peat, and marine core data), the cause of this warmth puzzled scientists until 2020. Until 2020, it was thought this Last Interglacial warmth may have been driven by Arctic vegetation changes.  We present an analysis of a variety of CMIP6 model simulations run during the Last Interglacial.  Only one model simulates a fully sea ice-free Arctic during the summer –it includes an advanced representation of melt ponds in the sea ice model. Melt ponds are shallow pools of water which form on the surface of Arctic sea ice. We find that the inclusion of melt ponds within models is likely crucial for understanding Last Interglacial sea ice loss and Arctic warmth, and touch on the relationship between Arctic sea ice changes in warm climate and on high equilibrium sensitivity CMIP6 models. Alongside the impact of different physics in the models, we also consider forcing aspects including the impact of the meltwater from deglaciation and top-of-the-atmosphere radiation (orbital).

How to cite: Sime, L., Diamond, R., Schroeder, D., Guarino, M. V., and Sivankutty, R.: Diverse models, diverse interglacial results? Sea ice physics versus model forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3033, https://doi.org/10.5194/egusphere-egu22-3033, 2022.

Understanding the sea ice variability and the mechanisms involved during warm periods of the Earth is essential for a better understanding of the sea ice changes at the present and in the future. Based on simulations with the model LOVECLIM, this study investigates the sea ice variations during the last nine interglacials and focuses on the inter-comparison between interglacials as well as their differences from the present and future. Our results show that, for the double CO₂ experiment and the Shared Socioeconomic Pathway (SSP)1-2.6, SSP2-4.5 and SSP5-8.5 scenario experiments, the global, Arctic and Southern Ocean sea ice areas simulated by LOVECLIM all fall in the range of the multi-model results from CMIP 6. In addition, the results show that the annual mean Arctic sea ice variation is primarily controlled by local summer insolation, while the annual mean Southern Ocean sea ice variation is more influenced by the CO₂ concentration but the effect of local summer insolation can’t be ignored. The lowest Arctic sea ice area results from the highest summer insolation at MIS-15, and the lowest Southern Ocean sea ice area at MIS-9 is explained by the highest CO₂ concentration and moderate local summer insolation. As compared to the present, the last nine interglacials all have much less sea ice in the Arctic annually and seasonally due to high summer insolation. They also have much less Arctic sea ice in summer than the double CO₂ experiment, which makes to some degree the interglacials possible analogues for the future in terms of the changes of sea ice. However, compared to the double CO₂ experiment, the interglacials all have much more sea ice in the Southern Ocean due to their much lower CO₂ concentration, which suggests the inappropriateness of considering the interglacials as analogues for the future in the Southern Ocean. Our results suggest that in the search for potential analogues of the present and future climate, the seasonal and regional climate variations should be considered.

Reference: Zhipeng Wu, Qiuzhen Yin, Zhengtang Guo, André Berger, 2022. Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future. Climate Dynamics, accepted.

How to cite: Wu, Z., Yin, Q., Guo, Z., and Berger, A.: Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3087, https://doi.org/10.5194/egusphere-egu22-3087, 2022.

Interglacials older than 450,000 years ago (ka) are still poorly documented at regional and global scale limiting our knowledge of the wide range of their potential variability and the understanding of the causes of such diversity. Here we present δ¹⁸O benthic foraminifera measurements along with sea surface temperature reconstructions and pollen data from IODP site U1385, collected during Expedition 339 « Mediterranean Outflow » on the southwestern Iberian margin, for the Early-Middle Pleistocene interglacials MIS 19, 17, 15 and 13 (~800 to 400 ka). The recorded vegetation and climate changes on land have been directly compared with changes in the eastern North Atlantic subtropical gyre and the global ice volume. This comparison reveals a different structure in the evolution of the Mediterranean forest during these interglacials. The highest forest development occurred during MIS 19e and 15e but in the middle part of MIS 13 (MIS 13c). In contrast with MIS 19, 15 and 13 marked by three more or less similar Mediterranean forest expansions, MIS 17 was characterised by one strong expansion in its middle part (MIS 17c), the strongest of the last 800,000 years, occurring just before the end of the Middle Pleistocene Transition, i.e. the establishment of the strong 100-kyr glacial cycles at ~700 ka.  The duration of the first forested phase was also variable depending on the interglacial with a length of ~12,000 years during MIS 19e and 15e, ~9,000 years for MIS 13c and as long as 16,000 years for MIS 17c. Interestingly, two Mediterranean forest expansions are recorded during two phases of ice growth, MIS 19b and 15b, indicating once more the decoupling between the evolution of global ice volume and the southern European environments. The comparison of the U1385 pollen record, located below 40°N, with sequences above 40°N, for example the Lake Orhid pollen record, shows that the structure and magnitude of the interglacials are different below and above this latitude. At Montalbano Jonico, southern Italy at 40°N, the forest expansion is also very strong (80%) during MIS 17 contrasting with the limited development in Lake Orhid. At this site, MIS 19 is further marked by a strong forest development contrasting with the limited expansion of the Mediterranean forest in SW Iberia.

How to cite: Sanchez Goñi, M. F., Oliveira, D., Morales-Molino, C., Desprat, S., Polanco-Martinez, J. M., Hodell, D., Naughton, F., and Rodrigues, T.: The Early-Middle Pleistocene interglacials in the Iberian margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3148, https://doi.org/10.5194/egusphere-egu22-3148, 2022.

Numerous studies have been made on paleoclimate and paleovegetation reconstructions and simulations of the past interglacials. However, systematical analysis of the global patterns of the correlation between vegetation pattern and astronomical forcing as well as CO₂ between different interglacials is rare. Given the distinct differences in orbital configurations and climate/vegetation variations between MIS-11 and MIS-13, we performed two sets of transient simulations using LOVECLIM 1.3, one driven by insolation change only, and another one by changes in both insolation and CO₂. These simulations allow us to investigate the relative effect of astronomical forcing and CO₂ on global and regional vegetation changes during these two interglacials. Our results show that the effects of precession and obliquity on vegetation depend strongly on regions, and the simulated results are in good agreement with vegetation reconstructions at key regions. The vegetation response differs widely between MIS-11and MIS-13, which is mainly caused by the difference in their astronomical configurations, and the difference in CO₂ concentration between these two interglacials plays a minor role. In addition to the effect of precession and obliquity, our simulations are also able to capture the half precession signal (~ 10 ka) in the climate and vegetation changes in the tropical regions in response to the tropical insolation.

How to cite: Su, Q., Lyu, A., Wu, Z., and Yin, Q.: Diverse manifestations of the impact of astronomical forcing and CO2 on climate and vegetation changes during MIS-11 and MIS-13, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4354, https://doi.org/10.5194/egusphere-egu22-4354, 2022.

In order to understand interglacial climate variability we also need to study interglacial periods prior to the Mid-Pleistocene Transition, i.e. within the 41 kyr world. Early Pleistocene interglacial periods, in particular from the interval directly preceding the onset of the Mid-Pleistocene Transition, provide ideal study cases since interglacial atmospheric carbon dioxide levels during that period appear to have been similar to or only slightly higher than during the warmest interglacials of the last 800 ka. Here we present the first results from a high-resolution, multi-proxy study of interglacial Marine Isotope Stage (MIS) 47 (1424-1452 ka) at IODP Site U1387 (36°48´N 7°43´W), drilled into the Faro Drift on the southern Portuguese margin at 559 m water depth. Nowadays, surface waters near Site U1387 originate from the subtropical gyre, whereas the intermediate-depth Mediterranean Outflow Water (MOW) is encountered at the seafloor. For our study, we use the stable isotope data of planktonic foraminifera species G. bulloides and G. ruber white and benthic foraminifera species P. ariminensis and C. pachyderma, biomarker-derived sea-surface temperatures (SST), the weight percentage of the sand fraction, and microfossil evidence.

Following a rapid transition, interglacial conditions were quickly established in the surface waters with SST at levels near or above 24°C, sometimes even exceeding 25°C, throughout much of MIS 47. Those are the warmest SST so far observed for the Pleistocene at that location, being more than three degrees warmer than modern SST. The common occurrence of tropical species in the planktonic foraminifera fauna hints to a persistent contribution of tropical waters to the surface waters and thus probably the northward expansion and/or intensification of the North Atlantic's subtropical gyre. The MOW, on the other hand, experienced an extended period of poor ventilation, most likely associated with low oxygen levels, as indicated by the extremely low benthic carbon isotope values and the occurrence of gypsum crystals in the sediments that formed when the pyrite in the sediments was oxidized after the cores were opened. Following evidence from younger interglacials, this MOW signal should be linked to reduced ventilation and overturning in the Mediterranean Sea as consequence of increased freshwater input caused by an intensified North African monsoon. The benthic δ¹⁸O record of MIS 47 indicates a three phased interglacial period with a minimum separating two maxima. On a subtle level, this phasing might also exist in the surface water records. This and potential causes need to be explored further in the future, when all high-resolution data is available. Overall, the Site U1387 records confirm MIS 47 as a "super"-interglacial, much more so than MIS 31, on the southern Portuguese margin. Insights from this warm interglacial and associated oceanographic conditions and changes in the planktonic and benthic microfossil floras and faunas might provide hints on how future warming in those waters could impact the regional ecosystems.

How to cite: Voelker, A. H. L., Rodrigues, T., Trotta, S., Marino, M., and Kuhnert, H.: A southern Portuguese margin perspective of Marine Isotope Stage 47 – an interglacial in the 41 kyr world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6616, https://doi.org/10.5194/egusphere-egu22-6616, 2022.

The climate system experienced several periodic oscillations over the last ca. 800 ka known as glacial-interglacial (G-IG) cycles. Disruptions of the global carbon cycle were evident on this time scale, promoting fluctuations in the atmospheric CO₂ concentration leading to global climate variability. In the more recent interglacials, both Antarctic temperatures and atmospheric CO₂ concentrations are significantly higher than in the previous “lukewarm interglacials” (ca. 800 – 430 ka) before the Mid-Brunhes Transition (MBT). Changes in the Atlantic Meridional Overturning Circulation (AMOC) and deepwater formation rate around Antarctica have been invoked to explain a 30 ppm increase in the atmospheric CO₂ ­during post-MBT interglacial periods. Deepwater variability is tightly coupled to the ventilation of CO₂ in the Southern Ocean by atmospheric and oceanic connections, contributing to carbon storage in the deep ocean and the atmospheric CO₂. Here, we present a new 770 ka benthic foraminifera δ¹³C record from sediment core GL-854 retrieved from the western South Atlantic (WSA) at 2200 m water depth. We compare our record with published δ¹³C data from the eastern margin to investigate the zonal gradient variability of the North Atlantic Deep Water (NADW) in the deep South Atlantic basin. WSA δ¹³C variability and absolute values strongly mimic the North Atlantic mid-depth record at the NADW formation region. This similarity is interpreted as NADW preferentially carrying a modified signal through the deep western boundary current towards the WSA (rather than towards the eastern margin) after the MBT. The δ¹³C gradient based on the difference between benthic foraminifera C. wuellerstorfi from both margins (Δδ¹³C_w-e) gradually increases after a transitional period between ca. 400 ka to 300 ka towards the Holocene. We suggest that the mechanism behind this long-term increasing trend on the Δδ¹³C_w-e record post-MBT is the result of enhanced production of North Component Water due to Agulhas Leakage intensification driven by reduced sea-ice extent after the MBT. Furthermore, reduced sea-ice extent decreases the Antarctic Bottom Water density and formation in the Southern Ocean, contributing to the deepening of the AMOC during post-MBT interglacial periods. Our interpretation proposes a framework connecting sea-ice and ocean-atmosphere dynamics to deepwater geometry within the South Atlantic basin, which ultimately contributed to the climate change observed across the MBT.

How to cite: Ballalai, J., Santos, T., Nascimento, R., Venancio, I., Piacsek, P., Dias, B., Belem, A., Costa, K., Vázquez Riveiros, N., and Albuquerque, A. L.: Increased zonal δ13C gradient in the deep South Atlantic after the Mid-Brunhes Transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8018, https://doi.org/10.5194/egusphere-egu22-8018, 2022.

The North Atlantic Oscillation (NAO) is currently the main mode of winter atmospheric variability in the extratropical Northern Hemisphere. It represents the fluctuation of the meridional sea-level pressure gradient in the North Atlantic, with high and low phases defined by high and low pressure gradients, respectively. High (or low) NAO phases are associated with wet and warm (or dry and cold) weather conditions in Northern Europe. In mid latitude regions such as the Mediterranean, this relationship is inverse, producing dry and cold (or wet and warm) conditions. Whether or not the average state of the NAO may have shifted in the past is much debated, with major implications for the understanding of past regional climate. Using a climate model, Felis et al. (2004) showed that the average state of the NAO during the Last Interglacial (130-115 ka BP) was significantly higher than during the pre-industrial period, with a high plateau from ~126 to 118 ka BP. However, proxy-based reconstructions of temperature and rainfall are needed to support this. Here, we use a new method, Brillouin spectroscopy on halite fluid inclusions, to reconstruct the evolution of temperature and hydrology in the Dead Sea, southern Levant, throughout the Last Interglacial. We find lower than modern Dead Sea temperatures and a lowering freshwater influx throughout the last interglacial. Using climate data from the recent decades, we demonstrate that the temperature of the Dead Sea hypolimnion mainly depends on winter air temperature, which is itself anti-correlated with the NAO. We also demonstrate that, during years of very high NAO, rainfall is drastically reduced in the lake catchment. In light of our analysis of modern climate data, the reconstructed cold and dry conditions in the Dead Sea area is consistent with the modelled higher NAO conditions.

How to cite: Guillerm, E., Gardien, V., Brall, N., Ariztegui, D., Schwab, M., Neugebauer, I., Waldmann, N., Lach, A., and Caupin, F.: Higher state of the North Atlantic Oscillation during the Last Interglacial (130-115 ka BP): evidence from temperature and hydrology in the Dead Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10148, https://doi.org/10.5194/egusphere-egu22-10148, 2022.

Investigating climate models responses and feedbacks under warmer climates is useful in building confidence in future climate projections. Here we focus on the summer sea ice in the Arctic during the Last Interglacial period (LIG), when the Arctic was warmer than the Pre-Industrial period (PI) by around 4.5 ± 1.7 K. Given that it is difficult to ascertain the state of Arctic sea ice from marine core proxies of sea ice state, we focus instead on summer surface air temperature (SSAT) in CMIP6-PMIP4 simulations and compare these with equivalent proxy data. All 12 models we have analysed show both warmer SSAT and a reduction in summer sea ice in the LIG compared to the PI, with an average warming of +3.6K and an average 52% decrease in minimum sea ice area.

We find that model-observation differences in LIG SSAT are linearly related to the percentage loss of summer Arctic sea ice. However this general finding does not fit the CNRM model result, which is an outlier. This simulation captures the observed pattern of SSAT, without being close to ice-free. However peculiarities in the CNRM set-up (forcing and sea ice model tuning) means it is unclear what can be drawn from this one result. CNRM aside, models tend to yield more accurate LIG SSAT changes when they are closer to an ice-free state in summer. The models which feature sea ice losses larger than the multi-model-mean sea ice loss, tend to have the smallest model-observation SSAT errors. The results of this study provides caveated support to the argument that Arctic could have been ice-free during LIG summers. That said, a careful examination of the SSAT dataset would also be value to the LIG community, given that these results are dependent on the LIG SSAT observational dataset.

How to cite: Sivankutty, R., Sime, L., Malmierca Vallet, I., and de Boer, A.: Summer Arctic temperatures in PMIP4 Last Interglacial simulations and their link to Arctic sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12679, https://doi.org/10.5194/egusphere-egu22-12679, 2022.

Past interglacials allow investigating the climatic processes and associated feedbacks during warm periods, which are characterized by different combinations of climatic forcing such as solar radiation, GHGs, and ice sheets. Arctic warming amplification, a common phenomenon between past interglacials and present warming, has seasonality in its feedback mechanism, and detailed study of these internal feedbacks is still lacking despite its global impact. In this study, the simulation experiments under conditions close to the past interglacial periods (MIS1; Holocene, MIS5e; Last Interglacial, and MIS11) are conducted using a coupled atmosphere-ocean-vegetation model MIROC (4m) AOVGCM, particularly focusing on the role of ice sheets and Arctic sea ice. Climate responses to inputs and conditions are compared to examine the seasonal effects of atmosphere-ocean-ice feedbacks on Northern hemisphere high-latitudes temperature. Ice sheet distribution is set as a boundary condition in addition to the orbital elements, land cover, and GHGs to account the effect of remaining ice sheets at the timing of peak insolation. Feedback Analysis is also conducted to quantify the contribution of each feedback element to the surface temperature change. It is demonstrated that an inter-seasonal effect of air-sea-ice-vegetation feedbacks contributes to Arctic warming amplification, where heat gained in summer is used for sea ice melting and ocean absorption, and is released in autumn and winter, resulting in annual warming. This process is amplified when considering vegetation feedbacks and seen commonly in MIS1, 5e, and 11. In periods when ice sheets remain, Arctic sea ice keeps a high degree of concentration in summer, and annual mean temperatures at Northern high latitudes are lower than would be expected from insolation intensity. These results imply that the presence of Northern hemisphere ice sheet has a significant effect on Arctic climate response to insolation intensity by suppressing feedbacks that contribute to Arctic amplification through the reduced melt of summer sea ice.

How to cite: Hirose, L., Abe-Ouchi, A., Yoshimori, M., Chan, W.-L., O'ishi, R., and Obase, T.: Arctic Amplification through Inter-seasonal Feedback Effect in Past Interglacials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12943, https://doi.org/10.5194/egusphere-egu22-12943, 2022.

Marine oxygen isotope records and ice cores in Antarctica suggest that Marine Isotope Stage (MIS) 9, an interglacial occurring about 300 ka ago, is a strong interglacial and has the highest greenhouse gases (GHG) concentrations during the past 800 ka. Model results also show that MIS-9 is the warmest interglacial among the last nine ones as a result of both its high CO₂ concentration and its high summer insolation in the northern Hemisphere (NH). However, the China loess records show that the paleosol S3 that corresponds to MIS-9 is not necessarily strong as compared to some other paleosol units such as the S4 soil that was formed during MIS-11, suggesting relatively drier climate condition during MIS-9. By contrast, in Tajikistan of southern central Asia, the paleosol S3 is the most developed soil over the past 800 ka, indicating a relatively warm and humid climate conditions. The difference in the paleosol formation and the MIS-9 climate between monsoonal China and central Asia is intriguing. In this study, we combine loess records from monsoonal China and central Asia as well as climate simulation results to understand the spatial difference of the MIS-9 climate in particular in comparison with the climate of MIS-11. The individual and combined contributions of insolation and greenhouse gases are quantified through simulations with the LOVECLIM model and using the factor separation technique. Our results show that the simulated effective moisture conditions between northern China and southern central Asia are consistent with the loess records and field observation. Insolation leads to much more annual mean precipitation than GHG during MIS-9 in southern central Asia, explaining a much wetter MIS-9 there. By contrast, both insolation and GHG lead to more annual mean precipitation and evaporation during MIS-9 in northern China, leading to only a slight difference in the effective moisture between MIS-9 and MIS-11. In addition, compared to MIS-11, the larger obliquity and higher GHG concentration during MIS-9 lead to an anomalous atmospheric circulation pattern similar to negative phase of North Atlantic Oscillation (NAO), favoring precipitation increase in southern central Asia and therefore explain strong soil development in Tajikistan.

How to cite: Lu, H., Yin, Q., Wu, Z., Shi, F., Hao, Q., Xia, D., and Guo, Z.: Impacts of insolation and CO2 on the spatial differences of the MIS-9 and MIS-11 climate between monsoonal China and central Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13117, https://doi.org/10.5194/egusphere-egu22-13117, 2022.

Interglacial intensity in past 800 kyr is characterized by a transition, about 430 kyr ago, between the older ones, which were relatively cool and low sea level, and the more recent ones, which were relatively warm and high sea level. This transition, as identified in Antarctic ice core and benthic calcite d¹⁸Oc records, corresponds to the so-called mid-Brunhes Transition (MBT). However, its origin and underlying dynamics remain elusive. Here we show, based on a start-of-art, stable water isotope enabled climate model, that additional ice volume to the present-day levels should be considered in order to reproduce the systematic enrichment in interglacial d¹⁸Oc before the MBT. This extra ice of ~18 e.s.l.m. likely exists in the Antarctic, which in turn weakens vertical mixing in Southern Ocean, potentially accounting for the low interglacial atmospheric CO₂ levels prior to the MBT. Our results further indicate that during MIS11c the unique climate background leads to extra Antarctic ice sheet melting, eventually giving rise to a systematic change in interglacial climate and hence accounting for the MBT.

How to cite: Zhang, X., Barker, S., Werner, M., Sun, Y., and Tzedakis, C.: Mid-Brunhes Transition caused by Antarctic ice sheet melting during MIS11c, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13443, https://doi.org/10.5194/egusphere-egu22-13443, 2022.

The mechanism of stochastic resonance (SR) in a bistable system was introduced [1] to explain the glacial-interglacial cycles in the Quaternary and is still regarded as a dynamical systems paradigm for those climate cycles. In the SR the stochastic forcing must satisfy a rather stringent condition; besides, glacial inceptions occur abruptly, as well as the glacial terminations. However, these conditions do not seem to be verified in the real climate system. Here it is shown that the alternative dynamical paradigm -that may be termed deterministic excitation (DE)- in which relaxation oscillations (ROs) are excited by the astronomical forcing in a purely deterministic framework, overcomes those limitations and may therefore provide a more plausible theoretical basis for the explanation of the glacial-interglacial variability.

In an excitable dynamical system a RO connects a basic state to an unstable excited state, which is then followed by a spontaneous, slow return to the original state. Such transition is self-sustained in a given parameter range of the autonomous system, otherwise it can be excited by an external deterministic time-dependent forcing (DE) or by noise (coherence resonance). Examples of DE in ocean dynamics are presented for the Kuroshio Extension in the North Pacific and for the Antarctic Circumpolar Current in the Southern Ocean.

A 4-dimensional nonlinear excitable spectral model of the wind-driven ocean circulation [2] is then used to briefly illustrate the main aspects of excitable climate dynamics, focusing on the occurrence of coherence resonance [3], on the DE of ROs under the action of an aperiodic forcing [4] and on the tipping points due to parameter drift [5]. Finally, a classical energy balance model is extended to obtain a minimal excitable model of the late Pleistocene ice ages [Pierini, in preparation]. The timing of the interglacials, determined by the DE caused by the variations of the Earth’s orbital eccentricity and axial tilt and precession, is found to be in significant agreement with proxy data. (Support from the IPSODES-P.N.R.A. project is acknowledged)

[1] Benzi R., Parisi G., Sutera A., Vulpiani A., 1982. Tellus 34, 10-16.

[2] Pierini S., 2011. J. Phys. Oceanogr. 41, 1585-1604.

[3] Pierini S., 2012. Phys. Rev. E 85, 027101.

[4] Pierini S., Ghil M., Chekroun M.D., 2016. J. Climate 29, 4185-4202.

[5] Pierini S., Ghil M., 2021. Sci. Rep. 11, 11126.

How to cite: Pierini, S.: On the functioning of the glacial-interglacial variability: deterministic excitation vs. stochastic resonance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1039, https://doi.org/10.5194/egusphere-egu22-1039, 2022.

  The Milankovitch Theory of orbital climate change postulates that changes in the caloric summer half-year insolation (or Northern Hemisphere summer insolation (NHSI) at ~65°N latitude) drive changes in the ice-sheets extent (i.e., global ice-volume) at Earth’s orbital periods (i.e., the sensu-stricto theory). These insolation-driven changes in turn, incite ancillary changes in other parts of the global climate systems via various forcing and feedback mechanisms (the sensu-lato hypothesis). In this theoretical framework the high-latitude glaciation processes took the center stage while the low-latitude global monsoon was essentially excluded. In the last two decades, large numbers of cave d¹⁸O records with precise radiometric chronologies have propelled speleothems to the forefront of paleoclimatology. Of particular interest are the speleothem records from North America that reveal a persistent orbital pacing of the North American climate at the precession band, which is nearly in phase with changes in the global ice-volume and atmospheric CO₂ but lags June insolation at 65°N by ~5000 years, in accordance with the sensu-stricto Milankovitch theory. Contrastingly, the low-latitude tropical speleothem records manifest an orbital-scale pattern of global monsoon, which is dominated by precession cycles with a nearly anti-phased relation between the two hemispheres. Importantly, the monsoon variations track summer (July/January) insolation without significant lags at the precession band. We thus suggest that precession-induced changes in summer insolation produce distinct climate variability in the ice-sheet proximal and tropical regions predominantly via the (delayed) ice-volume/CO₂ forcing/feedbacks and nearly-in-phase monsoon/CH₄ responses/feedbacks.

  As for global-scale millennial events that were superimposed on orbital-scale climate variations, the essence of these events—i.e., conventional ice age terminations and other smaller events (the so-called ‘low-amplitude versions of terminations’), is virtually similar. The time-series of millennial-scale variations after removing orbital insolation signals from the speleothem monsoon record and long-term trend in the Antarctic ice core temperature (δD) record characterize the millennial climate variances of both ice age termination and low-amplitude versions of termination events. Remarkably, the millennial-scale variations show significant obliquity and precession cycles that are in-phase with North Hemisphere June insolation, implying a critical role of changes in orbital insolation in triggering the ice age terminations. These observations, in turn, provide new insights into the classic ‘100 ka problem’.

  Indeed, a more comprehensive picture of orbital theory of climate is steadily emerging with the growth of new geological proxy data, particularly the low-latitude speleothem data from the vast global monsoon regime, providing critical complements to marine and ice-core data.

How to cite: Cheng, H.: Milankovitch Theory and Global Monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1422, https://doi.org/10.5194/egusphere-egu22-1422, 2022.

The stratigraphic records of shallow-marine environments are not commonly regarded as excellent climate archives because of their presumed temporal incompleteness. However, a recent study of lower Pleistocene strata in the Western Foreland Basin, Taiwan, reveals high-resolution records of past climate oscillations preserved within shallow-marine strata. Deriving such narratives is made possible because of the high accommodation and sedimentation rates in the basin, which enhanced the completeness of the stratigraphic record.

Here, we astrochronologically tune the Chinshui Shale and the lower part of the Cholan Formation of the Western Foreland Basin from approximately 3.5 to 2 Ma. These strata are calibrated to global deep-sea stable oxygen isotope (δ¹⁸O) records with established time scales detailing global climate change during the studied time period. The Chinshui Shale is mudstone-dominated and was deposited mostly in offshore settings, while the Cholan Formation comprises mainly heterolithic strata deposited in shallower settings (i.e., offshore transition, nearshore) of the paleo-Taiwan Strait. The data used herein are two borehole gamma-ray profiles through the Chinshui Shale and the Cholan Formation that have a proximal-distal relation to Taiwan. High gamma-ray values reflect clay-rich intervals and correlate to lower values of δ¹⁸O in the global reference records. Low gamma-ray values point to sand-rich packages and correlate with higher values of δ¹⁸O.

Preliminary results show that the alternating clay-rich to sand-rich deposits during the late Pliocene to early Pleistocene are orbitally paced. The results allow us to i) tune the upper Pliocene–lower Pleistocene Chinshui Shale and lower part of the Cholan Formation, ii) refine the magneto-biostratigraphic framework established for this time interval in the Western Foreland Basin of Taiwan, and iii) lay the groundwork for connecting climatic changes in Taiwan during this time period to the wider frame of global climate change. 

How to cite: Vaucher, R., Zeeden, C., Hsieh, A., Kaboth-Bahr, S., Lin, A. T., Horng, C.-S., and Dashtgard, S. E.: Towards an astrochronological tuned age model for the upper Pliocene–lower Pleistocene Western Foreland Basin of Taiwan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1435, https://doi.org/10.5194/egusphere-egu22-1435, 2022.

Inter-basinal heat and water exchange play a prominent role in driving global climate change on astronomical timescales, as part of the global thermohaline circulation. Tasman Leakage connects the Pacific and Indian Oceans at an intermediate water depth, south of Australia. Therewith, Tasman Leakage advects heat toward the Indian Ocean, and ultimately toward the Agulhas system. Hence, Tasman Leakage constitutes a non-negligible part of the present-day thermohaline circulation. The onset of Tasman Leakage likely occurred sometime in the Late Miocene (Christensen et al., 2021), but precise geochronology for the establishment of this inter-basinal connection is still lacking. Moreover, Tasman Leakage sensitivity to astronomical forcing remains to be constrained in detail. To understand Tasman Leakage on astronomical timescales, we present a new Miocene-to-recent multi-proxy dataset from Ocean Drilling Program (ODP) Sites 752 and 754, cored on Broken Ridge (30°53.475’S), southeastern Indian Ocean.

The dataset consists of new X-ray Fluorescence (XRF) core scans that provide element contents for 18 different elements, along with benthic carbon and oxygen stable isotopic records at 4 cm resolution. The XRF-derived Ca/Fe record is paced by 405-kyr eccentricity between 22 Ma and 13 Ma (early-middle Miocene), but then becomes more sensitive to obliquity and precession forcing. The new high-resolution benthic δ¹³C record confirms the onset of Tasman Leakage in the Late Miocene, more specifically at 6.6 Ma. This is when the Broken Ridge benthic δ¹³C signature no longer reflects an Antarctic Intermediate Water signal. The benthic δ¹⁸O record shows a strong ~110-kyr eccentricity imprint, indicating that Tasman Leakage might be most sensitive to this astronomical parameter. We conclude that the Neogene nannofossil oozes, preserved on Broken Ridge, constitute an excellent paleoceanographic archive that allows us to fingerprint Tasman Leakage sensitivity to astronomical forcing.

How to cite: Lyu, J., Christensen, B., Auer, G., and De Vleeschouwer, D.: Multiproxy paleoceanography from Broken Ridge pinpoints the onset of Tasman Leakage at 6.6 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1451, https://doi.org/10.5194/egusphere-egu22-1451, 2022.

The Pliocene sedimentary record provides a window into Earth’s climate dynamics under warmer-than-present boundary conditions. However, the Pliocene cannot be considered a stable warm climate that constitutes a solid baseline for middle-road future climate projections. Indeed, the increasing availability of time-continuous sedimentary archives (e.g., marine sediment cores) reveals complex temporal and spatial patterns of Pliocene ocean and climate variability on astronomical timescales. The Perth Basin is particularly interesting in that respect because it remains unclear if and how the Leeuwin Current sustained the comparably wet Pliocene climate in West-Australia, as well as how it influenced Southern Hemisphere paleoclimate variability. To constrain Leeuwin Current dynamics in time and space, this project constructed a new orbitally-resolved planktonic foraminifera (Trilobatus sacculifer) stable isotope record (δ¹⁸O and clumped isotopes Δ₄₇) for the Plio-Pleistocene (4–2 Ma) interval of International Ocean Discovery Program (IODP) Site U1459. It complements an existing TEX₈₆ record from the same site and similar planktonic isotope records from the Northern Carnarvon Basin (ODP Site 763 and IODP Site U1463). The comparison of TEX₈₆ and Δ₄₇ paleothermometers reveals that TEX₈₆ likely reflects sea surface temperatures (SST, 23.8–28.9 °C), whereas T. sacculifer Δ₄₇ calcification temperatures probably echo the state of the lower mixed layer and upper thermocline at the studied Site U1459 (18.2–20.8 °C). The isotopic δ¹⁸O gradient along a 19° S–29° S latitudinal transect, between 3.9–2.2 Ma, displays large variability, ranging between 0.5 and 2.0 ‰, whereby a low latitudinal gradient is indicative of a strong Leeuwin Current and vice versa. These results challenge the interpretation that suggested a tectonic event in the Indonesian Throughflow as the cause for the rapid steepening of the isotopic gradient (0.9 to 1.5 ‰) around 3.7 Ma. The tectonic interpretation appears obsolete as it is now clear that the 3.7 Ma steepening of the isotopic gradient is intermittent, with flat latitudinal gradients (~0.5 ‰) restored in the latest Pliocene (2.9–2.6 Ma). Still, the new analysis affirms that a combination of astronomical forcing of wind patterns and eustatic sea level controlled Leeuwin Current intensity. A period of relatively weak Leeuwin Current between 3.7 and 3.1 Ma is advocated; a time interval also marked by cooler conditions throughout the Southern Hemisphere. In conclusion, the intensity of the Leeuwin Current and the latitudinal position of the subtropical front are rooted in the same forcing: Heat transport through the Indonesian Throughflow (ITF) valve propagated to the temperate zone through Indian Ocean poleward heat transport. The common ITF forcing explains the observed coherence of Southern Hemisphere ocean and climate records.

How to cite: De Vleeschouwer, D., Peral, M., Marchegiano, M., Füllberg, A., Meinicke, N., Pälike, H., Auer, G., Petrick, B., Snoeck, C., Goderis, S., and Claeys, P.: Plio-Pleistocene Perth Basin water temperatures and Leeuwin Current dynamics (Indian Ocean) derived from oxygen and clumped isotope paleothermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1982, https://doi.org/10.5194/egusphere-egu22-1982, 2022.

In this study, we synthesize terrestrial and marine proxy records, spanning the past 620,000 years, to decipher pan-African climate variability and its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to El Niño Southern Ocean oscillation (ENSO) variability, a manifestation of the Walker Circulation, that was most likely driven by changes in Earth’s eccentricity. Our results demonstrate that low-latitude insolation was a prominent driver of pan-African climate change during the Middle to Late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa by increasing resource-rich and stable ecotonal settings thought to have been important to early modern humans.

How to cite: Kaboth-Bahr, S., Gosling, W. D., Vogelsang, R., Bahr, A., Scerri, E. M. L., Asrat, A., Cohen, A. S., Düsing, W., Foerster, V., Lamb, H. F., Maslin, M. A., Roberts, H. M., Schäbitz, F., and Trauth, M. H.: Paleo-ENSO influence on African environmentsand early modern humans, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2038, https://doi.org/10.5194/egusphere-egu22-2038, 2022.

Mechanisms driving cyclicity in the marine realm during hothouse climate periods in response to Earth’s orbit variations remains debated. Orbital cycles fingerprint in the oceanographic records results from the effect of terrestrial (eg. weathering-derived nutrient supply, freshwater discharge) and oceanic (eg. productivity, oxygenation) processes, whose respective contribution remains to be defined. Here we investigate the effect of extreme orbital configurations on oxygenation state of the ocean using ocean biogeochemistry simulations with the IPSL-CM5A2 Earth System Model under (CT) Cenomanian-Turonian boundary conditions. We also use an additional inert artificial tracer allowing to compute the age of water masses, corresponding to the time spent since the last contact with the surface. Our simulations show that small ocean ventilation changes triggered by orbitally-induced variations in high latitude deep water formation have strong impact on the oceanic oxygen spatial distribution. It is particularly true for the proto-Atlantic basin which is the less oxygenated basin during the CT (Laugie et al., 2021). The eight sets of orbital parameters tested here imply changes in the Atlantic anoxic seafloor area going from 20 to 80%. All three parameters describing the Earth’s orbit (eccentricity, precession and obliquity) show a substantial control on these fluctuations. We also note that orbital fluctuations result in important changes in continental runoff but the impact remains highly localized to coastal environments – the open ocean mainly responding to the ocean ventilation. Last but not least, changes in productivity induced by the orbital parameters remain spatially heterogeneous and could be responsible for more local signal within a single basin.

Laugié, M., Donnadieu, Y., Ladant, J. B., Bopp, L., Ethé, C., & Raisson, F. (2021). Exploring the impact of Cenomanian paleogeography and marine gateways on oceanic oxygen. Paleoceanography and Paleoclimatology, 36(7):e2020PA004202.

How to cite: Sarr, A.-C., Laugié, M., Donnadieu, Y., Ladant, J.-B., and Raisson, F.: Orbital-scale deoxygenation trends driven by ventilation in Cretaceous ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2362, https://doi.org/10.5194/egusphere-egu22-2362, 2022.

Combining both detailed geological records and climate modeling provides exciting opportunities to understand orbital effects on the early Mesozoic greenhouse climate across the supercontinent Pangaea. Lake sediments from the Newark-Hartford Basins (NHB) of the eastern US record cyclic climate changes in the tropics of Pangaea during the Late Triassic and earliest Jurassic (~233–199 Ma). We explore how the combined climatic effect of orbital forcing, paleogeographic changes and atmospheric pCO₂ variations could have contributed to major features of this record.

For this, we assess results from an ensemble of transient, orbitally driven climate simulations for nine geologic timeslices, three atmospheric pCO₂ values and two paleogeographic reconstructions. Each simulation is run with an idealized orbital forcing, with precession, modulated by eccentricity, and obliquity oscillating over a 250 kyr interval. The long duration and large number of simulations is achieved by utilizing the fast CLIMBER-X Earth System Model.

A transition from tropical humid to more seasonal and ultimately semi-arid climates is associated with the tectonic drift of the NHB region from the equator to ~20°N. The orbital modulation of the precipitation-evaporation balance that could be recorded in the lake sediments is most pronounced during 220 to 200 Ma, while it is limited by weak seasonality and increasing aridity before and afterwards, respectively. Lower pCO₂ values around 205 Ma contribute to drier climates and could have led to the damping of sediment cyclicity observed at this time. Eccentricity-modulated precession dominates the orbital climate response in the NHB area, with maximum humidity associated to high spring-summer insolation and enhanced moisture import from the Tethys sea. High obliquity further amplifies summer precipitation through the seasonally shifting tropical rainfall belt.

We furthermore show how contemporaneous proxy localities, e.g. in the Germanic Basin, Junggar Basin or Colorado Plateau, can also be evaluated in this model framework. Studying the varying climate response in these different areas provides directions towards an integrated picture of global astronomical climate pacing in the Late Triassic. Furthermore, the presented approach is readily applicable to other periods in Earth history.

How to cite: Landwehrs, J., Wagreich, M., Feulner, G., Willeit, M., Whiteside, J. H., and Olsen, P. E.: Astronomical Climate Pacing in a Model Framework for Late Triassic Lake Level Cycles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3744, https://doi.org/10.5194/egusphere-egu22-3744, 2022.

The early Eocene greenhouse climate is characterised by a series of ‘hyperthermal’ events, defined by transient negative excursions in marine carbonate carbon and oxygen isotopes. Proxy records of the larger magnitude hyperthermal events are consistent with massive carbon release to the ocean-atmosphere system and associated with global warming and ocean acidification. Such events therefore represent the best analogues for current anthropogenic climate change. However, the causes and nature of smaller early Eocene hyperthermals, particularly through the early Eocene Climatic Optimum (EECO), are less well understood. We know that hyperthermal events are paced by the 100 kyr (short) and 405 kyr (long) eccentricity cycles, indicating that Earth’s orbital parameters play a key role in driving carbon cycle perturbations, but the precise forcing mechanisms remain unclear. Additionally, few continuous records of the smaller, orbitally-paced hyperthermals exist and there have been no published high-resolution climate records from the Indian Ocean so far from this interval. High-resolution records across the full spectrum of hyperthermal events and from multiple ocean basins are needed to fully identify their cause(s). Here, we constrain the nature and magnitude of environmental change during hyperthermal events O-T in the Indian Ocean using a new, high-resolution benthic stable isotope record from IODP Expedition 369 Site U1514, Indian Ocean, from 50-51 Ma. Using spectral analysis techniques, we identify the dominant periodicities in the benthic stable isotope record and investigate the phasing between stable isotopes and other environmental records from Site U1514, including sedimentary Ca/Fe. We compare the Site U1514 stable isotope record with environmental records across this time interval from other sites to determine the synchronicity of climate and carbon cycle changes between different ocean basins, aiming to further examine the forcing mechanisms of these early Eocene hyperthermal events. 

How to cite: Kirby, N., Batenburg, S., Leng, M., Dunkley Jones, T., and Edgar, K.: Orbital forcing of early Eocene hyperthermal events: A new benthic foraminiferal record from the Indian Ocean, 50-51 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4667, https://doi.org/10.5194/egusphere-egu22-4667, 2022.

Due to tidal interactions in the Earth-Moon system, the spin of the Earth slows down with time and the Moon drifts away. This present recession of the Moon is now measured with great precision using Lunar Laser Ranging, but it has been realised, more than fifty years ago, that simple solid-Earth tidal models extrapolated backwards in time lead to an age of the Moon that is by far incompatible with the geochronological and geochemical evidence. Since then, in order to evade this paradox, more elaborated models have been proposed, taking into account the tidal frequency-dependent oceanic dissipation; but none so far has been able to fit both the estimated lunar age and the present rate of lunar recession. In this talk, we present a physical model that reconciles these two constraints and yields a unique solution of the tidal history. This solution fits remarkably well the available geological proxies and consolidates the cyclostratigraphic method, although such a fit was not imposed. The resulting evolution involves multiple crossings of resonances in the oceanic dissipation that are associated with significant and rapid variations in the lunar orbital distance, the Earth’s length of the day, obliquity, and precession frequency. 

How to cite: Farhat, M., Auclair-Desrotour, P., Boué, G., and Laskar, J.: The Resonant Tidal Evolution of the Earth-Moon Distance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5323, https://doi.org/10.5194/egusphere-egu22-5323, 2022.

Many paleoclimate records show that the end of interglacials of the late Pleistocene was marked by abrupt cooling events and increased millennial variability. Strong abrupt cooling occurring when climate was still in a warm interglacial condition is puzzling and its cause remains uncertain. In this study, we performed transient climate simulations for all the eleven interglacial (sub)stages of the past 800,000 years with the model LOVECLIM1.3 (Yin et al., 2021). Our results show that there exists a threshold in the astronomically induced insolation below which abrupt changes at the end of interglacials occur. When the summer insolation in the Northern Hemisphere (NH) high latitudes decreases to a critical value, it triggers a strong, abrupt weakening of the Atlantic meridional overturning circulation (AMOC) and a strong cooling in the NH followed by high-amplitude variability. The mechanism involves sea ice feedbacks in the Northern Nordic Sea and the Labrador Sea. Similar abrupt oscillations happen in the simulated temperature, precipitation and vegetation from low to high latitudes. Our simulated results are supported by observations from many marine and terrestrial records, including for example the planktic d18O record from the Iberian Margin, the Greenland ice core record and the Chinese speleothem records. Our study shows that the astronomically-induced slow variation of insolation could trigger abrupt climate changes. The insolation threshold occurred at the end of each interglacial of the past 800,000 years, suggesting its fundamental role in terminating the warm climate conditions of the interglacials. Our results show that the next insolation threshold will occur in 50,000 years, suggesting an exceptionally long interglacial ahead, which is in line with what has been suggested by previous modelling studies. 

Reference:  Yin Q.Z., Wu Z.P., Berger A., Goosse H., Hodell D., 2021. Insolation triggered abrupt weakening of Atlantic circulation at the end of interglacials. Science, 373, 1035-1040, DOI: 10.1126/science.abg1737

How to cite: Yin, Q., Wu, Z., Berger, A., Goosse, H., and Hodell, D.: Astronomical forcing as a trigger of abrupt climate changes at the end of interglacials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6073, https://doi.org/10.5194/egusphere-egu22-6073, 2022.

Some of the large climatic changes of the past originate in the variations of the Earth’s orbit and of its spin axis resulting from the gravitational pull of the planets and the Moon. These variations can be traced over several millions of years back in time (Ma) in the geological sedimentary records (e.g. Milankovitch cycles). Over the last decades, the Earth’s orbital and spin solutions have been used to establish a geological timescale based on the astronomical solutions. Nevertheless, extending this procedure through the Mesozoic Era (66-252 Ma) and beyond is difficult, as the solar system motion is chaotic. It will thus not be possible to retrieve the precise orbital motion of the planets beyond 60 Ma from their present state.

Astrogeo, a project funded by the European Research Council (ERC), will use the geological record as an input to break the horizon of predictability of 60 Ma resulting from the chaotic motion of the planets. This will be achieved by considering statistical methods and by using ancient geological data as an additional constraint in obtaining astronomical solutions. Astrogeo aims to provide a template orbital solution for the Earth that could be used for paleoclimate studies over any geological time. This will open a new era where the geological records will be used to retrieve the orbital evolution of the solar system. It will thus open a new observational window for retrieving not only the history of the Earth, but of the entire solar system. Here, we want to reach out to the broader cyclostratigraphic community to discuss suitable procedures and data sets to couple both theoretical solutions and geological observations. In particular, we are interested in examining high-quality data sets with clear and well-constrained (single or combined) expressions of the astronomical parameters of eccentricity, precession and obliquity.

How to cite: Sinnesael, M. and Laskar, J.: Integrating astronomical solutions and geological observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6423, https://doi.org/10.5194/egusphere-egu22-6423, 2022.

How the global carbon cycle and climate changes interact on orbital timescales under different boundary conditions remains elusive. Previous studies have found that changes in global ice-sheet volume and marine carbon cycle are synchronized at the eccentricity time scales with a slight lead of climate-cryosphere relative to carbon cycle throughout Oligo-Miocene (~34-6 Ma). Here, we analyze the evolutive phase relationship between benthic foraminiferal oxygen (δ¹⁸O) and carbon isotope (δ¹³C) to reveal an unnoticed phenomenon that variations of oceanic carbon cycle could lead those of global ice-sheet volume on 405-kyr cycle during Miocene Climate Optimum (MCO, ~17-14 Ma), which was a profound warming interval partly ascribed to the carbon emission from the eruption of the Columbia River Basalts Group (CRBG). Eccentricity sensitivity analysis indicate a relatively constant response of ice sheet to orbital forcing during MCO. Combined the results of box model, we propose that volcanic CO₂ input accelerates the response of marine carbon cycle to orbital forcing. The enhanced greenhouses effect probably had strengthened the low-latitude hydrological cycle and chemical weathering and ultimately generated the δ¹³C-lead-δ¹⁸O scenario.

How to cite: Liu, F., Huang, E., Du, J., Ma, W., Ma, X., Lourens, L., and Tian, J.: Perturbations of volcanic CO2 emission to orbital paced climate-carbon cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6429, https://doi.org/10.5194/egusphere-egu22-6429, 2022.

The Silurian (443.8-419.2 million years ago) is a period of important biodiversity changes, dynamic climate change, including strong sea level fluctuations and the development of low-oxygen conditions in the ocean^1-2-3. To date the Silurian lacks in (cyclostratigraphic) age constraints and in understanding in the way astronomical cycles modulate the Silurian climate, which hinders our understanding of Silurian climate dynamics. To assess the role of astronomical cycles in the pacing of the Silurian climate, we study the imprint of astronomical cycles on the record of the Sommerode-1 core from Bornholm, Denmark (53.65-118.66m).The core contains a near continuous Telychian record including the SOCIE and Valgu carbon isotope excursions/events^4-5-6.  The core was scanned at University of Bremen/ MARUM (November 2021) using the Bruker M4 Tornado µXRF scanner, enabling for a high-resolution cyclostratigraphic and chemostratigraphic study of the Telychian.

XRF core measurements provided semi-quantitative element data, spaced at 0.5 mm, were converted into element concentrations (ppm) using a set of reference standards. A Principal Component Analysis simplified the variability in our dataset into 3 components. PC1 has high loadings for Al, Si, K, Ti, Fe and Co, and is interpreted as a detrital component. PC2 has high loadings for Ca and Mn, and is interpreted as an indicator of oxygenation conditions. PC3 has high loadings for S, indicative for the sulphides/dysoxic/anoxic conditions^-8-9.

Peaks for Mn at 69-85m and S at 85-104m, indicate that part of the core (69-85 m) was deposited under oxic conditions while another part of the core (85-104 m) was deposited under anoxic/dysoxic conditions. We note that the transition to oxic conditions at 90 m coincides with the Valgu isotopic event⁴ while the SOCIE⁴ (80-70 m) event occurs during oxic conditions. Spectral analysis (wavelet, MTM and Evolutive Harmonic Analysis (EHA)) on the 3 components reveals the imprints of long and short eccentricity, obliquity and precession. An EHA spectra of the detrital component was used to trace the long eccentricity in the depth domain which was used to infer changes in sedimentation rates. The sedimentation rates are used to convert the record from the depth to time domain. Astronomical cycles filtered from the record in the time domain show that astronomical cycles exert a great control on the depositional record.  Indicating the astronomical cycles modulated the Telychian climate which in term paced oxygenation conditions at the sea-floor.

1.Melchin et al. (2005) The Silurian Period 525–558 –

2. Bond & Grasby (2017) Palaeogeogr., Palaeoclim., Palaeoecol. 478, 3–29. –

3. Saltzman (2005) Geology, 33, 7, 573-576. –

4. Hammarlund et al. (2019) Palaeogeogr., Palaeoclim., Palaeoecol. 526, 126–135. –

5. Schovsbo, et al. (2015). Geological Survey of Denmark and Greenland Bulletin, 33, 9–12.

6. Loydell, D. K., et al. (2017). Bulletin of the Geological Society of Denmark, 65, 135–160.

7. Algeo, T. J., & Maynard, J. B. (2004). Chemical Geology, 206(3–4), 289–318.

8. Ferriday, T., & Montenari, M. (2016). Stratigraphy & Timescales (Vol. 1).

9. Rothwell, R. G., & Croudace, I. W. (2015). Tracking Environmental Change Using Lake Sediments. (Vol. 2)

How to cite: Arts, M., De Vleeschouwer, D., Schovsbo, N. H., Thibault, N., Nielsen, A. T., and Da Silva, A.-C.: Astronomical modulation of oxygenation conditions during the Telychian (Silurian) recorded in the Sommerodde-1 core from Bornholm Denmark., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11342, https://doi.org/10.5194/egusphere-egu22-11342, 2022.

Pleistocene climate is primarily driven by changes of the Earth’s orbital parameters. However, the Mid-Pleistocene Transition (MPT) (~0.8-1.2Myr) which corresponds to a gradual change of interglacial-glacial cyclicity from weak 40kyr climatic cycles to the current strong 100kyr cycles, remains largely unexplained. So far, models only based on orbital forcing were not capable to reproduce this transition, discarding the hypothesis of an orbitally-driven transition. Internal Earth system climate causes were thus explored as primary drivers of the MPT, as a gradual decrease in atmospheric CO2 concentrations or the removal of the regolith beneath the northern hemisphere ice sheets. 
Here we present an improved version of the conceptual model of Parrenin and Paillard (2012) modelling ice volume variations over the past 2Myr. Our model switches between two states, a glaciation state and a deglaciation one, following a threshold mechanism related to the input parameters and the modelled ice volume itself. The modelled ice volume is compared to the ice volume reconstructions inferred from paleodata. 
 We reproduced the MPT using three different models. The “orbital” model which only use orbital forcing parameters as input. The “gradual” model, which is similar to the orbital model plus a continuous drop of a physical parameter in addition to orbital forcing parameters. The “abrupt” model, also similar to the orbital model plus a time-determined abrupt variation of a physical parameter in addition to orbital forcing parameters. 
For the first time, our conceptual model is able to simulate qualitatively the Mid-Pleistocene Transition with only changes in the orbital forcing parameters, reproducing the change in frequency and amplitude of the transition. Moreover, the hypothesis of a coupled influence of orbital forcing and a decreasing deglaciation threshold parameter is by far a better hypothesis than considering an abrupt change regarding our model results. In fact, the “gradual” model contains less parameters and a smaller data-model standard deviation of residuals than the “abrupt” model. Orbital forcing could thus have enabled the Mid-Pleistocene Transition. A combined influence with a decreasing parameter, such atmospheric  CO2 concentration, would have triggered this transition.

References 
Parrenin, F., & Paillard, D. (2012). Terminations VI and VIII (∼ 530 and∼ 720 kyr BP) tell us the importance of obliquity and precession in the triggering of deglaciations. Climate of the Past, 8(6), 2031-2037.

How to cite: Legrain, E., Parrenin, F., and Capron, E.: A new conceptual model to explain the mid-Pleistocene transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12044, https://doi.org/10.5194/egusphere-egu22-12044, 2022.

The paleomagnetic data obtained from the Neoproterozoic rocks stratigraphically related to glacial deposits suggest the ice sheets' near-equatorial occurrence. Based on these data, the Snowball Earth hypothesis proposing the Cryogenian period's total glaciations has been developed and became almost a paradigm. Quaternary glacial successions usually contain varves (seasonally laminated deposits) as they were formed in high latitudes. Therefore, we suggest that varves provide an independent sedimentological test of the paleolatitude position of Precambrian glacial deposits.

We carried out a sedimentological study on thinly laminated rhythmites in the Neoproterozoic glacial deposits in Southern Siberia, and found that they have features characteristic of seasonal varves. The studied rhythmites interstratify the Bolshoi Patom and Nichatka Formations' diamictites at the base of the Dal'nyaya Taiga Group. The seasonality is clearly manifested in the rhythmites of the Nichatka Formation. The rhythmites are represented by interbedding of millimeter-scale siltstones and mudstones with sandy and gravelly admixture. The coarse-sandy and gravelly component is interpreted as ice-rafted clasts, as it has characteristic features of dropstones and contains unconfined till pellets. Ice rafted clasts saturate siltstone laminas and are practically absent in argillite layers.
Thus, argillite laminas can be confidently recognized as deposits of the cold season, during which ice melting and iceberg rafting ceased. On the other hand, siltstone layers with dropstones are deposits of the warmer melting season. The rhythmite's diurnal nature is excluded by its complex structure of the silty layer of the rhythm, which is caused by several sedimentation events separated in time.  The entire set of microfacies of the Nichatka Formation rhythmites reveals similarities with varve microfacies produced by variable flows in ice-contact proglacial lakes. The upper part of the Bolshoi Patom Formation's rhythmites is also formed by varve-like pairs of thin siltstone and mudstone laminas. Dropstones are virtually absent in them, and, therefore, the seasonal nature of the rhythm is less confidently established. The siltstone within the rhythm may have a massive or normally graded texture. The argillite is approximately equal in thickness to the siltstone lamina (about 0.5 mm). The thickness of a pair of siltstone and argillite laminas may remain almost constant when more than 50 pairs are observed. This regularity of laminas thickness in rhythmite is not typical of a tidal setting, but it is difficult to rule out this rhythmite's diurnal nature.  These deposits display high similarity to varves produced by low energy suspension settling during the melt season. The observed seasonal nature of the rhythmites in the glacial deposits of the Dal'nyaya Taiga Group evidence against the validity of the Snowball Earth hypothesis, which assumes the presence of glacial caps near the equator in the Neoproterozoic. The study was supported by RSF Grant No. 20-77-10066.

How to cite: Rud'ko, S. and Shatsillo, A.: Varves versus Snowball: Seasonal rhythmite in the glacial deposits of the Nichatka Formation (South Siberia)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6598, https://doi.org/10.5194/egusphere-egu22-6598, 2022.

Multiple geochemical analyses may help us better constrain the ice-wedge formation and in-situ greenhouse gas (GHG) production mechanisms. Here we present new results from ice-wedge ice sampled at Zyryanka, Northeastern Siberia (65°93’N, 150°89’E). The plant remains and CO₂ gas were analyzed for ¹⁴C dating, and we obtained from 810 to 1750 years before 1950 CE for the Zyryanka ice wedge. δ(N₂/Ar) of the ice wedges ranges from -17.51 to -3.53 % with regard to modern air, indicating that the Zyryanka ice wedge was formed by both liquid water and dry snow. On the other hand, the δ(O₂/Ar) value of the Zyryanka ice wedges ranges from -72.88 to -37.58 % with regard to modern air, implying oxygen gas was consumed considerably by respiration of microorganisms in the ice-wedge ice. We also observed correlations among the three greenhouse gas species and oxygen gas concentrations. N₂O and CO₂ concentrations show a strong positive correlation (r = 0.94, p=0.01). We also found that the melting fraction (estimated from N₂/Ar) is positively correlated with CO2 (r=0.81, p=0.01) and CH₄ (r=0.87, p<0.05). Furthermore, O₂ concentration is negatively correlated with the CH₄ concentrations (r = -0.41, p<0.05) which may imply that CH₄ production is associated with biological oxygen consumption. The δ¹⁸O of ice melt ranges from -28.6 to -19.1 ‰ for the ice wedge and adjacent soil samples, showing a symmetric structure with low δ¹⁸O values in the ice wedge parts and high in the adjacent soils. Comparing with the δ¹⁸O value of modern precipitation in the Zyryanka region, it can be inferred that the ice wedge was mainly formed by filling with cold seasonal precipitation. Our study shows that the gas mixing ratios in ice wedges and water stable isotope analysis may help better understanding the biogeochemical environments during and after the formation of ice wedges.

How to cite: Ko, N., Park, H., Jung, H., Iwahana, G., Fedorov, A., and Ahn, J.: Understanding formation of ice wedges and origin of trapped greenhouse gas at Zyryanka, Northeastern Siberia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6669, https://doi.org/10.5194/egusphere-egu22-6669, 2022.

An appraisal of ancient Earth’s climate dynamics is crucial for understanding the modern climate system and predicting how this might change in the future. Major climate-shift events in the Earth’s past demonstrate the scale, duration and response of the climate system to various global and local climate stressors.   

More than 650 million years of deep-time paleoclimate changes are archived in the sedimentary succession of Svalbard; an archipelago located in the Norwegian High Arctic. The excellently outcropping geological successions of Svalbard date back to the Proterozoic, and record both temporal and spatial changing climatic and environmental conditions strongly linked to the northward continental drift of the archipelago from southern hemisphere in Precambrian to its present-day Polar latitudes.

The oldest deposits that record major climatic events and associated environmental perturbations in Svalbard include tillites related to several Cryogenian glacial events and the overlying Ediacaran carbonates. The Lower Paleozoic succession documents episodes of marine biodiversification, including the Great Ordovician Biodiversification Event (GOBE), which is linked to cooling of previously warm tropical oceans. The arid to semi-arid climate of the Devonian promoted a terrestrial plant diversification. The Lower Carboniferous coal-bearing strata were deposited in humid and tropical climate settings prevailing in northern Pangea. The Upper Carboniferous-Lower Permian succession consists of interbedded carbonates, evaporites and red siliciclastics, including remains of paleokarst. The continued northward drift into subtropical latitudes promoted a change back to arid to semi-arid climates, occurring during the overall global icehouse conditions. During the Late Permian, marine sponges were occupying most of the ecological niches, leading to the deposition of weathering-resistant spiculites. But these ecosystems were rapidly and dramatically impacted by the End Permian Mass Extinction (EPME), which lasted well into the Early Triassic.

By the Mesozoic, Svalbard was approaching mid-latitudes. The exposed in Svalbard deposits of Triassic mega-delta features evidence for a temperate or humid climate, indicated by thick coal beds that transitioned to an arid climatic environment at the end of the Triassic and Early Jurassic succession with caliche and calcareous soil profiles. The Lower Cretaceous strata (deposited at c. 66 °N) record several cold snaps despite the overall greenhouse climate characterizing the period and most notably the global crisis associated with the Aptian oceanic anoxic event 1a (OAE1a).

By the Paleogene, Svalbard had reached Arctic latitudes, and as characterised by overall moderate to warm temperate climate, punctuated by warming episodes, including the Palaeocene–Eocene Thermal maximum (PETM). The Neogene cooling is missing from onshore records, but high-resolution glacial climate evidence exists offshore and from geomorphology and unconsolidated strata of Late Quaternary-Holocene age.

In this contribution, we synthesize former and ongoing studies of deep-time paleoclimate in Svalbard and provide knowledge gaps to optimize the use of Svalbard as an archive for deep-time paleoclimate research. The exceptional exposures, accessibility, and completeness of the 650 million long sedimentary records makes Svalbard unique archive for deep-time paleoclimate research. In addition to Svalbard’s excellent outcrops, fully cored research and coal exploration boreholes provide an excellent foundation for further research with minimal environmental consequences.

How to cite: Smyrak-Sikora, A., Augland, L. E., Betlem, P., Grundvåg, S.-A., Helland-Hansen, W., Jelby, M. E., Jensen, M. A., Jochmann, M. M., Johanessen, E. P., Jones, M. T., Koevoets-Westerduin, M., Lord, G. S., Mørk, A., Olaussen, S., Planke, S., Senger, K., Stemmerik, L., Vickers, M., Śliwińska, K. K., and Zuchuat, V.: Deep-time paleoclimate archive in High Arctic, Svalbard, Norway, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7172, https://doi.org/10.5194/egusphere-egu22-7172, 2022.

One of the most dramatic warming episodes of the Mesozoic occurred near the Pliensbachian-Toarcian transition (Early Jurassic). The occurrence of abundant exotic clasts and glendonites in marine strata of Siberia suggests cold conditions during the late Pliensbachian, which may have led to the episodic growth of high latitude ice-sheets. These conditions ended abruptly during the early Toarcian when temperature rose rapidly across an episode of global biogeochemical perturbation known as the Toarcian Oceanic Anoxic Event (T-OAE). The rapid marine transgression coinciding with the T-OAE onset has been tentatively attributed to the rapid demise of these polar ice-sheets, which possibly released large amounts of methane in the atmosphere through permafrost thawing. Nevertheless, the scarce quantitative estimates of Pliensbachian-Toarcian temperatures have exclusively been obtained from low paleolatitude sites. Plus, existing temperature records are mostly based on oxygen isotope thermometry and hence remain equivocal in the absence of constraints on the ocean oxygen composition of Pliensbachian-Toarcian oceans and its temporal variability. Clumped isotope (Δ₄₇) data from aragonite bivalve shells from one NE Siberian site have recently provided the first quantitative evidence for extreme Toarcian polar warmth, with marine temperature estimates exceeding ~15°C north of the Anabar shield. In this study, we present new Δ₄₇ data from bivalve samples from Tyung River, south of the Anabar shield that allow to substantially expand this record both spatially and temporally. Clumped isotope data from aragonite shells confirm elevated marine temperatures (~13°C) at the end of the T-OAE in polar areas some 850 km away from the previous record. Upper Pliensbachian calcite shells of Harpax collected from coastal to deltaic, boulder-bearing deposits of a nearby site record much lower temperature (~3°C) and extreme ¹⁸O-depletion of environmental waters (δ¹⁸O = -6.5‰VSMOW). These results provide the first quantitative evidence for near-freezing polar temperatures during the Late Pliensbachian, which is a key prerequisite for the hypothesis of episodic ice-sheet growth prior to the T-OAE. Beyond glacio-eustasy, our new data offer a rare glimpse of extreme changes in polar temperatures across a transition from coldhouse to greenhouse climate and will certainly prove useful for future earth system simulations of Mesozoic climates. 

How to cite: Letulle, T., Suan, G., Rogov, M., Daëron, M., Vinçon-Laugier, A., Lutikov, O., Reynard, B., Montagnac, G., and Lécuyer, C.: First quantitative constraints on the Pliensbachian-Toarcian warming in polar regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7286, https://doi.org/10.5194/egusphere-egu22-7286, 2022.

The Permian-Triassic mass extinction (PTME) is considered to be the most severe extinction in Earth’s history. Following this extinction, the Early Triassic is known as an interval of divergent biotic recovery patterns, with several periods of unfavorable environmental conditions as suggested by global fluctuations in carbon isotope compositions of both organic and inorganic carbon reservoirs (e.g., Payne et al., 2004; Galfetti et al., 2007). Despite these global carbon isotope excursions, little is known about the evolution of the organic carbon cycle. The aim of this study is to improve our understanding of long-term organic carbon cycle dynamics, in particular the influence of pyrogenic carbon. Initial results for the Smithian and Spathian from sections sampled in Svalbard show an increase of polyaromatic hydrocarbons (PAHs) during the Spathian. Particularly, phenanthrene and anthracene concentrations increase amid the Smithian-Spathian boundary (SSB). These increases coincide with increased d¹⁸O_phosphate values (approx. 14 ‰ to 17 ‰) measured for conodonts in the same locality and are suggestive of a rapid cooling at the SSB. Global temperature decline in the late Smithian would decrease corresponding precipitation intensities, particularly in high latitude regions (Goudemand et al. 2019). Decreasing precipitation intensity generates much less runoff that, in turn, is associated with increases in wildfire activity in high latitude regions (Grosse et al. 2011). Increased wildfire activity may have contributed to increased atmospheric pCO₂ levels. In contrast, incomplete combustion of organic matter would also form a recalcitrant terrestrial organic carbon pool, which could act as a carbon sink.

How to cite: Blattmann, F. R., Luz, Z. A. S., Vennemann, T., Bucher, H., Schneebeli-Hermann, E., and Magill, C. R.: Early Triassic Cycling of Pyrogenic Carbon in Northern High Latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7362, https://doi.org/10.5194/egusphere-egu22-7362, 2022.

The central part of West Spitsbergen, Nordenskiöld Land, is characterized by comparably small extension of glaciers, high landscape diversity and the long-term development of river valleys. In doing so the number of objects suitable for paleobotanical, in particular, palynological research is limited. Holocene climate and vegetation in numerous studies were reconstructed by using palaeobotanical data from lake sediments and peat sequences. Fluvial sediments are widespread and include both terrigenous and organic deposits, but studies focussing on alluvium archives are rare. Such records relate to Coles and Gröndalen valleys.

During the researches of the Russian Arctic expedition in the Svalbard archipelago in 2019, the outcrop of marine sediments overlain by an alluvial stratum (with a general thickness of 4.2 m) was found and studied on the right slope of Semmeldalen valley (16 m a.s.l.). The sediments are represented by sand and silt with Mytilus edulis shells in situ (0.2 m), which are covered by gravel-pebble material (2.0 m), followed by stratum of interlayered silt, sand, loam with plant remains lenses and layers (2.0 m). The laboratory studies included radiocarbon dating and pollen analysis. Radiocarbon dating results show that the studied deposits were formed in the period from 9300 to 3500 cal BP.

According to pollen data, six stages of vegetation and climate changes were distinguished.  The first stage - about 9300 - 9000 cal. BP corresponds to the stage of sedimentation in a shallow sea bay under relatively favourable environmental conditions. The deposits contain rare microfossils of poorly preserved shrub forms. The almost total absence of Quaternary pollen and a spore in the second stage - gravel-pebble sequence - reflects a high rate of sedimentation in the river mouth during sea regression.  About 8700 cal BP (stage 3) the subshrub-sedge tundra developed in a relatively warm and humid climate. Following (about 8300 cal BP) it changed by the willow-sedge tundra (stage 4). The low content of microfossils at this stage is evidence of an increase in river runoff and, probably, an increase in the amount of atmospheric precipitation. Most probably study records contain a hiatus in sedimentation between 8000 - 4000 cal BP. The fifth stage is the increase in pollen amount and development of the willow-motley-grass tundra. The sixth stage reflects modern vegetation - willow-grass tundra.

The obtained dates and lithology description allow us to make a preliminary conclusion that a sharp decrease in sea level occurred about 9000 cal BP, thereby determining a radical restructuring of the natural environment of the study area. Preliminary results compared with published data show that there are local differences in valley development and environmental conditions changes in Central Svalbard during the Holocene.

How to cite: Soloveva, D., Verkulich, S., Savelieva, L., and Petrov, A.: Holocene environmental changes inferred from pollen record of Nordenskiöld Land alluvium sequences (West Spitsbergen Island): new data and review, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8394, https://doi.org/10.5194/egusphere-egu22-8394, 2022.

The extent of Arctic sea-ice during the Last Interglacial is poorly known. Climate models and sediment-based reconstructions generally suggest a relatively extensive ice cover, comparable to the modern day. Here, we show that Arctic sea-ice was much more reduced than previously assumed, with summers being ice-free. Our new evidence stems from a series of central Arctic Ocean sediment cores, including sites that underlie the thickest parts of the modern Arctic ice pack. Microfossil analysis reveals that the Arctic Ocean was invaded by Turborotalita quinqueloba, a typically subpolar planktonic foraminifer that is strongly associated with chilled Atlantic waters in the modern North Atlantic Ocean, and which is absent in modern sediments in the central Arctic Ocean. Given that the modern Arctic Ocean is characterised by a pronounced halocline with Atlantic waters subducting beneath a fresh and cool upper water mass, our findings suggest a shallowing of those Atlantic waters in the Arctic Ocean during the Last Interglacial. This process, dubbed ‘atlantification’, would be associated with retreating sea-ice, allowing T. quinqueloba to invade. Since the onset of the atlantification of the Arctic Ocean in response to climate change is increasingly being reported, we suggest that the Last Interglacial may serve as an important analogue for studying a fully-atlantified, seasonally ice-free Arctic Ocean.

How to cite: Vermassen, F., O'Regan, M., de Boer, A., West, G., and Coxall, H. K.: A seasonally ice-free Arctic Ocean during the Last Interglacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10379, https://doi.org/10.5194/egusphere-egu22-10379, 2022.

Ongoing climate change causes a global biodiversity loss and species extinction by reducing population size and decreasing genetic diversity. Massive extinction events happened in the past with the Megafauna extinction as the latest example. The Pleistocene-Holocene transition also witnessed the loss of the broadly established steppe-tundra biota, spanning most of Northern Hemisphere during the Pleistocene and supporting Pleistocene megafauna at the time. Understanding past extinction events via the investigation of Quaternary records can strengthen the current methods to forecast the effects of global warming on ecosystems. If loss of other organism groups were proportional to what has been shown for mammals, a large part of the Pleistocene steppe-tundra biota might have gone extinct. However, few example are known. The improved taxonomic resolution and high detectability of sedimentary ancient DNA provide a new tool to explore this. Here, we investigate potential plant taxa loss in the Northern Hemisphere between the late Pleistocene-Holocene transition using sedimentary ancient DNA (sedaDNA) metabarcoding. We summarized data from 500 samples comprising nine lake sediment cores from North-East-Asia and North-America spanning the last 50.000 years. Using patterns of past plant diversity (appearance-disappearance through time), we built communities to detect past taxa non-present in modern databases inferring potential candidates for extinction. Our results suggest that vegetation was resilient until the Pleistocene to Holocene transition and that loss appeared in parallel to the Megafauna extinction. Finally, we characterized this vegetation loss and identified that more specialist taxa contributing less to beta diversity are more sensitive to potential extinction than other taxa. This work holds great potential to reveal new insights into the evolution of the fragile boreal plant communities and the processes leading to extinction of species.

How to cite: Courtin, J., Alsos, I., Biskaborn, B., Diekmann, B., Huang, Y., Lammers, Y., Melles, M., Pestryakova, L., Schulte, L., Stoof-Leichsenring, K., and Herzschuh, U.: Identification and characterization of vegetation loss during the last 50,000 years in Beringia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11180, https://doi.org/10.5194/egusphere-egu22-11180, 2022.

The Late Paleozoic Ice Age (LPIA) in one of the coldest periods in the Earth history which led to the development of ice covers across the entire Gondwana from Carboniferous to Permian. The LPIA view is changing from a single ice sheet covering the entire Gondwana to a series of small and diachronous ice caps widespread through the supercontinent. Stratigraphic studies and facies analysis are key tools for the evaluation of the paleo-environmental depositional setting and, consequently, of the style of glaciation.

Tasmania is a key region because it was settled between northern Victoria Land (Antarctica) and Australia and the LPIA deposits could help to provide links between the two sectors of Gondwana. Tasmania constituted a sedimentary basin in the late Paleozoic and Mesozoic and thick sedimentary sequence, both marine and terrestrial, known as Parmeener Supergroup, crops out. The lowermost part of the Lower Parmeener Supergroup, consisting in the Wynyard Tillite and its correlative throughout the region, recorded glacial sedimentation linked with ice caps that developed in the region.

Here, we provide a detailed sedimentological analysis of two drillcores which recovered glacial sequences deposited in the Tasman Basin. The cores were placed into two separate sub-basins: the first hole, named Ross 1, is located in the central part of Tasmania and recorded ca. 60m of glaciogenic rocks of the Stockers Tillite; the second, named Cygnet 3, is located in the southern part of the island and recorded ca. 200m of glaciogenic rocks belonging to the Truro Tillite. The centimetric scale sedimentological analyses allow the identification of 14 lithofacies which were grouped into 6 facies association on the basis of depositional genesis. Facies associations vary from possibly sub-glacial or ice contact to ice distal. Deposition is dominated both by gravity and sediment remobilization processes and suspension settling with ice rafted debris accumulation. All of them are indicative of subaqueous deposition, likely glacimarine. Moreover, along the succession the glacial sequence stratigraphy approach was applied and glacial system tracts and bounding surfaces which define glacial sequences were identified. The stacking pattern of the facies associations allow to demonstrate that the glacial sequences record phases of advance and retreat of the glacial front into the basin within the main end of the main glacial phase. The facies associations, mainly interpreted as gravity driven deposits, together with the thin thickness, show that Ross 1 core was located in a basin margin position and that possibly recorded sub-glacial erosion, while Cygnet 3 core, which have greater thickness, shows facies associations mainly related with suspension settling, indicating a more basinal position. Petrographic analysis of the gravel size fraction constituting the diamictite and the ice rafted debris shows difference in the lithological composition of the two formations, sustaining the hypothesis that the sub-basins were fed by different ice caps.

How to cite: Zurli, L., Cornamusini, G., Liberato, G. P., and Conti, P.: Stratigraphy of the Late Paleozoic Ice Age glacial sequences in Tasmania (Australia): implications for the glaciation in southern Gondwana, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11379, https://doi.org/10.5194/egusphere-egu22-11379, 2022.

Although sedimentary ancient DNA (sedaDNA) is increasingly used to reconstruct past ecosystem changes, we do not yet know much about its preservation conditions across geological time, resulting in potential biases and uncertainties in data interpretation. In this study, we obtained sedaDNA records from around 15 lakes from the Arctic and sub-Arctic regions and the Tibetan Plateau covering the last 2 to 80 ka BP. In addition to the four preservation proxies recently introduced by Jia et al. (2021) (https://doi.org/10.1002/edn3.259), some new potential proxies of plant DNA metabarcoding (e.g., dissimilarity between PCR replicates) and metagenomics (e.g., average DNA fragment length, duplication rate, guanine-cytosine content, and deamination rate) have also been applied to quantify the extent of ancient DNA preservation and compared with other environmental proxy records from the cores. So far, our preliminary results from Lake Ilirney (67°21’N, 168°19’E) show that DNA content generally decreases along the core over the last 18 ka BP and then maintains at a relatively stable level up to the bottom of the core (ca. 53.4 ka BP), which is consistent with the variations in lake organic productivity reflected by TC, TOC, TOC/TN, pollen and diatom abundance, and Br. In addition, sedaDNA preservation conditions revealed by our preservation proxies are variable within the core. Good sedaDNA preservation is associated with strong physical weathering and glacial abrasion in the catchment, as indicated by high K/Ti and low Zr/Rb values, resulting in increased clastic input of clay minerals and fine sediments, which favors the adsorption of DNA molecules to sediment particles. This process might also help to deepen the lake and increase its water conductivity, which is beneficial for DNA adsorption and preservation. No clear correlation is found between sedaDNA preservation and paleoclimatic changes reconstructed by fossil pollen records. It should be noted that our results may also be influenced by the ability of the DNA extraction protocols we used to recover DNA from different types of sediments. To conclude, sedaDNA preservation may be highly influenced by sediment type and catchment erosion rate, and glacial lakes appear to be promising for sedaDNA studies in the future. Further analyses of sedaDNA records from other lakes are pending and will be finalized and presented at EGU 2022.

How to cite: Jia, W., Cabuk, U., R. Stoof-Leichsenring, K., G. Alsos, I., Lammers, Y., K. Biskaborn, B., and Herzschuh, U.: Uneven preservation of ancient DNA along lake sediment cores: A case study of high-latitude and high-elevation lakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11897, https://doi.org/10.5194/egusphere-egu22-11897, 2022.

Studies based on deep ocean drilling cores points to North-East Greenland as a focal point for ice sheet accumulation incurring much earlier than the Pleistocene Northern Hemisphere glaciation. The build-up of marine-based ice sheets in these parts is critical to the cooling of the Nordic Seas and the Arctic Ocean, considered as a pre-condition for the modern ocean “conveyor belt” circulation. However, proximal sedimentary records that can shed light on the timing and climate background of early Greenland Ice Sheet evolution are lacking. In 2008 a series of shallow cores were drilled by the Kanumas consortium on the NorthEast Greenland shelf and Cenozoic sediments were recovered at several sites. Here we present litho- and palynostratigraphic information, along with new cosmogenic isotope results, of a 110 m long sediment core (Kanumas 13). The core study, supported by regional seismic data, suggests that ice streams may have been active on the North-East Greenland margin since middle-late Miocene. Geochemistry and magnetic susceptibility data indicate that an abrupt change in sediment source occurred at 50.8 m. The shift in provenance is accompanied by a transition to more open marine conditions. The implications for the Greenland Ice Sheet and Artic climate development will be addressed in the presentation.

How to cite: Knutz, P., Nielsen, T., Sliwinska, K., Fyhn, M., Hopper, J., Jennings, A., Bierman, P., Christ, A., Corbett, L., and Hidy, A.: A rare record of late Neogene glaciation from the north east Greenland margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12021, https://doi.org/10.5194/egusphere-egu22-12021, 2022.

The Eocene bryozoans reveal a spectacular diversification in the stratigraphical column of the LMF, Seymour Island, showing a great variation in the colony growth-forms and taxonomy enhanced by a great radiation of a new taxa (Hara 2001).

The very base of the sandy, transgressive series in the lowermost part of the LMF (Telm1) includes loosely encrusting (membraniporiform), and unizooidal, flexible articulated or rooted colonies (catenicelliform), which are either taxonomically and morphologically different from the overlying fauna. At present such bryozoans are widely distributed in the tropical-warm temperate latitudes particularly deposited in the shallow-water settings (Hara 2015).

The massive, hemisperical cerioporine cyclostomes, reminiscent of the Cretaceous in the Northern Hemisphere and differently-shaped multilamellar cheilostomes represented by numerous new taxa are dominant biota in the lower part of Telm1-2 (Hara 2001, 2002).

The free-living lunulitiform, disc-shaped colonies, which occur in the middle part of the LMF (Telm4-Telm5), are characteristic for the warm, shallow-self environment with a temperature range of 10 to 29°C. Environmentally, lunulitids are absent when the bottom sediments is lower than 10-12°C. At present they inhabit the circumpolar to warm-temperate waters (Hara et al. 2018). They have bimineralic skeletons, with the traces of aragonite, which is indicative for the temperate shelf environment, sandy and often shifting substrate.

The bryozoans from the upper part of the LMF (Telm6-Telm7) are scarce, either represented by in-situ lepraliomorph biostrome layer up to 5 cm thick or poorly-preserved sole fragments of the bryozoans associated with penguins and fish remains.

Changes in the biotic composition of the diversified bryozoan biota of the late early Eocene-late Eocene in the stratigraphical column of the LMF mark a distinct environmental and climatic events, referred to EECO, MECO, and EOT for the upper part of this formation.

The isotopic δ¹⁸O analyses of the bryozoan skeletons from the lower part of the La Meseta Fm. show the temperature range from 13.4°C to 14.6°C (according to the equation given by Anderson & Arthur 1983; unpublished Hara 2021; what is consistent with isotopic data of other marine macrofaunal fossil records (see Ivany et al. 2008).

Anderson T.F., and Arthur M.A.1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. SEPM Short Course, 10: 1-151.

Hara U. 2001. Bryozoans from the Eocene of Seymour Island, Antarctic Peninsula. Palaeontologia Polonica 60: 33-155.

Hara U., 2002. A new macroporid bryozoan from Eocene of Seymour Island, Antarctic Peninsula, Polish Polar Research, 23: 213-225.

Hara U. 2015. Bryozoan internal moulds from the La Meseta Formation (Eocene) of Seymour Island, Antarctic Peninsula. Polish Polar Research, 36: 25-49.

Hara U., Mors T., Hagstrom J. & Reguero M. A., 2018. Eocene bryozoans assemblages from the La Meseta Formation of Seymour Island. Geological Quarterly, 62: 705-728.  

Ivany L.C., Lohmann K. C. Hasiuk F., Blake D.B., Glass A., Aronson R.B., & Moody R.M. 2008. Eocene climate record of the high southern latitude continental shelf: Seymour Island, Antarctica. Geological Society of America Bulletin, 120: 659-678.

How to cite: Hara, U.: Evolution of the Antarctic bryozoan biota as a response to environmental and climatic changes: (Eocene, La Meseta Formation, Seymour Island, Antarctic Peninsula), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12131, https://doi.org/10.5194/egusphere-egu22-12131, 2022.

Palsa mires are a common feature in the Subarctic zone of discontinuous permafrost. In these peatlands, the patchy distribution of frozen soil constrains relief, water regime and vegetation distribution. Because they lie at the edge of permafrost distribution, palsa mires are very sensitive to climate changes and become extremely valuable high-latitude terrestrial records. However, both (1) their origin, including their rapid development towards ombrotrophy because of uplift by ice accretion and (2) the irreversible geochemical effects of collapse and permafrost thaw make them challenging environmental archives. Understanding the Late Holocene evolution of these systems becomes a key framework to decipher potential consequences of the permafrost disappearance observed during the last decades. A 120 cm peat record was recovered on the Storflaket Palsa plateau (Abisko, Sweden, 68ºN) on June 2018.  This register contains more than 9000 years of paleoenvironmental information and was entirely made of peat, with two centimetric layers of volcanic ash interbedded at 74-77 and 46-47cm depth. A multidisciplinary approach using chemical (stoichiometry, stable isotopy and elemental composition) and biological proxies (macrofossil and pollen determination) was used to reconstruct the environmental evolution of the site. Bottom most layers (50-120cm) were characterized by peat made of different types of brown mosses and abundant aquatic fauna indicating that the area was covered by a high and stable water table that promoted organic matter accumulation in a percolation mire system. The very high accumulation rates and the extremely good preservation of macrofossil remains suggest a permafrost free area around 8000 cal yr BP. From 50 to 9 cm the peat is made of highly degraded brown moss, with increasing degradation towards the top. Chemical and macrofossil analyses indicate a strong oxidation processes due to peat exposition. The top layer (9 to 0 cm) is characterized by dry palsa peat and depicts very low accumulation rates, suggesting that this record is capturing the uplift movement of the peat mound by ice accretion and a shift from a minerotrophic and waterlogged mire system towards the development of a palsa plateau. Chemical and biological signals allow us to date the age of permafrost establishment later than 3000 cal. yr BP. The deposition of ash layers is linked to sudden inputs of phosphorus and metals leading to stoichiometric changes in peat composition.

How to cite: Margalef, O., Grau, O., Joosten, H., Pérez Haase, A., Pla Rabes, S., Fernández, P. R., Giralt, S., Sánchez, M., Pérez Obiol, R., Soriano, J. M., Pèlachs, A., Campderrós, S., Fernández Alarcón, C., and Peñuelas, J.: Late Holocene permafrost development triggers hydrological and geochemical changes in subarctic peatlands (Abisko, 68ºN), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12387, https://doi.org/10.5194/egusphere-egu22-12387, 2022.

Latitudinal temperature gradients are a critical component of the climate system and control the transport of heat and moisture. However, this process is poorly understood during past intervals of extreme greenhouse climate, in particular owing to models suggesting that gradients must be much steeper than proxy data imply. Palaeotemperature records Late Cretaceous–Early Paleogene can provide insight into how the global climate system operates under greenhouse conditions.

Much of our understanding of palaeotemperatures and gradients therein during this interval comes from marine sea-surface temperature proxy data, with very few terrestrial records. These palaeoclimate reconstructions are hampered by poor temporal resolution, difficulties in correlating between sites, and limited spatial coverage.

Lipids from fossil peats across North America provide an opportunity to investigate terrestrial palaeotemperatures across the Cretaceous–Paleogene boundary and how these differ across a range of latitudes. Here we present a mean annual air temperature record spanning this interval from the Canadian High Arctic (~75°N palaeolatitude). Our data show that temperatures ranged from 0–18°C, compared with 13–27°C at contemporaneous peat-accumulating sites in Saskatchewan (~60°N palaeolatitude). These data indicate a temperature gradient of approximately 10°C. These values are similar to those modelled for the latest Cretaceous, and the latitudinal difference is comparable to the modern gradient across North America (UCAR), albeit ~20°C warmer.

Our study demonstrates that although the Arctic experienced high terrestrial temperatures, the K-Pg interval saw a well-defined latitudinal temperature gradient. Further, our reconstructions fill an existing gap in the terrestrial record and highlight the value of fossil peats in palaeoclimate studies.

How to cite: O'Connor, L., Jerrett, R., Price, G., van Dongen, B., Crampton-Flood, E., and Lengger, S.: An organic geochemical reconstruction of North American temperature gradients over the Cretaceous-Paleogene boundary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12640, https://doi.org/10.5194/egusphere-egu22-12640, 2022.

Rapid sea-level rise, due to melting and destabilization of present-day ice sheets will likely have important consequences on human societies. Observations provide evidences of increased mass loss in the West Antarctic Ice Sheet (WAIS) over the recent decades, partly due to ocean warming. Despite improvements in both climate and ice-sheet models, there are still significant uncertainties about the future of West Antarctica, due, in part, to our misunderstanding of the process responsible for the marine ice sheet evolution. Paleoclimate studies provide important information on ice-sheet collapse in a warming world.

Our study is based on the Eurasian Ice Sheet (EIS) complex, including the British Island Ice Sheet (BIIS), the Fennoscandian Ice Sheet (FIS) and the Barents Kara Ice Sheet (BKIS). Because large parts of both the BKIS and the WAIS are marine-based, the BKIS at the LGM can be considered as a potential analogue to the WAIS.

To improve our understanding of the mechanisms responsible for the EIS retreat, we performed transient simulations of the last EIS deglaciation (21 000 – 8 000 yr BP) with the GRISLI ice sheet model forced by 5 PMIP3/PMIP4 models, and two transients GCM models, TRACE21K and iLOVECLIM. Our main goal is to investigate the sensitivity of the EIS grounding line retreat to climate forcing, sea-level rise and glaciological processes with a focus on the BKIS evolution during the deglaciation and the behaviour of the large Bjornoyrenna ice stream.  

How to cite: van Aalderen, V., Charbit, S., Dumas, C., and Quiquet, A.: The last deglaciation of the Eurasian ice sheet (21,000 - 8,000 yr BP): a sensitivity study to PMIP3/PMIP4 coupled atmosphere-ocean models outputs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-530, https://doi.org/10.5194/egusphere-egu22-530, 2022.

The early Cenozoic Antarctic ice sheet has grown non-linearly to a continental-scale ice sheet close to the Eocene-Oligocene boundary when environmental conditions were favourable. These favourable conditions included the movement of the continent towards the South Pole, the thermal isolation of the Antarctic continent and declining atmospheric CO₂ concentrations.  Once the threshold for ice sheet growth was reached, a series of positive feedbacks led to the formation of a continental-scale ice sheet.

The thresholds for growth and decline of a continental scale ice sheet are different. The ice sheet state is dependent on the initial conditions, an effect called hysteresis. Here we present the hysteresis behaviour of the early Cenozoic Antarctic ice sheet for different bedrock elevation reconstructions. The ice sheet-climate coupler CLISEMv1.0 is used and captures both the height-mass balance and the ice-albedo feedback accurately. Additionally, the influence of the different orbital parameters on the threshold to glaciation and deglaciation is investigated in detail. It appears that the long-term eccentricity cycle has a significant influence on the ice sheet growth and decline and is able to pace the ice sheet evolution for constant CO₂ concentration close to the glaciation threshold.

How to cite: Van Breedam, J., Huybrechts, P., and Crucifix, M.: Hysteresis and orbital pacing of the early Cenozoic Antarctic ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1501, https://doi.org/10.5194/egusphere-egu22-1501, 2022.

In this study, we investigate the sensitivity of the glacial Alpine hydro-climate to changes of the Laurentide ice sheet (LIS). Bridging the scale gap by using a chain of global and regional climate models, we perform sensitivity simulations of up to 2 km horizontal resolution over the Alps for the Last Glacial Maximum and the Marine Isotope Stage 4. In winter, we find wetter conditions in the southern part of the Alps during glacial conditions compared to present day, to which dynamical processes, i.e.  changes in the wind speed and direction, substantially contribute. During summer, we find the expected drier conditions in most of the Alpine region during glacial conditions, as thermodynamics suggests drier conditions under lower temperatures. The sensitivity simulations of the LIS changes show that an increase of the ice-sheet thickness leads to a significant intensification of glacial Alpine hydro-climate conditions, which is mainly explained by dynamical processes. The findings demonstrate that the Laurentide ice-sheet topography plays an important role in regulating the Alpine hydro-climate and thus permits a better understanding of the precipitation patterns in the complex Alpine terrain at glacial times.

How to cite: Velasquez, P., Messmer, M., and Raible, C. C.: The role of the Laurentide ice-sheet topography in the Alpine hydro-climate at glacial times, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1635, https://doi.org/10.5194/egusphere-egu22-1635, 2022.

During the Last Glacial Maximum (LGM, 23,000 to 19,000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ~ 38 °S to 55 °S. From limited paleoclimatic evidence, especially that derived from glacial landforms, it becomes clear that maximum ice sheet expansions in the Southern and Northern Hemispheres were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation as well as its major drivers. Ice sheet modelling combined with glacial geochronology and paleoclimate reconstructions can provide important information on the PIS geometry, ice volume and its contribution to the sea level low during the LGM. It can also help to test different paleoclimate scenarios and identify climate models that capture regional climate responses to the global change in a realistic manner.

Here we present an ensemble of numerical simulations of the PIS during the LGM with an aim to constrain the most likely LGM climate conditions that can explain the reconstructed geometry of the PIS in a satisfactory manner. The PIS model is driven by the climate forcing that fuse near-surface air temperatures and precipitation rates from the ERA5 reanalysis with the paleoclimate model outputs from the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) and the in-house Community Earth System Model (CESM) experiments. Our analysis suggests a strong dependence of the PIS geometry on the near-surface air temperature forcing. All the ensemble experiments designed with PMIP and in-house CESM experiments fail to reproduce the ice sheet extent between 38 and 42 °S. The most realistic performance for the LGM ice sheet extents south of 38 °S has been derived using those climate models that have a higher spatial resolution. The latter helps these models to capture regional climate conditions in a more physically consistent manner. It should be kept in mind that this analysis is based on the evaluation of the modelled ice sheet extents only, as geological evidence on the former ice sheet thickness is still scarce. Nevertheless, it can be shown that a realistic ice sheet geometry during the LGM is consistent with a regional decrease in air temperature of 7 to 12 °C and an increase in precipitation of 400 to 1500 mm/year along the western sectors of the PIS.

How to cite: Retamal-Ramírez, F., Castillo, A., Bernales, J., and Rogozhina, I.: Reconstruction of the Patagonian Ice Sheet during the Last Glacial Maximum using numerical modelling and geological constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1774, https://doi.org/10.5194/egusphere-egu22-1774, 2022.

Long-term simulations of ice sheets and their interaction with the climate system require the application of Earth system models with interactive ice sheet components. To this end we present the first experiments performed with the CMIP6-type Norwegian Earth System Model (NorESM2) including a Greenland ice sheet model component. We present our coupling and modelling strategy, which builds on earlier work with the Community Earth System Model and show first results for two NorESM2 version with different resolution of the atmospheric component. We have performed and analyzed pre-industrial spinup and control experiments, historical runs and future projections under scenario ssp585, following the ISMIP6 protocol.

How to cite: Goelzer, H., Langebroek, P., and Born, A.: Coupled Greenland ice sheet-climate simulations with the Norwegian Earth System Model (NorESM2), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2516, https://doi.org/10.5194/egusphere-egu22-2516, 2022.

Benthic δ¹⁸O levels vary strongly during the warmer-than-modern early- and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO₂ levels and orbital settings. Earlier transient simulations lacked ice-sheet-atmosphere interactions, and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet-atmosphere interactions, running IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO₂ levels (between 280 and 840 ppm) as well as varying ice sheet configurations (between no ice and a large East Antarctic ice sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo-temperature feedback, partly compensated by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO₂ and ice volume. Together, these ice-sheet-atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations. Forced by quasi-orbital 40-kyr forcing CO₂ cycles, the ice volume variability reduces by 21% when ice-sheet-atmosphere interactions are included, compared to when forcing variability is only based on CO₂ changes. Thereby, these interactions also diminish the contribution of AIS variability to benthic δ¹⁸O fluctuations. Evolving bedrock topography during the early- and mid-Miocene reduces ice volume variability by 10%, under equal 40-kyr cycles of atmosphere and ocean forcing. 

How to cite: Stap, L. B., Berends, C. J., Scherrenberg, M. D. W., van de Wal, R. S. W., and Gasson, E. G. W.: Net effect of ice-sheet-atmosphere interactions reduces simulated transient Miocene Antarctic ice sheet variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2829, https://doi.org/10.5194/egusphere-egu22-2829, 2022.

The Cordilleran Ice Sheet in western North America was of comparable size and topographic setting to the modern Greenland Ice Sheet and exhibited similar dynamics. Ice streams channelled rapid flow and the western ice margin terminated in both marine and terrestrial environments. Reconstructing Cordilleran Ice Sheet retreat can therefore provide a helpful analogue for how the Greenland Ice Sheet may respond to changing climate and underlying topography in the future. Moreover, deglaciation in this region controlled routes available for early human migration into the Americas. Here, we present cosmogenic ¹⁰Be nuclide exposure ages from glacial erratics and bedrock on the west coast of British Columbia (53.4°N, 129.8°W) that add to existing chronologies along ~600 km of coastal North America. Collectively, these data show deglaciation back to the present coastline by ca. 18–16 ka. Retreat then slowed and ice seemingly stabilised close to the present coastline for several thousand years until ca. 14–13 ka. Ice may still have been lost during this period of relative stability, but through vertical thinning rather than lateral retreat. We attribute initial retreat to destabilisation and grounding line retreat resulting from rising sea level and/or ocean warming in the northern Pacific. Subsequent stability at the present coast was likely due to the transition from marine to terrestrial margins despite increasing temperatures that may have driven ice sheet thinning. Hence, we show the importance of understanding both climatic and non-climatic drivers of ice sheet change through time. We also show that hundreds of kilometres of coastline were free of ice prior to an important period of early human migration into the Americas.

How to cite: Darvill, C., Menounos, B., Goehring, B., and Lesnek, A.: Reconstructing Cordilleran Ice Sheet stability in western Canada during the Last Deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2831, https://doi.org/10.5194/egusphere-egu22-2831, 2022.

It is well known that the climate during the last glacial period was far from stable. The presence of layers of ice-rafted debris (IRD) in deep-sea sediments has been interpreted to reflect quasi-periodic episodes of massive iceberg calving from the Laurentide Ice Sheet (LIS). Several mechanisms have been proposed, yet the ultimate cause of these events is still under debate. From the point of view of ice dynamics, one of the main sources of uncertainty and diversity in model response is the choice of the basal friction law. Therefore, it is essential to determine the impact of basal friction on ice-stream surges. Here we study the effect of a wide range of basal friction parameters and laws for the LIS under constant LGM boundary conditions by running ensembles of simulations using a higher-order ice-sheet model. The potential feedbacks among till mechanics, basal hydrology and thermodynamics are also considered to shed light on the behaviour of the ice flow. Our aim is to determine under what conditions, if any, physically-based internal oscillations are possible in the LIS. Increasing our understanding of both basal friction laws and basal hydrology will improve not only reconstructions of paleo ice dynamics but also help to constrain the potential future evolution of current ice sheets.

How to cite: Moreno, D., Alvarez-Solas, J., Montoya, M., Blasco, J., and Robinson, A.: Could the Laurentide Ice Sheet have exhibited internal oscillations?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3080, https://doi.org/10.5194/egusphere-egu22-3080, 2022.

Understanding the response of ice sheets to global temperature changes is a critical issue for the climate community. To accurately simulate future ice sheet evolution, we need to know the strength of feedbacks between the climate and ice sheets. Testing the ability of coupled climate-ice sheet models to simulate past ice sheet extent can provide a way to evaluate the models and ground truth projections. One example is the Last Glacial Maximum (LGM), when huge ice sheets covered the Northern Hemisphere, especially over the North America. Here, we performed simulations of the North American ice sheet and climate of the LGM with a recently updated ice sheet-atmosphere coupled model Famous-Ice (Smith et al. 2021, Gregory et al. 2020). The model consists of a low-resolution atmospheric general circulation model Famous (Smith et al. 2008) and an ice sheet model BISICLES (Cornford et al. 2013). It calculates the surface mass balance over ice sheets based on an energy budget scheme and incorporates an updated albedo scheme, which accounts for albedo changes associated with modifications in surface air temperature, grain size and density of the snow. The atmospheric model reproduces the surface mass balance of the modern Greenland ice sheet reasonably well (Smith et al. 2021). Simulations of projections of future sea-level rise (Gregory et al. 2020) and the LGM (Gandy et al. in prep) have also been performed with Famous-Ice using a different ice sheet model GLIMMER.

We present simulations of the LGM with interactive ice sheets in North America and Greenland using FAMOUS-BISICLES. Uncertain input parameters controlling the surface temperatures and ice albedo are varied in our simulations. The global temperature is specified by applying fixed sea surface temperature in the atmospheric model producing a global cooling that ranges from -3K to -6.5K in the simulations. The bare ice minimum albedo is varied from 0.2 to 0.7, which corresponds to the range in PMIP3 models. Our results show a better representation of North American ice sheet when forced with a colder LGM (-6.5K) and high bare ice albedo. We will further discuss potential roles of model biases and compare our results with simulations performed with FAMOUS-GLIMMER (Gandy et al. in prep).

How to cite: Sherriff-Tadano, S., Gandy, N., Ivanovic, R., Gregoire, L., Lang, C., Gregory, J., and Smith, R.: Simulations of North American ice sheet at the LGM with FAMOUS-BISICLES and its sensitivity to global temperatures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3293, https://doi.org/10.5194/egusphere-egu22-3293, 2022.

Ice sheets and the rest of the climate system interact in various ways, notably via the atmosphere, ocean and solid earth. Atmospheric and oceanic temperatures and circulations affect the evolution of ice-sheets, and conversely ice-sheet evolution impacts the rest of the climate system via various processes, including albedo modification, topographic changes and freshwater flux release into the ocean. To correctly model the evolution of the climate system and sea level rise, these feedbacks therefore need to be considered.

Under the highest emission scenario, temperature is expected to reach levels comparable to the Eocene epoch in a few centuries [1]. At this time, there was no widespread glaciation in Antarctica.

The work of Garbe et al [2] has shown that the Antarctic ice sheet has a hysteresis behavior and gave different temperature thresholds leading to committed Antarctic mass loss. For example, between 6 and 9 degrees of warming (a global temperature increase comparable to the one expected in 2300 for the most emissive scenario), the loss of 70% of the present-day ice volume is triggered. However, the modelling study used idealized perturbations of the climate fields based solely on global mean temperature. More specifically, global mean temperature is translated into local changes of ocean and surface air temperature and increased until a complete deglaciation of the Antarctic ice-sheet is reached. In addition the study did not take into account the ice sheet change feedback on the climate system.

In our work we intend to go a step further by taking into account both the influence of atmosphere and oceanic temperature and circulations on the ice sheet in a physical way, as well as the influence of the ice sheet on the rest of the climate system.

To do so, we use the coupled ocean-atmosphere-vegetation intermediate complexity model iLOVECLIM [3], fully coupled to the GRISLI ice-sheet model for Antarctica [4, 5].

We perform several multi-millenia equilibria simulations for different pCO2 levels, thanks to the relative rapidity of both the iLOVECLIM and GRISLI models. These simulations lead to different atmospheric and oceanic temperatures and Antarctic mass loss. 

These coupled simulations allow us to explore the impact of the ice sheet feedback on the climate and to investigate the differences compared to cases where these feedbacks are not included. The influence of the model parameters linked to the ice sheet coupling is also studied.

References :

[1] Westerhold et al 2020, “An astronomically dated record of Earth’s climate and its predictability over the last 66 million years”

[2] Garbe et al 2020 “The hysteresis of the Antarctic Ice Sheet”

[3] Quiquet et al 2018, “Online dynamical downscaling of temperature and precipitation within the iLOVECLIM model (version 1.1)”

[4] Quiquet et al 2018, “The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet”

[5] Quiquet et al 2021 “Climate and ice sheet evolutions from the last glacial maximum to the pre-industrial period with an ice-sheet–climate coupled model”

How to cite: Leloup, G., Quiquet, A., Dumas, C., Roche, D., and Paillard, D.: Antarctic-climate multi-millenia coupled simulations under different pCO2 levels with the iLOVECLIM-GRISLI model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4740, https://doi.org/10.5194/egusphere-egu22-4740, 2022.

The response of ice sheets to climate changes can be diverse and complex. The amplitude, speed and irreversibility of the melting of the ice sheets due to current anthropogenic emissions remain largely uncertain after 2100. Being able to reconstruct the evolution of the ice sheets during the past climate changes is a possible approach to constrain their future evolution in time scales further than the end of the century.

Here we aim to reconstruct the evolution of the Antarctic ice sheet during the Last Interglacial (LIG, ~ 130 to 115 kyr BP). The LIG was 0.5 to 1˚C warmer than the pre-industrial era with a sea-level between 6 to 9 m above present level. In other words, the Antarctic ice sheet during the LIG can be considered as an analogue to its future evolution. Moreover, it is the interglacial on which we have the most geological records to compare with simulation results.

Knowing that the oceanic forcing is the main driver of the Antarctic ice sheet retreat, we introduced the sub-shelf melt module PICO (Reese et al. 2018) in the ice sheet model (GRISLI, Quiquet et al. 2018) in order to physically compute the melt. We use outputs from the Earth Sytem Model (iLOVECLIM, Roche et al. 2014) to force idealized experiments. Several time periods will be covered: present-day, last glacial maximum and LIG. This work is a first step towards a fully coupled iLOVECLIM-GRISLI-PICO simulation to explicitly take into account the ice sheet climate - interactions in a physical way in simulations of the Antarctic ice sheet during the LIG and future centuries.

How to cite: Menthon, M., Bakker, P., Quiquet, A., and Roche, D.: Antarctic sub-shelf melt during the present and the last interglacial and its impact on ice sheet dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5016, https://doi.org/10.5194/egusphere-egu22-5016, 2022.

For simulating ice sheet – climate interactions on multi-millennial time-scales, a set-up that uses a two-way coupled Earth System Model would be ideal. However, running these simulations over multi-millennium time-scales while including ice sheets, is not feasible. Alternatively, ice sheet models can be forced by interpolating climate time-slices, allowing for a transient forcing to an ice sheet model at limited computational costs.

Here, we compare two methods that interpolate between climate time-slices to create a transient forcing for ice sheet simulations. Firstly, we use a glacial index method, in which the climate is linearly interpolated between time-slices based only on prescribed atmospheric CO₂ concentrations. Secondly, we use a climate matrix method in which the interpolation is not only dependent on the prescribed CO₂ concentration, but also on internally generated thickness, volume and albedo. As a result, the climate matrix method captures ice-sheet atmosphere feedbacks.

Here we present ice sheet simulations of the Last Glacial Cycle using IMAU-ICE forced with Last Glacial Maximum (LGM) and Pre-Industrial time-slices. For the time-slices we use the output from nine Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) GCMs. Our aim is to compare and to evaluate the differences in ice sheet evolution and LGM volume and extent resulting from the different PMIP3 models and the interpolation method used for transient simulations.

For most PMIP3 forcings, both the North-American and Eurasian ice sheets build up quicker in the climate matrix method compared to the glacial index method, which is in better agreement with paleo-observations. This is mostly a result from precipitation differences between the two interpolation methods: In the climate matrix method the interpolation of precipitation is dependent on internally generated ice thickness instead of only CO₂. Therefore, when ice thickness is smaller than LGM, the interpolation tends to shift more towards pre-industrial in the climate matrix method compared to the glacial index method. As precipitation is larger during pre-industrial compared to LGM in most Eurasian and North-American regions, this leads to a larger precipitation in the climate matrix method, increasing ice sheet volume. Similarly, the climate matrix method results into warmer temperatures in ice-free areas as the interpolation is dependent on both CO2, albedo and insolation. However, for most PMIP3 models, this ice sheet-temperature feedback does not cancel-out the increased precipitation in the climate matrix method.

How to cite: Scherrenberg, M. D. W., van de Wal, R. S. W., Berends, C. J., and Stap, L. B.: Simulating the Last Glacial Cycle using a Glacial Index and Climate Matrix Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5261, https://doi.org/10.5194/egusphere-egu22-5261, 2022.

Budgets of remaining anthropogenic carbon emissions have been estimated to keep global warming below a limit (IPCC report 2021). A main impact of global warming is the rise of the sea level caused by melting of the Greenland ice sheet. However, the response of the Greenland ice sheet to temperature rise is strongly nonlinear. Melting depends on the time interval at which the ice sheet is exposed to high temperatures and on its rate of change, and a short time interval of high emission would therefore not necessarily result in the same sea level rise as long intervals of low emission. In order to make adequate predictions about sea level rise associated with melting of the Greenland ice sheet at specific times in the future, it is therefore crucial to explore the impact of cumulative emissions in combination with the emission duration.

We simulate Earth’s evolution for the next 20,000 years using CLIMBER-X, a fully coupled Earth System model of intermediate complexity, including modules for atmosphere, ocean, land surface, sea ice and the interactive 3-D polythermal ice sheet model SICOPOLIS, which is applied to the Greenland ice sheet at a spatial resolution of 16 km. In a first step, we explore equilibrium states of the volume of the Greenland ice sheet using constant partial pressures of atmospheric CO₂. We also explore tipping points related to these states, i.e. unstable states of the ice volume where smaller values would lead to further melting until the associated stable state is reached. Next, we investigate the critical cumulative carbon emission to cross these tipping points. Finally, we assess the influence of the emission duration on crossing the tipping points and on the convergence rate towards the associated equilibrium states. We also investigate to what extent future negative emissions could limit sea level rise.

Our results show how high carbon emission rates, even throughout a short time interval, cause the Greenland ice sheet system to rapidly approach equilibrium states of smaller ice volume. This convergence cannot completely be offset by future negative emissions. In contrast, a quick decrease of global emissions, even if in combination with an extended time period of small net emissions in the future, would substantially delay sea level rise and could even prevent the system from crossing the tipping points.

How to cite: Höning, D., Calov, R., Talento, S., Willeit, M., and Ganopolski, A.: Impact of cumulative anthropogenic carbon emissions, emission duration, and negative emission scenarios on melting of the Greenland ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5599, https://doi.org/10.5194/egusphere-egu22-5599, 2022.

Transitions from a stable, periodically oscillating ice-sheet system to a perpetual ice stream has potentially far-reaching implications for the timing of the onset of the last deglaciation as well as for climate transitions such as the Younger Dryas. These periodical ice-sheet oscillations known as Heinrich-type ice sheet surges are among the most dominant signals of glacial climate variability. They are quasi-periodic events during which large amounts of ice are discharged from ice sheets into the ocean. The addition of freshwater strongly affects the ocean circulation, resulting in a pronounced cooling in the North Atlantic region. In addition, changes in the ice sheet geometry also have significant effects on the climate. Here, we use a coupled ice sheet-solid earth model that is driven with forcing from a comprehensive Earth System Model that includes interactive ice sheets to identify key drivers controlling the surge cycle length of Heinrich-type ice-sheet surges from two main outlet glaciers of the Laurentide ice sheet. Our simulations show different surge initiation behaviour for the land-terminating Mackenzie ice stream and marine-terminating Hudson ice stream. For both ice streams, the surface mass balance has the largest effect on the surge cycle length. Ice surface temperature and geothermal heat flux also influence the surge cycle length, but to a lesser degree. Ocean forcing and different frequencies of the same forcing have a negligible effect on the surge cycle length. The simulations also highlight that a certain parameter space exists under which stable surge oscillations can be maintained. This parameter range is much narrower for the Mackenzie ice stream than for the Hudson ice stream. Leaving the stable regime results in a dynamical switch that turns the system from periodically oscillating system into a perpetual ice stream system. This transition can lead to a volume loss of up to 36% for the respective ice stream drainage basin under otherwise glacial climate conditions.

How to cite: Schannwell, C., Mikolajewicz, U., Ziemen, F., and Kapsch, M.-L.: Sensitivity of Heinrich-type ice sheet surges and their implications for the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6242, https://doi.org/10.5194/egusphere-egu22-6242, 2022.

This study investigates how large proglacial lakes affected regional climate and surface mass balance (SMB) of retreating ice sheets during the last deglaciation. For this purpose we have modified the atmosphere model ECHAM6. The approach is here to limit the surface temperature of proglacial lakes to values below 4°C, while other lakes in ECHAM6 can freely evolve according to a mixed layer scheme.

As a first application we investigate the impact of proglacial lakes during the Allerød interstadial at 13 ka (ka is thousand years before present) with three atmosphere stand-alone experiments:

(i) with 13ka land surface boundary conditions (GLAC1d, Ivanovic et al., 2016) and a modern lake configuration

(ii) same as (i) but with additional lakes around the North American and Fennoscandian Ice Sheets

(iii) same as (ii) but the additional lakes are treated according to our proglacial lake approach.

Over the ocean we use boundary conditions taken from a 15ka coupled climate simulation. These three simulations were evaluated with respect to the regional climate response and the SMB was calculated using the diurnal Energy Balance Model (dEBM, Krebs-Kanzow et al., 2021). Preliminary results are indicating an overall positive effect of regular lakes, and in particular proglacial lakes, on the SMB of the great ice sheets over Northern America and Scandinavia during the Allerød interstadial.

References:

Ivanovic, R. F., Gregoire, L. J., Kageyama, M., Roche, D. M., Valdes, P. J., Burke, A., Drummond, R., Peltier, W. R., and Tarasov, L.: Transient climate simulations of the deglaciation 21–9 thousand years before present (version 1) – PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev., 9, 2563–2587, https://doi.org/10.5194/gmd-9-2563-2016, 2016.

Krebs-Kanzow, U., Gierz, P., Rodehacke, C. B., Xu, S., Yang, H., and Lohmann, G., 2021: The diurnal Energy Balance Model (dEBM): a convenient surface mass balance solution for ice sheets in Earth system modeling, The Cryosphere, 15, 2295–2313, https://doi.org/10.5194/tc-15-2295-2021.

How to cite: Sijbrandij, L., Gierz, P., Hinck, S., Krebs-Kanzow, U., Lohmann, G., and Niu, L.: The influence of proglacial lakes on climate and surface mass balance of retreating ice sheets – An Investigation of the Laurentide and Fennoscandian ice sheets,13 ka BP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6247, https://doi.org/10.5194/egusphere-egu22-6247, 2022.

Here we present first results from a series of transient glacial cycle simulations which were conducted with the Community Earth System model (CESM, version 1.2) coupled to the Penn State University ice sheet-ice-shelf Model (PSUIM). The coupling is achieved by applying CESM-simulated surface air temperature, precipitation, surface shortwave radiation and subsurface-ocean temperatures to the PSUIM. CESM is forced in return by PSUIM-simulated ice sheet cover, topography, and freshwater fluxes. The coupled model, which uses a ~ 4 degree horizontal resolution in the atmosphere and ocean and ~ 40 km for the ice-sheets in both hemispheres, includes representations of the lapse-rate, desert-elevation and albedo-dust feedbacks. The coupled model, which uses moderate bias corrections for temperature and precipitation, reproduces the ice sheet evolution over the last glacial cycle in reasonable agreement with paleo-climate data. In this presentation we will further highlight the sensitivity of simulated glacial variability to changes in key surface parameters as well to the individual orbital and greenhouse gas forcings. Our results reveal that only the combination of orbital and CO₂ forcings can generate the full glacial/interglacial amplitude. Single forcings are insufficient to generate glacial variability, which emphasizes the need to understand the mechanisms that led to the orbital pace-making of CO₂ during the Pleistocene.

How to cite: Yun, K.-S. and Timmermann, A.: A transient glacial cycle simulation with the coupled CESM1.2-PSUIM climate-ice-sheet model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6624, https://doi.org/10.5194/egusphere-egu22-6624, 2022.

The mid-Miocene Climatic Optimum (MMCO, ~17-15 Ma) and the mid-Miocene Climatic Transition (MCT, ~15-13.5 Ma),  represents a period of high policy relevance because of the high atmospheric pCO2 concentrations. Exploring this period offers the opportunity to investigate the Antarctic Ice Sheet (AIS) response to CO2 forcings that are close to those projected in the medium to worse case emission scenarios. A set of equilibrium simulations with the 3D ice sheet model Yelmo allows us to study the envelope of the AIS volume and extent during the MMCO (17 Ma) and MCT (14 Ma). These simulations are forced off-line with equilibrium climatic conditions  obtained with the Atmosphere-Ocean General Circulation Model (AOGCM) IPSL CM5A2.  Two values of the reconstructed atmospheric pCO2, i.e. 420 ppm and 700 ppm, are prescribed, for an orbital configuration corresponding to minimum and maximum insolation values at 75°S each (9 climate simulations in total). Thanks to these different configurations we simulated the AIS dynamics. Results show that at 17 Ma, warmer conditions produce an AIS that is drastically reduced with respect to today’s configuration. At 14 Ma, cooler climatic conditions allow the AIS to expand again. This is in agreement with the geological records of the AIS dynamics that reveal a substantial expansion of the ice sheet at the end of the MCT. Since Antarctica is the only ice sheet at this time, our set of climate and ice-sheet simulations capture the envelope of ice volume and extent of the AIS. Moreover, such studies contribute to a better understanding of the 𝛿¹⁸O records and of the evolution of deep ocean temperature versus ice volume and global mean sea level change.

How to cite: Segalla, D., Blasco Navarro, J., Ramstein, G., Fluteau, F., Robinson, A. J., Alvarez-Solas, J., Montoya Redondo, M. L., and Colleoni, F.: Antarctic Ice Sheet  simulations using Yelmo ice sheet model and a series of IPSL CM5A2 climate simulations between 17 Ma and 14 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7293, https://doi.org/10.5194/egusphere-egu22-7293, 2022.

The most prominent events of ice-sheet collapse in the recent geological past are so-called Heinrich events observed during millennial-scale climate oscillations of the last glacial period. They are characterized by the dispersal of ice(berg) rafted debris and freshwater across the North Atlantic, with the Hudson Strait suggested as the predominant source region. One potential mechanism triggering iceberg release invokes cryosphere-ocean interactions, where subsurface warming destabilizes the Laurentide ice sheet. In this scenario, the build-up of a subsurface heat reservoir is caused by an extensive sea ice cover in the Labrador Sea in combination with a reduced overturning circulation in the North Atlantic, preventing the release and downward mixing of heat in the water column.

Here we present high-resolution reconstructions of sea ice dynamics in the outer Labrador Sea between 30 ka and 60 ka at IODP Site U1302/03, located on Orphan Knoll. Sea ice reconstructions are based on a suite of sympagic and pelagic biomarkers, including highly branched isoprenoids and sterols. These results suggest a transition from reduced/seasonal to extended/perennial sea ice conditions preceding the onset of iceberg rafting associated with Heinrich event 3, 4, 5, and 5a by a couple of hundred to a thousand years. Our preliminary results thus support the importance of sea ice in the Labrador Sea for triggering Heinrich events. Future results from the same core will have to confirm the timing and extent of subsurface warming and ocean circulation dynamics.  

How to cite: Detlef, H., Mørk Jensen, M., Glasius, M., and Pearce, C.: Sea ice dynamics in the Labrador Sea across Heinrich events during MIS 3, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7563, https://doi.org/10.5194/egusphere-egu22-7563, 2022.

At the Last Glacial Maximum, the Eurasian Ice Sheet (EIS) was one of the largest ice masses, reaching an area of 5.5 Mkm² at its maximum. Recent advances in numerical ice sheet modelling hold significant promise for improving our understanding of ice sheet dynamics, but remain limited by the significant uncertainty as to the appropriate values for the various model input parameters. The EIS left behind a rich library of observational evidence, in the form of glacial landforms and sediments. Integrating this evidence with numerical ice sheet models allows inference on these key model parameters, leading to a better understanding of the behaviour of the EIS and a framework for advancing numerical ice sheet models. To quantify how successfully a particular model run matches the available data, model-data comparison tools are required. Here, we model the EIS using the Parallel Ice Sheet Model (PISM), a hybrid shallow-ice shallow shelf ice sheet model. We perform sensitivity analyses to reveal the most important parameters controlling the evolution of our modelled EIS. Results from this analysis allow us to reduce the parameter space required for a future ensemble experiment. This ensemble experiment will utilise novel model-data comparison tools which compare ice-free timings to geochronological evidence and modelled flow directions with drumlins. Unlike previous model-data comparison routines, our tools provide a more nuanced, and probabilistic, assessment of fit than a simple pass-fail. This offers significant benefits for future parameter selection.

How to cite: Archer, R., Ely, J., Heaton, T., and Clark, C.: Sensitivity of the Eurasian Ice Sheet: Improved model-data comparison routines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7694, https://doi.org/10.5194/egusphere-egu22-7694, 2022.

Ice mass loss from Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. Interactions between the ice shelves (the floating portions of the ice sheet that buttress the grounded ice) and the ocean are key processes in this mass loss. The most rapid recent observed mass loss from the Antarctic Ice Sheet is in the Amundsen Sea, where buttressing is declining as small ice shelves are being thinned rapidly by melting driven by inflows of warm Circumpolar Deep Water, leading to important grounding line retreats. Recent research indicates that ice sheets, especially the parts that rest on a bed below sea level such as most of the Amundsen sector, are particularly prone to an unstable and irreversible retreat that might lead to an important and fast global sea level rise.

As part of the European Horizon 2020 research project TiPACCs that assesses the possibility of near-future irreversible changes, so-called tipping points, in the Southern Ocean and the Antarctic Ice Sheet, we conduct numerical simulations perturbating the current conditions of the ice-ocean system in the Amundsen Sea Sector. More particularly, we use the Stokes flow formulation of the open-source ice flow model Elmer/Ice, forced with melt parametrization under the ice shelves to determine the effect of ocean warming on the ice-sheet evolution –eventually looking for the existence of future tipping points in the region. Since 3D-Stokes models can be numerically expensive, using the same Elmer/Ice framework (datasets, ocean and climate forcing), we compare our results to the more efficient but sometimes less accurate 2D-shallow–shelf(y)-Approximation (SSA). This methodology allows us to entangle the differences between the two models and better constrain the uncertainty linked to TiPACCs pan-Antarctic simulations based on the SSA.

How to cite: Mosbeux, C., Gagliardini, O., Jourdain, N., Urruty, B., Chekki, M., Gillet-Chaulet, F., and Durand, G.: Tipping Points in the Amundsen Sea Sector, a comparison between 2D and 3D ice-sheet models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9235, https://doi.org/10.5194/egusphere-egu22-9235, 2022.

Snowfall is by far the most important positive contributor to the overall mass balance of the Antarctic Ice Sheet, potentially buffering temperature-induced dynamical ice loss in a warming climate. Previous studies have proposed that Antarctic snowfall will increase along the Clausius-Clapeyron relationship, describing the saturation water vapour pressure as a function of temperature (7% change for 1°C of warming). Due to cold temperatures and continentality in the interior, this general, first-order explanation may not hold true for snowfall changes across the ice sheet. In this study, we investigate how this first-order approximation can be modified to more reliably represent snowfall changes in a warming climate for simulations of the Antarctic Ice Sheet.

To characterise the present-day precipitation pattern, we use reanalysis data and make use of state-of-the-art model data from the CMIP6 modelling project as well as regional model data. We analyse how the sensitivity of Antarctic precipitation to temperature changes is represented in models and how it potentially changes in the future. We use least-squares linear regression to determine the sensitivity factor, Antarctica’s x-factor, that is used in ice-sheet models to scale precipitation. 

With our statistical analyses, we show that sensitivities of column-integrated water vapour, precipitation, snowfall, net precipitation, and surface mass balance to temperature changes are fairly similar under present-day conditions; implying that the exponential relationship of saturation water vapour pressure to temperature could generally lead to additional mass gains of the Antarctic Ice Sheet with warming. However, we find that the relationship of Antarctic precipitation to temperatures across the ice sheet is not constant, but decreases with ongoing warming. Taking these changes into account could give a more reliable estimate of future precipitation changes than existing approaches. We demonstrate that a linear approximation of the exponential relationship between Antarctic precipitation and temperature becomes more and more imprecise in a warming climate, both for computing the sensitivity factor and to scale Antarctic precipitation in models.

We propose a new way to extract the sensitivity factor of Antarctic precipitation to temperature which takes regional variations and the temperature dependence into account. The temperature dependence becomes more important the higher the warming becomes. Considering local warming rates, we show the necessity of introducing a temperature-dependent scaling factor in ice-sheet models, especially for high-end or long-term sea-level projections.

How to cite: Nicola, L., Notz, P. D., and Winkelmann, P. R.: Antarctica’s x-factor: How does Antarctic precipitation change with temperature?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9983, https://doi.org/10.5194/egusphere-egu22-9983, 2022.

With a volume of 58 m sea-level equivalent, the Antarctic Ice Sheet represents the largest potential source of future sea-level rise under global warming. While the ice sheet gains mass through snowfall at the surface, it loses mass through dynamic discharge and iceberg calving into the ocean, as well as by melting at the surface and underneath its floating ice shelves.

Already today, Antarctica is contributing to sea-level rise. So far, this contribution has been comparatively modest, but is expected to increase in the future. Most of the current mass losses are concentrated in the West Antarctic Ice Sheet, mainly caused by sub-shelf melting and ice discharge. Because air temperatures are low and thus surface melt rates are small, any significant melting at the surface is restricted to the low-elevation coastal zones. At the same time, most of the mass loss is offset by snowfall, which is projected to further increase in a warming atmosphere.

As warming progresses over the coming centuries, the question arises as to how long the mass losses on the one side will be compensated by the gains on the other. In 21st-century projections, increasing surface mass balance is outweighing increased discharge even under strong warming scenarios. However, in long-term (multi-century to millennium scale) warming simulations the positive surface mass balance trend shows a peak and subsequent reversal. Owing to positive feedbacks, like the surface-elevation or the ice-albedo feedback, this effect can be enhanced once a surface lowering is triggered or the surface reflectivity is lowered by initial melt.

Here, we implement a simplified version of the diurnal Energy Balance Model (dEBM-simple) as a surface module in the Parallel Ice Sheet Model (PISM), which extends the conventional positive-degree-day (PDD) approach to include the influence of solar radiation and parameterizes the ice albedo as a function of melting, implicitly accounting for the ice-albedo feedback.

Using a model sensitivity ensemble, we analyze the range of possible surface mass balance evolutions over the 21st century as well as in long-term simulations based on extended end-of-century climatological conditions with the coupled model. The comparison with the PDD approach hints to a strong overestimation of surface melt rates of the latter, even under present day conditions. The dEBM-simple further allows us to disentangle the respective contributions of temperature- and insolation-driven surface melt to future sea level rise.

How to cite: Garbe, J., Zeitz, M., Krebs-Kanzow, U., and Winkelmann, R.: The evolution of future Antarctic surface melt using PISM-dEBM-simple, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10008, https://doi.org/10.5194/egusphere-egu22-10008, 2022.

Glaciers retreating along the western Antarctic Peninsula (AP) reveal previously entombed soils and plants. We collected black (dead) mosses to constrain the timing of late Holocene glacier advances at four sites along the AP from ice-free terrain and from rapidly retreating ice margins. The results of radiocarbon measurements from 39 black mosses were used to infer glacier activity over the past 1500 years along with established criteria for sample collection. The criteria ensure robust estimates of when plant growth ended, referred to hereafter as “kill date”. From these kill dates we report distinct periods of ice advance during ca. 1300, 800, and 200 calibrated calendar years before 1950 (cal yr BP) and the first estimates of glacier rate of advance around 800 cal yr BP of 2.0 and 0.3 meters per year from Gamage and Bonaparte Points (southern Anvers Island), respectively. Kill dates reveal a narrow range of ages within a region, suggesting that multiple glacier termini advanced together, and that the rate of local advances may have varied by an order of magnitude. Other evidence for glacier advances in the northern AP ca. 200 cal yr BP and ages of penguin remains (a proxy for penguin colony abandonment) centered ca. 800 cal yr BP from several sites across the AP coincide with our kill dates. Combining several lines of terrestrial evidence for past glacier activity is critical to improving our understanding of the regional synchroneity of glacial dynamics and cryosphere-biosphere connections.

How to cite: Groff, D., Beilman, D., Yu, Z., and Ford, D.: Kill dates from re-exposed black mosses constrain past glacier advances along the western Antarctic Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10758, https://doi.org/10.5194/egusphere-egu22-10758, 2022.

A leading contender for explaining the mid-Pleistocene transition (MPT) from small 40 kyr glaciations to large, abruptly terminating 100 kyr ones is a shift to high friction bed under the Northern hemisphere ice sheets – the North American ice sheet in particular. The regolith hypothesis posits that this occurred with the removal of deformable regolith – laying bare higher-friction bedrock under ice sheet core domains. Is the regolith hypothesis consistent with the physics of glacial removal of mechanically weak surface material?                

Self-consistency of the regolith hypothesis has not been tested for a realistic, 3D North American ice sheet, capturing the transition from soft to hard bedded and 40 to 100 kyr cycles, fully considering basal processes and sediment production. To test self-consistency, we simulate the pace and distribution of regolith removal in a numerical ice sheet model incorporating the relevant glacial processes and their uncertainties. Specifically, the Glacial Systems Model includes: fully coupled sediment production and transport, subglacial hydrology, glacial isostatic adjustment, 3D thermomechanically coupled hybrid ice physics, and internal climate solution from a 2D non-linear energy balance model. The sediment model produces sediment via quarrying and abrasion while transporting material englacially and subglacially. The subglacial hydrology model employs a linked-cavity system with a flux based switch to tunnel drainage, giving dynamic effective pressure needed for realistic sediment and sliding processes. Deflection and rebound of the Earth's surface are calculated for a range of solid Earth visco-elastic rheologies.  The coupled system is driven only by prescribed atmospheric CO2 and orbitally derived insolation.

Starting from a range of initial sediment distributions and simulating an ensemble of model parameter values, we model the rate and spatial distribution of regolith dispersal and compare this against the inferred range of Pliocene regolith thickness, the present day sediment distribution, and the timing of the MPT. A first order fully coupled representation of ice, climate and sediment interactions captures the transition within parametric and observational uncertainty. The system gives the shift from 40 to 100 kyr glacial cycles while broadly reproducing the present day sediment distribution, inferred early Pleistocene extent, LGM ice volume and deglacial margin locations.

How to cite: Drew, M. and Tarasov, L.: A test of the Regolith Hypothesis with fully coupled glacial sediment and ice sheet modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10821, https://doi.org/10.5194/egusphere-egu22-10821, 2022.

The North American Ice Sheet Complex (comprising the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass in the Northern Hemisphere that grew towards and waned after the Last Glacial Maximum. The existing ice margin chronology available for the North American Ice Sheet Complex is based on radiocarbon data only and does not reflect other geochronometric information constraining the last deglaciation, such as cosmogenic exposure- or optically stimulated luminescence ages. Here we present a series of newly produced ice margin isochrones from 25 ka to present, in a time step of 500 years. For each isochron, we draw maximum, best estimate, and minimum ice margin position in an attempt to capture the existing uncertainty. The ice margin isochrones are based on (i) an up-to-date dataset of radiocarbon ages (~5000), (ii) ¹⁰Be and ²⁶Al cosmogenic nuclide data that directly date ~80 ice-marginal features over North America, (iii) ~350 optically stimulated luminescence ages dating the deposition of an aeolian cover immediately post-deglaciation, (iv) the ice-sheet scale glacial geomorphology record. Our effort brings the information on the last North American Ice Sheet Complex deglaciation on par with that for the Eurasian Ice Sheets and should serve the broad community of Quaternary research from archaeology to numerical ice sheet modelling.

How to cite: Margold, M., Dalton, A. S., Heyman, J., Dulfer, H. E., and Norris, S. L.: New ice margin chronology for the last deglaciation of the North American Ice Sheet Complex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11345, https://doi.org/10.5194/egusphere-egu22-11345, 2022.

Over the past decade, Greenland has experienced several extreme melt events, the most pronounced ones in the years 2010, 2012 and 2019. With progressing climate change, such extreme melt events can be expected to occur more frequently and potentially become more severe. So far, however, projections of ice loss and sea-level change from Greenland typically rely on scenarios that only take gradual changes in the climate into account. 
Here we investigate the effect of extreme melt events on the ice dynamics and overall mass balance of the Greenland Ice Sheet in simulations using the Parallel Ice Sheet Model (PISM). While the extremes generally lead to thinning of the ice sheet by enhanced melting, they partly also decrease the overall ice surface velocities due to a reduced driving gradient. In our simulations, we find that taking extreme events into account leads to additional ice loss compared to the baseline scenario without extremes. We find that the sea-level contribution from Greenland could increase by up to 45 cm by the year 2300 if severe extreme events are considered in future projections. We conclude that both changes in the frequency and intensity of extreme events need to be taken into account when projecting the future sea-level contribution from the Greenland Ice Sheet.

How to cite: Beckmann, J. and Winkelmann, R.: Effects of extreme melt events on the Greenland ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11407, https://doi.org/10.5194/egusphere-egu22-11407, 2022.

Coupled climate-ice sheet models are crucial to evaluating climate-ice feedbacks' role in future ice sheet evolution. Such models are calibrated to reproduce modern-day ice sheets, but current observations alone are insufficient to constrain the strength of climate-ice feedbacks. The extent of the Northern Hemisphere ice sheets during the last glacial maximum, ~20,000 years ago, is well known and could provide a benchmark for calibrating coupled climate-ice sheet models. We test this with the FAMOUS-ice coupled Climate-Ice Sheet model (Smith et al., 2020), a fast GCM coupled to the Glimmer ice sheet model. We ran Last Glacial Maximum simulations using FAMOUS-ice with interactive North American Ice Sheet, following the PMIP4 protocol (Kageyama et al., 2018). We find that the standard model setup, calibrated to produce a good present-day Greenland (Smith et al., 2020), produced a collapsed North American ice sheet at the Last Glacial Maximum. We ran ensembles of hundreds of simulations to explore the influence of uncertain ice sheet, albedo, atmospheric, and oceanic parameters on the ice sheet extent. The North American continent deglaciated rapidly in most of our simulations, leaving only a handful of useful simulations out of 280. We thus developed a method to efficiently identify regions of the parameter space that can produce a reasonable ice-sheet extent. This involved emulating the equilibrium ice volume and area as a function of the surface mass balance at the start of our simulations. We then ran three waves of short simulations for 20-50 years to identify parameter values and surface mass balance conditions potentially suitable to grow a realistic ice sheet. This enabled us to find ~160 simulations with good ice extent.

Through analysis of these simulations, we find that albedo parameters determine the majority of uncertainty when simulating the Last Glacial Maximum North American Ice Sheets. The differences in cloud cover over the ablation zones of the North American and Greenland ice sheet explains why the ice sheets have different sensitivities to surface mass balance parameters. Based on our work, we propose that the Last Glacial Maximum can provide an “out-of-sample” target to avoid over calibrating coupled climate-ice sheet models to the present day.

References:

Kageyama, M. et al. The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments. Geosci. Model Dev. 10, 4035–4055 (2017).

Smith, R. S., George, S., and Gregory, J. M.: FAMOUS version xotzt (FAMOUS-ice): a general circulation model (GCM) capable of energy- and water-conserving coupling to an ice sheet model, Geosci. Model Dev., 14, 5769–5787, https://doi.org/10.5194/gmd-14-5769-2021, 2021.

How to cite: Gregoire, L., Gandy, N., Astfalck, L., Ivanovic, R., Sherriff-Tadano, S., Smith, R., and Williamson, D.: De-tuning a coupled Climate Ice Sheet Model to simulate the North American Ice Sheet at the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11503, https://doi.org/10.5194/egusphere-egu22-11503, 2022.

As part of a project working to improve coupled climate-ice sheet modelling of the response of ice sheets to changes in climate across different periods since the Last Glacial Maximum, we present simulations of the modern Greenland climate and ice sheet using the FAMOUS-BISICLES model.

FAMOUS-BISICLES, a variant of FAMOUS-ice (Smith et al., 2021a), is a low resolution (7.5°X5°) global climate model that is two-way coupled to a higher resolution (minimum grid spacing of 1.2 km) adaptive mesh ice sheet model, BISICLES. It uses a system of elevation classes to downscale the lower resolution atmospheric variables onto the ice sheet grid and calculates surface mass balance using a multilayer snow model. FAMOUS-ice is computationally affordable enough to simulate the millennial evolution of the coupled climate-ice sheet system, and has been shown to simulate Greenland well in previous work using the Glimmer shallow ice model (Gregory et al., 2020).

The ice sheet volume and area are sensitive to a number of parametrisations related to atmospheric and snow surface processes and ice sheet dynamics. Based on that, we designed a perturbed parameters ensemble using a Latin Hypercube sampling technique and ran simulations with climate forcings appropriate for the late 20^th century. The ice sheet area and volume are most correlated to parameters that set the snow/firn albedo while the relationship is less simple for parameters related to clouds and precipitation.

We compare FAMOUS-ice SMB and coupled behaviour against the more sophisticated, higher resolution, CMIP6-class UKESM-ice coupled climate ice sheet model for a late 20^th century simulation as well as an abrupt 4XCO₂ experiment.

Our simulations produce a large range of climate and ice sheet behaviours, including a stable control state for the modern Greenland, and we have been able to highlight the sensitivity of the system to other sets of parameters and future changes in climate.

How to cite: Lang, C., Lee, V., Sherriff-Tadano, S., Gandy, N., Gregory, J., Ivanovic, R., Gregoire, L., and Smith, R. S.: Evaluation of a coupled climate ice sheet model over the Greenland ice sheet and sensitivity to atmospheric, snow and ice sheet parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11929, https://doi.org/10.5194/egusphere-egu22-11929, 2022.

The temporal evolution of Greenland’s surface mass balance (SMB) exerts an essential control on its volume, geometry, and sea-level contribution. Surface mass balance simulations based on future climate projections reveal considerable uncertainties. Here, we investigate Greenland’s SMB during past climate periods and assess the uncertainties due to model dependent climate forcing. Specifically we analyse the SMB of the pre-industrial climate and the mid-Holocene warm period.

We study the surface mass balance of the Greenland ice sheet with respect to uncertainties due to model dependent climate forcing. For this purpose, we create an ensemble based on the output of climate models of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the Paleomodel Intercomparison Project (PMIP4) (Brierley et al., 2020). This ensemble is used to simulate the SMB with the diurnal energy balance model (dEBM) (Krebs-Kanzow et al, 2021). As part of the analysis, we inspect anomalies and inter-model deviations of the mid-Holocene climate forcing, and evaluate the spread of spatial patterns of SMB anomalies in CMIP6/PMIP4. Our results indicate that the model-dependent climate forcing adds considerable uncertainty to SMB estimates over Greenland during the Holocene.

References

Brierley, C. M., Zhao, A., Harrison, S. P., Braconnot, P., Williams, C. J. R., Thornalley, D. J. R., Shi, X., Peterschmitt, J.-Y., Ohgaito, R., Kaufman, D. S., Kageyama, M., Hargreaves, J. C., Erb, M. P., Emile-Geay, J., D'Agostino, R., Chandan, D., Carré, M., Bartlein, P. J., Zheng, W., Zhang, Z., Zhang, Q., Yang, H., Volodin, E. M., Tomas, R. A., Routson, C., Peltier, W. R., Otto-Bliesner, B., Morozova, P. A., McKay, N. P., Lohmann, G., Legrande, A. N., Guo, C., Cao, J., Brady, E., Annan, J. D., and Abe-Ouchi, A., 2020: Large-scale features and evaluation of the PMIP4-CMIP6 midHolocene simulations, Clim. Past, 16, 1847–1872, doi:10.5194/cp-16-1847-2020, 2020. 

Krebs-Kanzow, U., Gierz, P., Rodehacke, C. B., Xu, S., Yang, H., and Lohmann, G., 2021: The diurnal Energy Balance Model (dEBM): a convenient surface mass balance solution for ice sheets in Earth system modeling, The Cryosphere, 15, 2295–2313, https://doi.org/10.5194/tc-15-2295-2021.

How to cite: Neugebauer, R., Rodehacke, C. B., Lohmann, G., and Krebs-Kanzow, U.: Uncertainties of Surface Mass Balance in Greenland for the mid-Holocene as derived from CMIP6/PMIP4 simulations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12018, https://doi.org/10.5194/egusphere-egu22-12018, 2022.

Glaciers on Tibetan Plateau and its surrounding areas were much more extensive during Last Glacial Maximum (LGM) when global mean temperature was 5-8 K lower than today. Accurately reconstructing glaciers on and around Tibetan Plateau remains vital towards understanding glaciers’ sensitivity against climate change, and vice versa.

Previous simulations on glaciers in High Mountain Asia during LGM are usually forced with prescribed climatology without considering the bi-directional feedbacks. We instead coupled a climate model (CESM) to an ice-sheet model (ISSM). Our results show that the interactions between HMA glaciers and climate was significant. Uncoupled runs that ignore such interaction yielded glacial coverage roughly 10% more than coupled runs. Regional glacial features change considerably in coupled simulation. Glaciers on the mid-west Tibetan Plateau decreased while those in Qilian Mountains, Tianshan Mountains and Pamir Plateau saw pronounced increase. Compared with uncoupled simulations, our coupled results is in better agreement with reconstructions of LGM glaciers.

KEY WORDS: Glacier; Ice-sheet; Tibetan Plateau; High Mountain Asia; Numerical simulation; Climate modelling

How to cite: Wei, Q., Liu, Y., and Hu, Y.: Dynamic glaciers improve LGM simulation in High Mountain Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12930, https://doi.org/10.5194/egusphere-egu22-12930, 2022.

The Greenland and Antarctic ice sheets are losing mass to the ocean. This additional freshwater flux to the ocean is only expected to increase in the future, but it is usually not included in current climate model simulations as ice sheets are not modelled interactively. However, this freshwater flux will influence multiple aspects of the climate response. We develop a plausible, future freshwater forcing scenarios for both ice sheets and use a high-resolution, eddy-permitting version of EC-Earth3 to simulate the response to a high emission scenario. We investigate the effect of this additional freshwater on sea ice, ocean circulation, surface temperatures, and sea level by comparing the simulations to the HighResMIP EC-Earth3 simulations without ice sheet mass loss.

How to cite: Jüling, A., Le Bars, D., Lambert, E., Devilliers, M., and Drijfhout, S.: Effects of future freshwater forcing from ice sheet mass loss in a high-resolution climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13289, https://doi.org/10.5194/egusphere-egu22-13289, 2022.

The Western Pacific Warm Pool (WPWP) significantly affects the heat budget and associated climate over the Indian Ocean region. The reduction in the WPWP is manifested in the form of reduced Indonesian Throughflow (ITF) and may be well represented by the census count and oxygen isotope records of planktic foraminifera.

The present study is an attempt to reconstruct the episodes of reduction in the WPWP during the Quaternary, on the basis of extremely low relative abundance of planktic foraminifera Pulleniatina (Pu.) obliquiloculata from the ODP Hole 769B in the Sulu Sea. This species is a thermocline dweller, that thrives in tropical to warm subtropical latitudes. It is considered to be an indicator of Kuroshio Current and shows a direct correlation with the expansion of the WPWP.

In the ODP Hole 769B, Pu. obliquiloculata shows a low relative abundance during the Quaternary, except a few instances of significant increase, so much so that it comprises almost 50% of the entire faunal assemblage. The rising trend is characteristic of high SST and an expansion in WPWP. We have identified seven distinct events of sharp decline in the relative abundance of Pu. obliquiloculata (<5%) and named these events as Pulleniatina Minimum Events (PMEs). These events are: PME-1- (2.21-2.08 Ma); PME- 2 (1.8-1.36 Ma); PME- 3 (0.9-0.87 Ma); PME-4 (0.79-0.65 Ma), PME-5 (0.48-0.44 Ma), PME-6 (0.16-0.13 Ma) and PME-7 (0.04-0.02 Ma) in descending stratigraphic order. We interpret these events to mark be the result of the reduction in the WPWP. We have also found the occurrence of temperate fauna during the stratigraphically younger last five PMEs (PME7 to PME3), which indicate reduction in the Western Pacific Warm Pool (WPWP) probably caused by glaciations. The glacial events probably enhanced the Oyashio Current, which caused the influx of cool fertile waters in the Sulu Sea. The evidence of the increased fertility in the Sulu Sea is marked by the increased relative abundance of Neogloboquadrina dutertrei, a fertility indicator species, during the PME7 to PME3. The PME2 and PME1 show no presence of temperate fauna. These events of reduction in the WPWP may be attributed to the development of El Niño like conditions.

The PMEs were also correlated with the five PL events recorded by Sinha et al (2006) from ODP Hole 763A in the Eastern Indian Ocean. These PL events: PL-1- (2.22 Ma); PL-2 (1.83 Ma); PL-3 (0.68 Ma), PL-4 (0.45 Ma) and PL-5 (0.04 Ma), represented reduced strength of ITF either due to the glacial events (PL-3 to PL-5 events) or due to ENSO induced changes (reduction) in the WPWP (PL-1-and PL-2 events).

The PMEs show striking correlation with the PL events, giving testimony to episodes of reduction in the WPWP during Quaternary.

How to cite: Singh, V., Singh, A., and Sinha, D.: Pulleniatina Minimum Events from the Sulu Sea as evidence for Reduction in the Western Pacific Warm Pool during Quaternary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12, https://doi.org/10.5194/egusphere-egu22-12, 2022.

The Permian time is characterized by various geodynamic and biotic events. The rifting of Gondwana and the formation of the super-continent Pangea are the most important events. The cessation of major Gondwana rifting and thermal cooling has subsequently resulted in the development of marine Tethyan settings at the margin of the northwestern Indian Plate. Based on detailed outcrop-based lithostratigraphical investigations, a total of three formations have been distinguished. The presence of diagnostic foraminifer’s species able to assign Wordian, Capitanian-Wuchiapingian, and Late Wuchiapingian to Changhsingian ages to these rock units respectively. The detailed biostratigraphic and sedimentological analyses of the upper Permian units of northern Pakistan divulged three phases of the carbonate platform development. Initially, the early Permian pure clastic Gondwana deposits were replaced by the Tethyan setting during the middle Permian (Wordian) time whereby the wave-dominated delta was established as the sea-level rises. However, such deltaic deposits were gradually evolved into a pure carbonate system during the Capitanian time in response to gradual transgression. The Capitanian and Wuchiapingian times show the development of a diverse shallow carbonate platform along the northwestern Indian Plate. The late Permian global regression has significantly disturbed the carbonate factory and subsequently developed river-dominated deltaic deposits of carbonate and clastic mixed system. Such a mixed system was again evolved in a carbonate platform during the Early Triassic.

How to cite: Wadood, B., Li, H., and Khan, S.: Evolution of the Permian carbonate platform on Gondwana shelf, Pakistan: sedimentological and biostratigraphic approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-227, https://doi.org/10.5194/egusphere-egu22-227, 2022.

The intertrappean sediments and the bole beds of the Deccan volcanic province hold clues to the climatic condition in India during the Cretaceous/Paleocene transition. Earlier isotopic studies of the bulk clays from the ‘bole beds’ showed that the rainwater composition was lighter (δ¹⁸O  -8‰) relative to the present-day (δ¹⁸O ~ -5‰). This was ascribed to an increase in the rainfall (amount effect). However, later reconstruction of the mean annual precipitation (MAP) from the intertrappean paleosol carbonates suggested that the amount was no different than the modern-day precipitation. One possible reason for this disagreement can be due to the low preservation potential of proxies used in these studies. The present study was carried out by analysing authigenic silica which is resistant to post-depositional modifications. Such silica deposits are abundant throughout the Deccan intertrappean sediments occurring as cherts, chertified limestone and silicified fossils. They form during the interaction of silica-rich water with the existing sediments or fossils, the silica being derived by leaching of the volcanic ash by surface run-off and/or from siliceous hydrothermal waters. Silicified woods were analyzed for their triple oxygen isotope ratios (expressed as δ¹⁷O and δ¹⁸O) to determine the silicification temperature and the isotopic composition of the silicifying fluid. The distribution of the obtained silicification temperature and water composition of diverse samples indicates a widely variable silicification environment. The silicification took place at temperatures from 25°C  (near surface temperature)  to 90°C (at relatively shallower levels of 50-100 m). In addition, the δ¹⁸O (VSMOW) values of silicification fluid varied from -14‰ to near 0‰. The geological, floral and faunal evidence suggest deposition of these woods in a continental fluvio-lacustrine environment. Isotope modelling of the data suggest a two-component fluid mixing between hydrothermal water and a lake water. Assuming this fluid to be derived from a mixture of meteoric water and volcanic hydrothermal water, the δ¹⁸O value of the local meteoric water is estimated to be -14‰ to -12‰. These values are lower by about 9‰ to 7‰ compared to today (mean annual δ¹⁸O over central India being ~-5‰). We ascribe this to an increase in the mean annual rainfall by about 400 mm. It is possible that the late cretaceous precipitation increased due to the warming caused by a high CO₂ environment.

How to cite: Ghoshmaulik, S., Bhattacharya, S. K., Hazra, M., Roy, P., Khan, M. A., Liang, M.-C., and Sarkar, A.: Evidence of high rainfall in India during Deccan eruptions based on triple oxygen isotope composition of petrified woods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-465, https://doi.org/10.5194/egusphere-egu22-465, 2022.

During the Messinian Salinity Crisis (5.97-5.33 Ma), evaporite deposition throughout the Mediterranean basin records a
series of dramatic environmental changes as flow through the Strait of Gibraltar was restricted. In the first stage of
evaporite deposition, cycles of gypsum appear in shallow basins on the margins of the Mediterranean. The complex
environmental history giving rise to these cycles has been investigated for decades but remains somewhat mysterious.
Notably, whether the evaporites are connected to significant changes in Mediterranean sea level is an open question.
In one proposed model, competition between tectonic uplift and erosion at the Strait of Gibraltar gives rise to self-sustaining
sea-level oscillations, or limit cycles, which trigger evaporite deposition. I show that limit cycles
are not a robust result of the proposed model and discuss how any oscillations produced by this model depend on
an unrealistic formulation of a key model equation. A more realistic formulation would render sea-level limit cycles improbable,
if not impossible, in the proposed model.

How to cite: Baum, M.: Limit Cycle Model of Messinian Salinity Crisis Incorrect and Irreproducible, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1042, https://doi.org/10.5194/egusphere-egu22-1042, 2022.

The Miocene-Pliocene transition (MPT) in the Mediterranean area represents one of the unresolved geological riddles of the Neogene. The MPT coincides with the end of the Messinian salinity crisis (MSC, Hsü et al., 1977), an event that led to the deposition of massive volume of evaporite on the Mediterranean seafloor. The final stage of the MSC started at ~5.53 Ma and its uppermost part corresponds to the “Lago-Mare” phase, characterized by the occurrence of brackish shallow water ostracods of Parathethyan origin. The “Lago-Mare” deposits are sharply overlain by Zanclean (earliest Pliocene) marine sediments, astrocronologically dated to start at 5.33 Ma (Van Couvering et al. 2000).

The interpretation of this abrupt environmental change is strongly debated. One scenario assumes a catastrophic flooding of all Mediterranean sub-basins that were previously disconnected from the Atlantic Ocean and from each other (Caruso et al., 2020). An alternative scenario invokes a gradual refilling started during the Lago-Mare phase and continued during the basal Pliocene (early Zanclean) (Roveri et al., 2008; Stoica et al., 2016; Merzeraud et al., 2018).

To investigate the paleoenvironmental conditions across the MP transition, we investigated six sections along a west to east transect of the Apennines foredeep, using an integrated approach that merge the traditional stratigraphic, palaeontological, geochemical, and petrographic data with the analysis of molecular fossils (lipid biomarkers).

The top of the Messinian sediments is marked by a bioturbated dark layer in all six studied sections. The presence of glauconite at the top of the dark layer and of firm ground burrows of the Glossifungites icnofacies filled with Zanclean sediments suggest starved sedimentary conditions and the partial lithification of the sea floor during the earliest Zanclean. In addition, the benthic foraminifera indicate an increase of bottom oxygen content and a deepening of the basin across the MPT. Preliminary results of over 40 samples indicate excellently preserved molecular fossils both in the “Lago-Mare” sediments and in the Zanclean open marine deposits with a predominance of terrestrially-derived higher-plants long chain n-alkanes (LC_alk) and of glycerol dialkyl glycerol tetraethers (GDGTs) of both marine and terrestrial origin. Future analyses will focus on the compound specific carbon and hydrogen isotopes of LC_alk to further constrain precipitation and vegetation changes associated to the MPT. Changes in seawater (via isoprenoidal GDGTs) and land temperatures (via branched GDGTs) will be also reconstructed.

How to cite: Pilade, F., Dela Pierre, F., Natalicchio, M., Vasiliev, I., Birgel, D., Mancini, A., Lozar, F., and Gennari, R.: THE END OF THE MESSINIAN SALINITY CRISIS IN THE MEDITERRANEAN: new data on the Miocene-Pliocene boundary., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2053, https://doi.org/10.5194/egusphere-egu22-2053, 2022.

High-amplitude shifts in sedimentary δ¹³C characterize the Cretaceous system and have been proven to be of great use for supraregional chemostratigraphic correlation. Here we present an upper Berriasian to lower Coniacian (c. 142 – 88 Ma) composite carbon isotope record based on 14 drill cores, two outcrops and almost 5000 samples. The total record comprises a composite thickness of about 1500 m. All cores and successions are located in the larger Hanover area, which represents the depocenter of the North German Lower Saxony Basin (LSB) in early to mid-Cretaceous times.

Boreal Lower Cretaceous sediments are predominantly represented by CaCO₃-poor mud- and siltstones of up to 2000 m thickness in northern Germany, which become more carbonate-rich during the Albian-Cenomanian transition and even chalkier in the upper Cenomanian to Coniacian interval. A number of global carbon isotope key events including the Valanginian Weissert Event, the OAEs 1a, b and d (Aptian-Albian) as well as for the early Late Cretaceous the Mid-Cenomanian Event (MCE), the OAE 2 (Cenomanian-Turonian Boundary Event) and the Navigation Event, among others, have been identified allowing for a detailed comparison with Tethyan and other Boreal records. Thus, this new detailed chemostratigraphy provides a unique opportunity to potentially overcome many still existing Boreal–Tethyan correlation issues. The presented record can be considered to be almost complete, albeit a small gap in the early Albian cannot be ruled.

How to cite: Bornemann, A., Erbacher, J., Blumenberg, M., and Voigt, S.: A new Berriasian to Coniacian composite carbon isotope record from the Boreal Realm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2200, https://doi.org/10.5194/egusphere-egu22-2200, 2022.

The late Miocene-early Pliocene Biogenic Bloom was a significant event defined by the anomalously high marine biological productivity documented in the Indian, Pacific, and Atlantic Oceans; but its causes and consequences at different paleogeographical settings are not yet fully understood. Previous records from Ocean Drilling Program (ODP) Site 1085 (Cape Basin, Southeast Atlantic Ocean) indicate enhanced biological productivity between 7 and 4 Ma, as supported by increased linear sedimentation rates, benthic foraminiferal accumulation rates, and increased total organic carbon mass accumulation rates (Diester-Haass et al., 2002; 2004). To look into the paleoenvironmental consequences of the Biogenic Bloom, we investigated the benthic foraminiferal turnover at this site. Results were integrated with an age model based on a bio-astrocyclostratigraphic tuning and low-resolution carbon and oxygen stable isotope records on benthic foraminifera (i.e. Cibicidoides mundulus) across an interval spanning from the Tortonian (late Miocene) to the Zanclean (early Pliocene). Quantitative analyses of the assemblages and statistical analyses point to increased food supply to the seafloor. The proliferation of phytodetritus exploiting taxa such as Alabamina weddellensis and Epistominella exigua point to an episodic nutrient supply related to seasonal phytoplankton blooms during the Biogenic Bloom.

Reference

Diester-Haass, L., Meyers, P. A., & Vidal, L. (2002). The late Miocene onset of high productivity in the Benguela Current upwelling system as part of a global pattern. Marine Geology, 180(1-4), 87-103.

Diester-Haass, L., Meyers, P. A., & Bickert, T. (2004). Carbonate crash and biogenic bloom in the late Miocene: Evidence from ODP Sites 1085, 1086, and 1087 in the Cape Basin, southeast Atlantic Ocean. Paleoceanography, 19(1).

Acknowledgements

University of Padova DOR grant, CARIPARO Foundation Ph.D. scholarship.

Spanish Ministry of Economy and Competitiveness and FEDER funds (PID2019-105537RB-I00).

How to cite: Gastaldello, M. E., Agnini, C., Westerhold, T., Dallanave, E., and Alegret, L.: The response of benthic foraminifera to the late Miocene-early Pliocene Biogenic Bloom: the record from Southeast Atlantic Ocean (ODP Site 1085), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2260, https://doi.org/10.5194/egusphere-egu22-2260, 2022.

The Nordkapp Basin is located in the southwest Barents Sea. It was formed by rifting in the late Palaeozoic. As the area containing the basin moved north from the equator the climate changed from warm and arid to temperate and humid. Initially a large carbonate platform developed in the Barents Sea in the Carboniferous and Permian. The change in climate due to northward drift caused the platform to shift from a carbonate to clastic platform at the end of the Permian. The sea level changed several times during the Mesozoic due to a combination of eustatic changes and salt diapirism. The depositional environment in the area had been interpreted from multiple cores to vary from onshore coastal plain and delta plain to shelf environment due to the large scale sea level changes. In this work, the cores have been revisited to study smaller scale changes within the environments that had been recognised but not described extensively. The nature of small scale changes is different in different environments and can be seen in different aspects like the bioturbation intensity and clay and sand content. This work will compare the smaller scale sea level changes across the different environments encountered in the cores.

How to cite: Sandvold, M. and Felix, M.: Small scale changes superimposed on larger scale sea level-induced changes in cores from the Nordkapp Basin., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2502, https://doi.org/10.5194/egusphere-egu22-2502, 2022.

Lithuania is located in the eastern part of the Silurian Baltic Basin which was located near the equator during the Silurian. Kurtuvėnai -161 borehole is located in the Northwest Lithuania. The Silurian geological section of investigated interval is composed of siliciclastic and carbonate deposits and represents deep marine environments.

Samples for stable carbon isotope analysis were collected from 1441 – 1316 m depth interval. The sampling intervals range from 0.2 up to 1m. The stable carbon isotope values from carbonates were measured using Thermo Gasbench II coupled with a Thermo Delta V isotope ratio mass spectrometer.

In the investigated interval 10 graptolites biozones were distinguished: Lapworthi Biozone is distinguished in the lowest part of the section and linked to the Adavere Regional Stage (uppermost Telychian); the centrifugus - belophorus biozones mark the Jaani Regional Stage; perneri - lundgreni biozones correspond to the Jaagarahu; and parvus - nassa biozones marks the Gėluva Regional Stage of the Wenlock.

According to the δ¹³C_carb isotope analysis results, a positive excursion was detected in the lower part of the studied interval from 1422.8 m up to 1390.8 m depth. There, the δ¹³C_carb maximum value is 3.87 ‰. This positive δ¹³C_carb anomaly can be linked to the Ireveken positive stable carbon isotopes excursion and the centrifugus – belophorus biozones interval of the lower Wenlock. We can also observe a positive δ¹³C_carb excusion in the upper part of Homerian (from 1327 m depth) which potentially can be the lower part of the Mulde positive stable carbon isotopic event.

In summary, the δ¹³C_carb values varied from -1.35 ‰ up to 3.92 ‰ in studied interval of Kurtuvėnai-161 borehole. A more detailed biostratigraphic and lithological study is needed for a better understanding of the integrated stratigraphy of the Silurian geological section in the Kurtuvėnai-161 borehole in the future.

How to cite: Želvys, T., Spiridonov, A., Cichon-Pupienis, A., Garbaras, A., and Radzevicius, S.: Preliminary report on δ13Ccarb isotope excursion through the Silurian of Kurtuvėnai - 161 borehole, Northwest Lithuania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2950, https://doi.org/10.5194/egusphere-egu22-2950, 2022.

The Cambrian is the most poorly dated period of the past 541 million years of Earth history. This hampers analysis of profound environmental and biological changes that took place during this period. Astronomically forced climate cycle recognized in sediments and anchored to radioisotopic ages provides a powerful geochronometer that has fundamentally refined Mesozoic–Cenozoic time scales but not yet the Palaeozoic. Here we report a continuous astronomical signal detected as geochemical variations (1 mm resolution) in the late Cambrian Alum Shale Formation that is used to establish a 16 Myr-long astronomical time scale, anchored by radioisotopic dates. The resulting time scale is biostratigraphically well-constrained, allowing correlation of the late Cambrian global stage boundaries with a 405-kyr astrochronological framework. This enables a first assessment, in numerical time, of the evolution of major biotic and abiotic changes, including the end-Marjuman extinction and the Steptoean Positive Carbon Isotope Excursion, that characterized the late Cambrian Earth.

How to cite: Zhao, Z., Thibault, N., W. Dahl, T., H. Schovsbo, N., L. Sørensen, A., M.Ø. Rasmussen, C., and T. Nielsen, A.: Synchronizing Rock Clocks in the Late Cambrian, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3197, https://doi.org/10.5194/egusphere-egu22-3197, 2022.

The current “global warming” has been widely attributed to a human-induced greenhouse effect however, until the natural variability of climate is totally understood, it is extremely difficult disentangle the natural and human-induced climatic signal and the resulting effects in a short and long period. In order to understand the role that each component plays in the climate processes it becomes essential to acquire considerably longer records than the time it takes for them to undergo significant changes. The wealth of paleoclimatic information, and the improvement of our knowledge, relies on high-quality and high-resolution data availability, provided that these are anchored to accurate age models.

AMUSED (https://progetti.ingv.it/index.php/it/amused) is a project funded by the Istituto Nazionale di Geofisica e Vulcanologia aimed at reconstruct the climate variability in the central Mediterranean region during the middle-late Quaternary, with focus to the Holocene, by integrating paleoclimate multi-proxies data acquired from different paleoenvironmental settings. In detail, the project investigates lacustrine, speleothem and marine successions in central Italy at different temporal scales and resolution (i.e., from orbital to sub-millennial scale). Additionally, the project aims at the evaluation and reduction of the natural CO₂ emission trough plantation of CO₂-absorbing flora in the Colli Albani volcanic district.

The lacustrine sedimentary succession of the Castiglione maar (Colli Albani Volcano) that based on low-resolution previous studies should account for the last 280 kyr, has been selected as main continental target of the project. Intense Quaternary peri-Tyrrhenian volcanism, produced a large number of tephra that emplaced in the adjacent continental sedimentary basins, making this area suitable for the application of tephrochronology, useful for correlation and synchronization of geological records. Preliminary geophysical exploration surveys (electrical resistivity tomography and ground magnetic) were conducted across the Castiglione maar to reconstruct the subsurface structure and geometry of the basin and identify the best drilling site. Two parallel borehole (C1 and C2) were drilled in order to maximize the amount of recover and avoid large stratigraphic gaps. We retrieved 116 and 126,5 m of alternating sands, clay and silt sediments for drills C1 and C2, respectively. An additional core C3 has been afterwards located between the two boreholes, to increase the recovery of the upper 15 m of succession, strongly disturbed in the two former drills. Several tephra layers were already identified and sampled.

The sediment cores will be sampled for high-resolution multi-proxies analyses: stratigraphic, micropaleontological, palynological, geochemical (stable isotopic composition), and paleomagnetic. Moreover, a robust chronology for Castiglione records will be produced by combining ⁴⁰Ar/³⁹Ar dating of the tephra layers back to 280 kyr, and ¹⁴C dating within the last 45 kyr. In addition, a paleomagnetic chronostratigraphy will be derived, providing original target curves and an environmental magnetic investigation will be carried out, by using rock magnetic properties variations in sediments as environmental/climatic proxies.

How to cite: Macrì, P., Caricchi, C., D’Ajello Caracciolo, F., Di Roberto, A., Giaccio, B., Minelli, L., Nicolosi, I., Scateni, B., Siravo, G., and Smedile, A.: AMUSED: A MUltidisciplinary Study of past global climatE changes from continental and marine archives in the MeDiterranean region. The Castiglione maar drilling (central Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3547, https://doi.org/10.5194/egusphere-egu22-3547, 2022.

Carbonate deposits from the easternmost part of the Getic Carbonate Platform form good quality outcrops in the Postăvaru and Piatra Mare Massifs (Patrulius 1976). The average thickness of the carbonate succession reaches 400 m in these areas (Patrulius 1976). In the Postăvaru Massif, the Mesozoic succession consists of Upper Jurassic−Lower Cretaceous carbonate deposits which are covered by upper Albian−Cenomanian Conglomerates (Săndulescu 1964). In the Piatra Mare Massif, the carbonate succession comprises Callovian−Berriasian olistoliths which are embedded in the general mass of the upper Aptian Conglomerates (Săndulescu et al. 1972).

  We collected approximately 600 limestone samples from various sections, in the Postăvaru and Piatra Mare Massifs.

The following sections are located in the Postăvaru Massif: Valea Dragă, Drumul Albastru, Larga Mare, Vârful Postăvaru, Muchia Cheii-Trei Fetițe, Trei Fetițe-Poiana Secuilor, Trei Fetițe-Cabana Postăvaru.

Detailed sampling was performed in the Piatra Mare Massif, in the following sections: Bunloc Est, Bunloc Vest, Cariera Bunloc, Cheile Baciului, Cabana Piatra Mare, Valea Gârcinului, Șura de Piatră, Șura de Piatră-Vârful Piatra Mare, Piatra Scrisă, Coada Pietrei Mari, Șirul Stâncilor, Peștera de Gheață, Prăpastia Ursului and Tamina.

The following facies associations were identified: bioclastic intraclastic grainstone/rudstone, coral-microbial boundstone, packstone to floatstone with pelagic microfossils, bioclastic packstone-grainstone, peloidal oncoidic packstone-grainstone, bioclastic grainstone with black pebbles, wackestone with cyanobacteria nodules, fenestral wackestone, non-fossiliferous mudstone.

The micropaleontological association contains dasycladalean algae [Salpingoporella pygmea (Gümbel), Petrascula bursiformis Etallon, Aloisalthella sulcata (Alth), encrusting organisms [Bacinella type structures, Crescentiella morronensis (Crescenti), Koskinobulina socialis Cherchi & Schröder, Radiomura cautica Senowbari-Daryan & Schäfer, Perturbatacrusta leini Schlagintweit & Gawlick, Taumathoporella parvovesiculifera (Raineri)], foraminifera [Bramkampella arabica Redmond, Coscinoconus alpinus (Leupold), Coscinoconus delphinensis (Arnaud-Vanneau et al.), Coscinoconus sagittarius (Arnaud-Vanneau et al.), Frentzenella involuta (Mantsurova), Protopeneroplis striata Weynschenk, Protopeneroplis ultragranulata Gorbatchik] and pelagic microorganisms (Calpionella alpina Lorenz).

The identified microfacies types indicate that carbonate material was deposited in two distinct depositional settings. The first one includes slope to basin areas while the second one comprises inner platform depositional environments. The presence of abundant C. alpina and various representatives of the genus Coscinoconus (C. delphinensis, C. sagittarius) indicates that deposition continued in the area at least until the lower Berriasian.  

Acknowledgements

This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS-UEFISCDI, project number PN-III-P1-1.1-PD-2019-0456, within PNCDI III

 References  

Patrulius D (1976) Upper Jurassic−Lower Cretaceous carbonate rocks in the eastern part of the Getic Carbonate Platform and the adjacent flysch troughs. In: Patrulius D, Drăgănescu A, Baltreș A, Popescu B, Rădan S (eds) Carbonate Rocks and Evaporites-Guidebook. International Colloquium on Carbonate Rocks and Evaporites, Guidebook Series 15, Institute of Geology and Geophysics, Bucharest, pp 71-82

Săndulescu, M., 1964. Geological structure of the Postăvarul-Runcu Massif (Brașov Mountains) (in Romanian). Anuarul Comitetului Geologic, 34 (2): 382–422.

Săndulescu M, Patrulius D, Ștefănescu M (1972 a) Geological Map of Romania, scale 1:50 000, Brașov Sheet, 111 a (in Romanian). Institutul Geologic, București

How to cite: Mircescu, C. V., Bucur, I. I., and Pleș, G.: Upper Jurassic – Lower Cretaceous limestones from the easternmost Getic Carbonate Platform (Southern Carpathians, Romania). Microfacies, microfossils and depositional environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4119, https://doi.org/10.5194/egusphere-egu22-4119, 2022.

The culmination of climate cooling at the Eocene-Oligocene boundary, known as the Terminal Eocene Event (TEE), forced the eustatic sea level fall crucial for isolation of the Paratethys from the Tethys Ocean. The isolated, northern marginal region contained starved Carpathian Flysch basins characterised by reduced circulation, dysaerobic bottom conditions and increased influx of riverine freshwater. The Cergowa Beds (Lower Oligocene) serve as an example of the icehouse period-related deposition of sandstones and subordinate sandstones-mudstones emplaced by sediment gravity flows in a predominantly anoxic depository dominated by dark shales and associated fine-grained facies of the Menilite Beds. Autochthonous calcareous nannoplankton species indicative of brackish water conditions reflect the Cergowa basin isolation and strong influence by freshwater influx during the zone NP23. This stage was dominated by high volume, high-density sediment gravity flows, occasionally triggered by hyperpycnal effluents. Coalified terrestrial organic matter, especially abundant in the proximal sector and including tree trunk fragments up to 2 m in length, suggests direct connection existed between the fluvial supply and redeposition by sediment gravity flows, probably via a shelf-edge delta supplying the Cergowa basin. The marginal character of the Cergowa basin enables to detect even subtle episodes as: (i) the CCD fluctuations, reflecting coccolithophorid-rich productivity, which is recorded as the laminated pelagic Tylawa Limestones, or (ii) local slope disequilibria reflected by hybrid flows interpreted as resulting from synsedimentary tectonic deformations of the basin floor. Generally, the Alpine orogenic movements enhanced the basin isolation and shoaling by tectonic uplift of the source area. However, the late stage of the Cergowa basin development, dated by the nannoplankton zone NP24, represents an open sea realm supplied by turbidity currents of decreasing density, with time suppressed and finally replaced by the anoxic sediments of the Menilite Beds type. Therefore, the deepening of the marine environment progressed against the prevailing global cooling and continuing eustatic sea-level fall. This apparent discrepancy emphasises the importance of the regional tectonic deformations of the basin that superseded the global climatic influence.

How to cite: Pszonka, J. and Wendorff, M.: Interplay of global climatic and regional tectonic controls in marginal basins, with an example of the Cergowa Beds deposition (Outer Carpathians) during the Oligocene icehouse, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4237, https://doi.org/10.5194/egusphere-egu22-4237, 2022.

Climate-controlled sea-level rise and fall have important effects on the depositional processes of strata. During periods of widespread glaciation, climate cycles influence sea-level rise and fall by controlling ice sheet growth and melting. The Late Cretaceous period was characterized by a typical greenhouse climate, and evidence for the presence of ice is strongly debated. However, the sedimentary record shows short-term larger sea-level fluctuations, and there is growing evidence for aquifer-eustasy (Sames et al. 2020) as an additional mechanism controlling sea-level rise and fall during this period. Field observations, microscopic observations, and analytical studies on upper Santonian to lower Campanian coal-bearing strata of the Gosau Group in the Northern Calcareous Alps (Hofer et al. 2011) have led to the identification of marginal marine mixed carbonate-siliciclastic cycles. Coal layers and lacustrine fine-grained sediments are present and attest to continental sedimentation with raised groundwater table, whereas intermittent marine strata with foraminifera and calcareous nannoplankton give evidence for marine incursions and high sea-level intervals. In a frame of a University of Vienna project, such Upper Cretaceous coal-bearing cycles in European basins will be investigated in detail to infer regional and Tethyan-wide controlling processes on sea-level and groundwater-table.

How to cite: Xiang, X., Wagreich, M., and Draganits, E.: Investigating Greenhouse climate control on coal-bearing cycles in the Tethyan Upper Cretaceous Gosau Group (Northern Calcareous Alps, Austria）, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4298, https://doi.org/10.5194/egusphere-egu22-4298, 2022.

This study investigates the Paleogene deep-water depositional system of the Gosau Group at Gams, Styria (Austria). The examined sections of Danian to Ypresian age (NP1-NP12) comprise sediments of the Nierental and Zwieselalm formations. Four deep-water clastics facies assemblages were encountered, (1) carbonate-poor turbidites, (2) carbonate-rich turbidites, (3) marl-bearing turbidites and (4) a marl-dominated facies. Slump beds and mass flow deposits are common in all facies.

The examined sections predominantly consist of sandy and silty graded beds, including fine breccia layers at the base, to silty shales or claystones on top. Normal grading, lamination, amalgamation of sandy beds and bioturbation are characteristic for all sections. The thickness of sandstone beds varies strongly from only centimeters to several meters, but in general, sandy beds get thicker at sections dated at late Selandian age or younger. Within thinner beds Bouma T_bcd intervals are present. Thus, most sections contain sequences of thin to medium-bedded, fine-grained turbidites.

Based on heavy mineral, thin section, microprobe, and paleoflow analyses, provenance was from the surrounding Northern Calcareous Alps (NCA) rocks and exhuming metamorphic Upper Austroalpine units to the south. Provenance indexes based on heavy mineral assemblages indicate the dominance of an upper greenschist to lower amphibolite facies source of the investigated sediments. In addition, biogenic-calcareous material was delivered by adjacent contemporaneous shelf zones.

The sedimentary depocenter was situated at the slope of the incipient Alpine orogenic wedge, in frontal parts of the NCA, facing the subducting Penninic Ocean/Alpine Tethys. The evolution of the Gams Basin was connected to the eoalpine and mesoalpine orogeny, and the adjunctive transpressional setting. The Gams slope basin provided a fairly small depositional area and accommodation space on the incipient alpine orogenic wedge, and the pervasive tectonic deformation of the NCA destroyed and obscured important features of the formerly confined source-to-sink system. However, the Gams deep-water depositional system is interpreted as an aggrading or prograding submarine fan, deposited into a small confined slope basin, positioned along an active continental margin, bound and influenced by (strike-slip) faults, related to crustal shortening. The development of the Gams slope basin and its infilling sequences was mainly dominated by tectonism and sediment supply, rather than by eustatic sea-level fluctuations. General greenhouse conditions, with enhanced chemical weathering under seasonal conditions are assumed for the entire Gosau Group of Gams (Upper Cretaceous to Eocene), which enhanced erosion and facilitated a greater terrestrial sediment supply. Particularly an increased input of siliciclastics around the PETM is noticeable, including significant numbers of sandy turbidites. The basin was cut off during the Eocene due to renewed orogeny. A Quaternary analogue for the Paleogene basin setting of the Gams area is represented by the Santa Monica Basin in the California Continental Borderland.

How to cite: Koukal, V. and Wagreich, M.: The Paleogene Gosau Group of Gams slope basin of the incipient Eastern Alpine orogenic wedge (Austria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4589, https://doi.org/10.5194/egusphere-egu22-4589, 2022.

Oceanic Anoxic Event 2 (ca. 94 Ma; OAE2) was one of the largest Mesozoic carbon cycle perturbations, but associated carbon emissions, primarily from the Caribbean large igneous province (LIP) and marine burial fluxes, are poorly constrained. Here, we use the carbon cycle box model LOSCAR-P to quantify the role of LIP volcanism and enhanced marine organic carbon (C_org) burial as constrained by the magnitude and shape of the positive stable carbon isotope (δ¹³C) excursion (CIE) in the exogenic carbon pool and atmospheric pCO₂ reconstructions. In our best fit scenario, two pulses of volcanic carbon input—0.065 Pg C yr^–1 over 170 k.y. and 0.075 Pg C yr^–1 over 40 k.y., separated by an 80 k.y. interval with an input of 0.02 Pg C yr^–1—are required to simulate observed changes in δ¹³C and pCO₂. Reduced LIP activity and C_org burial lead to pronounced pCO₂ reductions at the termination of both volcanic pulses, consistent with widespread evidence for cooling and a temporal negative trend in the global exogenic δ¹³C record. Finally, we show that observed leads and lags between such features in the records and simulations are explained by differences in the response time of components of the carbon cycle to volcanic forcing. 


How to cite: Papadomanolaki, N. M., van Helmond, N. A. G. M., Paelike, H., Sluijs, A., and Slomp, C. P.: Quantifying volcanism and organic carbon burial across Oceanic Anoxic Event 2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4796, https://doi.org/10.5194/egusphere-egu22-4796, 2022.

The Eocene, as the warmest epoch during the Cenozoic, has received much attention as it can inform us about the features of global warmth, highly relevant to a “high-CO₂” future. However, there is still a lack of knowledge regarding some key features of global warm climates, such as how higher global temperatures might have affected the duration and intensity of seasonality.  Furthermore, recognizing seasonal cycles is essential when interpreting proxy data and reconstructing paleo climate, e.g. in order to understand inter-annual bias between proxies. 

In the current study the seasonal variations in sea surface temperature (SST) and fresh water input into the Anglo-Paris Basin (subjacent areas of the Paleo-North Sea) was investigated. Marginal seas, like the Paleo North Sea, are an important intersection between the continental and marine realm, and are especially sensitive to short-term climate variations.

In order to resolve seasonal and perennial changes in SST and freshwater balance, we measured Ba/Ca, δ¹⁸O, and the clumped isotopic composition (∆₄₇) of exceptionally well-preserved fossil molluscs. Although δ¹⁸O is commonly used for the reconstruction of temperature, its calculation often assumes a constant δ¹⁸O value of seawater, which might not be true on seasonal scales and/or within swallow marine basins. In this context, ∆₄₇ was employed to determine the average temperature amplitude, due to its independence from δ¹⁸O_seawater. Additionally, Ba/Ca was used to account for periods with enhanced fresh water input, because barium mostly enters the oceans via fluvial systems and could therefor indicate seasonally enhanced and isotopic lighter fresh water input.            

The bivalve species Venericor planicosta was employed as proxy archive, due to its long life span (10-20 years) and its wide distribution in the Anglo-Paris Basin during the Eocene. The pristinely preserved, aragonitic bivalve shells were sampled by micro-milling (δ¹⁸O, ∆₄₇), as well as, laser ablation (Ba/Ca), to generate proxy records with high temporal resolution.

The isotopic data reveal well pronounced seasonal oscillation with a sinusoidal shape and a maximum difference of 2‰, from -3,5‰ to -5,5‰. On average, the inter-annual variation of the δ¹⁸O record is around 1‰. The Ba/Ca record, on the other hand, shows a flat background with recurring large and sharp peaks. While the baseline Ba/Ca values are around 20 µmol/mol, the peaks can reach up to 300 µmol/mol. The peaks largely fall together with periods of depleted δ¹⁸O values. These results hint to a possible seasonal bias of temperature records in the Anglo-Paris basin based purely on δ¹⁸O, due to variable δ¹⁸O of seawater. This is further implied by the back-calculation of δ¹⁸O_seawater from ∆₄₇ measurements, revealing a range from 2‰ to -4‰. 

How to cite: Kniest, J. F., Davies, A., Todd, J. A., Sigwart, J. D., Evans, D., Fiebig, J., Voigt, S., and Raddatz, J.: Eocene seasonality resolved by coupled Ba/Ca and stable oxygen isotope ratios in bivalve shells, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4815, https://doi.org/10.5194/egusphere-egu22-4815, 2022.

Lower and Middle Jurassic sedimentary deposits in southern Germany have accumulated in a shallow-marine shelf environment and are typically dominated by clayey lithologies with minor occurrences of sandstones and limestones. The sedimentary evolution and paleoclimatic significance of these poorly exposed deposits often remain largely unexplored. Here we present a suite of high-resolution x-ray fluorescence (XRF) core scanning data from southern Germany covering the Upper Toarcian and Aalenian stages. The overall objective of this study is to identify Transgressive-Regressive cycles based on the analysis of three cores obtained during scientific drilling campaigns in 2019-2021. Cores have been analyzed with an Avaatech XRF Core Scanner at a 10 mm sampling interval, an energy of 10 keV and a current of 500 µA to measure element intensities ranging from aluminium through iron. Resulting trends in elemental ratios indicative for subtle grain-size variations such as Si/Al are used to reconstruct shoreline trajectories and establish a sequence stratigraphic framework (see Thöle et al. 2020). Particularly the thick and largely homogenous Opalinuston Formation appears suitable in that respect, likely resulting from extraordinarily high sedimentation rates during the lower Aalenian in southern Germany, thus providing a complete but unexplored archive of paleoclimatic signals.

References:

Thöle, H., Bornemann, A., Heimhofer, U., Luppold, F. W., Blumenberg, M., Dohrmann, R., & Erbacher, J. (2020). Using high‐resolution XRF analyses as a sequence stratigraphic tool in a mudstone‐dominated succession (Early Cretaceous, Lower Saxony Basin, Northern Germany). The Depositional Record, 6(1), 236-258.

How to cite: Mann, T., Bornemann, A., and Erbacher, J.: A sequence-stratigraphic framework for the Toarcian – Aalenian from southern Germany based on x-ray fluorescence core scanning data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4877, https://doi.org/10.5194/egusphere-egu22-4877, 2022.

The deep Southern Ocean (SO) circulation is of major significance for the understanding of the ocean´s impact on Earth’s climate as uptake and release of CO_­­­2 depend strongly on the redistribution of well and poorly ventilated water masses.

Neodymium isotopes preserved in deep sea sediment have proven useful to study the deep ocean circulation and water mass provenance thanks to basin scale isotope gradients between the Pacific and the North Atlantic. Here we present novel neodymium isotope data (ε_Nd) of three sediment cores in 2.8, 3.3 and 3.6 km depth in the Atlantic sector of the SO to assess the presence of old and poorly ventilated Pacific sourced Deep Water (PDW) during the past 150 ka.

The sediment cores indicate dramatic temporal changes of ε_Nd spanning a range of 7.7 ε-units from -1.0 to -8.3. While the ε_Nd variability of the two deeper cores is driven by changes in ocean circulation, the shallowest drilling site is likely influenced by a local source of radiogenic Nd, such as weathering of volcanic material.

During peak glacial periods with maximum ice extent and a shoaled AMOC we observe radiogenic ε_Nd values of ~-2.5 to -3.5. This confirms a predominance of glacial PDW at depths of >3 km with proportions close to 100% and thus increasing the water volume portion with enhanced respired carbon. We further advocate for the persistent presence of PDW even during interglacials although with a much smaller proportion.

Hence, our results enforce the leading role of the SO in storing and reinjecting respired CO₂ into the deep Atlantic Ocean and the Atmosphere during glacial-interglacial terminations.

How to cite: Hallmaier, M., Rückert, E. M., Link, J. M., Lütkes, L., and Frank, N.: Dominance of Pacific Sourced Deep Water in the Atlantic sector of the Southern Ocean during the last glacials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5602, https://doi.org/10.5194/egusphere-egu22-5602, 2022.

The late Cretaceous climate is represented by an 8-10 °C decline of global mean temperatures that terminated global warmth of mid-Cretaceous times. Causal mechanisms of the cooling are still not well constrained and discussed in the interplay of reduced volcanic greenhouse gas emission and intensified silicate weathering as a global carbon cycle feedback. The lithium isotopic composition (δ⁷Li) of marine carbonates is a proxy for the chemical weathering intensity of silicate rocks, and thus provides information about the role of silicate weathering as thermostat and sink for atmospheric CO₂.

Here, we present the first detailed chalk-derived Late Cretaceous δ⁷Li record (91-66 Ma) of the boreal white chalk in Northern Germany (Lägerdorf-Kronsmoor-Hemmoor) and from sections in southern England as archive for the seawater lithium isotopic composition. In the course of this study, we will also analyze the archives of skeletal calcite from brachiopods, belemnites and rudists, which should enable us to identify systematic offsets among different calcifiers related to vital effects by the direct comparison of fossilized shells and their surrounding sediments.

To handle the potential impact of clay contamination in bulk carbonates, we applied a pre-leaching and leaching procedure with 1 M ammonium acetate and 0.05 M nitric acid. The method was tested for a 1.85 Ma old sample of coccolith ooze from the Manihiki Plateau (equatorial West Pacific Ocean), which has consistent δ⁷Li values and shows a systematic negative 3-4 ‰ offset to modern seawater. In addition, the degree of potentially leached silicates is monitored by the analysis of E/Ca ratios, like Al/Ca.

In total, our late Cretaceous lithium isotope record shows a trend of rising δ⁷Li values between +16 and +25 ‰. Superimposed, the curve displays a rise in the Santonian, a local maximum in the early Campanian followed by a drop to a local minimum in the late Campanian. Subsequently, the δ⁷Li values rise again towards elevated values in the Maastrichtian. Overall, the shape of the δ⁷Li curve strongly resembles the evolution of deep-sea temperatures based on benthic oxygen isotopes suggesting a close link between climate and weathering. Thereby, more positive δ⁷Li values correspond to cooling periods and the late Campanian lowering of δ⁷Li values parallels the intermittent deep-sea warming. Such a pattern points towards a strong relationship between the congruency of silicate weathering and climate on a multi-million year time scale.

How to cite: Huber, S. J., Schlidt, V., Lenk, L., Seitz, H.-M., Raddatz, J., and Voigt, S.: Insights from the first detailed record of Late Cretaceous seawater lithium isotopic composition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5761, https://doi.org/10.5194/egusphere-egu22-5761, 2022.

The study of astronomical climate forcing and the application of cyclostratigraphy experienced a spectacular growth over the last decades. In 2018, the first Cyclostratigraphy Intercomparison Project (CIP) workshop constituted the first attempt to compare different methodological approaches and unite the global community around standard, uniform and reliable procedures. Two major conclusions were: [1] There is a need for further organization of the cyclostratigraphic community (e.g. to streamline different methodologies); [2] Cyclostratigraphy is a trainable skill, but currently many universities lack specific resources for training and education. Today, a regular newsletter, a dedicated free open-access journal “Cyclostratigraphy and Rhythmic Climate Change (CRCC)”, a scientific podcast titled CycloPod, and an educational website “www.cyclostratigraphy.org” connect the cyclostratigraphy community. The newly created CycloNet (Research Foundation Flanders FWO Funding) expands this effort into a real and sustainable scientific research network with partners from all around Europe, and open to the global community. At the same time, CycloNet creates a platform for streamlining and integrating new multi-disciplinary approaches. The main scientific targets for CycloNet in the next five years are: [1] Set up a diverse and sustainable community structure, relying on exchange, interaction and training, [2] Boost research by novel methodological approaches applying advanced signal processing techniques, [3] Organize a second Cyclostratigraphic Intercomparison Project. With this poster, we reach out to the broader community to exchange ideas on concepts and activities that CycloNet can help to develop further towards the future.

How to cite: Claeys, P., Sinnesael, M., De Vleeschouwer, D., and Zeeden, C.: CycloNet: European Cyclostratigraphy Network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6334, https://doi.org/10.5194/egusphere-egu22-6334, 2022.

During the Middle-Late Eocene, the Earth transitioned from a greenhouse to icehouse period. Within this period, a warming phase of 500 kyr called MECO (Middle Eocene Climatic Optimum) took place at the beginning of the Bartonian (from 40.5 Ma to 40 Ma - C18n). This event is characterized by a negative shift in the δ¹⁸O profile of benthic foraminifera associated with an increase of 4 to 6 °C in surface and deep ocean waters. The peak of the MECO is also characterized by a short δ¹³C negative excursion at 40.0 Myr during an overall increasing trend of δ¹³C. This positive trend of the δ¹³C curve appears to be related to an atmospheric increase in the pCO², but the causes remains unclear.

Unlike the oceanic domain, few datas exist for the characterization of the MECO in coastal areas. Additionally, important component of the climatic context, such as the seasonal gradient of temperature, remain unknown. To unravel these uncertainties, this work focuses on the nearshore Eocene sedimentary records of the Paris Basin, which presents an important and remarkably well preserved paleobiodiversity of marine mollusk shells. Previous studies have confirmed that the MECO event is well recorded in Bartonian sediments, but due to several uncertainties, its stratigraphic position remains to be specified. Here we present a composite section that spans a stratigraphic interval covering the middle Lutetian (falunière de Grignon outcrop) and the Bartonian (Horizon de Mont-Saint Martin Formation, le Guépelle section and the Sables de Cresnes Formation). Thus, we combine different proxies provided by ¹⁸O, ¹³C and ∆₄₇ analyses of marine mollusk shells sampled in these sections in order to clarify the stratigraphic position of the MECO in the sedimentary succession of the Paris Basin and to constrain the climatic expression of this hyperthermal event in shallow marine environment. 

Isotopic analyses were performed on the shells of 3 Bartonian mollusks species: 2 bivalves represented by Bicorbula gallica and Crassostrea cucullaris and 1 gastropod represented by Torquesia sulcifera. Stable isotope (δ¹⁸O and δ¹³C) results both show a characteristic negative excursion at the end of the Sables du Guépelle formation, in the lower part of the Bartonian. Clumped isotope analyses were performed on some specimens of B. gallica and T. sulcifera in order to better constrain the composition of δ¹⁸O_w throughout the stratigraphic interval studied. These results indicate significant decreases in local δ¹⁸O_w over the lifetime of most individuals, interpreted as large infra-annual variations in salinity. Paleotemperatures calculated from the previously constrained δ¹⁸O_carbonate increase by 4 to 10 °C during the MECO event , while the seasonal temperature variation decreases from 11-13 °C to 8 °C during the negative isotopic excursion of the end of the Sables du Guépelle formation.

Based on these new results, we propose that the MECO is recorded in the top of the Sables du Guépelle formation marked by a warming period and a lower seasonal temperature gradient. These results lead to a better chimio-chronostratigraphic calibration of the Bartonian deposits of the Paris Basin.

How to cite: Marlot, L., Huyghe, D., Briais, J., Emmanuel, L., Daëron, M., Flehoc, C., Merle, D., and Aguerre, O.: Marine mollusk shells record the seasonal variations of temperature during the Mid Eocene Climatic Optimum in the Paris Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6583, https://doi.org/10.5194/egusphere-egu22-6583, 2022.

Over the last decades, significant increases in temperature and in the incidence of extreme climatic events have been registered in the Iberian Peninsula. Environmental changes  are easily recorded in high mountain lakes, due to their sensitivity and isolated location. Since paleolimnological information can be very useful for planning and modelling future climate change scenarios, it is necessary to find suitable lakes and test their sensitivity to current and past climatic shifts in order to adequately fulfill these tasks.

In order to test the suitability of the Bassa Nera pond as an indicator of global climatic change, this study aims to examine the variations of different  paleoindicators over the last 15,000 years. The variations of paleoenvironmental data can be then compared with the changes of different biological indicators (chironomids, diatoms, pollen), to find likely correlations that can be used to figure out future climatic scenarios and to provide information for environmental management.

For this study, a core of approximately 1,100 cm was extracted (PATAM 12-A-14) and dated with radiometric techniques. Sedimentological analysis was performed by applying conventional stratigraphic techniques and X-ray fluorescence methods. The variability of the sedimentary sequence allowed us to reconstruct the different climatic events. The pond recorded a long sedimentary sequence encompassing the last 15,000 years. The sedimentological analysis allowed us to establish 5 different stratigraphic units which we have separated in two principal sections. The first section is formed by organic rich facies while the remains of the core is composed mainly of clays and silts facies with some sand layers.

These data will be very useful to establish which and how past climatic events have affected this high mountain basin, when reconstructing the evolution of main paleolimnological indicators of environmental change. And in conjunction with subsequent studies, it will establish whether or not the suitability of the Bassa Nera as a sentinel of climatic global change. This in turn will allow the  establishment of a network of sentinel lakes in the Iberian Peninsula.

How to cite: Blasco, A., Calero, M. A., Rull, V., Cañellas-Boltà, N., Garcés, S., Montoya, E., and Vegas-Vilarrúbia, T.: The Bassa Nera pond (Central Pyrenees), a potential sentinel of climatic changes over the last 15,000 years., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6605, https://doi.org/10.5194/egusphere-egu22-6605, 2022.

New high-resolution seismic data (Sparker) and very-high-resolution parametric echosounder (PES) data acquired in an area of the southern North Sea (the Flemish Bight) reveal its Quaternary seismic stratigraphy in unprecedented detail. The identified seismo-stratigraphic units and geomorphological features have been examined with the view to better understand the Quaternary evolution of the southern North Sea.

Seven acoustic units were recognised, including Lower Pleistocene deltaic sediments, Eemian to lower Weichselian shallow marine to coastal (lagoonal) clay-silt-sands, and Holocene coastal peat layers overlain by intertidal and marine sediments. Four erosional events were identified, two of which can be traced as regionally occurring surfaces, and two occurring as localised incisions. Mapping of geomorphological features revealed potential Elsterian moraines in the UK sector, an Elsterian ice-pushed ridge in the Dutch sector and possible permafrost-related structures (probably dating to MIS3).  Seven newly dated peat samples, acquired near a tidal sand ridge known as the Brown Bank from depths between 31 m and 34 m below sea level and dating to between 9.5 and 10.9 cal ka BP, indicate that this area was terrestrial during the early Holocene.

The results form the basis to further improve the regional Quaternary stratigraphic framework of the area, to better understand the region’s (de)glacial history, to enhance sea-level reconstructions and to examine the area’s geographical importance for human occupation during Prehistory.

How to cite: Plets, R., De Batist, M., Missiaen, T., De Clercq, M., Garcia, D., Mestdagh, T., Versteeg, W., Fitch, S., Harding, R., Gaffney, V., Busschers, F., and van Heteren, S.: Quaternary seismic stratigraphy of the Flemish Bight (southern North Sea): a re-evaluation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7244, https://doi.org/10.5194/egusphere-egu22-7244, 2022.

A 55 meters thick section at Cuchia, Basque-Cantabrian Chain, North Spain, mainly formed by Lower Cretaceous Wealden facies, has been intensively investigated from the micropalaeontological viewpoint. The carbonate beds intercalated within this series yield a rich and diverse charophyte assemblages of high biostratigraphic interest, which could be studied for the first time after successful preparation following the acetolysis method.

Twenty-two charophyte taxa were identified forming two distinct charophyte assemblages belonging to two successive charophyte biozones. The first charophyte assemblage, from the lower part of the studied section, is composed of Echinochara lazarii, Atopochara trivolvis var. triquetra, Globator mallardii var. trochiliscoides, Clavator grovesii var. gautieri, Clavator harrisii var. dongjingensis, C. harrisii var. harrisii, C. calcitrapus var. jiangluoensis, C. calcitrapus var. calcitrapus, Ascidiella stellata var. stellata, A. triquetra, Hemiclavator neimongolensis var. neimongolensis, H. neimongolensis var. posticecaptus, Mesochara voluta gr. voluta and Favargella sp. According to Pérez-Cano et al. (2021), such a charophyte assemblage belongs to the new Eurasian “Hemiclavator neimongolensis var. neimongolensis” biozone, late early Barremian–early late Barremian in age as calibrated by Sr isotope stratigraphy and by correlation with marine biostratigraphy.

The second charophyte assemblage, which occurs in the upper part of the studied section is composed of the species E. lazarii, A. trivolvis var. triquetra, A. trivolvis var. trivolvis, C. grovesii var. jiuquanensis, C. harrisii var. dongjingensis, C. harrisii var. harrisii, C. harrisii var. reyi, Ascidiella cruciata, H. neimongolensis var. neimongolensis, H. neimongolensis var. posticecaptus, Mesochara voluta gr. voluta, Munieria grambastii, Clavatoraxis sp., Charaxis sp.  and Tolypella sp. vel. Mesochara sp. According to Pérez-Cano et al. (2021), such a charophyte assemblage belongs to the new Eurasian “Clavator grovesii var. jiuquanensis” biozone, late Barremian–early Aptian in age as calibrated by Sr isotope stratigraphy and by correlation with marine biostratigraphy.

As the overlaying succeeding limestones is early Aptian in age, our results allow constraining the chronostratigraphy of the Wealden series at Cuchia section to the late early Barremian– late Barremian, instead of Hauterivian–Barremian (Najarro et al., 2011) as previously thought, leading for a more detailed stratigraphic correlation of the Cuchia section to equivalent units of the Iberian plate, especially from the Iberian Chain and the Pyrenees.

References.

Najarro, M., Rosales, I., Martin-Chivelet, J. (2011). Major palaeoenvironmental perturbation in an Early Aptian carbonate platform: Prelude of the Oceanic Anoxic Event 1a. Sedimentary Geology 235, 50–71. https://doi.org/10.1016/j.cretres.2021.104934

Pérez-Cano, J., Bover-Arnal, T., Martín-Closas, C. (2021). Barremian–early Aptian charophyte biostratigraphy revisited. Newsletters on Stratigraphy (in press). DOI: 10.1127/nos/2021/0662

How to cite: Trabelsi, K., Mai, A. T., Sames, B., Herrle, J. O., and Wiese, F.: Charophyte biostratigraphy of the Lower Cretaceous (Wealden) Cuchia section, Basque-Cantabrian Chain, North Spain: Interest for regional stratigraphic correlation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7766, https://doi.org/10.5194/egusphere-egu22-7766, 2022.

From 2019 to 2021, three cores were drilled at different locations in the southern German Swabian Alb as part of the SEPIA project (Sequence Stratigraphy of the Aalenian in Southern Germany). They comprise sediments of 200 to 250 m length and are penetrating Lower and Middle Jurassic strata from the Pliensbachian to Bathonian stages (~ 190-166 Ma). The aim of this project is the development of a sequence stratigraphic model of the South German Basin at the transition from the Lower to Middle Jurassic time. Conclusions should be drawn towards the source area of the sediments as well as on the influence of sea level fluctuations on sedimentation.

Today, the Swabian Alb is a SW-NE trending mountain chain consisting of mainly carbonate rocks, and is one of the most distinctive regions in Germany where Jurassic strata is cropping out. During the middle Jurassic, Europe was almost completely covered by a shallow epi-continental sea including several small emerging areas or islands, located at latitudes about 15° lower than today. Southern Germany experienced predominant deposition of fine clastic sediments in a tropical climate. The most common sediments of this period are dark clays and oolithic ironstones, whereas condensation and discontinuity surfaces occur in many instances. Accommodation space for these sediments was not only generated by changes in sea level, but also by continuing subsidence of the area, explaining the inhomogeneous thickness and changes in facies of the sediments.

The geophysical downhole logging data of the stratigraphic record is used to develop a lithological classification and correlation of the boreholes sediments by the application of a cluster analysis to the data. Furthermore, the downhole logging data is used to perform cyclostratigraphy in selected intervals. The focus of the intervals chosen for cyclostratigraphy lies on the Aalenian stage, as this stage holds the most continuous and extended record in all three boreholes. Predicted timespans of these intervals yield similar results of ~800-1100 ka for all three boreholes and might provide a new benchmark for progressive improvement, especially for cyclostratigraphic analyses of the Lower Aalenian Opalinusclay Formation.

How to cite: Leu, K., Zeeden, C., Wonik, T., Mann, T., Erbacher, J., and Bornemann, A.: Litho- and cyclostratigraphy of the Aalenian Opalinusclay Formation in the Swabian Alb deduced from downhole logging data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8150, https://doi.org/10.5194/egusphere-egu22-8150, 2022.

A semi-3D stratigraphic architecture of the Lower Ktawa Group, deposited during the early Late Ordovician on the northern Gondwana platform in a shallow marine environment, was investigated in the Anti-Atlas. The logging of 42 sections reveals that the Lower Ktawa is dominated by shales, punctuated by fine to coarse sandstones forming successive cuestas. Here, focus is put on three main sand cuestas recording major sea-level drops.

The lowermost cuesta (Foum-Zguid Member) outcrops along >85 km, and dips southward. Three facies associations albeit with complex lateral relationships were distinguished: 1. In the West, coarse-grained cross-bedded sandstones. 2. In the central part, sandstones dominated by Hummocky-Cross-Stratifications (HCS), in amalgamated beds towards the West but isolated within shales towards the East. 3. In the East, dominance of highly bioturbated sandstones. A second cuesta (“Tissint Member”) outcrops exclusively on the western part of the transect, approximately 25-50 m above the Foum-Zguid cuesta, and also dips South-southwestward. This 40 m-thick sandstone complex has a sharp base and is composed of fine to coarse cross-bedded sandstones. At its northeastern limit, the 40 m-thick succession disappears within 3.5 km. The upper cuesta (Bou-Hajaj Member, 5-40 m thick) is found ca.160 m above the base of the Ktawa Group and outcrops in the eastern zone of the study area. Its southern part is characterized by the thickest stack of sandstones, organized in a shallowing upward trend, and comprises HCS-beds and channelized structures a few meters in width. The eastern part is dominated by coarse, bioturbated, cross-bedded sandstones lacking shallowing upward stacking patterns. Its dip is northward, in the opposite direction to the underlying two members. Moreover, from satellite images, a clinothem dipping towards the Northeast is identified, together with the dissociation of the cuesta in two sets pinching out northwestward.

On a regional scale, the directly underlying First Bani Group was reconstructed as a shallow shelf having a northward oriented proximal-to-distal trend (Marante, 2008). A study of the Ktawa Group ca. 200 km Northeast of our study zone evidenced a southwestward proximal-to-distal trend (Meddour, 2016). Furthermore, a regional depocenter of the Ktawa Group is generally thought to occur eastward from our study.

Three interpretation lines are considered to reconcile these apparently contradictory observations: 1. A locally eastward oriented proximal-to-distal trend within a complex sequence stratigraphic framework including superimposed high-frequency cycles. 2. A range of source feeders that may be successively active along an irregular coastline, thereby forming lobes with opposite dispersal patterns. 3. An interplay of reactivation of Panafrican faults (Anti-Atlas/Ougarta) cannot be excluded and may have locally changed the place(s) of maximum accommodation space during deposition. It may also have induced the formation of shoals that would have been partially eroded and recycled. Thus, these apparently contradictory proximal-to-distal trends may actually depict a turning point in the re-organization of the basin predating the end-Ordovician glacial advance.

How to cite: Harlet, D., Douillet, G. A., Ghienne, J.-F., Dietrich, P., Bouscary, C., Razin, P., and Schlunegger, F.: Semi-3D stratigraphic architecture of a siliciclastic shallow-marine platform: Insights from the Ktawa Group (Late Ordovician) in Morocco, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8721, https://doi.org/10.5194/egusphere-egu22-8721, 2022.

Sedimentary successions capture the history of geological features and events observable on present-day earth surface as well as those exposed earlier but currently buried or lost to erosion. The Mesozoic rocks in the Kutch Basin (western India) deposited between Middle Jurassic and Early Cretaceous reveal interesting provenance information on lost orogens and buried basins. The southwesterly sediment transport direction indicates north and northwest of the Indian subcontinent as the source area. Detrital zircon and monazite U-Th-Pb geochronology identify dominant sediment input from source rocks equivalent to the late Neoproterozoic Pan-African orogeny (500–650 Ma) along with substantial input from those equivalent to the Cambro-Ordovician Bhimphedian (aka Kurgiakh) (400–500 Ma) orogeny. All other contributing source rocks (ranging from 700 Ma to 3300 Ma) are traceable to the source area following the sediment transport direction. However, outcrops of crystalline rocks with zircon and monazite ages corresponding to the dominant age components are virtually lacking. Rocks equivalent to the Pan-African orogeny are found only as sparse isolated outcrops in the source area. In contrast, this orogeny is well reported from the southern granulite terrain (India), Madagascar, Seychelles and Eastern Africa. Therefore, considering the position of continents during the Mesozoic and the predominance of a 500–650 Ma sediment source in the Kutch Basin, the Pan-African orogenic belt possibly extends to north and north-western India. The current dearth of these outcrops suggests extensive erosion during the Mesozoic greenhouse climate and/or burial under the Deccan Flood Basalts. The other dominant source (400–500 Ma), equivalent to the Bhimphedian orogeny, currently reported as isolated outcrops in the Himalayan-fold-thrust belt (northern India) might have been disturbed and buried by thrusting during the Cenozoic Himalayan orogeny. This study also reveals a large gap of nearly 280 Ma between the youngest detrital zircon (458 Ma) and the depositional age (~170 Ma). This gap may be explained by (i) input of recycled sediment from an older basin, and/or (ii) absence of younger metamorphic events in the source area. The evidences of sediment recycling from thin-section petrography and ultra-stable heavy mineral assemblages (dominated by zircon, rutile and tourmaline) suggest the possibility of a so far unknown (buried or completely eroded) sedimentary basin older than the Kutch Basin. The on-going study of detrital rutile grains in these sediments may provide an alternative explanation for the 280 Ma gap by revealing lower temperature metamorphic events that are not recorded by U-Th-Pb ages of zircon and monazite.

How to cite: Chaudhuri, A., Dunkl, I., Schönig, J., von Eynatten, H., and Das, K.: Geochronology of sediments as a tool to identify lost geological features - a case study from the Mesozoic sedimentary succession of the Kutch Basin, western India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8915, https://doi.org/10.5194/egusphere-egu22-8915, 2022.

The mean cooling of the global ocean during the Last Glacial Maximum (LGM) was recently estimated to 2.6°C using noble gases trapped in ice cores (1). The ocean, however, is highly heterogeneous with respect to its internal temperature varying both in latitude and water depth. While temperature changes in the deep ocean are small at about 2 - 3 °C (1,2), the upper ocean is more dynamic. Regional temperature anomalies of up to 7°C are predicted during the LGM compared to modern interior ocean temperature by global ocean circulation models (3). Due to the temperature drop to near freezing conditions and the global increase in salinity from ice sheet growth, the oceans’ deep interior became strongly haline stratified (2). Temperatures of the glacial ocean thermocline are, however, less well constrained.

Here, thermocline temperature reconstructions since the last glacial based on the Li/Mg ratio in cold-water coral skeletons are presented. The coral samples, collected from 300 - 1200 m water depths from different sites in the Atlantic (43°N to 25°S), reveal synchronous 5 - 7°C cooling during the last glacial period compared to today, as well as a dramatic shoaling of the thermocline. At the end of the LGM, warming of the upper thermocline ocean occurred early in the southern hemisphere followed by a fluctuating warming and thermocline deepening in the northern Hemisphere. This supports the oceanic climate seesaw proposed by Stocker and Johnson in 2003 (4). We thus propose dramatic changes in the export of polar waters towards the Equator and an enhanced subsurface ocean stratification leading to a mostly polar Atlantic with a shallow permanent thermocline during the glacial.

References:

1) Bereiter et al., Nature 553, 39-44 (2018).
2) Adkins et al., Science 298, 1769-1773 (2002).
3) Ballarotta et al., Clim. Past 9, 2669-2686 (2013).
4) Stocker and Johnsen, Paleoceanography 18, 1087 (2003).

How to cite: Lausecker, M., Hemsing, F., Krengel, T., Förstel, J., Schröder-Ritzrau, A., Border, E. C., Orejas, C., Titschak, J., Wienberg, C., Hebbeln, D., Wefing, A.-M., Montagna, P., Douville, E., Matos, L., Raddatz, J., and Frank, N.: Severe cooling of the Atlantic thermocline during the last glacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9308, https://doi.org/10.5194/egusphere-egu22-9308, 2022.

We can only fully understand the past, present and future climate changes by bringing together data and process understanding from a broad range of environmental sciences. In theory, climate modelling provides a wealth of data of great interest to a wide variety of disciplines (e.g., chemistry, geology, hydrology), but in practice, the large volume and complexity of these datasets often prevent direct access and therefore limit their benefits for large parts of our community.

We present the new online platform “climatearchive.org” to break down these barriers and provide intuitive and informative access to paleoclimate model data to our community. The current release enables interactive access to a recently published compilation of 109 HadCM3BL climate model simulations. Key climate variables (temperature, precipitation, vegetation and circulation) are displayed on a virtual globe in an intuitive three-dimensional environment and on a continuous time axis throughout the Phanerozoic. The software runs in any web browser — including smartphones — and promotes data exploration, appeals to students and generates public interest.

We also show current work on the next phase of the platform, which aims to develop new tools for integration into a more quantitative research workflow. These include easy online generation and download of maps and time series plots of the underlying monthly model data. The data can also be exported as global fields or CSV files for any user-selected location for further offline analysis, such as use in spreadsheets. Finally, we will discuss and outline future integration of new sources of model and geochemical proxy data to simplify and advance interdisciplinary paleoclimate research.

How to cite: Steinig, S., Alexander, T., Lunt, D., Valdes, P., Duggan, Z., Lee, P., Navratil, J., Offokansi, I., and Swann, M.: “climatearchive.org”: 540 million years of climate data at your fingertips, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9361, https://doi.org/10.5194/egusphere-egu22-9361, 2022.

The Hangenberg Crisis, at the Devonian-Carboniferous Boundary, severely affected the marine realm. The crisis is characterised by several events associated with change in the sedimentation and biotic extinctions and turnovers. The Hangenberg Black Shale event that recorded the extinction peak in the pelagic realm corresponds to a widespread development of oceanic anoxia and/or dysoxia. The Hangenberg Sandstone event is associated with an extinction of neritic fauna in shallow-water settings, including the final demise of several classical Devonian faunas (stromatoporoids, quasiendothyrid foraminifers, placoderms, etc.). The succession of these events is nowadays explained by a combination of sea level fluctuations (third order transgressive sequence, out-of-sequence regression) and global climatic changes. Through the identification of Milankovitch cycles in the Chanxhe record, we aim at getting a better understanding of the timing and orbital forcing of the different events of the Hangenberg Crisis in shallow-water settings.

The sedimentary record of the interval of interest at Chanxhe is composed of 16 m of alternating decimetre-thick carbonate beds with shaly siltstones, which displays a clear cyclicity. The carbonate-siliciclastic alternations (~0.8 m) are bundled into larger cycles (~5 m) which are separated by intervals dominated by the shaly facies. This is followed by 11 m of carbonate dominated lithology with thin shale layers displaying a less clear cyclicity with ~3 m thick cycles. Then the equivalent of the Hangenberg dark shales is recorded as two dark shaly intervals separated by a carbonate bed. After the Hangenberg dark shales, the section displays carbonates, with the Devonian Carboniferous boundary in massive carbonates 7 m above the top of the black shales.

Samples have been collected along the record every 10 cm which were measured by the portable X-Ray Fluorescence device (Tracer 5, Bruker), allowing to provide elemental data throughout the record. Spectral analysis is applied on Ca and Al, to identify the main cyclicity in the record. The 0.8 meter-thick limestone/shale alternations is clearly recorded in the Ca and Al records and are associated with precession cycles (18 kyr), while the 5 m-cycles are associated with short eccentricity (100 kyr). Prior to the Hangenberg anoxic events, the 100-kyr cycles became less clear and shorter (~ 3 m) which is interpreted as a minimum eccentricity. During the Hangenberg, the cyclicity returns. However, after the Hangenberg and near the Devonian Carboniferous boundary, the facies become very homogeneous, consisting of massively bedded carbonates with no observable cyclicity,  which is also  other contemporaneous sedimentary successions (e.g. China, Poland).   

How to cite: Da Silva, A.-C., Franck, L., Arts, M., and Denayer, J.: Timing and pacing of the Hangenberg Crisis (Devonian-Carboniferous Boundary) in the Chanxhe sections, Belgium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9471, https://doi.org/10.5194/egusphere-egu22-9471, 2022.

5.33 Million years ago, a mile-high marine cascade terminated the Messinian Salinity Crisis due to partial collapse of the Gibraltar arc/sill that isolated a largely desiccated Mediterranean from the Atlantic Ocean. Atlantic waters may have refilled the basin within 2 years. Prevailing hypotheses suggest that normal marine conditions were established across the Mediterranean immediately after the catastrophic flooding. Here we use new proxy data and modelling to show that normal conditions were likely for the western Mediterranean (wMed), but that flooding caused massive wMed salt transfer to the eastern Mediterranean (eMed), which became a hyper-salinity-stratified basin. Hyper-stratification inhibited deep-water ventilation, causing anomalously long-lasting organic-rich (sapropel) sediment deposition. Model:data agreement indicates that hyper-stratification breakdown required 26,000 years. Testing an alternative hypothesis—reconnection of a largely refilled Mediterranean—reveals hyper-stratification in both the wMed and eMed, which would have left sapropels in both basins, in disagreement with observations. Our findings offer novel insight into the processes involved in re-establishing normal marine conditions following abrupt refilling of a previously desiccated ocean basin.

How to cite: Amarathunga, U., Hogg, A., Rohling, E., Roberts, A., Grant, K., Heslop, D., Hu, P., Liebrand, D., Westerhold, T., Zhao, X., and Gilmore, S.: Aftermath of catastrophic flooding of a desiccated ocean basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9593, https://doi.org/10.5194/egusphere-egu22-9593, 2022.

Carbon dioxide (CO₂) emissions are rapidly rising leading to warmer oceans, surface ocean acidification, and complex changes in marine biogeochemical cycling. Calcareous nannoplankton: single-celled marine haptophytes, are likely particularly susceptible to such environmental changes, because they form microscopic plates made out of calcium carbonate (calcite). As these organisms lie at the base of the marine food web, it is critical that we understand how they respond to climate change over longer (millennial) timescales so that we can better predict the long-term effects of current and future environmental change on marine communities.

The high CO₂ world of the early Eocene (~56 to 48 Ma) is characterized by multiple transient warming events (‘hyperthermals’), and is generally considered to be one of the best geologic analogues for future climate change. Here, we present preliminary, low-resolution calcareous nannoplankton assemblage data from the early Eocene of recently-drilled IODP Site U1553 (Campbell Plateau) in the South Pacific Ocean. Sediment cores recovered from Holes C and D at Site U1553 provide arguably one of the most complete and expanded early Eocene records yet from this relatively understudied region, including many of the previously recognized hyperthermals. This coupled with the high calcium carbonate content of the sediments, makes it an ideal case study for exploring millennial-scale changes in calcareous nannoplankton community composition and morphometry during transient warming events.

Within this presentation, we predominantly focus on the Paleocene-Eocene Thermal Maximum (PETM): the largest and best-studied of the early Eocene hyperthermals. Our results suggest that the turnover in nannoplankton species during this warming event was very similar to that observed at other southern high latitude sites such as Maud Rise. More minor ecological ‘jostling’ appears to have occurred prior to the onset of the PETM and following the event; however, the significance of these smaller changes in community composition have yet to be statistically analyzed at the time of writing. It is our aim to combine our assemblage counts with morphometric data to determine whether calcareous nannoplankton acted as a source or sink of carbon dioxide during the early Eocene hyperthermal events. We will also extend our dataset to include several of the smaller hyperthermals that succeeded the PETM, to elucidate whether calcareous nannoplankton exhibit a scaled or threshold response to warming.

How to cite: Jones, H., Niederbockstruck, B., and Röhl, U. and the IODP Expedition 378 Scientists: Calcareous nannoplankton community composition across multiple early Eocene hyperthermal events at International Ocean Discovery Program (IODP) Site U1553 (Campbell Plateau, SW Pacific), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9745, https://doi.org/10.5194/egusphere-egu22-9745, 2022.

Understanding the evolution of lower latitude climate from the most recent glacial periods of the latest Pleistocene to post glacial warmth in the continental tropical regions has been obstructed by a lack of long and continuous time series. Here we examine sediments from Lake Chalco, located in the Valley of Mexico, central Mexico (19°30’N, 99°W). The basin represents a hydrological closed system surrounded by the Trans-Mexican Volcanic Belt aging from the Oligocene to the present. We use borehole logging to conduct a cyclostratigraphic analysis of the Lake Chalco sediments, and incorporate other available dating information. More than 400 m of sediments are logged for several geophysical properties including magnetic susceptibility and spectral gamma radiation.

Gamma radiation can be used to identify elemental isotopes in the geological record, which is used for stratigraphic correlation and paleoclimatic investigations. Among the lake deposit of Chalco sub-basin, 388 total tephra layers (≥1 mm in thickness) were reported from the core description. Tephra layers with specific gamma ray signatures, presenting a challenge for extracting the primary signals caused by environmental and climatic agents. Here, we apply a tailored protocol to identify tephra layers embedded in other sediments using high-resolution gamma ray spectroscopy. This facilitates dividing the overall sediment column into representative horizons of tephra and non-tephra.

After extracting the non-volcanic primary signal, we apply a suite of evolutive cyclostratigraphic methods to the Lake Chalco logging data, with a focus on gamma ray data. The high-resolution results suggest that the Lake Chalco sediments contain several rhythmic alterations with a quasi-cyclic pattern comparable with the Pleistocene benthic stack. This allow us to calculate a ~500-kyr time span for the sediment deposition in Lake Chalco. By using cyclostratigraphic analysis on data captured by geophysical downhole logging, we demonstrate the potentially broad applicability of this method for downhole logging data and provide further insight into the sedimentation history of Lake Chalco.

How to cite: Sardar Abadi, M., Zeeden, C., Ulfers, A., and Wonik, T.: Downhole gamma ray data to reconstruct an age-depth model of the terrestrial record at Lake Chalco, Central Mexico, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9934, https://doi.org/10.5194/egusphere-egu22-9934, 2022.

The deep water formation in the Labrador and Nordic Seas is crucial for the global thermohaline circulation nowadays and it remains debated whether changing boundary conditions in terms of global warming may influence the deep convecting activity. Deep convection leads to the formation of Iceland Scotland Overflow Water (ISOW), which is an essential part of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). However, surface conditions in the Nordic Seas were unlikely always favorable for the formation of deep water in the past.

During Marine Isotope Stage (MIS) 11, a strong and active AMOC [e.g. 1] was reconstructed, which also contributed to the mass loss of the Greenland Ice Sheet [2]. However, cold and fresh surface conditions prevailed in the central Nordic Seas [3], which have been ascribed to freshwater input from the higher latitudes [4]. Thus, the question arises, whether and where deep water formation took place in the Nordic Seas.

Here, we reconstruct authigenic neodymium isotopes extracted from deep sea sediment from the Gardar Drift from 470 to 374 ka. IODP Site U1304 is located directly in the modern flow path of ISOW and should therefore sensitively track changes of this water mass in the past. Today, it is characterized by a strongly radiogenic neodymium isotopic composition, which markedly differs from other North Atlantic water masses.

Starting right at the onset and for the full length of the interglacial MIS 11c, a radiogenic Nd isotopic composition is switched on and prevailed indicating the presence of ISOW at the core site. More unradiogenic conditions indicate the return to glacial like conditions during a short event in MIS 11b. However, during MIS 11a the radiogenic values point again to a persistent presence of ISOW.

Thus, although the boundary conditions in terms of freshwater fluxes and sea level were significantly differing in the central Nordic Seas, the deep water formation presumably happened in the southern part of the Nordic Seas. This led to the active formation of ISOW, which in turn helped drive the active and strong AMOC during MIS 11.

[1] Dickson et al. (2009), Nat. Geosci. 2: 428-433.

[2] Rachmayani et al. (2017), Paleoceanography 32: 1089-1101.

[3] Kandiano et al. (2016), GRL 43: 10929-10937.

[4] Doherty and Thibodeau (2018), Front. Mar. Sci. 5: 251.

How to cite: Link, J. M. and Frank, N.: Persistent ISOW formation during MIS 11, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10018, https://doi.org/10.5194/egusphere-egu22-10018, 2022.

Brachiopods are a phylum of Animalia which are characterized by a rich fossil record. But this record shows drastic decrease in brachiopod diversity and environmental occupancy through time. One set of explanations says that the decline is related to the state shifts in dominance after mass extinction events (usually P-Tr). Another explanatory set suggests that the dominant cause of brachiopod decline is competition with other functionally similar clades. The competition hypothesis predicts that there should be a monotonic decrease in some fitness metric at organismal or species level. Often overlooked is the influence of long-term tectonic processes which control size, geometry and topology of environments on the changes in dominance of brachiopods. Here we tested this hypothesis by analyzing the dynamics of longitudinal and latitudinal ranges of brachiopod genera in the post-Cambrian Phanerozoic using the Paleobiology Database global paleogeographic occurrence data. The major pattern revealed in the study is that while latitudinal ranges were approximately constant through the eon, the longitudinal ranges experienced long-term trend-like decline. In the beginning of the Phanerozoic and also during the Cretaceous-Cenozoic, average ranges of brachiopod genera were much more elliptic in the west-east direction, while in the middle of the Phanerozoic they become almost circular in their shape. The latitudinal ranges reflect average temperature tolerance of a genus, while the longitudinal ranges reflect capacity of a genus to expand in similar climatic conditions, thus reflecting its potential of expansion fitness. The scale by scale analysis of range shapes and continental fragmentation index found consistent scale independent positive correlation of ellipticity (in W-E direction) with higher fragmentation of continents. Therefore the analyses revealed statistically significant patterns that support the hypothesis of a strong tectonic control on the shapes and sizes of average geographic ranges of brachiopod genera. Smallest ranges with lowest ellipticity occurred in Triassic-Jurassic. Therefore, the loss of genus level expansion fitness due to tectonic amalgamation of Pangaea should have been an important factor which contributed to the failure of brachiopods to fully recover after P-Tr extinction event.

This study was supported by the project S-MIP-21-9 “The role of spatial structuring in major transitions in macroevolution”.

How to cite: Spiridonov, A., Balaukauskas, L., and Lovejoy, S.: Phanerozoic scale modulation of brachiopod longitudinal expansion fitness forced by plate tectonics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10150, https://doi.org/10.5194/egusphere-egu22-10150, 2022.

The Albian-Santonian interval (113-83 Ma) is considered as a transitional period between the Early Cretaceous times, marked by a succession of short climatic variations associated with volcanism episodes and the Late Cretaceous times, marked by a progressive decrease of temperatures. This 30 Myr-longed interval is characterized by a gradual increase of temperature in oceanic domain, which culminates during the Cretaceous thermal Maximum, at the end of the Turonian (~ 90 Ma). Although the evolutions of continental weathering and climatic conditions are well documented in oceanic domain of low to middle latitudes, especially in Atlantic and Tethyan oceans, their record are less well known in high latitudes, especially in the proto-Indian Ocean. Thanks to the Exp IODP 369, two new boreholes, U1512 and U1513, drilled respectively in the Bight Basin (Southern Australia) and in the Mentelle Basin (Southwestern Australia), provide the opportunity to study the Albian to Santonian deposits at high latitudes (~60°S). Cores of the site U1513 recovered a sedimentary sequence from Albian to Santonian whereas the site U1512 record a continuous sequence from Turonian to Santonian. An integrated study, coupling mineralogical determination (XRD analyse and SEM observation) and isotopic analyses of neodymium on clay fraction was done on both sites in order to determine climatic and weathering conditions in these southern high latitude zone.

Our study reveals that the clay fraction are dominated by smectites (>85% in average) with lower proportions of kaolinites (< 25%) and traces of illites (<5%) associated with opal-CT and clinoptilolites. SEM observations have demonstrated a negligible impact of both burial diagenesis and authigenesis on clay assemblage. They are thus interpreted as the products of the alteration of rocks and pedogenic blankets from adjacent landmasses. At Site U1513, the Albian clay fraction contains noticeable proportions of kaolinites (5 to 25%), which progressively decrease during the Cenomanian and disappear at the Cenomanian-Turonian boundary (~94 Ma). Turonian to Coniacian deposits are almost exclusively composed of smectites. The decrease in kaolinite proportions is coeval with a decrease in ε_Nd values, which indicates a probable diminution in the erosion of Australian Archean rocks. At Site U1512, clay mineral assemblages, show slight variations along the borehole, which reflects stable weathering conditions during the 10 Myr of the Turonian-Santonian interval.

The dominance of smectites and to a lesser extent of kaolinites seem to indicate a warm to temperate and humid climate for high latitude zone during the Albian-Santonian interval. The decrease in kaolinite proportions from Albian to early Turonian in U1513 reflect probably a decrease of hydrolysis conditions associated with increasing temperatures and sea-level rise in southwestern Australian margins. The absence of noticeable variations from the Turonian to the Santonian in both sites would be the result of a stable continental climate for several million years after the Cretaceous thermal maximum (~ 90 Ma). The persistent presence of kaolinites in U1512 (southern Australia) could be due to the proximity of the Bight Basin with Australian Western Highlands.

How to cite: Munier, T., Riquier, L., Baudin, F., Metgalchi, A., Revillon, S., and Boudouma, O.: Continental weathering and climate conditions in southern high latitudes during the Albian-Santonian interval (U1512 and U1513 sites, Exp IODP 369, SW Australia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10544, https://doi.org/10.5194/egusphere-egu22-10544, 2022.

The Coniacian-Santonian was a time of strong differentiation in marine sedimentation, characterized by organic carbon-rich black shales and dark carbonates interpreted as the last oceanic anoxic event, OAE3, versus organic carbon-poor white/reddish limestones, chalk and claystones known as Cretaceous Oceanic Red Beds (CORBs). Based on compiled geochemical and isotope proxy data, two high-resolution global carbon isotope curves for carbonate and organic matter were reconstructed based on statistical analysis. Three main levels of short amplitude (around 0.5‰) carbon isotope excursions were identified. These excursions, each some 0.4 to 0.7 Ma in duration, were characterized by regionally restricted benthic anoxia and sea-level highstands that controlled regional organic matter accumulation during the OAE3 subevents defined herein as OAE3a (late mid-Coniacian, ca. 86.9 Ma, Kingsdown Event), OAE3b (late mid-Santonian, ca. 85.0 Ma, Horseshoe Bay Event), and OAE3c (late Santonian to Santonian-Campanian Boundary Event, ca. 83.5 Ma). Based on a compilation oxygen isotope temperature data and reconstructed pCO₂ trends, the Coniacian-Santonian was characterized by: 1) a steady state phase of warm greenhouse climate during the Coniacian, followed by (2) a hot greenhouse during the early Santonian that might be consistent with activation of the Central Kerguelen large igneous province, and (3) a longer-term cooling of the warm greenhouse climate from the mid-Santonian onwards. Organic matter-rich deposition is largely restricted to the low-latitude Atlantic and adjacent epeiric and shelf seas. Areas of enhanced oceanic circulation systems with a westwards directed Tethyan current and regional eddies of water mass flow had a negative feedback resulted in well-developed water column oxygen content within the Tethys.

How to cite: Wagreich, M. and Mansour, A.: The Coniacian-Santonian Oceanic Anoxic Event OAE3 - global correlation of subevents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11382, https://doi.org/10.5194/egusphere-egu22-11382, 2022.

The Toarcian oceanic anoxic event (T-OAE), dated as early Toarcian is considered one of the most extreme paleoenvironmental perturbations in Earth’s history. It is characterized by global warming, accelerated weathering, sea level rise, oceanic anoxia and acidification and extensive accumulation of organic matter. In Jurassic times, calcareous nannoplankton was already a most efficient rock-forming group and therefore pelagic sedimentary successions preserve invaluable data to track changes across the T-OAE. In this work, we focus on Schizosphaerella across the T-OAE recovered in the uppermost Pliensbachian–lower Toarcian Sogno Core that consists of a fully pelagic, continuous, well-dated record from a deep plateau (~1500 m water depth) in the Lombardy Basin (northern Italy). The objective of this investigation is the quantification of changes in size and abundance of the micrite-forming schizosphaerellids to derive their biocalcification tempo and mode in response to the T-OAE perturbations, to assess the implications of Schizosphaerella biocalcification changes, in terms of abundance and size, for the pelagic carbonate sedimentation. Absolute abundances and morphometric changes obtained for “small Schizosphaerella punctulata” (valve width < 7 μm),  S. punctulata (valve width > 7 μm) and “encrusted S. punctulata” (all specimens characterized by a crust surrounding the valve) revealed large fluctuations in the investigated interval. We identify an abundance fall caused by the failure of S. punctulata and “encrusted S. punctulata” during the core of the T-OAE, that along with the increased abundance of small specimens produced the reduction of average dimensions. Thus, the average size decline is not the result of a general valve reduction, but rather derives from the increase in abundance of small specimens (< 7 μm). This is substantiated by absolute abundances of individual S. punctulata morphogroups that unambiguously demonstrate that such a pattern is not an artefact of relative abundances (closed sum problem).

We hypothesize that the concomitant drop in abundance and shrinkage of valve size is related to hyperthermal conditions associated with excess CO₂ and ocean acidification.

Finally, the co-occurrence in the same samples of S. punctulata specimens (> 7 mm) with and without a crust, is indicative of species-specific diagenetic effects. Based on the S. punctulata ultrastructure we conclude that specimens without diagenetic crusts belongs to S. astrea while encrusted specimens are attributable to S. punctulata and we infer that the presence of the diagenetic crust could be taxonomically diagnostic to distinguish S. punctulata from S. astrea.

How to cite: Faucher, G., Visentin, S., Gambacorta, G., and Erba, E.: Size and abundance variations of Schizosphaerella across the Toarcian Oceanic Anoxic Event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11752, https://doi.org/10.5194/egusphere-egu22-11752, 2022.

The taxonomy and phylogeny of the Miocene to Recent genus Sphaeroidinellopsis have been documented in previous studies, but the evolution of this lineage remains unclear. Some authors debated this genus in the past, choosing a variety of parameters to discriminate between morphospecies. Here we present new high detail analyses of specimens from Ocean Drilling Program (ODP) Site 925 (Ceara Rise, western equatorial Atlantic) and ODP Site 959 (Deep Ivorian Basin, eastern equatorial Atlantic). We present transitional individuals Sphaeroidinellopsis disjuncta–Sphaeroidinellopsis kochi, a speciation event never described before. These transitional specimens are characterized by extreme morphological features such as elongated and sac-like final chambers, requiring amendments to the current classification and taxonomy of these morphospecies. An alternative hypothesis is presented to assess these new observations within the evolutionary mosaic of Sphaeroidinellopsis.

How to cite: Fabbrini, A., Zaminiga, I., Ezard, T., and Wade, B.: A way-out from the maze of middle Miocene Sphaeroidinellopsis (planktonic foraminifera), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11783, https://doi.org/10.5194/egusphere-egu22-11783, 2022.

The late Cenomanian-Turonian interval is characterized by major changes in the global carbon cycle, identified by stable carbon isotope excursions with associated climatic variations (e.g., OAE2, Late Turonian Events). These changes are linked to significant paleoceanographic modifications that impacted the biota, especially primary producers (e.g., calcareous plankton), forcing extinctions and evolutionary radiations. A reliable biostratigraphy is an essential tool to correlate both environmental and biotic changes worldwide.

Calcareous nannofossils and planktic foraminifera are well recognized as useful markers for biostratigraphy and paleoecological studies. However, the Cenomanian-Turonian calcareous nannofossil biohorizons are still poorly constrained because the nannofossil assemblages suffer from marked provincialism and taxonomic uncertainty that can blur their biochronological potential.

In order to improve the calcareous nannofossil biostratigraphic scheme of the late Cenomanian-Turonian interval, we present new data from the Breonio section (northeastern Italy), in the southwestern part of the Trento Plateau, and from the Quero section (northeastern Italy), located in the western Belluno Basin (central-western Tethys).

The analyses of calcareous nannofossil and planktic foraminiferal assemblages were integrated with the δ¹³C, δ¹⁸O and CaCO₃ curves. The δ¹³C values highlight several positive, global, stable carbon isotope shifts in both sections. The CaCO₃ signal of the Quero section suggests that the isotopic signal is pristine because the CaCO₃ values are not coupled with δ¹³C isotope shifts. On the contrary CaCO₃ curve seems generally to reflect the lithological signal. On the basis of biostratigraphic data the detected positive shifts have been correlated with the late Cenomanian-Turonian events, specifically, the Oceanic Anoxic Event 2, Holywell, Round down, Pewsey, and Late Turonian Events 1, 2, 3. The stratigraphic position of biohorizons with respect to the globally recognized δ¹³C excursions can provide a valuable mean to evaluate their potential synchronism/diachronism.

Our preliminary data show a good correspondence with the recent calcareous nannofossil-planktic foraminiferal integrated scheme (Geologic Time scale 2020; Gale et al. 2020) for the late Cenomanian-Turonian interval, although some calcareous nannofossil markers were not recorded. Interestingly, some «standard» and additional calcareous nannofossil events are promising proxies for the Late Turonian Events 1 and 2.

References

Gale A.S., Mutterlose J. & Batenburg S. (2020). The Cretaceous Period, in Gradstein F.M. et al., eds., Geologic Time Scale 2020: Boston, Elsevier, pp. 1023-1086.

How to cite: Simonato, M., Gardin, S., Giusberti, L., Luciani, V., Preto, N., Roghi, G., Barbieri, S., Xausa, F., and Fornaciari, E.: Integrated calcareous plankton biostratigraphy and stable isotopes stratigraphy of Cenomanian-Turonian interval of Breonio and Quero sections (central-western Tethys), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11890, https://doi.org/10.5194/egusphere-egu22-11890, 2022.

Introduction

Marl-limestone alternations are well known rhythmical inter-bedded deposits that commonly occur in many hemipelagic to pelagic deposits of the Phanerozoic. It is quite well established that the origin of these lithological variations are astronomically-driven climatic variations (22, 41, 100 and 405 ka being the main periods) e.g. [1]. However, the exact sedimentological control is not clear: several models attribute these alternations to cyclic changes in the carbonate flux, whereas the terrigenous silicoclastic flux remained relatively constant. On the opposite, some models suggest that the carbonate flux was constant while the silicoclastic flux changed cyclically.

Material and methods

To disentangle these different scenarios, we collected marlstone and limestone samples from two sedimentary successions of Bajocian, Middle Jurassic (3 marl-limestone- couplets over 3.5 m) and Valanginian, Lower Cretaceous (1 marl-limestone couplet over 1 m) age from the Southern French Alps (Barles). We measured their carbonate contents, the nannofossil proportion, as well as their extraterrestrial ³He (³He_ET) concentrations in ~200 mg decarbonated aliquots.

Results and discussion

The carbonate content ranges from 45% in marls to 86% in limestones. Importantly, for all samples, measured ³He_ET concentrations are constant in the silicoclastic fractions, within uncertainties. Hence, our results indicate that sedimentation rates at the astronomical timescale in the examined examples were mainly controlled by large changes in the CaCO₃ net fluxes, leading to variable dilution of the terrigenous and ³He_ET fractions. Nannofossil counting shows that pelagic CaCO₃ fluxes of coccolithophores are inversely correlated to the total CaCO₃ along the marl-limestone alternations and represent less than 4% of the total carbonate content. Hence, in this setting, these marl-limestone alternations were more probably driven by variations in the CaCO₃ supply from the nearby carbonate platform. Finally, assuming a constant ³He_ET flux of 0.1 pcc/cm²/ka [2], and the whole thickness of Bajocian and Valanginian strata in this region, the measured ³He_ET concentrations imply sedimentation rates that are broadly compatible with current duration estimates of these two stages.

References:

[1] Eldrett J. S. et al. (2015) Earth. Plan. Sci. Let., 423, 98-113.

[2] Farley K.A. et al. (2012) GCA, 84, 314-328.

How to cite: Blard, P.-H., Suchéras-Marx, B., Suan, G., and Mezine, T.: Extraterrestrial 3He shows that Mesozoic marl-limestone alternations are mainly driven by CaCO3 variations at the astronomical timescale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12195, https://doi.org/10.5194/egusphere-egu22-12195, 2022.

The Cambrian Explosion is a fundamental turning point in the evolution of life that occurred during the Cambrian Period (~541 to ~485 million years ago), which involved the origination and explosive radiation of all major animal phyla. The bursts of evolution characterizing this period appear concurrently with major modifications to the physico-chemical conditions of the world’s oceans, and are recorded in critical fossil localities where soft-tissues are exceptionally well preserved, including Lagerstätten such as the Burgess Shale and Chengjiang Biota. As a result of the severe lack of biostratigraphically-correlatable fossils (due to widespread endemism during the Cambrian) and sparse high-precision radioisotopic dates, the Cambrian time scale remains among the least defined stage of all the Phanerozoic Eon, with a minimum uncertainty of ±2 million years at its stage boundaries. The absence of a high-resolution geological time scale for the Cambrian Explosion hampers our ability to robustly address widely debated questions concerning the origins and rates of the evolutionary and ecological events, their relationship with paleoceanographic conditions, their responses to astronomically-forced climate change, including from Milankovitch “grand” cycles, and whether these events were globally synchronous.

Using an integrated set of geophysical/chemical proxies with advanced time series techniques on selected stratigraphic sections, this project aims at (1) Generate sets of high- resolution geophysical and geochemical stratigraphic proxies enabling to capture Milankovitch forcing within the selected sedimentary records, (2) Building a high-resolution time scale to improve our knowledges on the timing of major Cambrian evolutionary milestones and geochemical changes and (3) Determine the relationships between Cambrian evolutionary and ecological events with the paleoceanographic changes and Milankovitch cycles.

How to cite: Pas, D., Jamart, V., and Daley, A.: Generating a highly resolved astronomical time scale for the evolutionary and ecological events during the Cambrian Explosion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12868, https://doi.org/10.5194/egusphere-egu22-12868, 2022.

Drilling undertaken in the 1990s at the Kalkkop impact crater, situated in the semi-arid, Nama-Karoo biome of South Africa, revealed lacustrine sedimentary deposits. This is an invaluable archive for a region synonymous with a paucity of terrestrial-based, continuous, and high-resolution records. In 2019, a new 90 m core was retrieved from the palaeolake and subjected to a detailed sedimentological log. Sedimentary facies analysis was applied to investigate the changes in past depositional environments, themselves reflecting local changes in hydroclimate. Sedimentological evidence indicated deposition in an overall low-energy environment, intermittently interrupted by brief high energy events. Employment of grey scale image analysis on the top 20 m revealed dry conditions persisted for longer and became more frequent towards the present surface. This was inferred by the darker layers referring to more minerogenic input which is associated with wetter conditions and lighter layers suggesting more pure carbonates and linked to dry conditions. This prolonged aridity impacted the longevity and alkalinity of the Kalkkop lake, resulting in carbonate precipitation, silica dissolution, and complete desiccation. Limited biological remains (diatoms, n=5) support this hypothesis. The body of evidence, namely carbonate precipitation and long persistence of arid spells, as well as the extremely low abundance of silica-based biological remains (pollen, diatoms, phytoliths), supports a transition toward a semi-arid environment by ~250 ka. This remarkable new record of past environmental and climatic changes recorded by the Kalkkop palaeolake core is the subject of ongoing research at the University of Cape Town, South Africa.

How to cite: Mpangala, L. E., Kirsten, K., Haberzettl, T., Murungi, M., Mavuso, S., and Pickering, R.: Sedimentary facies analysis and palaeoenvironmental reconstruction of the Kalkkop palaeolake, Eastern Cape, South Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-402, https://doi.org/10.5194/egusphere-egu22-402, 2022.

Konya closed basin, located on the Anatolian plateau, hosted plenty of cultures and civilizations throughout the Holocene. The abundance of archaeological settlements and the current ecological fragility of the basin have increased the scholarly focus on the region. The basin offers a long-term and multi-dimensional record of human-environment interactions that reflect social, environmental, political, and economic processes. Paleolimnology studies are significant to reconstruct the paleoclimate and the paleoenvironment of the region. Sediment cores obtained from the basin, which is known to be paleo lake formerly and its surrounding lakes, provide multiple proxy records. Although plenty of paleoenvironmental studies were conducted in the region, reaching a temporally and regionally homogenous and long-term dataset is not straightforward. First, this research aims to build a paleoenvironmental synthesis of the Konya Basin. Secondly, it aims to reveal the climatic changes in the region throughout the Holocene quantitatively. In this study, Macrophysical Climate Model (MCM) was run with thirty years of observation data from a total of 20 meteorological stations located in and around the study area. The model outputs were compared with the local proxy records (oxygen isotopes and pollen records) obtained from the lacustrine environments of the region. MCM is a heat-budget modeling method to precisely recognize the mean centers of high and low sea-level pressure systems that manage the weather and wind patterns at mid-latitudes. The MCM model allows us to predict meteorological parameters at the interval of 100 years from the present to 40,000 years ago. Preliminary findings from the MCM point to the wetter and warmer periods in the Early Holocene, similar to isotope proxies in the region. Towards the end of the Early Holocene, precipitation decreases, and the driest climatic conditions occur in the Middle Holocene. The model outputs confirm the cessation of the active alluvion process in the Middle Holocene, which was experienced due to the reduction in the seasonality of precipitation. It was seen that increasing trend in winter temperatures during the Holocene for analyzed stations. On the advancing parts of the research, the findings from this study will be used in an agent-based modeling platform to understand the complex human-environment interaction in the region.

How to cite: Erdem, N. and Arıkan, B.: Modeling Holocene paleoclimate of Konya basin and comparison with proxy data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-606, https://doi.org/10.5194/egusphere-egu22-606, 2022.

The Lake Turkana region in northern Kenya and southern Ethiopia is famous for its fossil richness including key sites for human evolution studies. Modern Lake Turkana is the last of numerous mega-paleo-lakes, that has persisted to dry up completely at the end of the last African Humid Period (AHP, 15 – 5 ka). The adjacent paleo-lakes Suguta (2,000 km²) and Chew Bahir (2,500 km²), which are desiccated today, have formed together with paleo-lake Turkana (20,000 km²) a N-S oriented mega-lake during the AHP that has being separated only by small morphological Barriers. While Turkana, Suguta and Chew Bahir have been part of intensive research during the past decades, paleo-lake Chalbi with 10,000 km² in size just 10 km east of Lake Turkana was out of sight for most archaeologists and geoscientist. Here we present the first attempts for enhancing our understanding of the paleoenvironmental consequences of paleo-lake Chalbi close to one of the key regions in human evolution.

How to cite: Fischer, M. L. and Junginger, A.: The Great Lakes of Turkana – a Novel Perspective on the African Humid Period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-667, https://doi.org/10.5194/egusphere-egu22-667, 2022.

Climate may have played a critical role in early hominin evolution and dispersion, with rapid changes from humid to hyper-arid observed in East African palaeoclimate records. Many studies show linkages between these climate changes and hominin speciation and dispersion; however, few of them have focused on annual to decadal climate variability. This new study presents paleoenvironmental records (diatom assemblages and oxygen isotopes in diatom biogenic silica, d¹⁸O_diatom) from the Ol Njorowa Gorge in Kenya. The study site is located west of the African Rift Valley, from where important hominin dispersals are believed to have taken place. The study site preserves a stratigraphic record of interbedded diatomite beds spanning a key period of theorised hominin dispersals; 150,000 to 80,000 years ago. In this study, diatom assemblages and d¹⁸O_diatomrecords are used to understand past changes in moisture and precipitation patterns over East Africa as well as changes in lake water chemistry. d¹⁸O_diatom has been used in both lacustrine and oceanic settings since the early 2000s. It is however an under-utilised proxy that holds great potential, especially for diatomites from exposed lake beds where carbonate material is scarce or inexistant. The study also uses high resolution scanning XRF data from diatomite blocks to develop an age model for the diatomite beds at an annual timescale.

How to cite: Porchier, C. A., Maslin, M. A., Hill, T., Williams, D. M., Cox, E., Mackay, A. W., Swann, G. E. A., and Leng, M. J.: Paleoenvironmental reconstruction in East Africa at a critical period of hominin dispersion out-of-Africa (150-80 kyr), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1100, https://doi.org/10.5194/egusphere-egu22-1100, 2022.

It has previously been suggested that climate shifts during the last 2 million years played an important role in the evolution of our genus Homo. However, quantifying this linkage has remained challenging. Here we use an unprecedented transient Pleistocene Coupled General Circulation model simulation in combination with an extensive compilation of fossil and archaeological records, to study the spatio-temporal habitat suitability of five hominin species over the past 2 million years. We show that astronomically-forced changes in temperature, rainfall and terrestrial net primary production had a major impact on their observed distributions. During the early Pleistocene hominins primarily settled in environments with weak orbital-scale climate variability. This behaviour changed drastically after the mid-Pleistocene-transition when archaic humans became global wanderers who adapted to a wide range of spatial climatic gradients, which increased  the likelihood for habitat overlap and cladogenic transitions. Our robust numerical simulations of climate-induced habitat changes provide a novel framework to test hypotheses on our human origin.

How to cite: Timmermann, A., Yun, K., Raia, P., Zollikofer, C., Ponce de Leon, M., Willeit, M., Ganopolski, A., Zeller, E., Ruan, J., and Zeller, E.: Simulating climate effects on archaic human habitats and species successions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2707, https://doi.org/10.5194/egusphere-egu22-2707, 2022.

Lake Victoria is the largest tropical lake on the planet. Located in East Africa at an altitude of 1135 m asl, it lies across the limits between two major climatic zones with a temperature and moisture gradient and associated tropical biomes, the rain forest, and the savanna. At higher altitudes > 1200–2500 m a.s.l. temperatures are significantly lower and vegetation forms an Afromontane belt. Primarily triggered by climate shifts, these three biomes and fire regimes have been dynamically interspersing over the last 17,000 years.

Here, we present a robust ¹⁴C chronology mainly based on macroscopic charcoal using the MICADAS system of LARA at the University of Bern, new palynological data used as biostratigraphic control, and the first continuous charcoal record in Lake Victoria to establish the fire history.

Our pollen and macro–charcoal records, support the assumption that throughout time regional fire dynamics are controlled by biome’s changes, and that climate was the main driver of these vegetation shifts at least until the Iron Age. Our results indicate that during the Last Glacial Maxima and Heinrich Stadial 1, under dry and colder climates the savanna was dominating, with low fire regimes before 15,000 cal yr BP and increased fire occurrence between 15,000 and 14,000 cal yr BP. After this period, the Afromontane forest started to expand, and warmer and humid climates promoted the growth of rain forests and reduced fire events, which is particularly observed in the African Humid Period (between ca. 11,500 and 5000 cal yr BP). Subsequently, our records indicate a global maximum of fire occurrence at 5000 cal yr BP, followed by unexpectedly low fire regimes during the Iron Age and the subsequent periods.

This work is part of a SINERGIA project funded by the Swiss National Foundation which seeks to unravel the long-term causes and consequences of Lake Victoria’s ecosystem dynamics with a special focus on the evolution of fish species and other biotas from the late Pleistocene to the present.

How to cite: Temoltzin-Loranca, Y., Gobet, E., Vannière, B., van Leeuwen, J. F. N., Courtney-Mustaphi, C., Wienhues, G., Szidat, S., Grosjean, M., and Tinner, W.: Postglacial fire regime changes and vegetation dynamics at Lake Victoria, Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2788, https://doi.org/10.5194/egusphere-egu22-2788, 2022.

Based on a set of various marine palaeoclimate proxy records, we investigate African climate variations during the past 5 million years. We use a collection of modern approaches from non-linear time series analysis to identify and characterise dynamical regime shifts as changes in signal predictability, regularity, complexity, and higher-order stochastic properties such as multi-stability. We observe notable nonlinear transitions and important climate events in the African palaeoclimate, which can be attributed to phases of intensified Walker circulation, marine isotope stage M2, the onset of northern hemisphere glaciation, and the mid-Pleistocene transition, and relate them to variations of the Earth's orbital parameters.

How to cite: Marwan, N., Donges, J. F., Donner, R. V., and Eroglu, D.: Integrative multivariate study of past African climate variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6559, https://doi.org/10.5194/egusphere-egu22-6559, 2022.

Genomic data document multiple episodes of interbreeding among Neanderthals, Denisovans and Homo sapiens. When, where and how often the interbreeding between these hominin populations took place remains unclear. Here, we study the Neanderthal-Denisovan admixture during the past 400 thousand years using a novel habitat model that integrates extensive fossil, archeological, and genetic data with unprecedented transient Coupled General Circulation Model simulations of global climate and vegetation. Our Pleistocene hindcast of habitat suitability reveals pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia. These shifts, which influenced timing and intensity of potential interbreeding events, can be attributed to the response of climate and vegetation to past variations in atmospheric CO₂ and northern hemisphere ice-sheet volume. Therefore glacial/interglacial climate swings likely played an important role in archaic human gene flow and genetic diversification.

How to cite: Ruan, J., Timmermann, A., Yun, K.-S., Zeller, E., and Lemmon, D.: Simulating Pleistocene climate effect on archaic human interbreeding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6682, https://doi.org/10.5194/egusphere-egu22-6682, 2022.

Climate influenced the evolution of hominins, though the mechanisms and scales are still not well understood. We know that long-term climatic variations, such as wet-dry climate cycles and sea-level change, can change landscapes dramatically. Changes in landscapes can drive early hominins to find different locations to settle, but what kind of environments did they prefer and what role did changing climates play in all this? To research this question, we modeled the climate of the past 3 million years using CESM, made a best estimate of the global biome landscape, and compared the results to an extensive archeological database of hominin findings.

This analysis shows us that early hominins living in Africa predominantly lived in open habitats. When hominins expanded northwards, they adapted to more forested landscapes. While they were able to adapt, most hominin locations were found in areas with less variability and higher local biome diversity, suggesting that hominins prefer stable environmental conditions with a variety of resources nearby. This preference for stability and a landscape that offers diverse biomes is seen for all hominins regardless of species.

How to cite: Zeller, E., Timmermann, A., Yun, K.-S., and Raia, P.: Early hominins were variability avoiders and diversity seekers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6824, https://doi.org/10.5194/egusphere-egu22-6824, 2022.

The East African (hydro-)climate response to perturbations during the deglacial transition (e.g. Older and Younger Dryas) is complex and expressed heterogeneously in different paleoclimatic records. Lake Victoria (LV), Africa’s largest lake, desiccated entirely during the dry last glacial (>16.3 kyr BP) and subsequently refilled as climate conditions got more humid, reaching a highstand during the Early Holocene. However, existing sediment records from LV do not have sufficient resolution to fully resolve short-term hydroclimate changes during the deglacial transition (especially between 14 and 11 kyr BP). There is little direct evidence of late-glacial lake level fluctuations in LV so far because intermediate water depth coring sites suitable to record intermittent lowstands are missing.

By analysing sediment cores along a near-shore/shallow water (current water depth 22 m) to offshore/deep water (current water depth 63 m) coring transect covering the past 16,000 years, we aim at a more accurate spatial and temporal reconstruction of LV’s deglacial lake level history in response to regional hydroclimate changes.

Core stratigraphy and geochemical evidence, combined with a robust radiocarbon chronology, demonstrate a stepwise infilling of the Lake Victoria basin after its last complete desiccation (< 16.3 kyr BP). Following the dry late glacial Heinrich 1 event, an intermediate water level prevailed between 16.3 and 14.4 kyr BP, with uninterrupted deposition of fine-grained, organic matter-rich pelagic muds at our deep-water site and coarser, sandy-clay deposits at the near shore site. A second dry episode during the Older Dryas (~14 kyr BP) is marked by an abrupt decline in lake level with deposition of coarse mollusc shell bearing sediments at the near shore site indicating a littoral depositional environment. This shift in hydroclimate in the Lake Victoria basin is congruent with a brief period of cooling and drying during the Bölling/Alleröd (Dansgard Oeschger Event 1), which is also recorded in other East African Lakes. Subsequently, Lake Victoria reached maximum water levels with the onset of the African Humid Period in the early Holocene at around 11 kyr BP, which is expressed by elevated input of chemically weathered material (e.g. Rb/K) and deposition of fine-grained muds at both the near shore and offshore sites.

How to cite: Wienhues, G., Temoltzin-Loranca, Y., Vogel, H., and Grosjean, M.: New sedimentological evidence of Lake Victoria’s palaeohydrological variability during the last deglacial transition (16-10 kyr BP), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7105, https://doi.org/10.5194/egusphere-egu22-7105, 2022.

The chronology of the arrival of Homo erectus on the island of Java is a cornerstone of paleoanthropology. Understanding the dispersal routes of Homo erectus, but also of other hominin lineages in Asia and across Southeast Asia, depends on this timing. Their dispersal across Sundaland, in particular, is challenged by an extremely transient climatic and geological environment during Early Pleistocene. Furthermore, ages of first appearance of Javanese H. erectus remain controversial. New age constraints based on cosmogenic nuclides ¹⁰Be and ²⁶Al produced in situ indicate that H. erectus reached Java and dwelled at Sangiran at least ~1.4 Ma ago and more probably around 1.8 Ma. During this period, Java was just emerging from the sea while the adjacent Sundaland was a vast and continuous expanse of climatically and environmentally hospitable land connecting Java to mainland Asia, which facilitated the prior dispersal of hominins and terrestrial faunas to the edge of Java. This ancient age makes H. erectus the contemporary of the earliest members of the genus Homo in Africa and Asia, and rejuvenates the question of dispersal and evolutionary pathways across Eurasia and Sundaland.

How to cite: Husson, L., Lebatard, A.-E., Zerathe, S., Braucher, R., Noerwidi, S., Aribowo, S., Carcaillet, J., Natawidjaja, D. H., Bourlès, D. L., and Team, A.: Early Pleistocene route to Sangiran opened to Javanese Homo erectus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7177, https://doi.org/10.5194/egusphere-egu22-7177, 2022.

Understanding the chronology and environmental context of the earliest hominin expansions into Eurasia is of considerable interest in palaeoanthropology, however, our current knowledge is based on a handful of sites.  Dated to 1.85–1.78 Ma, Dmanisi (southern Georgia) is not only the locus of the earliest Homo fossils in Eurasia but has also yielded stone tools and rich assemblages of vertebrate fossils (1,2).  Whilst Dmanisi fundamentally changed our views on the timing of hominin expansions out of Africa and the technological capabilities of these populations, it has long represented a single site in the region, and little is known about the broader environmental context.

The Debed Valley (located in the Lori Depression, northern Armenia) represents a key area in which to improve our understanding of this early hominin expansion. The area lies at the southeast margins of the Javakheti Plateau, a large volcanic province spanning both southern Georgia and northern Armenia. Current chronological study of the Javakheti-derived lavas places the interval of volcanic activity between 2.1 and 1.6 Ma (3,4). The lavas are exposed along the Debed valley and trap sediment sequences below, within, and atop the flows. 

Here, we present the first results of our ongoing paleoenvironmental and geoarchaeological investigations in the Debed valley. We first present a model of landscape evolution during the Early Pleistocene based on detailed geologic and geomorphic mapping in the valley. We then describe preliminary results from two of the key sequences in the valley: 1) the open-air archaeological site of Haghtanak-3, from which a Mode 1 lithic assemblage has been recovered, and 2) the fluvio-lacustrine sequence of Dzoragyugh-1 paleolake.  We discuss the stratigraphic, sedimentological, and chronological (⁴⁰Ar/³⁹Ar and palaeomagnetism) results from each site and provide linkages between these sites, the geomorphic evolution of the Debed valley, and Dmanisi sequence. Through this, we highlight the environmental and archaeological significance of sedimentary archives in northern Armenia for understanding the nature and environmental context of early hominin expansions into Eurasia.  

1) Ferring, R., Oms, O., Agustí, J., Berna, F., Nioradze, M., Shelia, T., Tappen, M., Vekua, A., Zhvania, D. and Lordkipanidze, D., 2011. Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85–1.78 Ma. Proceedings of the National Academy of Sciences, 108, 10432-10436.

2) Mgeladze, A., Lordkipanidze, D., Moncel, M.-H., Despriee, J., Chagelishvili, R., Nioradze, M., Nioradze, G., (2011). Hominin occupations at the Dmanisi site, Georgia, Southern Caucasus: raw materials and technical behaviours of Europe's first hominins. Journal of Human Evolution 60, 571–596.

3) Lebedev, V.A., Bubnov, S.N., Chernyshev, I.V., Chugaev, A.V., Dudauri, O.Z. and Vashakidze, G.T. (2007). Geochronology and genesis of subalkaline basaltic lava rivers at the Dzhavakheti Highland, Lesser Caucasus: K/Ar and Sr-Nd isotopic data. Geochemistry International 45, 211–225.

4) Trifonov, V.G., Lyubin, V.P., Belyaeva, E.V., Lebedev, V.A., Trikhunkov, Ya.I., Tesakov, A.S., Simakova, A.N., Veselovsky, R.V., Latyshev, A.V., Presnyakov, S.L., Isanova, T.P., Ozhereliev, D.V., Bachmanov, D.M. and Lyapunov, S.M. (2016). Stratigraphic and tectonic settings of Early Paleolithic of North-West Armenia. Quaternary International 420, 178– 198.

How to cite: Sherriff, J. E., Adler, D. S., Arakelyan, D., Gasparyan, B., Lauer, T., Preece, K. J., Sier, M. J., and Wilkinson, K. N.: Developing a chronological and environmental framework of Early Pleistocene hominin expansions in the Caucasus region: Current research in northern Armenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7421, https://doi.org/10.5194/egusphere-egu22-7421, 2022.

The Early Pleistocene dispersal of Homo out of Africa  is a highly studied and debated topic.  One of the controversies centres on the question of what type of environments hominin species expanded out of Africa into. We conducted a literature review of 163 papers published since 2000 studying the environmental settings of the first Out of Africa expansion. We found that the literature is polarised between two types of hypotheses. On one hand there are papers which describe Homo in the Early Pleistocene as inflexible (compared to Homo sapiens) and incapable of persisting in non-savannah environments, e.g. the ‘savannahstan’ hypothesis. On the other hand there are papers which describe Homo as flexible and able to persist in various environment types, e.g. the variability selection hypothesis. By investigating these hypotheses we are able to move closer to answering the question - as Homo dispersed out of Africa, did they diversify to exploit new environments, or remain within the ranges of their African niche? We analysed the reconstructions of early Homo environments included in these papers. We found that the qualitative language used to describe hominin environments is problematic and impedes the formation of clear conclusions about the environments occupied by early Homo species. However, by forcibly quantifying the descriptions used in 69 (of the original 163) papers we found that the research does not strongly support the savannahstan hypothesis. Instead the environments inhabited by Homo are consistently reconstructed as a mix of environment types (grassland, forest, savannah etc.), with a slight skew towards open habitats. Based on these results, we tentatively suggest that Homo exhibited a preference for heterogeneous “edge” environments during the Pleistocene and as they dispersed out of Africa. However,  in order to further investigate the potential preference of Homo for heterogeneous environments and to build confidence in reconstructions of early human environments in general, quantified reconstructions of the vegetation composition and distribution at early Homo sites are needed. 

How to cite: Foister, T., Tallavaara, M., Fortelius, M., and Wilson, O. E.: Homo heterogenus: Variability in Pleistocene Homo environments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9664, https://doi.org/10.5194/egusphere-egu22-9664, 2022.

The stratigraphic interval spanning the Aptian-Albian transition is marked by a cluster of short-lived marine anoxic episodes referred to as Oceanic Anoxic Event 1b (OAE 1b). These short-lived episodes are, from the oldest to the youngest, the Jacob, Kilian, Paquier and Leenhardt events. We here aim at testing the impact of the long Milankovitch cycles (1.2-Myr and 2.4-Myr) on the recurrence of these oxygen-deficiency episodes by establishing a precise astrochronology of the OAE 1b interval from the Col de Pré-Guittard section (Albian GSSP, Vocontian Basin, SE France). The section belongs to the “Marnes Bleues Formation”, which is a thick (several hundred metres) clayey formation, interrupted by thin limestone beds and black shale layers, slumps and turbidites, all deposited in the hemipelagic part of the Vocontian Basin. Organic-matter carbon isotope ratios and Total Organic Carbon have been measured to precisely locate these events within the Col de Pré-Guittard section. A magnetic susceptibility signal was obtained from 3500 bulk rock samples collected every 5 cm. The sampling was performed on two parts of the Col de Pré-Guittard section to avoid a multi-decametric slump outcropping in one of the two section below the Kilian Level. However, two thin turbidite layers, near the Jacob and the Paquier events, remained unavoidable. Spectral analyses were performed using the Multi-Taper Method and the evolutive Fourier Transforms. These spectral analyses show the pervasive control of the 100-kyr eccentricity cycle and demonstrates a duration of (i) 1.6 Myr from the Jacob to the Kilian events, (ii) 1.5 Myr from the Kilian to the Paquier events, and (iii) 1.0 Myr from the Paquier to the Leenhardt events. Duration do not correspond to long Milankovitch cycles and thus do not favour the sole orbital control on the pacing of the anoxic events of the Aptian-Albian transition. Thus, other global forcing factors, as the volcanism, or local factors, as basin-scale paleoceanographic and climatic changes, have to be considered to explain this recurrence of anoxic conditions in the Vocontian Basin.

How to cite: Martinez, M., Ait-Itto, F.-Z., Boué, D., Deconinck, J.-F., and Bodin, S.: Is there an orbital control on the pacing of anoxia across the Aptian-Albian boundary (~113 Ma)?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10011, https://doi.org/10.5194/egusphere-egu22-10011, 2022.

Multiproxy paleoenvironmental research in Ethiopia is limited to a handful of studies, mostly situated in central and northern Ethiopia. This results in lasting uncertainties about the nature and timing of the vegetation response to climatic changes such as the African Humid Period and the Holocene aridification, and the imprint of human activities on the vegetation.

Here we present the sedimentary ancient DNA (sedaDNA) and XRF results as part of a multiproxy study in the Gamo Highlands in the southern Ethiopian rift valley. A six meter long sediment core spanning the last 18 thousand years was retrieved from a wetland at Gelba at 2300 m asl in the Gamo Highlands. Previous pollen and charcoal analyses on the core showed a past vegetation dominated by Afromontane forest taxa over the entire record. A first shift in the pollen-based reconstructed vegetation was a decrease of afroalpine vegetation around 13 cal. ka BP, with a relative increase of Afromontane forest taxa. Around 7 cal. ka BP wooded grassland taxa increased. At ca. 2.5 cal. ka BP a sudden change in the vegetation was detected, with increased disturbance indicators and charcoal particles.

Samples spanning the entire core we analyzed for their plant DNA content targeting the extracellular DNA. For the last 2.5 cal. ka BP, both extracellular and total DNA extraction was applied to the investigated samples. The results showed similar results for both approaches, whilst them also being complimentary by each detecting additional taxa. The majority of DNA sequences was derived from herbs and wetland plants, indicating a relatively local vegetation signal. A first observable change in the DNA record occurs at 7 cal. ka BP (with e.g. decreasing Convolvulaceae), but the strongest shift is observed in the period 2.5-2 cal. ka BP, with in particular an increase of Lythraceae and Polygonoideae. The DNA analysis has some taxa in common with the pollen analysis, but both proxies complement each other strongly due to the dominant local versus regional signal they provide. Despite the difference in detected plant taxa, the timing of vegetation transitions matches well between both records.

The XRF results show a highly minerogenic sediment input in the late glacial period. From ca. 13 cal. ka BP, a strong decrease in minerogenic input is observed and the sediment becomes more organic. At ca. 7.5 cal. ka BP, the minerogenic input increases again until 3 cal. ka BP, followed by fluctuating levels of minerogenic elements and increasing phosphorus levels in the last 2000 years.

How to cite: Augustijns, F., Giguet-Covex, C., Tilahun, A. K., Broothaerts, N., and Verstraeten, G.: The paleoenvironmental history of the wetland Gelba in the Gamo Highlands of Ethiopia: a Holocene vegetation reconstruction with sedimentary ancient DNA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10334, https://doi.org/10.5194/egusphere-egu22-10334, 2022.

There are many interdisciplinary theories as to how climate variability impacted hominin migration, and subsequently human evolution. One such hypothesis concerns so-called “green corridors,” in which climate and biome variability periodically opened vegetated corridors between habitable areas. The periodic opening of these corridors may have acted as a pump through uninhabitable barrier regions, allowing for more wide-spread dispersal. We present results from a climate-forced agent-based model that furthers the green corridor hypothesis to include the effect of stochastic resonance in penetrating barrier regions. In other words, while it intuitively makes sense that hominins would explore and disperse as green corridors opened up, the potential for green corridors to act as a dispersal pump likely depended on having the right amount of stochasticity (randomness) in hominin movement to resonate with orbitally-paced climate signals, effectively penetrating these corridors and dispersing into other regions. We integrate data from a 2-million-year CESM model, from the BIOME4 vegetation model, and from archaeological archives to create a map of habitat suitability based on a species-specific climate envelope. This habitat suitability forces the agent-based hominin migration model, in which agents seek more habitable areas and the added randomness in that agent movement is varied. While our conclusions are largely independent of species, we show results from a Homo erectus migration simulation. In my presentation I will discuss how stochastic hominin movement, the opening up of green corridors, and climate variability affected hominin dispersal throughout the Plio-Pleistocene.

How to cite: Lemmon, D., Timmermann, A., Zeller, E., Ruan, J., Yun, K., and Raia, P.: Stochastic Resonance between Climate Variability and Hominin Migration in an Agent-Based Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11141, https://doi.org/10.5194/egusphere-egu22-11141, 2022.

Surveying at the landscape scale to find archaeological sites is a particular challenge in the dryland environments of Arabia, the Sahara and other similar hyper-arid regions. Here we present how novel high-resolution palaeoydrological mapping of the entirety of the Saharo-Arabian desert belt has not only revealed large numbers of palaeolakes, shorelines and past drainage courses, but also proved particularly fruitful for finding new palaeolithic sites, and lacustrine pleistocene proxy records in Arabia. We describe the integrated survey methodologies which have helped us to locate large numbers of new sites in Arabia, including the earliest fossil and footprints of our species in Arabia, thus helping to enhance our understanding of pleistocene climatic change in these deserts, and of Hominin dispersals into and through them.

How to cite: Breeze, P., Drake, N., Manning, K., and Petraglia, M.: Integrated approaches to locating Pleistocene archaeological and proxy sites in drylands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12497, https://doi.org/10.5194/egusphere-egu22-12497, 2022.

More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic activity of the cambium. Despite this importance, there are still few attempts to quantitatively describe cambium dynamics.

In this study, we present a state-of-the-art Band Model of Cambium Development, based on the hypothesis of the kinetic heterogeneity of the cambial zone and the connectivity of the cell structure as the forming water-conducting tissue of the coniferous tree.

The new model significantly simplifies the assessment of seasonal cell production for individual trees of studied forest stand based on the same climate signal. It allows the entire range of individual absolute variability in the forming rings of any tree in the stand to be quantified.

Due to the simplicity new approach can be applied for the most of conifer forests where the climate plays a role of limiting growth factor.

How to cite: Shishov, V., Tychkov, I., and Zelenov, G.: A Band Model of Cambium Development as a new tool of xylogenesis development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-174, https://doi.org/10.5194/egusphere-egu22-174, 2022.

Stable carbon (δ¹³C_c) and oxygen (δ¹⁸O_c)isotopes measured in tree-ring cellulose, together with tree-ring width (TRW), have been used extensively to investigate the effects of past climatic conditions on tree growth. By contrast, the information recorded by the third major chemical component of tree-ring cellulose, the non-exchangeable carbon-bound hydrogen, has been explored far less due to methodological drawbacks and lack of understanding of ²H-specific fractionations. In this first Europe-wide assessment we investigate the signals stored in the hydrogen isotope ratios in tree-ring cellulose (δ²H_c), from a unique collection of 100-years records, from two major genera (Pinus and Quercus) across 17 sites (36°N to 68°N).

The climate correlation analyses showed weak climate signals in the δ²H_c high-frequency chronologies, compared to those recorded by δ¹³C_c and δ¹⁸O_c, but similar to the TRW ones. The δ²H_c climate signal strength varied across the continent and was stronger and more consistent for Pinus than for Quercus. The δ²H_c inter-annual variability was strongly site-specific. Focusing on the effect of extreme climatic conditions during years with extremely dry summers, we observed a significant ²H-enrichment in tree-ring cellulose for both genera. Our findings clearly indicate that δ²H_c registers information about hydrology and climate, but it also records non-climatic signals such as physiological mechanisms associated with carbohydrates storage remobilization ²H-specific fractionations and growth.

To disentangle the climatic and non-climatic signals in δ²H_c, we investigated its relationships with δ¹⁸O_c and TRW. We found significant relationships negative between δ²H_c and TRW at 7 sites and positive between δ²H_c and δ¹⁸O_c at 10 sites, while the rest of the sites did not show any significant relationships. The agreement with the TRW chronologies confirms the relationship between growth and δ²H_c, while the divergencefrom δ¹⁸O suggests a loss of the hydrological signal in δ²H_c. These highlights, once again,a stronger physiological component in the δ²H signature independent from climate. Advancements in the understanding of ²H-fractionations and their relationships with climate, physiology, and species-specific traits are therefore needed to improve the mechanistic modeling and interpretation accuracy of δ²H_c in plant physiology and paleoclimatology. Such advancements could lead to new insights into trees’ carbon allocation mechanisms, and responses to abiotic and biotic stressors.

How to cite: Vitali, V., Martínez-Sancho, E., Treydte, K., Andreu-Hayles, L., Dorado-Liñán, I., Gutiérrez, E., Helle, G., Leuenberger, M., Loader, N. J., Rinne-Garmston, T. K., Schleser, G., Allen, S., Waterhouse, J., Saurer, M., and Lehmann, M.: The unknown third - exploring the climatic and non-climatic signals of hydrogen isotopes in tree-ring cellulose across Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-673, https://doi.org/10.5194/egusphere-egu22-673, 2022.

Trees are one of the best sources of high-resolution proxy data to understand the past climate. By analyzing Tree Ring Width (TRW) data with climate variables and indicators, we can find main clues, which can help us to encode paleoclimate signals. Nowadays, scientists try to model TRW data with various climate data versus reconstructing the mentioned data for an extended period through different statistical methods. One of the newest methods is AI (Artificial Intelligence). This study aimed to model TRW data with the most effective climate variables by comparing the statistical methods vs. the AI method. First, seven climate variables were gathered from the nearest synoptic station (Sokcho) to the TRW site (Whachae Peak-Sorak), in northeast South Korea, during 1901–1998. The climate variables include maximum temperature (Tmax), minimum temperature (Tmin), mean temperature (Tm), diurnal temperature range (DTR = Tmax – Tmin) (°C), precipitation (Pr) (mm), and vapor pressure (VP) (hPa). The in-situ data were applied to correct the Climate Reach Unit (CRU, Version 4.03). Moreover, we have checked two meteorological drought indices, namely the Palmer drought index (PDSI) and standardized precipitation index (SPI). We applied two regression methods (namely multiple linear regression (MLR) and stepwise regression (SR)) and one AI (Nonlinear autoregressive with exogenous input (NARX)) method. In the first step of analyzing data, we did not see any specific significant results for the relationship between drought effects and TRW data in the case study. Then in the second step, modeling continued with the climate variables. Finally, the results demonstrated that among the three used methods, the NARX method achieved the best outcomes, as MLR with r = 0.44 (p < 0.003); SR with r = 0.27 in p < 0.001; and the NARX model was the best outcomes with r = 0.78. This study revealed that regression methods were not strong enough to reconstruct TRW data. Whereas, by noticeable results, the AI method has obtained the best performance.    

How to cite: Salehnia, N. and Ahn, J.: Applying artificial intelligence in modeling the relationship of tree ring growth index with different climate variables, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2212, https://doi.org/10.5194/egusphere-egu22-2212, 2022.

Large earthquakes can increase the amount of water feeding stream flows, raise groundwater levels, and thus grant plant roots more access to water in water-limited environments. Here, we quantify growth and photosynthetic responses of Pinus radiata plantations to the Maule Mw 8.8 earthquake in geometrically simple headwater catchments of Chile's Coastal Range. To this end, we combine high-resolution wood anatomic (lumen area) and biogeochemical (δ¹³C of wood cellulose) proxies of daily to weekly tree growth sampled from trees on valley bottoms and close to ridge lines. We find that, immediately after the earthquake, at least two out of six tree trees on the valley floor had enlarged lumen area and lowered δ¹³C, while trees along the hillslope ridge had a reverse trend. Our findings favor a control of soil water on this response, largely consistent with models that predict how enhanced postseismic vertical soil permeability causes groundwater levels to rise on valley floors, but fall along the ridges. Statistical analysis with non-parametric boosted regression trees reveals that streamflow discharge gained importance for photosynthetic activity on the ridges, but lost importance on the valley floor after the earthquake. We conclude that earthquakes may stimulate ecohydrological conditions favoring tree growth over days to weeks by triggering stomatal opening. The weak and short-lived signals that we identified, however, imply that such responses are only valid under water-limited, rather than energy-limited tree, growth. Hence, dendrochronological studies targeted at annual resolution may overlook some earthquake effects on tree vitality.

How to cite: Mohr, C., Manga, M., Helle, G., Heinrich, I., Giese, L., and Korup, O.: Trees Talk Tremor—Wood Anatomy and δ13C Content Reveal Contrasting Tree-Growth Responses to Earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2223, https://doi.org/10.5194/egusphere-egu22-2223, 2022.

Tree rings provide an invaluable long-term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree-ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree's growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥3-month seasonal windows) and negative to temperature (usually maximum temperature, over ≤3-month seasonal windows), with concave-down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (45% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals a more complete picture of the factors influencing growth than has previously been possible.

How to cite: Anderson-Teixeira, K. and the ForestGEO dendrochronology team: Joint effects of climate, tree size, and year on annual tree growth derived from tree-ring records of ten globally distributed forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3077, https://doi.org/10.5194/egusphere-egu22-3077, 2022.

Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ¹³C_LM and δ²H_LM values) have been shown to be reliable proxies of past temperature variability. Recent studies revealed δ²H_LM values even work in temperate environments where classical tree-ring width and maximum latewood density data are less skilful. In this presentation, we report 100 years of annually resolved δ¹³C_LM values of four beech trees (Fagus sylvatica) from a temperate site near Hohenpeißenberg in southern Germany. The series are compared with regional to continental scale climate observations to assess their potential for paleoclimate reconstruction. The δ¹³C_LM values were corrected for both the Suess effect to mitigate the effect of decreasing δ¹³C in atmospheric CO₂ and the physiological tree response to increasing atmospheric CO₂ concentrations using different factors for possible changes in discrimination. The calibration of δ¹³C_LM chronologies against regional instrumental data reveals highest temperature sensitivity with mean summer, annual, and previous-year September to current-year August temperatures.

We additionally compared the new δ¹³C_LM chronology with the previously produced δ²H_LM series of the same trees to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. The δ²H_LM values predominantly reflect large-scale temperatures since highest correlations were found with western European temperatures. Weak and mainly non-significant correlations were found between precipitation and both isotopic chronologies (δ¹³C_LM and δ²H_LM values). Our findings described for the first time the great potential of using δ¹³C_LM values from temperate, low elevation environments as a proxy for local temperatures, whereas the combination of both proxies supports the reconstruction of temperature variations at different spatial and temporal scales.

How to cite: Wieland, A., Greule, M., Roemer, P., Esper, J., and Keppler, F.: Climate signals in stable carbon and hydrogen isotopes of lignin methoxy groups: assessing the potential for temperature reconstructions at different spatial and temporal scales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3369, https://doi.org/10.5194/egusphere-egu22-3369, 2022.

Drought legacy effects in radial tree growth have been extensively studied over the last decade and are found to critically influence carbon sequestration in woody biomass. Typically quantified as a deviation from “normal” growth, drought legacy magnitude and statistical significance depend on the definition of expected vs. unexpected growth variability under average conditions – a definition that has received insufficient theoretical validation.

Here, we revisit popular legacy effect analyses using the International Tree-Ring Data Bank (ITRDB) and employ a synthetic data simulation to disentangle four key variables influencing the magnitude of legacy effects. We show that legacy effects i) are mainly influenced by the overall auto-correlation of radial growth time series, ii) depend on climate-growth cross-correlation, iii) are directly proportional to the year-to-year variability of the growth time series, and iv) scale with the chosen extreme event threshold. Our analysis revealed that legacy effects are a direct outcome of the omnipresent biological memory.

We further found that the interpretation of legacy effects following individual drought events at specific sites is challenged by high stochasticity, and show that the commonly perceived stronger legacy effects for conifers are the result of higher auto-correlation compared to deciduous broadleaves. Given that the existing literature has not sufficiently addressed biological memory, we present two pathways to improve future assessment and interpretation of legacy effects. First, we provide a simulation algorithm to a posteriori account for auto-correlated residuals of the initial regression model between growth and climate, i.e. a corrected Null model to determine statistical significance, thereby retrospectively adjusting expectations for “normal” growth variability. The second pathway is to a priori include lagged climate parameters in the regression model. This substantially reduces the magnitude of observed legacy effects and thus challenges us to revisit estimates of drought-induced growth deviations by considering the full spectrum of expected growth behavior. 

How to cite: Klesse, S., Babst, F., Evans, M. E. K., Hurley, A., Pappas, C., and Peters, R. L.: Drought legacy effects in radial tree growth are rarely significant under heightened statistical scrutiny, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3881, https://doi.org/10.5194/egusphere-egu22-3881, 2022.

Tree-ring widths represent the most commonly used proxy to reconstruct the climate of the last millennium at high resolution, thanks to their large-scale availability. The approach often relies on a relationship between tree-ring width series and climate estimated on the basis of a linear regression. The underlying linearity and stationarity assumptions may be inadequate. Dendroclimatic process-based models, such as MAIDEN (Modeling and Analysis In DENdroecology), may be able to overcome some of the limitations of the statistical approach. MAIDEN is a mechanistic ecophysiological model that simulates tree-ring growth starting from surface air temperature, precipitation and CO₂ concentration daily inputs. In this study, we successfully include the MAIDEN model into a data assimilation procedure as a proxy system model to robustly compare the outputs of an Earth system model with tree-ring width observations and provide a spatially-gridded reconstruction of continental temperature, precipitation and winds in the mid to high latitudes of the Southern Hemisphere over the past centuries. More specifically, we evaluate the benefits of using process-based tree-growth models such as MAIDEN for reconstructing past climate with data assimilation compared to the commonly used linear regression. The comparison of the reconstructions with instrumental data indicates an equivalent skill of both the regression- and process-based proxy system models in the data assimilation framework. Nevertheless, the MAIDEN model still brings important advantages that could result in more robust reconstructions beyond the instrumental era. Moreover, improvements continuously made in such models or in their calibration procedure also offer encouraging perspectives. Important steps have thus been made to demonstrate that using a process-based model like MAIDEN as a proxy system model is a promising way to improve the large-scale climate reconstructions with data assimilation.

How to cite: Rezsöhazy, J., Dalaiden, Q., Klein, F., Goosse, H., and Guiot, J.: Using a process-based dendroclimatic proxy system model in a data assimilation framework: a test case in the Southern Hemisphere over the past centuries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4552, https://doi.org/10.5194/egusphere-egu22-4552, 2022.

The Amazon is the largest catchment in the world, discharging ca. 17% of global freshwater, and plays an important role in the global water and carbon cycles. Recent decades have seen an increase in floods of the Amazon river, but also increases in dry season severity and length. Instrumental long-term climate data to assess the magnitude of these changes are relatively scarce. Tree-ring based climate reconstructions may help improving past climate records from this vast region and put these changes in historical perspective.

While standard tree ring widths chronologies in the tropics are generally weakly related to climate, tree ring d¹⁸O records from Cedrela odorata in Bolivia are a proven proxy for Amazon basin-wide rainfall, and thus Amazon river discharge. However, these “terra firme” trees grow during the wet season and thus do not provide information on the dry season. Here we present a new proxy for dry season precipitation from Amazonian floodplain trees of Macrolobium acaciifolium from the western Amazon. As this species grows during the non-flooded period, the dry season, their tree ring d¹⁸O records should pertain variation of dry season precipitation d¹⁸O. A comparions of tree ring d¹⁸O from floodplain and terra firme trees show opposing trends since the 1970s, indicating increases in wet season precipitation and decreases in dry season precipitation. These records are consistent with recent trends in peaks and troughs of Amazon river levels, and provide support of a recent intensification of the Amazon hydrological cycle. We conclude that tree-ring d¹⁸O records are an important tool for tropical climate reconstructions, and even allow climate reconstructions with seasonal resolution. In addition, as signals arise from variation in (meteorological) precipitation d¹⁸O, tree ring d¹⁸O chronologies do not need detrending, and show highly synchronized patterns even over very large scales, allowing rigorous cross-dating between species and sites, and facilitating further development in this vast region

How to cite: BRienen, R., Cintra, B., Baker, J., Gloor, E., Schöngart, J., Boom, A., Helle, G., and Leng, M.: Oxygen isotopes in Amazon tree rings as indicators of change in the hydrological cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5358, https://doi.org/10.5194/egusphere-egu22-5358, 2022.

While carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in tree-ring cellulose are widely used as climatic and physiological proxy in dendro sciences, the processes that are affecting the fractionation of non-exchangeable hydrogen (δ²H) isotopes and shaping the tree-ring δ²H profile are barely understood and thus not widely applied yet.

To establish a first comprehensive comparison of the photosynthetic and post-photosynthetic ²H-fractionation of northern-hemisphere trees, we sampled leaves and twigs of 152 trees representing 73 species, 48 genus, 19 families and 12 orders containing both evergreen and deciduous angio- and gymnosperms in a common garden, as well as diurnal cycles (6 species from 6 families) of leaf sugar. We extracted leaf water and sugar, as well as twig water and the current year twig xylem cellulose for δ²H analysis. Leaf sugar and twig cellulose were measured with a newly established hot water vapour equilibration method.

Our findings show a wide variation in ²H-fractionation between species growing at a common site. The measured δ²H values ranged from -63.5 to –33.4‰ for xylem water, between -22.3 and +28.5‰ for leaf water, between -160.9 and +12.6‰ for leaf sugar and between -79.1 and +6.9‰ for twig cellulose. The biological fractionation between leaf water and leaf sugar ranged between -169.6 and +24.2‰ and between leaf sugar and current year twig cellulose from -34.6 to +116.8‰. In general, sugar and cellulose of gymnosperms were significantly more ²H depleted than those of angiosperm species, with no impact of the leaf shedding behaviour to the measured δ²H values. We observed significant differences in the δ²H values between different orders and families, but not between genus and species within a family or genus, respectively. This pattern indicates that the photosynthetic and post-photosynthetic ²H-fractionation are based on conservative metabolic reactions with a generally low mutation rate.

Additionally, the results from our diurnal sampling of leaf sugar are showing first evidence for a dynamic and species-specific nature of the photosynthetic ²H-fractionation, which is in contrast to current models, which are assuming the same constant ²H-fractionation processes for all plant species.

We conclude that the here presented results will help to improve our understanding of the mechanisms influencing the δ²H values of leaf sugar and tree-ring cellulose and thus enabling the scientific community to use δ²H in tree-ring cellulose as the third isotope-proxy for dendrochronological studies.

How to cite: Schuler, P., Vitali, V., Saurer, M., Gessler, A., Buchmann, N., and Lehmann, M.: The phylogenetic impact on photosynthetic and post-photosynthetic hydrogen isotope fractionation in 73 tree species, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5772, https://doi.org/10.5194/egusphere-egu22-5772, 2022.

Stable isotope analyses (δ¹⁸O, δ²H) combined with the tree-ring dating have enormous potential for tracing freshwater resource availability under changing climate and in the context of the impacts of other human activities. This study focusses on the isotopic composition of tree-rings in combination with an anatomical analysis of the European Larch (Larix Decidua) species from different upstream and downstream sites along the Turtmänna river in south-western Switzerland. The results show distinctive patterns of year-to-year tree-ring growth from their constructed chronology dated back to 1851 (i.e. a 170-year record). A trend of a decreasing growth was noted over the last two decades. Decreasing growth was correlated (r = 0.50) with a decrease in precipitation and an increase in temperature (r = 0.30) during the growing season (between June and October) of previous and current years. The isotopic analysis shows a depletion in ¹⁸O in the trees fed by glacial meltwater close to the river as compared to the trees fed by precipitation distal to the river. Given the changes in climate, trees closer to the river are becoming more dependent on river-derived water, which in turn is sourced from melting glaciers. This hence has important consequences for the hydropower generation and water availability.

How to cite: Islam, N., Vennemann, T., and Lane, S. N.: Use of stable isotope signals from tree rings as proxy for tracing the combined effects of climate change and hydropower on glacier-derived water resources in the Turtmänna river catchment, Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5873, https://doi.org/10.5194/egusphere-egu22-5873, 2022.

Intensifying climate change is successively increasing the frequency and intensity of extreme climate events such as droughts. In 2018–2019, Central European forests were hit by two consecutive hotter drought years that were unprecedented in their severity at least in the last 250 years. Such hotter droughts, where drought coincides with a heat wave, may have severe detrimental impacts on forest ecosystems as highlighted by reports of widespread tree defoliation and mortality across Central Europe in 2018–2019. Here, we examine the effect of this unprecedented event on tree growth and physiological stress responses (measured as increase in wood carbon isotope composition, Δδ¹³C) in a Central European floodplain forest ecosystem. We used tree rings of the dominant tree species Quercus robur, Acer pseudoplatanus and Fraxinus excelsior to compare growth responses, Δδ¹³C and drought legacy effects during the consecutive drought years 2018–2019 with effects observed in former single drought years (2003, 2006, 2015). We found that tree growth was, except for F. excelsior, not reduced in 2018 and that drought responses in 2018 were comparable to responses in former single drought years. This indicates that water availability in floodplain forests can partly buffer drought effects and meteorological water deficits. Nonetheless, the 2018 drought – which was the hottest and driest year since the start of records – induced drought legacies in tree growth while former drought years did not. Consistent with this observation, all tree species showed strong decreases in growth and increases in Δδ¹³C in the second hotter drought year 2019. The observed stress responses in 2019 were stronger than in any other examined drought year. We posit that the cumulative effect of two consecutive hotter drought years likely caused this unprecedented stress response across all species. Drought responses were consistent for both drought-stress indicators (growth response and Δδ13C), but the timing and magnitude of responses were species-specific: Q. robur exhibited the overall smallest response, followed by A. pseudoplatanus with the strongest response in F. excelsior. We discuss these species-specific differences in light of the species’ stomatal control (inferred from high-resolution sap flow measurements during drought at our site) and species’ resistance to xylem cavitation. Overall, our findings highlight that consecutive hotter droughts constitute a novel threat to forests, even in floodplain forests with comparably high levels of water supply. These results and similar research may contribute towards understanding and forecasting tree species responses to more frequent hotter droughts under intensifying climate change.

How to cite: Schnabel, F., Purrucker, S., Schmitt, L., Engelmann, R. A., Kahl, A., Richter, R., Seele-Dilbat, C., Skiadaresis, G., and Wirth, C.: Impacts of the 2018-2019 drought: cumulative growth and stress responses in a floodplain forest ecosystem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6271, https://doi.org/10.5194/egusphere-egu22-6271, 2022.

Instrumental data derived from meteorological stations provide a fairly reliable record of climate variability for at least the last century for most parts of Europe. Proxy-based climate reconstructions have been extensively developed throughout the continent over recent decades to extend these records further back in time. However, to date, parts of central and eastern Europe remain underrepresented, leading to gaps in high-resolution climatic information even in recent centuries. This issue is predominantly linked to large uncertainties in existing records and limitations in data quality associated with a generally weak climatic sensitivity of available proxy records. The REPLICATE project, presented here, aims to address this deficiency by utilizing various tree-ring parameters from temperature-sensitive Norway spruce (Picea abies). The samples, collected from treeline or near-treeline environments, will be used to develop a set of temperature reconstructions across four sub-regions of the Carpathian Mountains. By doing so, we aim to contribute to filling in the spatial paleoclimatic and data quality gap in central-eastern Europe. To improve the climatic signal, we utilized a combination of tree ring width (TRW) corrected for non-climatic (disturbance) trends and blue intensity (BI) series derived from scanned images as a surrogate for maximum latewood density. We also developed a novel tree-ring parameter similar to BI based on high-resolution reflected light microscope images of the tree sample surface – termed surface intensity (SI) – which accounts for resolution and color bias limitations commonly encountered in BI datasets. Additionally, traditional thin section-based quantitative wood anatomy (QWA) parameters and their reflected light surface imaging-based counterparts (sQWA) were also included. Integrating this range of tree-ring parameters in a complementary fashion helps isolate, optimize and extract stronger climatic signals by accounting for and minimizing a range of parameter-specific limitations and biases, yielding improved calibration with a more accurate representation of low-frequency climatic trends and high-frequency extremes. From these multi-parameter tree-ring chronologies, annually resolved, robust, high-quality summer temperature reconstructions, extending to the early to mid-17th century, are under development for four Carpathian locations (i.e., northern Slovakia, western Ukraine, northern and central Romania). Initial results indicate that the reconstructions based on such a multi-parameter approach can produce paleoclimatic records with reduced uncertainty that explain between 50% and 60% of the regional temperature variability. These reconstructions will contribute to a more highly resolved temperature dataset in a part of Europe with considerable research potential, resulting in an improved spatial representation of past European temperature fluctuations. Also, by providing a reliable historical context to evaluate return periods and magnitudes of temperature extremes, they will contribute to assessing potential future socioeconomic impacts of climate change (e.g., on agriculture) and developing possible mitigation solutions.

How to cite: Nogueira, J., Rydval, M., Begović, K., Lexa, M., Schurman, J., Jiang, Y., von Arx, G., Björklund, J., Seftigen, K., and Tumajer, J.: Multi-parameter reconstruction of the past 400 years of Carpathian temperatures from tree rings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6541, https://doi.org/10.5194/egusphere-egu22-6541, 2022.

'Blue Rings' (BRs) are distinct wood anatomical anomalies recently discovered in several tree species. Studies connect their occurrence to lower than normal temperatures during the cell wall lignification phase of xylogenesis which usually continue after radial growth is completed, following the growth season. BRs are also potentially more sensitive to temperature than frost rings which require freezing temperatures (linked with the forcing of volcanic eruptions) to form. Therefore, systematic analysis of blue rings can add another level of time resolution and/or sensitivity to dendroclimatic studies.  North American bristlecone pine is an invaluable resource for paleoclimatological reconstruction due to its extreme longevity (its specimens are reported to commonly exceed the age of 4000 years), high durability and favourable environmental conditions which hamper decay, enabling the construction of chronologies spanning more than 8000 years. Preliminary results for the last 1000 years reveal that BRs in bristlecone pine coincide significantly with major volcanic eruptions. Detailed analysis of recorded temperature conditions in the years of BRs formation can therefore provide additional information on the impact of volcanic eruptions on climate in periods where meteorological observations are unavailable. To establish baselines for this, we present the climatic context of BR occurrence in bristlecone pine for the period since 1895 where modelled surface mean monthly temperatures are available for the grid cell pertaining to the study area location (4km spatial resolution, from PRISM Climate Group, Oregon State University). A group of 83 cores of bristlecone pine (originating from the vicinity of the Sheep Mountain/Patriarch Grove area of the Ancient Bristlecone Pine Forest in the White Mountains of California, 37.5 W 118.2 N) was thin sectioned on a GSL 1 microtome and further prepared following Gärtner & Schweingruber (2013) safranine and astrablue staining procedures to reveal lignified cell walls in red and underlignified cell walls in blue. Scanned and digitized thin-sections were measured and cross-dated noting years of BR occurrence.  A generalized linear mixed-effects model (GLMM) was fit with mean monthly temperatures and distance from treeline (DTL) as independent variables, and a binary response variable representing the absence (0) or presence (1) of a BR in a particular year, in a particular sample. Results indicate that BRs positively correlate with mean monthly temperatures of February and October and negatively with April, June, August, September and DTL. BR formation most strongly correlates with September temperatures, and interestingly, also lacks correlation with July temperatures.

How to cite: Siekacz, L., Pearson, C., Salzer, M., and Koprowski, M.: Climatic context of blue ring formation in high elevation bristlecone pine (Pinus longaeva D.K. Bailey)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6713, https://doi.org/10.5194/egusphere-egu22-6713, 2022.

Climate controls forest biomass production through direct effects on cambial activity and indirectly through interactions with CO₂, air pollution, and nutrients availability. Atmospheric concentration of CO₂ and sulfur or nitrogen deposition could exert a robust indirect control on wood formation, since they influence the stomatal regulation of transpiration and carbon uptake, that is, intrinsic water use efficiency (iWUE). Here we provide 120-year long time series of iWUE, tree growth, climatic and sulfur and nitrogen(SN) deposition trends for two widespread tree species, Pinus sylvestris (PISY) and Picea abies (PCAB), at their lower and upper distribution margins in Central Europe. The main goals were to explain iWUE trends using theoretical scenarios and climatic and SN deposition data and to assess the contribution of climate and iWUE to the observed growth trends. Our results show that after a notable increase in iWUE between the 1950s and 1980s, the positive trend slowed down. Substantial rise of iWUE since the 1950s resulted from a combination of an accelerated increase in atmospheric CO₂ (C_a) and a stable level of leaf CO₂ (C_i). The offset of observed iWUE values from the trajectory of iWUE growth proportional to increase in C_a (constant C_i/C_a scenario) was explained by trends in SN deposition (all sites) together with the variation of drought conditions (low-elevation sites only). Increasing iWUE over the 20th and 21st century improved tree growth at low-elevation drought-limited sites. In contrast to low-elevation sites, recent warming was the main reason for the growth increase at high-elevation PCAB. We propose that SN pollution should be considered to explain the steep increases in iWUE of conifers in the 20^th century in a broader area of Central Europe and in other regions with a significant SN deposition history.

How to cite: Treml, V., Tumajer, J., Jandova, K., Oulehle, F., Rydval, M., Cada, V., Treydte, K., Masek, J., Vondrovicova, L., Lhotakova, Z., and Svoboda, M.: Increasing water-use efficiency mediates effects of atmospheric carbon, sulfur, and nitrogen on growth variability of central European conifers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6826, https://doi.org/10.5194/egusphere-egu22-6826, 2022.

High-resolution palaeoclimate proxies are fundamental to our understanding of the diverse climatic history of the Australian mainland, particularly given the deficiency in instrumental datasets spanning greater than a century. Annually resolved, tree-ring based proxies play a unique role in addressing limitations in our knowledge of interannual to multi-decadal temperature and hydroclimatic variability prior to the instrumental period. Here we present cross-dated ring-width (RW) and minimum blue-intensity (BI) chronologies spanning 70 years (1929 – 1998) for Podocarpus lawrencei Hook.f., the Australian mainland's only alpine conifer, based on nine full-disk cross-sections from Mount Loch in the Victorian Alps. Correlations with climate variables from observation stations and gridded data reveal a significant positive relationship between RW and mean monthly maximum temperatures in winter throughout central Victoria (r = 0.62, p < 0.001), and a significant negative correlation to winter precipitation (r = -0.51, p < 0.001). We also found significant negative correlations between RW and monthly snow depth data from Spencer Creek in New South Wales (r = -0.60, p < 0.001). Of the assessed BI parameters, delta blue-intensity (ΔBI; the difference between early- and late-wood BI) displayed the greatest sensitivity to climate, with robust spatial correlations with mean October to December maximum and minimum monthly temperatures (r = -0.43, p < 0.001; r = -0.51, p < 0.001) and July precipitation (r = 0.44, p < 0.001), across large areas of northern Victoria. These promising findings highlight the utility of this species for future work. With the very limited availability of suitable long-lived and cross-datable species on the Australian mainland, these results have implications for the significant advancement of palaeoclimate records in southeastern Australia and the potential for improvement in our understanding of past climate in the region.

How to cite: O'Connor, J., Henley, B., Brookhouse, M., and Allen, K.: Piloting novel multi-centennial palaeoclimate records from mainland southeast Australia., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6899, https://doi.org/10.5194/egusphere-egu22-6899, 2022.

Abstract:

As a widespread species, sessile oak (Quercus petraea) populations occupy a wide range of ecological conditions with different local selection pressures, especially different drought exposure, which would have favoured different locally adapted populations. Water-use efficiency (WUE), which is defined at the tree level as the ratio between the biomass produced and the quantity of water transpired during the same period of time, is an interesting candidate trait for adaptation to drought. Six hundred trees from sixteen different provenances planted in 1993 in a common garden in the North-Eastern of France were harvested during the 2014-2015 winter. Intrinsic WUE (WUE_i), estimated from carbon isotope composition (δ¹³C) measurements of tree-rings, was compared among and within provenances for three contrasted years: (i) 2000, a wet year; (ii) 2003, a severely dry year; (iii) and 2005, a moderately dry year. The main purpose was to assess the drought-adaptive character of WUE_i for sessile oak trees. For this, (i) the adaptive character of WUE_i was evaluated by relating population mean WUE_i to the mean pedoclimatic conditions of their provenance sites. (ii) The phenotypic plasticity of WUE_i to drought was evaluated by comparing  the values observed in 2003 and 2005 to those of  2000 ; this plasticity was also related to the mean pedoclimatic conditions of their provenance sites. (iii) The contribution of WUE_i to tree and population fitness was assessed from the relationship between WUE_i and tree growth. Significant differences in δ¹³C (thus WUE_i) were found among populations. However, no linear relationship was established between mean population δ¹³C and the mean pedoclimatic conditions of the provenance sites. Based on these results observed on juvenile sessile oak trees in the relatively wet conditions of the common garden, no local adaptation in terms of WUEi was detected. An increase in drought intensity resulted in an increase in population WUE_i and all provenances displayed a similar plasticity of WUE_i to drought, suggesting no among population diversity for drought responses. A significant correlation between WUE_i and tree growth was detected only during the wet year, when populations with a higher WUE_i also had a higher growth index. Moreover, a much larger variability in WUE_i was demonstrated within populations (2–4‰) than among-population (0.6‰).

Key words : Climate change, assisted migration, local adaptation, water-use efficiency, fitness, diversity

How to cite: Rabarijaona, A., Ponton, S., Bert, D., Ducousso, A., Richard, B., Levillain, J., and Brendel, O.: Among-provenance diversity and phenotypic plasticity of water-use efficiency in sessile oak populations growing in a mesic common garden., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7275, https://doi.org/10.5194/egusphere-egu22-7275, 2022.

Oxygen isotopes (δ¹⁸O) in tree rings carry a strong potential to retrospectively evaluate tree water uptake and physiological response to climate. Their interpretation can, however, be challenging due to the complexity of the isotopic fractionations along the soil-tree-atmosphere continuum. Indeed, several processes play a role in defining the final tree-ring isotopic signal: source water variations, evaporative processes at the soil surface and leaf level, and mixing of xylem water that might exchange with new assimilates associated with phloem transport and synthesis of wood constituents. Disentangling these influences along the growing season and how climate conditions modify them are remaining challenges to exploit the full potential of δ¹⁸O tree-ring records as a climate proxy.

In this study, we aim at identifying the contribution of leaf water enrichment and source water on the tree-ring δ¹⁸O signature by assessing intra-annual variations of δ¹⁸O along the soil-leaf-tree ring pathway of larch (Larix decidua Mill.). We focus on two sites with contrasting water availability in the Lötschental valley (Swiss Alps) and three consecutive growing seasons (2011-2013). Our approach takes into consideration specific timing of the involved processes with a high spatio-temporal resolution: environmental conditions, diurnal sapflow-derived transpiration rates, δ¹⁸O analysis of xylem and leaf water, and intra-annual tree-ring δ¹⁸O measurements coupled with wood formation kinetics. Structural equation models (SEM) were applied to statistically assess the relations among δ¹⁸O values of the different pathway components. Furthermore, we calibrated mechanistic models of leaf-water and tree-ring cellulose δ¹⁸O to explore site-specific contributions of the fractionation processes (e.g., Péclet effect and the proportion of xylem-cellulose synthesis exchange [P_ex]) and investigated their climatic drivers.

Our results showed that intra-annual xylem water δ¹⁸O and transpiration rates differed between sites and years whereas needle water δ¹⁸O did not differ significantly between sites (but between years). However, tree-ring cellulose δ¹⁸O values were higher at the dry site resembling those differences observed in xylem water δ¹⁸O. SEMs reinforced these results since xylem water δ¹⁸O contributed more to cellulose δ¹⁸O in comparison to needle water δ¹⁸O, and this effect was more prominent at the dry site. Vapor pressure deficit (VPD) had strong control on the overall leaf water-related ¹⁸O-fractionations. However, mechanistic leaf-water δ¹⁸O models did not indicate a relevant role of the Péclet effect in our study. Most importantly, mechanistic models of cellulose δ¹⁸O revealed that P_ex was variable along the growing season and its variability was significantly associated with variations in VPD.

Our study suggests that the imprint of the source water signal on the δ¹⁸O signature in tree rings is highly dominant, particularly during episodes of high VPD, potentially overwriting signals coming from leaf fractionation processes.

How to cite: Martínez-Sancho, E., Fonti, P., Gregori, A., Gessler, A., Lehmann, M., Saurer, M., and Treydte, K.: Vapor pressure deficit governs the relative contribution of leaf and source water to intra-annual δ18O variations of tree rings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7577, https://doi.org/10.5194/egusphere-egu22-7577, 2022.

Within the field of dendrochronology, different sub-disciplines arise using the information stored in the wood for a variety of purposes. In this study, we use dendroprovenance to develop a methodology that allows us to infer the source area of instream large wood (LW) at the river basin scale applying fingerprinting techniques.

LW is mainly supplied to fluvial ecosystems by riparian vegetation and nearby areas, and the presence of wood in a river determines its geomorphology and ecology; but also, it is associated with an increase in danger and risk to infrastructures and population. For this reason, research on the origin of LW is essential to better understand LW processes and to facilitate decision-making in the management of the forest and the river.

The tracers we have used so far are the stable isotopes coming from the water molecule: hydrogen (D/H) and oxygen (¹⁸O/¹⁶O). These isotopes show spatial variations depending on evaporation-precipitation processes and resulting isotopic fractionation. Subsequently, the water absorbed by a tree growing in a particular place stores this isotopic signal, and when that tree (or a piece of it) falls and becomes part of the river ecosystem, we can use this isotopic signal to infer the origin of the wood.

Our study site is a 50 km reach of the Rhone River between Lake Geneva and Genissiat dam (3000 km² of catchment) in France, where all arriving wood is stored upstream from the dam. The goal is to differentiate the wood coming from the two main tributaries, the Arve and Valserine rivers (located in different mountain systems) since they are the main wood suppliers at Genissiat.  

Preliminary results show clear differences in the isotopic composition when comparing samples from one tributary and the other, with the most notable differences in the most recent tree rings.

Lastly, we plan to analyze other tracers such as minor and trace elements that are linked to the geology and combine them with the isotopic ratios in a multivariate analysis to determine the origin of the wood in a more accurate manner. Consequently, we will have developed a new dendroprovenance method that can be extrapolated to other fields, taking a step forward in the application of our knowledge about tree rings.

How to cite: del Hoyo Gibaja, J., Vennemann, T., Vauridel, M., and Ruiz-Villanueva, V.: Dendroprovenancing instream wood at the watershed scale applying fingerprinting techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7719, https://doi.org/10.5194/egusphere-egu22-7719, 2022.

A composite Silver fir tree ring width chronology from seven mountain sites in the Eastern Carpathian Mountains (Europe) was established for AD 1588-2021, with SSS>0.8 and EPS>0.85 for AD 1750-2012. The bootstrap correlation analysis of the tree ring index with monthly climate parameters (temperature and precipitation) shows a positive and relatively time constant response to mean winter-spring temperature (November to March). The correlation between Silver fir tree ring proxy and winter-spring temperature is high and statistically significant (0.556 at p<0.05). The reconstruction statistics (R2, RE, CE and DW) indicate a good skill of the regression model between proxy data and winter temperature back to 1901. RE and CE statistics range between 0.32 and 0.39, and DW has values between 2.05 and 2.18. These results show good reliability of the model, and for the entire period, the reconstruction explains ~ 30% of winter temperature variability. The temperature reconstruction from AD 1750 shows inter-decadal fluctuation induced by low frequencies sinusoids (waves). The reconstructed mean winter temperatures for the 1750-2012 period was -2.93°C with -0.31°C colder than the 1961-2009 reference period. The longest period with high frequencies of years with low temperatures was recorded in 1740-1800, coinciding with the end of the Little Ice Age. After this coldest winter period, a six-year period with extreme warm winters was identified. The warming trend was more distinguishable science AD 1880 to the present, especially through the high frequency of mild winters. The coldest reconstructed winters for entire period were find in 2003 (anomalies= -1,56), 2012 (anomalies = -1,32) and 1965 (anomalies = -1,24). The warmest winters were recorded in 2001 (anomalies = +1,71), 1998 (anomalies = +1,48) and 2007 (anomalies = +1,37). The pattern of spatial correlation between proxy data and winter-spring temperature releases a wide extend of high correlation (>0.5), covering the North-Western Carpathians, continues with the Eastern chain of the Carpathian Mountains and finishes with the extreme South-East of Romania. Correlation with the Central Europe gridded temperatures is significant (>0.4), and with the Alpine Arc grid, temperatures are quite low (0.3). This result provides a regional scale of the winter-spring temperature reconstruction, suggesting a possible west-east gradient across Europe, potentially influenced by the interplay between the eastward expansion of Atlantic influence and the westward expansion of the West Asian influence.

How to cite: Popa, I., Roibu, C., Perșoiu, A., Kern, Z., and Sidor, C.: Silver fir tree ring width: a proxy for winter temperature variability in the Carpathians?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8154, https://doi.org/10.5194/egusphere-egu22-8154, 2022.

Rapid temperature and vapor pressure deficit (VPD) increase along with precipitation decrease over the past decades lead to massive wildfires and permafrost degradation in boreal forests. Conifer trees growing in subarctic regions are highly sensitive to these climatic changes due to their location at the high latitudes, where air temperature is the limiting factor, but also water relations have a strong impact on tree growth.

In this study, we aimed (i) to assess the usability of local vs. gridded climate data; (ii) to reveal how conifer trees capture temperature and moisture signals based on the local weather station data vs. gridded data from the two Siberian sites in northeastern Yakutia and eastern Taimyr, and one site from northwestern Canada in Mackenzie Delta; (iii) to perform trend analysis of climatic data and δ¹⁸O in tree-ring cellulose; and (iv) to carry out spatial correlation analysis of oxygen isotope patterns and determine the distribution of climatic signal over broad geographical scales in the Siberian and Canadian subarctic.

Comparative analysis of the local and gridded climatic data (air temperature, precipitation and VPD) for the three study sites showed that mainly temperatures are highly correlated between each other. Subarctic trees grow in a temperature-limited environment; therefore, the large spatial coherence of temperature signals is not surprising. Conversely, insignificant correlations between local and gridded for precipitation and rather low correlations for VPD is attributed to the more heterogeneous nature of moisture variables at larger spatial scales. Therefore, analyzing moisture changes in the subarctic using local weather station data is advantageous compared to gridded data.

Trend analysis of the climate data showed that drastic changes in climate variability occurred from the 1980s in the investigated subarctic regions and were even more pronounced from 2000 to 2021. Recent warming and development of drought conditions were stronger in the Canadian subarctic than the Siberian subarctic sites. Drastic precipitation changes, temperature and VPD increase mainly occurred during winter, spring and autumn in the studied subarctic regions. New updated stable isotope chronologies from remote subarctic regions allowed us to accurately reconstruct moisture changes using precipitation and VPD data from the local weather stations while reconstructing air temperature using gridded data.

This research was funded by the Russian Science Foundation (RSF) grant number 21-17-00006.

How to cite: Churakova (Sidorova), O. V., Zharkov, M. S., Fonti, M. V., Trushkina, T. V., Barinov, V. V., Taynik, A. V., Porter, T. J., Kirdyanov, A. V., Arzac, A., and Saurer, M.: Tree-ring oxygen isotope patterns from Siberian and Canadian subarctic to test usability of local versus gridded climate data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8756, https://doi.org/10.5194/egusphere-egu22-8756, 2022.

Information regarding the Spatio-temporal behavior of extreme natural phenomena, such as avalanches, has become necessary due to the increase in human casualties and property damage in recent decades. Thus, the prevention of geomorphological risks associated with high mountain areas requires knowledge of the characteristics of geomorphological processes that occur here. Avalanches occupy a central place among these phenomena with the greatest destructive capacity (Voiculescu, 2000).

The aim of this study is to 1) reconstruct the past activity of snow avalanches in the Tarcu Mountains and to fill a gap in knowledge due to the lack of such studies in the studied area and 2) to point out the synchronicity of major events with those reconstructed in other mountain areas in the Southern Carpathians: Bucegi, Făgăraş, Piatra Craiului, Parâng Mountains. The morphology of the investigated area determines the formation of constrained avalanches. For events reconstruction, we used semi-quantitative Shored index (Shroeder, 1980). We identified 51 events in a 101-year chronology in Picea abies: 12 events with I_t  between 10-20% and 6 events with I_t  between 20-40%. The relatively young age of the trees is a good indicator of the disturbances caused by past events. We based our reconstruction on dating growth disturbances such as reaction wood, traumatic resin ducts, and scars. Reaction wood, very present in our case, highlighted the intensity of avalanche activity and the expansion of events. Resin ducts and scars are a good indicator of avalanches that brought us important information in the dating of events and helped us to delimit the affected areas (the 2005 synchronous event with other 9 couloirs). The return period values are higher than those obtained by Corona et al. (2010) in the French Alps (2.5-12 years), smaller than those obtained by Corona et al. (2007) in the Swiss Alps (slightly over 20 years) and similar to those obtained by Decaulne et al. (2012) in Northern Iceland (15-20 years). 11 events synchronous with events of another 11 couloir (1985, 1987, 1988, 1998, 2000, 2005, 2006, 2007, 2008, 2010, 2016).

In the future we want to highlight the type of avalanche by relating the activity of avalanches to cold season temperatures by using the Standardized Winter Index (IIS) (Micu, 2009; Voiculescu, Onaca, 2014) and climate scenarios, cf. Germain et al. (2009). Our study can be the basis for the elaboration of hazard and risk maps, in the perspective of tourist investments in the Tarcu Mountains or in the development of tourist activities in safe conditions.

How to cite: Feher, R., Chiroiu, P., and Voiculescu, M.: Snow avalanche activity in the Țarcu Mountains, Southern Carpathians. Comparative analysis based on tree ring studies., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8925, https://doi.org/10.5194/egusphere-egu22-8925, 2022.

Radial growth, wood density and climate-growth relationship of four Douglas fir provenances were analysed separately for the juvenile and the adult phase. Two pairs of provenances were selected from an existing IUFRO provenance trial planted in 1971 based on their diameter at breast height and vitality. Increment cores were extracted from individual trees, on which we measured tree-ring widths (RW), earlywood widths (EWW) and latewood widths (LWW). Wood density was assessed in standing trees using resistance drilling. The climate-growth correlations were calculated between provenance chronologies of RW, EWW, LWW and latewood share, and day-wise aggregated Standardised Precipitation-Evapotranspiration Index (SPEI). We calculated the accumulated drought effects by aggregating climatic water deficits into a log-logistic probability distribution to obtain the SPEI index series of different seasons, starting from three weeks to nine months, including the effect of previous growing season. In all provenances, RW, and consequently EWW and LWW, were wider in juvenile period than in adult period. Share of latewood was in all cases higher in juvenile wood then in mature wood. All four provenances have similar wood density in both analysed growth phases. The general effect of wet conditions in current growing season was positive, indicating that Douglass fir’s radial growth was favoured in moist years, and reduced in dry years. The significant positive effect of SPEI on LW was observed also at the beginning of previous growing season. Our analysis showed that when selecting the most promising provenance for planting, it needs to be considered that growth rate may change from juvenile to adult period. Only by combining climate-growth analysis with measurements of external tree features we can compare and assess the suitability of certain provenances for planting in current and future climate.

How to cite: Krajnc, L., Hafner, P., Jevšenak, J., Gričar, J., and Brus, R.: Tree rings, wood density and climate-growth relationships of four Douglas fir provenances in sub-Mediterranean Slovenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9627, https://doi.org/10.5194/egusphere-egu22-9627, 2022.

Climate change is a global-scale issue of societal, economic, and political importance and so understanding the climate of the present within the context of past climate variability is of vital importance. Dendroclimatic reconstructions play a key role in contextualizing recent climate change by improving our understanding of historical climate conditions. The climatically-sensitive blue intensity (BI) tree-ring parameter is gaining prominence as a more affordable and accessible alternative to traditional X-ray densitometry. Yet the accurate representation of low-frequency trends and high-frequency extremes using scanner-based BI remains a challenge due to color-related biases and resolution limitations. As part of the REPLICATE project, which aims to develop a set of robust multi-parameter temperature reconstructions from Carpathian Norway spruce (Picea abies) tree rings, methodological advances in sample surface preparation, imaging and measurement techniques have produced series analogous to BI from ultra-high resolution (~74 700 true dpi) images. Series from these microscope-based reflected light images of the tree-ring sample surface, termed surface intensity (SI), represent the binary (black-white) segmentation of wood anatomical structure, which approximates anatomical density. By eliminating color altogether and using a high-resolution system, the most substantial drawbacks of scanner BI (i.e., discoloration and resolution biases) are bypassed and hence climate signal optimization is achieved by more accurately representing low-frequency climatic trends and high-frequency extremes. A comparison of SI chronologies with a multi-parameter tree-ring dataset from a large-scale parameter assessment study by Björklund et al. (2019) showed that this novel SI parameter can outperform its BI couterpart in terms of common signal (interseries correlation) and climate signal strength, and that it is on par with the best-performing X-ray densitometric chronologies. However, existing programs are not currently designed to effectively capture SI measurements and so additional development of measurement software is required to unlock the full potential of this new parameter. Continued improvement of high-resolution imaging techniques will aid the attainment of unbiased long tree-ring chronologies by overcoming color biases and resolution issues, but also holds promise for the development of surface quantitative wood anatomy (sQWA) datasets from reflected light images of samples. These improvements will therefore not only lead to more accurate dendrochronological paleoclimatic records and climate reconstructions but will also find future application in a broad range of dendrochronological contexts.

How to cite: Rydval, M., Björklund, J., von Arx, G., Begović, K., Lexa, M., Nogueira, J., Schurman, J., and Jiang, Y.: High-resolution wood surface imaging for dendrochronology: towards the development of unbiased reflected light timeseries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10771, https://doi.org/10.5194/egusphere-egu22-10771, 2022.

To reliably predict future changes, it is crucial to understand the response of the climate system to past changes in radiative forcing, which are investigated using climate models as well as information extracted from paleoclimate archives such as speleothems. Hydrological changes in past, present, and future are, however, far less understood and more uncertain than changes in temperature.

Speleothems are terrestrial archives in the low to mid latitudes. Their growth rate changes are hypothesized to reflect local changes in precipitation amount, albeit the response may be non-linear and subject to karst specific processes. Full coverage of glacial-interglacial cycles and high precision dating through U/Th measurements makes them a suitable archive to assess and constrain state-dependent precipitation changes. However, speleothem inherent features, such as growth hiatuses or large and abrupt changes in growth rates, are a challenge for current age-depth modelling methods.

Here, we compare modelled precipitation amount from the Paleoclimate Modeling Intercomparison Project (PMIP), in particular time slices of the Last Glacial Maximum (around 21.000 years before present) and the Mid-Holocene (around 6.000 years before present) to growth rate changes of speleothems from the global speleothem database SISALv2. We perform case studies on a large ensemble of synthetic speleothems to systematically assess the resolution of age measurements necessary to reliably detect and model growth rate changes. These synthetic speleothems cover a large range of characteristic speleothem features observed in the SISALv2 database and are analyzed by six different age-depth modeling methods (linear regression, linear interpolation, copRa, StalAge, Bacon, and Bchron). Comparing the simulated changes with speleothems selected from SISALv2 according to these criteria can thus help to constrain past precipitation changes and subsequently confine uncertainty of future changes.

How to cite: Buehler, J., Roesch, C., Weitzel, N., Scholz, D., Comas-Bru, L., and Rehfeld, K.: Last Glacial Maximum to present day precipitation changes from speleothem growth rates and in climate simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-318, https://doi.org/10.5194/egusphere-egu22-318, 2022.

We reconstructed changes in summer and winter precipitation using a well-dated (±18 years 2σ error) speleothem spanning 4.2-3.1 ka BP from Dharamjali Cave in the central Himalaya. The record was sampled at a sub-annual resolution for a suite of trace elements, as well oxygen and carbon stable isotopes. Calcium isotopes at decadal resolution provide additional hydroclimatic evidence. This DHAR-1 stalagmite records a 230-year period of increased drought frequency in both the summer and winter seasons after 4.2 ka BP, with aridity events centered on 4.19, 4.11 and 4.02 ka BP each lasting between 25 and 90 years. The data after 3.97 ka BP support a recovery in summer monsoon rainfall, peaking around 3.7 ka BP. The significance of this new record includes remarkable coherence between the moisture proxies over 4.2-3.97 ka BP in a well-dated record, which provides confidence in the duration of droughts and timing of monsoon recovery. It also places seasonal climate variability on a timescale relevant to human decision-making, which is particularly significant for this region nearby the Indus River Basin. The Indus Civilization reached its urban apex by 4.2 ka BP, and archaeologists have documented a shift in settlement locations, population, health, and agricultural strategies thereafter for a period of several centuries. This stalagmite record provides valuable insights into seasonal precipitation availability during a critical climatic and cultural transition phase.

How to cite: Giesche, A., Hodell, D. A., Petrie, C. A., Haug, G. H., Adkins, J. F., Plessen, B., Marwan, N., Bradbury, H. J., Hartland, A., French, A. D., and Breitenbach, S. F. M.: Northwest Indian stalagmite shows evidence for recurring summer and winter droughts after 4.2 ka BP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-396, https://doi.org/10.5194/egusphere-egu22-396, 2022.

Understanding the spatial and temporal variability of rainfall which is regulated by the strength of Asian monsoon requires an observational network dispersed across the continental landmass. The operation of monsoonal circulation during the last one million years is possible to be reconstructed using the geochemical and isotopic record available from cave speleothems. The monsoonal circulation brings rain and excess precipitation due to interplay of monsoonal wind strength which is governed by the seasonal movement of Intertropical Convergence Zone (ITCZ) from ocean to the continent. A consensual view is that both the operation of East Asian Summer Monsoon (EASM) and Indian Summer Monsoon (ISM) are in accordance with the orbital forcing. However, the lack of terrestrial records of ISM rainfall variability over glacial interglacial time scales precludes insights into pan-Asian monsoon forcing and related mechanisms. Here, we present independent estimates of temperature change from the clumped isotope record in speleothem from Belum cave, continental India, covering glacial interglacial transition (MIS-9). The palaeo data is used in conjugation with the already reported δ¹⁸O records from Chinese caves and Mean Annual Precipitation from Chinese Loess Plateau (CLP), which are influenced by the EASM, to understand the spatial variability of δ¹⁸O records and its significance in regulation of moisture transport process away from equator. A comparative study across latitudes, particularly at the peak of the interglacial period MIS 9 (after ~320 ka) brings to light the intensification of rainfall accompanied by relatively higher temperature (~35°C in Belum cave- 15.10°N) exhibited by both the ISM system and EASM System (Xiao cave 26.04°N). However, shift in δ¹⁸O record of caves above 30° N (Sanbao and Linzhu caves) is less, though the trend is similar. A recent study of CLP (36.35°N) reported a drop in mean precipitation by ~300mm post 320 ka. Such variation of the mid-latitude precipitation intensity may probably be a consequence of the combined effect of ice volume and snow cover in the Northern hemisphere and low latitude climate changes.

How to cite: Subba, R., Ghosh, P., Thirumalai, K., Partin, J., Yadava, M. G., Shen, C. C., Clemens, S. C., Lone, M. A., Yu, T. L., Allu, N. C., and Ramesh, R.: Spatial heterogeneity of monsoon precipitation over the Asian continent during the termination of MIS-9, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-477, https://doi.org/10.5194/egusphere-egu22-477, 2022.

Caves are important fossil repositories providing records extending back over million-year timescales. While the physical processes of cave formation are well understood, a more important parameter to studies of palaeontology, palaeoanthropology and archaeology — that of the timing of initial cave development and opening — has proved more difficult to constrain. The Naracoorte Cave Complex (NCC) in southern Australia is a World Heritage site with a rich record of Pleistocene vertebrate fossils, including extinct megafauna, and serves as a natural laboratory in which to investigate these fundamental cave processes. Using U-Th-Pb dating of speleothems we show that the NCC is at least 1.32 million years old, extending the current understanding of initial speleothem formation by ~70% and the antiquity of initial cave development at this site by at least ~20%. We use charcoal and pollen trapped in the same speleothems to place robust constraints on the timing and extent of subsequent cave opening. The findings of this study provide an important means for researchers working on the plethora of fossil-rich sites worldwide to assess the potential upper limit of vertebrate fossil records within caves.

How to cite: Weij, R., Woodhead, J., Sniderman, K., Hellstrom, J., Reed, E., Bourne, S., and Drysdale, R.: The tip of the iceberg: U-Pb dating shows that cave systems can be twice as old as their surface expression, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-506, https://doi.org/10.5194/egusphere-egu22-506, 2022.

Multiple factors control δ¹³C values in speleothems and complicate their paleoclimatic and paleoenvironmental interpretation. Therefore, most studies avoid the presentation of δ¹³C values, and instead, focus only on δ¹⁸O. This development can be observed with regard to most recent cave studies from tropical South America, in which stalagmite δ¹⁸O were preferentially published without the consideration of δ¹³C data. Here we present a large δ¹³C dataset of 98 speleothem records covering multiple time scales from South America, of which 42 remained unpublished or were not available until now. Our main objective is concentrating on the support of existing and emerging databases, such as SISAL, and providing new data for the speleothem community and climate modelling.

As a first approach, we review the δ¹³C values for the last two millennia and evaluate the environmental influencing factors on this proxy, e.g., local hydroclimate, altitude, temperature, and abundant vegetation types. Our results indicate that the main factors controlling variations in δ¹³C values are due to changes in the local hydroclimate and, to a minor extent, in temperature. For this time period, most of the isotope records show a significant correlation between the δ¹³C and δ¹⁸O values, indicating a close relationship between local hydroclimate and large-scale atmospheric processes related to shifts of the South American Monsoon System (SAMS). Furthermore, in most of the karst systems studied here, the predominant occurrence of C3 plants growing on soils above the caves is responsible for a considerable lowering of δ¹³C values (≤6‰) in most of the speleothems.

How to cite: Novello, V. F. and Rehfeld, K. and the South American Speleothem Group: Investigating δ13C values in stalagmites from tropical South America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1057, https://doi.org/10.5194/egusphere-egu22-1057, 2022.

Speleothem archives (cave carbonates) are widely distributed in terrestrial regions, and provide highly resolved records of past changes in climate and vegetation encoded in the oxygen and carbon isotope proxies. The SISALv2 database, created by the PAGES-SISAL Phase 1 Working Group, provided 700 speleothem records from 293 cave sites, 500 of which have standardized chronologies. The database provides access to records that were hitherto unavailable in the original publications and/or repositories, and has enabled regional-to-global scale analysis of climatic patterns using a variety of approaches such as data-model comparisons. 

The PAGES-SISAL Phase 2 Working Group is a continuation of the previous efforts to index speleothem datasets, focusing on the following objectives: (i) exploring ways to synthesise modern cave monitoring data to provide robust modern baselines and improve proxy interpretations, (ii) adding trace element proxies of Mg, Sr, Ba, U, and Sr isotopes to the SISAL database to increase our understanding of regional climatic variability, (iii) a database-update to incorporate ~100 identified speleothem datasets that are currently not in the database, (iv) providing a javascript web app with a user-friendly GUI to increase SISAL data accessibility.

Here, we present preliminary information on available cave monitoring metadata synthesized from the Cave Monitoring Database (product of a Cave Monitoring workshop in Innsbruck, Austria) and published speleothem trace element records, highlighting regions where overlapping stable isotope, trace element and monitoring datasets are available, and identifying gaps. We show the proposed database structures for cave monitoring and speleothem trace element data, linking them to the speleothem entities in the existing SISAL database with persistent identifiers, and introduce the Beta version of the SISAL GUI. We briefly present a synopsis of the SISAL-community level discussions on best practices for reporting trace element data, and reducing data measured with high resolution laser ablation methods. 

We welcome feedback on PAGES-SISAL Phase 2 activities listed above, and encourage participation and collaboration from interested researchers in different stages of their academic career and working in different geographical regions and allied disciplines.

How to cite: Kaushal, N., Lechleitner, F. A., Tanos, P., Hatvani, I. G., Kern, Z., Wilhelm, M., Burstyn, Y., and Baker, A.: SISAL speleothem database updates - link to modern monitoring data, additional proxies and increased accessibility, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1576, https://doi.org/10.5194/egusphere-egu22-1576, 2022.

Temperature in the inner section of most caves (i.e., away from well ventilated entrance sections) is controlled by external air temperature transferred underground by heat conduction. The key parameter that controls heat conduction is the thermal diffusion coefficient, that is specific for different materials. Although thermal diffusion coefficients can be calculated for specific carbonate rocks, the underground karst is not composed exclusively of bedrock since dissolution creates large pores and conduits filled with air and water that greatly impact thermal diffusion coefficients.  

We studied a 5-year temperature record of the entrance of Los Pilones Cave, in central Spain. The cave entrance is a sub-horizontal and meandering crawlway that limits the advection even in winter, making this cave ideal to study thermal conduction processes. Cave temperature was recorded along the 30 m section from the entrance by 10 TINITAG thermistors and external temperature was measured at ground and 2 m elevation levels. The thickness of bedrock cover above the cave was measured with a DISTO2 laser meter equipped with compass and clinometer providing uncertainties <0.05m.

The bedrock cover above the ceiling of the cave ranges from 8 to 15 m and all cave temperature records show annual thermal oscillations with different amplitudes and lag times in relation to the external annual thermal cycles. Cave temperature measurements support that heat conduction is the main heat transfer mechanism controlling cave temperature variability. Thermometers located under a thicker bedrock cover record less thermal amplitude of the annual signal and enhanced delays. The thermal diffusion coefficient was calculated from averaging the results from the thermal anomaly recorded at different depths and the lag time recorded at different depths. The dispersion of regression analyses (r²>0.9) is large compared to analyses performed on non-karst bedrocks, supporting the existence of local heterogeneities in the underground karst. We also noticed that the lag times of individual loggers changed during the studied period (interannual variability), which can be attributed to variable ratios of water saturation in the local porosity. Therefore, when reporting the thermal diffusion coefficient of karst terrains, their triphasic nature (i.e., rock, water and air) should be considered. So, the average thermal diffusion coefficient of a specific cave could vary in space or time beyond calculated uncertainties depending variable hydrological conditions.

Acknowledgements:

The project leading to this research has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No.101030314.

How to cite: Domínguez-Villar, D., Krklec, K., and Sierro, F. J.: The peculiar nature of thermal diffusion coefficients in karst terrains and their control on cave temperatures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2048, https://doi.org/10.5194/egusphere-egu22-2048, 2022.

Speleothemoxygen isotope records from East Asia have been utilized to reconstruct Asian summer monsoon (ASM) variability over the last several hundred thousand years. However, what the isotope variation represents on orbital to annual timescales remains greatly debated. The high-resolution speleothem records combined with modern meteorological observation are essential for better understanding this debate. Here, we report a stalagmite δ¹⁸O (δ¹⁸Oc) record of the highest resolution (average of ~1-yr) between 1730 to 8590 yr BP from Majiaping (MJP) Cave, Guizhou Province, southwest China. This record is precisely dated based on the ¹⁴C dating method combined with ²³⁰Th/U, ²¹⁰Pb, and lamination counting dating methods. The result shows that the ¹⁴C dating method can establish a reliable chronology for stalagmites that cannot be dated by ²³⁰Th/U. The comparisons of the precipitation δ¹⁸O with the local temperature, rainfall amount, and moisture sources show that the δ¹⁸Oc record from southwest China is mainly controlled by the “amount effect” on annual to decadal timescale modified by ENSO. The consistent long-term δ¹⁸Oc trends among all monsoonal regions in the low latitudes of the northern hemisphere indicate that on the orbital timescale the δ¹⁸Oc trend reflects changes in the large-scale spatial circulation of the atmosphere, which is controlled by the changes of northern hemisphere summer insolation. Ensemble Empirical Mode Decomposition (EEMD) and Bernaola-Galvan Segmentation Algorithm (BGSA) analyses reveal that on the semi-millennium timescale, the δ¹⁸Oc record of the MJP stalagmite shows 8 weak East Asian summer monsoon events during 8.2ka BP, 7.3 ka BP, 5.9 ka BP, 5.5 ka BP, 4.2 ka BP, 3.1 ka BP, 2.4 ka BP and 1.9 ka BP. The comparisons of the structural feature and forcing factor of the first 7 events with the 1.9 ka event indicate that the first 7 events correspond to the changes in total solar irradiance and the 1.9 ka event may be related to the internal forcing of the Earth system controlled by the ENSO. On the interannual-multidecadal timescale, the δ¹⁸Oc record shows the high-frequency cyclicities of 3~7-yr and 30~70-yr which are related to ENSO and PDO according to modern instrumental records. However, the relationships among ENSO, PDO, and the δ¹⁸Oc are not constant during the Holocene.

How to cite: Liang, M.-Q., Li, H.-C., Mii, H.-S., Ma, Z.-B., Li, T.-Y., and Löwemark, L.: Paleoclimatic evolutions during the Holocene: A stalagmite δ18O record from Majiaping Cave, Guizhou, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3100, https://doi.org/10.5194/egusphere-egu22-3100, 2022.

Continental carbonates constitute an interesting topic of study since they are important archives recording climate and paleoenvironmental changes. In Tunisia, calcretes are formed during the Pliocene-early Pleistocene (Villafranchian). They mainly occur in the center and on the coastal plain of Djeffara (Southern East) while their presence is more sporadic in the North of the country. Continental carbonates may form in the soil, groundwater, and palustrine and lacustrine environments. Four criteria are used to differentiate these different environments: host rock, components and micromorphological texture, subaerial exposure (seasonality), and flora and fauna.

The purpose of this study is to investigate the palaeoenvironmental significance of Tunisian calcretes for the Plio-Pleistocene. For this aim, well-developed carbonate beds were studied along a north-south transect that crosses the climatic boundaries between the latitudes 33 ° and 37 ° N: North (N36º.43.713 E10º.06.681’) Center (N35º.07.077 'E10º. 14.545 ') and South (N33º.28.898' E10º.20.597 ').

Based on the macroscopic, petrographic, and cathodoluminescence observations in association with scanning electron microscopy results, we classified thin sections extracted from the massive horizons in all sites into 8 facies types:

The Northern site is characterized by 1) pisolithic calcretes and 2) laminar calcretes showing several beta microfabrics such as rhizolith, peloids, intraclasts, coated grains, bioclast debris, cracks, alveolar septal, spherulite, and organic matter. Moreover, 3) pseudo microkarst carbonates were detected in Northern Tunisia by the presence of vertical layers, peloids, intraclasts, circum crack grain, pedotubules, and rhizoconcretions, and bioclasts.

At the central site, 4) laminar calcretes are characterized by planar layers. Both 5) massive brecciated calcretes and 6) mottled nodular brecciated calcretes are distinguished by the abundance of cracks. All these facies types’ shows similar pedogenic components such as peloids, coated grains, gastropod shell, alveolar septal, ooids, and bioclasts.

The southern site is characterized on the one hand by 7) laminar calcretes composed of peloids, nodules, coated grains, cracks, and on the other hand by 8) groundwater nodules showing a massive aspect with alpha microfabrics. In all sites, the nodular horizons are pedogenic.

Thus, our Plio-early Pleistocene calcretes formed in three main depositional environments: pedogenic, groundwater, and palustrine. The groundwater calcretes are formed under phreatic conditions while the Tunisian pedogenic calcretes and palustrine carbonates exhibit subaerial exposure characteristics (cracks). Except for southern groundwater calcretes, all other types of carbonates show biogenic traces. The palustrine carbonates developed above lacustrine mud. Whereas, pedogenic and groundwater calcretes, develop on different types of host rocks (siliceous and clayey). The difference between fabrics indicates that during the Pliocene-early Pleistocene calcrete form in the north in palustrine settings while it forms in groundwater context in the south. Furthermore, the transition between the different environments is controlled mainly by variation in the water table suggesting a variable but generally more humid climate during the Plio-Pleistocene in North Africa.

How to cite: Jarraya, F., Mauz, B., Rogerson, M., Elmejdoub, N., Sghari, A., and Kallel, N.: Palaeo-environmental and palaeo-climatic significance of Tunisian calcretes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3106, https://doi.org/10.5194/egusphere-egu22-3106, 2022.

[1]D. Rudzka et al., (2011), GCA 75, 4321-4339.

[2] C. Welte, et al., (2016), Anal. Chem. 88, 8570– 8576.

[3] C. Welte et al., (2021), Clim. Past 17, 2165–2177.

[4] J. Fohlmeister et al., (2013), The Holocene 23, 749-754.

How to cite: Welte, C., Fohlmeister, J., Wertnik, M., Eglinton, T. I., and Spötl, C.: Radiocarbon and stable C isotope variability of two Holocene stalagmites from the high-alpine Spannagel Cave, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3454, https://doi.org/10.5194/egusphere-egu22-3454, 2022.

Cave monitoring is an important method to investigate the deposition mechanism and factor influencing the trace elements in drip water and speleothemsThe Mg and Sr concentrations and the Mg/Ca and Sr/Ca ratios and ⁸⁷Sr/⁸⁶Sr in drip water and speleothems are often used to explore climate and environmental changes.Systematic monitoring was performed on the Mg and Sr contents, Mg/Sr ratio and ⁸⁷Sr/⁸⁶Sr of soil, soil water, cave drip water, and the active speleothems (AS) in Furong Cave in Chongqing, southwest China, during 2009–2018 (A.D). The results were interpreted in conjunction with the changes in the ⁸⁷Sr/⁸⁶Sr ratios to explore the main sources and controlling factors of Sr and other trace elements in drip water. (1) Mg and Sr concentrations and ⁸⁷Sr/⁸⁶Sr ratios in soil water were increased which was related to the prolonged residence time of water in the soil in winter and spring because of less rainfall. It indicates that the trace element contents of soil water reflect seasonal changes of the rainfall. (2) The Mg and Sr contents were higher in drip water than in soil water, as well as the ⁸⁷Sr/⁸⁶Sr ratios of drip water was closer to that of the bedrock, which indicates that the overlying bedrock was the main source of the trace elements in drip water and the speleothems in Furong Cave. (3) Mg contents and Mg/Sr ratios in drip water and AS showed decreasing trend corresponding to the increasing annual rainfall in the monitoring period which resulted in the shorter water-rock contact time. (4) The growth rate of AS may be an important factor to control the Sr contents in AS because of the similar increasing trend. (5) The Mg and Sr contents and the Mg/Sr ratios of drip water and AS did not exhibit seasonal variations due to the mixing of the fissure water and complex hydrology condition of the overlying bedrock, however, the geochemical indexes (Mg and Mg/Sr ratio) showed an opposite trend to the annual rainfall variation. This study suggests that the variations of Mg, Sr and Mg/Sr ratios of drip water and AS can response to the rainfall on the multi-year timescale, which contributes critical insights into the paleoclimate interpretation of proxies of speleothems in the cave with hundreds of meters thick bedrock. 

How to cite: Li, J., Li, T.-Y., Shen, C.-C., Yu, T.-L., Zhang, T.-T., Wu, Y., Zhou, J.-L., Chen, C.-J., and Zhang, J.: Variations and Significance of Mg/Sr and 87Sr/86Sr of drip water and active speleothem in Furong Cave, Southwest China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3565, https://doi.org/10.5194/egusphere-egu22-3565, 2022.

Abrupt events punctuate the climate of the Holocene epoch, providing valuable insight into rapid climate change. The most notable abrupt event of the Holocene was the 8.2 ka event, when a large influx of meltwater into the North Atlantic reduced northward heat transport in this region. The event provides valuable insight into the global climate response to North Atlantic freshening. Here, we examine the timing, duration and magnitude of the climate response using a global network of speleothem oxygen isotope (δ¹⁸O) records.

Firstly, we objectively identified abrupt climate events in 402 globally distributed speleothem records from the SISAL (Speleothem Isotopes Synthesis and AnaLysis) database (Atsawawaranunt et al., 2018; Comas-Bru et al., 2020) during the Holocene. Secondly, we examined the timing, duration and anomalies of the 8.2 ka δ¹⁸O excursions using 70 speleothem δ¹⁸O records.

We show that the 8.2 ka event is the most globally coherent and significant abrupt event of the last 12,000 years, with an abrupt δ¹⁸O excursion identified in >70% of speleothem records. The δ¹⁸O anomalies are regionally homogeneous; they are negative across Europe and the Mediterranean, positive across Asia, and negative in South America and southern Africa. The excursion is not registered in the Indonesia/Australia region. The median timing of the event from the speleothem records is 8223 ±12 to 8062 ±14 years BP, indistinguishable from the timing in Greenland ice cores of 8247 to 8086 ± 47 years BP (Thomas et al., 2007). The median duration of the 8.2 ka event excursion in speleothems is 159 ±11 years, indistinguishable from the duration in Greenland of 160.5 ± 5.5 years (Thomas et al., 2007). There is no significant difference between the timing and duration in regions both near (Europe) and far (Asia) from the North Atlantic. This globally synchronous timing and duration supports a rapid and widespread climate response, likely via rapid atmospheric teleconnections.

Atsawawaranunt, K., et al., 2018. The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems. Earth System Science Data, 10(3), pp.1687-1713.

Comas-Bru, L., et al., 2020. SISALv2: a comprehensive speleothem isotope database with multiple age–depth models. Earth System Science Data, 12(4), pp.2579-2606.

Thomas, E.R., Wolff, E.W., Mulvaney, R., Steffensen, J.P., Johnsen, S.J., Arrowsmith, C., White, J.W., Vaughn, B. and Popp, T., 2007. The 8.2 ka event from Greenland ice cores. Quaternary Science Reviews, 26(1-2), pp.70-81.

How to cite: Parker, S. and Harrison, S. P.: The timing, duration and magnitude of the 8.2 ka event in global speleothem records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3953, https://doi.org/10.5194/egusphere-egu22-3953, 2022.

Terrestrial ecosystems, including soil and the biosphere, represent important reservoirs of carbon sources and cycling (IPCC, 2000). However, the reaction of terrestrial ecosystems to the changing climate remains poorly constrained. Over the past 20 years, interest in the organic matter (OM) fraction of speleothems, typically comprising 0.01-0.3% of the total carbon (Blyth et al., 2016), has increased due to its potential to offer information about past ecosystems. The sources of speleothem OM are not fully understood and are likely to be a combination of contributions from overlying vegetation, soil, microbial activity within the karst system, and cave fauna. Due to the link that the inner cave environment has with the karst, the signal of non purgeable organic carbon (NPOC) sourced from the overlying soil, vadose zone, or within the cave itself may be preserved within speleothems (Blyth et al., 2013). Hence, the isotopic characterisation (𝛿¹³C and ¹⁴C) of stalagmite NPOC has the potential to give information about past ecological and climactic state of the surrounding region (Blyth et al., 2013).

Presented here are the first results of a high-resolution process study of organic and inorganic carbon fluxes in the Milandre cave (Switzerland), whereby the main carbon source reservoirs will be monitored for two years. The total organic carbon content of cave waters ranges from 0.6 -1.3mg/L. The 𝛿¹³C of CO₂ in gas samples from atmospheric air (-9.24 ‰), soil air (-12.68 - -27.20‰), gas well air (-24.97- -25.78‰), and cave air (-14.29 - -25.32‰) were analysed. The soil air, well air and cave air have 𝛿¹³C values which range from close to atmospheric 𝛿¹³C to the most 𝛿¹³C depleted cave air end member which suggests differing levels of gas mixing throughout the system. Ultimately, this information will be used to constrain the source of speleothem NPOC and allow the assessment of its suitability as a proxy for ecosystem change.   

Blyth, A., Hartland, A. and Baker, A., 2016. Organic proxies in speleothems – New developments, advantages and limitations. Quaternary Science Reviews, 149, pp.1-17.

Blyth, A., Smith, C., and Drysdale, R., 2013. A new perspective on the 13C signal preserved in speleothems using LC-IRMS analysis of bulk organic matter and compound specific stable isotope analysis. Quaternary Science Reviews, 75, pp. 143-149.

IPCC, 2000: Land Use, Land-Use Change and Forestry. (R.Watson, I.Noble, B Bolin, N.H. Ravindranath,D.J. Verardo and D.J. Dokken (eds.)).  Cambridge University Press, UK, pp.375

How to cite: Rowan, S., Luetscher, M., Szidat, S., and Lechleitner, F. A.: High Resolution Monitoring of Organic Matter at Milandre Cave, Switzerland. Implications for Future Paleoecosystem Proxies., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4066, https://doi.org/10.5194/egusphere-egu22-4066, 2022.

Globally, near-surface permafrost is likely to warm, thin or disappear in many areas subject to future climate warming and wetting, creating a positive atmospheric feedback where the permafrost is rich in carbon. Unfortunately, substantial uncertainty exists as to the extent and timing of thawing in response to atmospheric forcing. Cryogenic cave carbonates (CCCs),  a recently described type of speleothem, precipitate when cave ice forms and thus provide opportunities to constrain periods when permafrost was present at a given cave site. Here, we present a unique dataset comprising 38 ²³⁰Th/U ages of CCCs from two caves in the Mendips, southwest England (51°N), and two caves in the Peak District, central England (53°N), all of which are currently ice-free. Whilst many ages are clean, reliable and high precision, the accuracy of those containing initial ²³⁰This improved greatly by constructing isochrons and applying further statistical methods.

The ages of CCCs reveal two distinct periods of isothermal permafrost conditions, peaking during i) the early Bølling–Allerød interstadial at approximately 14,463 ± 145 yBP* and ii) the late Younger Dryas around 11,719 ± 229 yBP. Such isothermal conditions (i.e., where values of mean annual ground temperature are commonly a fraction of a degree below 0°C and exist through much of the depth profile of permafrost) are thought to represent the later stages of permafrost warming prior to its disappearance. We attribute this isothermal, disequilibrium permafrost evolution during the last deglaciation of the British–Irish Ice Sheet to climatic variations linked to North Atlantic sea-ice extent and seasonality.

*years before 1950

How to cite: Toechterle, P., Edwards, R. L., Gunn, J., Atkinson, T., Murton, J. B., Luetscher, M., and Moseley, G. E.: Permafrost Evolution on the British Isles during the Last Deglaciation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4293, https://doi.org/10.5194/egusphere-egu22-4293, 2022.

Speleothems from well-monitored Cloşani Cave (Romania), have provided excellent records of past rainfall amount and European winter hydro-climate variability (Warken et al., 2018). Here we present new data allowing to extend the precipitation history of Central-Eastern Europe back to the Last Glacial Maximum (LGM) as well as MIS 3. High-precision ²³⁰Th/U ages show that the two analysed speleothems (C09-1 and C09-2) grew nearly continuously during the past 20 ka, with only one growth interruption between c. 11 and 9.7 ka BP. In addition, C09-2 also covers the Dansgaard/Oeschger (D/O) Stadials/Interstadials 16 to 14 between 60 and 52 ka BP. Consistently with previous results, the speleothem proxies (δ¹⁸O and δ¹³C values, as well as laser ablation ICPMS trace element profiles) provide a comprehensive picture of local and regional hydro-climate variability on centennial to glacial/interglacial timescales.

Over the course of the record, all proxies reveal millennial-scale features associated with prominent transitions during MIS 3, i.e., D/O events 16 to 14, as well as during the deglaciation, i.e., the Bølling-Allerød (BA) and Younger Dryas (YD). Local wetness as indicated by Mg/Ca ratios exhibits large variability, including pronounced swings between dry conditions during MIS 3 interstadials, and wetter conditions during stadials. After speleothem growth re-initiated at 20 ka BP, Mg/Ca ratios indicate a progressive drying until 15 ka BP, followed by an interval with enhanced variability from the Late Glacial to the Early Holocene. During the subsequent mid to late Holocene, from 8 ka BP to present, the local hydroclimate was characterized by relatively stable conditions. This dataset thus provides new insights into Central-Eastern European precipitation variability, and possibly also into its linkages to the North Atlantic realm.

References:

Warken, S.F., Fohlmeister, J., Schröder-Ritzrau, A., Constantin, S., Spötl, C., Gerdes, A., Esper, J., Frank, N., Arps, J., Terente, M., Riechelmann, D.F.C., Mangini, A., Scholz, D., (2018). Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record. Earth and Planetary Science Letters 499, 122-133. DOI: 10.1016/j.epsl.2018.07.027

How to cite: Warken, S. F., Riechelmann, D. F. C., Fohlmeister, J., Schröder-Ritzrau, A., Spötl, C., Jochum, K. P., Scholz, D., Constantin, S., and Frank, N.: Multi-proxy speleothem records attest to Central-Eastern Europe hydro-climate variability during MIS 3, the LGM, and the Holocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4294, https://doi.org/10.5194/egusphere-egu22-4294, 2022.

Speleothems have become a cornerstone in atmospheric ¹⁴C reconstruction. In particular, the part of the IntCal20 calibration curve before 34 ka BP (Reimer et al., 2020) heavily relies on a set of speleothems from Hulu Cave in China (Cheng et al., 2018). The interpretation of speleothem ¹⁴C archives, however, is often exacerbated by the so-called dead carbon fraction (DCF) in speleothem carbonate. It quantifies the percentage of old, ¹⁴C-free carbon from dissolved bedrock carbonate or aged soil organic matter, and is controlled by various parameters. Modelling efforts to disentangle these parameters have already been made by previous studies.

Here, we present forward-modelled DCF time series obtained by coupling CaveCalc, a numerical model for speleothem chemistry and isotopes (Owen et al., 2018), with IntCal20 and results from paleoclimate modelling. To compare our coupled model with an extensive DCF measurement record from Sofular Cave in Northern Turkey, we convert time-dependent soil respiration output from the Max Planck Institute Earth System Model version 1.2 (MPI-ESM1.2) to soil pCO₂ via a simplistic soil respiration model and use it as input for CaveCalc. The resulting forward-modelled DCF is in very good agreement with the long-term trends of the measurement record and demonstrates that soil respiration has been the main driver of DCF variability in the Last Glacial Maximum and the Early Holocene at Sofular Cave.

Further, we show that, holding soil respiration and all other climate parameters constant, adding only 10 % of 1000 year old carbon to the soil CO₂ can cause variations of up to 200 years in the DCF. This finding suggests that the DCF variability of only 50 years, which is assumed for Hulu Cave by Reimer et al. (2020), might be significantly higher, and underlines the importance of including additional records, like the one from Sofular Cave, to the next generation of calibration curves.

References:

Reimer, P. J., Austin, W. E. N., Bard, E., Bayliss, A., et al.: The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP), Radiocarbon, 62(4), 725-757, doi:10.1017/RDC.2020.41, 2020.

Cheng, H., Lawrence Edwards, R., Southon, J., et al.: Atmospheric ¹⁴C/¹²C changes during the last glacial period from Hulu Cave, Science, 362(6420), 1293–1297, doi:10.1126/science.aau0747, 2018.

Owen, R., Day, C. C., and Henderson, G. M.: CaveCalc: A new model for speleothem chemistry & isotopes, Computers & Geosciences, 119, 115–122, doi:10.1016/j.cageo.2018.06.011, 2018.

How to cite: Hubig, A., Therre, S., Kleinen, T., and Frank, N.: Using Earth system model output to simulate DCF variability in speleothems: Implications for atmospheric 14C calibration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4401, https://doi.org/10.5194/egusphere-egu22-4401, 2022.

The transport and incorporation mechanisms of radiocarbon (¹⁴C), stable carbon isotopes (δ¹³C) and trace metal ratios into speleothems have been investigated intensively in the past. This provides a crucial understanding for the detection of climate and ecosystem signals (precipitation, vegetation variability) or even changes in atmospheric composition like radionuclide concentration. The Dead Carbon Fraction (DCF) in tropical settings often revealed a positive correlation with hydrological proxies, highlighting its relation with the amount of soil water infiltration. In contrast, more arid regions can have dominant aged stocks of soil organic matter (SOM) diluting the ¹⁴C concentration of the soil CO₂, which is responsible for an enhanced decoupling between speleothem DCF and hydrological proxies.

Here, we present a compilation of several new and published stalagmite ¹⁴C records in context with the predominant climatic parameters controlling their carbon signature. The records cover humid, tropical climates in Puerto Rico, temperate settings in Northern Turkey, as well as semi-arid alpine caves, and arid locations on the Arabian Peninsula. The range of mean DCF values is extreme, from below 10 to more than 60 % with δ¹³C values between -10 and 0 ‰. Climate-controlled mechanisms like the sensitivity of vegetation to net-infiltration changes are revealed, especially for more arid regions where aged SOM significantly contributes to stalagmite geochemistry.

In a first application, we revisit a published multi-proxy glacial record of a stalagmite from Socotra Island, which allows us to disentangle the increasing soil infiltration towards Termination I and the resulting long-term DCF trends. This is achieved by exploiting the correlation of a humidity proxy (Mg/Ca) with DCF and implementing a transfer function to correct for soil carbon effects in ¹⁴C.

Our approach hints at vast opportunities to better understand the control mechanisms in stalagmite carbon signature and correct for climate-induced effects. Therefore, it can aid future research in the search for stalagmite records which trace, for instance, atmospheric nuclide signals or bear unresolved climate-related trends.

How to cite: Therre, S., Fohlmeister, J., Warken, S. F., Schröder-Ritzrau, A., Friedrich, R., and Frank, N.: Disentangling climate-dependent stalagmite proxies using radiocarbon timeseries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4875, https://doi.org/10.5194/egusphere-egu22-4875, 2022.

Cryogenic cave carbonates (CCC) have become a valuable tool for providing evidence for past permafrost presence, particularly in low-elevation mid-latitude temperate locations (e.g. Germany and UK) and high-elevation mid-latitude periglacial environments (e.g. Austria and Spain). This study focuses on CCC from a low-elevation high-latitude site in the continuous permafrost of the high Arctic. Specifically, the fine-grained form of cryogenic cave carbonates (CCC_fine), which precipitate from rapidly freezing thin water films on top of cave ice, are investigated from Eqik Qaarusussuaq (cave) in northeast Greenland (80.2°N). Under contemporary conditions, the sampling site in the interior of the cave is dry, cold (-14.7°C) and ice-free, thus water infiltration to facilitate CCC_fine formation is not possible.

Previously, ²³⁰Th/U dating efforts of CCC_fine have suffered from poor age precision due to high detrital Th contamination. Similarly, ¹⁴C dating has been hindered by the unknown reservoir effect (dead carbon fraction). To address these dating issues, we applied a multi-method dating approach to produce a unique dataset comprising eleven ¹⁴C ages as well as six ²³⁰Th/U ages from a single patch of CCC_fine. An isochron indicates that the CCC_fine formed synchronously and that the cleanest ²³⁰Th/U age is representative for the whole patch. The dead carbon fraction is calculated based on this ²³⁰Th/U age.

The results of ²³⁰Th/U dating (97±34 a BP) agree with the calibrated ¹⁴C age range (40-70 a BP (37.9%), 115-139 a BP (28.2%), 226-254 a BP (29.4%)) that the CCC_fine from Eqik Qaarusussuaq most likely formed towards the end of the Little Ice Age or shortly after.

How to cite: Donner, A., Töchterle, P., Spötl, C., Hajdas, I., Li, X., Edwards, R. L., and Moseley, G. E.: Combined 14C and 230Th/U dating of fine-grained cryogenic cave carbonates from a permafrost cave in Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5867, https://doi.org/10.5194/egusphere-egu22-5867, 2022.

Carbon, oxygen and clumped isotope (Δ₄₇) values were measured from recently inactive travertine mounds located in Santovka and Dudince (Slovakia) to provide information about the origin of carbon, precipitation conditions, and paleotemperature. δ¹⁸O and δ¹³C analyses of carbonates were performed at the Institute for Geological and Geochemical Research (IGGR), Research Centre for Astronomy and Earth Sciences (Budapest, Hungary) and the clumped isotope analysis were performed at the Isotope Climatology and Environmental Research Center (ICER) of the Institute for Nuclear Research (Debrecen, Hungary). δ¹³C values show a range between +5.3‰ and +9.7‰ (V-PDB) and δ¹⁸O values (V-PDB) range between –11.2‰ and −7.5‰. These data are in accordance with the typical isotopic signature of thermogene travertines. Positive δ¹³C values also suggest that the thermal waters were charged with isotopically heavy CO₂ of deep origin, possibly produced through metamorphic reactions, as decarbonation of carbonate rocks. Calculated δ¹³C_CO2 values of −4.2% to −0.9‰, more positive than values of CO₂ coming from the pure igneous source possibly, support this suggestion. Mineral and thermal waters in Slovakia are mainly observed in the Inner Carpathians depressions and lowland, making the most plausible carbon sources as being the Triassic limestones and dolomites, where the aquifers were formed. Clumped isotope composition (Δ₄₇) of the inactive Santovka Mound and two inactive mounds from Dudince were measured. D_{47(CDES 25)} values range from 0.646 ± 0.012‰ and 0.717 ± 0.010‰, corresponding to temperature estimates (T(Δ₄₇)) that range from 17°C to 43°C using the calibration of Petersen et al. (2019) and 12°C to 33°C, using Kele et al. (2015) calibration. Calculated paleotemperatures of the paleosprings are slightly higher than the present equivalents measured directly in thermal water wells from Santovka and Dudince (14.5 °C to 26.9°C). δ¹⁸O (V-PDB) of the travertine precipitating fluid was calculated using the T(Δ₄₇) data, giving values on the range of –11.1‰ and −5.8‰, while the δ¹⁸O_water values measured from thermal water well on Santovka and Dudince vary from –11.3‰ to 10.1‰ The observed difference in the δ¹⁸O_water values could be interpreted as the influence of the present-day precipitation (–10.4‰ to –8.7‰) on the waters on this region.

How to cite: Vieira, D., Rinyu, L., and Kele, S.: Stable and clumped isotope characterization of travertine spring mounds from Santovka and Dudince (Southern Slovakia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7556, https://doi.org/10.5194/egusphere-egu22-7556, 2022.

It has now been over 25 years since stable isotope data from lake sediment cores was first used to provide quantitative evidence of increased aridity in the Yucatán peninsula during the Maya Terminal Classic period (c.800-1000CE); a time in which Maya civilisation underwent major societal shifts and depopulations, frequently termed the Classic Maya Collapse. While palaeoclimatic evidence of reduced precipitation during the Terminal Classic from sediments and, more recently, speleothems is now plentiful, the degree of uncertainty in their chronology and proxy interpretation has precluded analysis of the precise link between decadal and sub-decadal scale drought events and the abandonment of individual Maya archaeological sites on similar timescales.

We present a sub-seasonal-resolution stable isotope record from the stalagmite Tecoh06-1, from Tzabnah Cave (near Tecoh, Yucatán), which spans 185 years of the Terminal Classic. By utilising a prior visual layer count and milling at varying resolution to yield 10-20 samples per lamina, we here record seasonal-scale annual fluctuations in both δ¹⁸O and δ¹³C. With each lamina confirmed to be annual, we have developed a known-duration record which can be temporally fixed by conventional U/Th dating, greatly reducing the associated degree of chronological uncertainty. This is the first local palaeoclimate dataset to record seasonality through the Terminal Classic, and additionally it replicates a lower-resolution record from the same cave, published by Medina-Elizalde et al. (2010), to a satisfactory degree over the sampled period.

Using this palaeoseasonal record we can now reliably characterise the multiple decadal-scale intervals wherein precipitation remained low year-round. These intervals would have likely been those with the most significant detrimental impact on Maya agriculture and society. 

How to cite: James, D., Carolin, S., Breitenbach, S., Endsley, E., Gallup, C., Brenner, M., Curtis, J., Rolfe, J., Nicolson, J., and Hodell, D.: An ultra-high-resolution seasonal-scale stalagmite palaeoclimate record from the Yucatán peninsula, spanning the Maya Terminal Classic period., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7862, https://doi.org/10.5194/egusphere-egu22-7862, 2022.

The interpretation of paleoclimate records from speleothems remains a challenging task due to the individual characteristics of each specimen and cave system. Through recent advances in techniques like confocal microscopy and high-resolution geochemical analysis, fluorescent layers in speleothems have become a significant source of information to enhance paleo-seasonal reconstructions, improve age models and, consequently, constrain rates of past climate changes. In this framework, speleothem fluorescence originates from organic matter produced in the soil above the cave, from ancient organic compounds in the bedrock or from microbial processes within the karst. However, the mechanisms leading to the incorporation of fluorescent banding into calcite as well as the properties of transport, storage and decomposition of organic matter in natural karst systems are still under debate. We present results from a one-year monitoring study of fluorescence properties in drip water, sampled from May 2020 to May 2021 in a quasi-monthly resolution at 3-6 locations within the cave system La Vallina in Northwestern Spain. We have measured absorbance spectra and fluorescence exitation-emission matrices; and compare it to drip water geochemistry, fluorescence of active speleothems at the same site and vegetation type above the cave. Our results indicate high gradients of fluorescent properties in drip waters already on a small spatial scale. In the site where active speleothems show fluorescent banding, a humic-like fluorescent signal prevails in cave waters (AC peak, according to Coble nomenclature), while other sites are more likely to be influenced by microbial activity (B/M peak). Humic-like fluorescence is stronger in drip waters during the autumn season, probably due to the increased input by colloids. Yet, simple relationships between the fluorescence in drip water and colloid-associated trace elements like Cu and Y cannot be confirmed. Further, the difference in drip water fluorescence is small compared to the actual intra-seasonal difference retrieved by confocal microscopy in active stalagmites. Therefore, we find drip water composition unlikely to be solely responsible for seasonal enriched fluorescence incorporation in speleothems and favour conceptual models taking moisture-limitation and adsorption into account.

How to cite: Endres, L., Jacquin, C., Traber, J., Gonzàlez-Lemos, S., Rodriquez-Rodriquez, L., Sliwinski, J., Kaushal, N., Kost, O., and Stoll, H. M.: New insights from fluorescent organic matter in natural cave systems and active speleothems: a one-year monitoring study from Northwestern Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8035, https://doi.org/10.5194/egusphere-egu22-8035, 2022.

South Africa has an extraordinary record of human evolution spanning the last ~3 million years, from the fossil remains of our early pre-human relatives in the Cradle of Humankind World Heritage site, through to more recent evidence for the emergence of modern humans. Common to almost all these sites are the presence of carbonate deposits, be they caves, rock shelters or open-air sites. Knowing how old the sites are, understanding the depositional environment and the potential to use the carbonates as records of past hydroclimate variability has motivated many years of research into them. While U-Th dating is a precise, robust, and very useful chronometer in human evolution, the biggest breakthroughs in the last decade have come from U-Pb dating. However, aspects of this chronometer remain a challenging analytical exercise, more-so as the technique becomes routinely applied to carbonates with less-than-ideal U/Pb ratios.

Here we present insights into both the U and Pb concentrations, distributions, and isotope ratios, from a relatively large U-Pb dataset ranging from ~3 Ma to just under 1 Ma. We divide the U-Pb ages into three categories defined by the % error on the U–Pb age (the good, the bad and the ugly), and use thin section petrography and laser ablation trace element transects through the flowstones to investigate the factors controlling the quality of the ages. Our data confirms the expected negative exponential relationship between U–Pb age and 234U/238U. There is no apparent relationship between U concentration and residual 234U/238U, suggesting U concentration patterns are controlled by 238U, not 234U. We show that variability in the amount of inherited Pb across the sampling layer (average variability of 63% relative to sample average) – not uranium (23% variability) or by extension radiogenic Pb – is a main factor controlling the resulting isochron’s quality.

The thin section petrography reveals all flowstones have undergone heavy diagenesis, the dominant fabric consisting of mosaic calcite with relic aragonite. However, we argue that the trace element signals, the abrupt, sympathetic step-like variation is Sr, U and in some cases Ba and Mg, indicate that this diagenesis is conservative. We do show what a completely recrystallized flowstone looks like, where the original trace element signals are completely obliterated, and it is impossible to resolve a U–Pb age. We identify a mixture of crystal and fluid dominated patterns, both of which are ultimately related to flow dynamics, in turn related to changes in external hydroclimate.

We look forward to future development in in situ laser ablation U-Pb dating, which will allow for even more material to be dated. There is great potential to extract valuable palaeoclimate records out of these old, U–Pb dated flowstones, which would be very interesting given their association with important early human evolution sites in South Africa. We predict these two areas will see rapid development in the coming years.

How to cite: Pickering, R., Engel, J., and Edwards, T.: The good, the bad and the ugly: 20 years of U-series dating carbonates from South Africa., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8103, https://doi.org/10.5194/egusphere-egu22-8103, 2022.

This research is based on broader study investigating drivers of decadal to centennial-scale variations in the Central American Monsoon (CAM), a sub-region of the broader North American Monsoon. In the context of the Global Monsoon system, the precipitation patterns of CAM are of particular interest because of the placement/shifting of the ITCZ through time, its proximity to the AMOC system, and that existing precipitation records from this area have revealed a heterogenous pattern throughout the past 2 kyr.

Here we present new carbon and oxygen isotopic records of two speleothems, MO-AL-3 and MO-CU-2, recently collected from Mona Island, Puerto Rico. These speleothems together cover the last 2 kyr BP, thus significantly expanding the hydrologic history of the Northeastern Caribbean from speleothem records. Previous studies, mostly from the Western Caribbean, have revealed that Caribbean SSTs as well as solar and volcanic forcing are involved, to different degrees, as driving mechanisms determining the strength of the InterAmerican monsoon systems over the late Holocene. The study of precise, independent chronologies extracted from speleothems, and comparing them to local and regional coral/sclerosponge SST reconstructions, allows for an improved understanding of precipitation patterns of the Caribbean overtime. This new record allows the investigation of decadal to centennial-scale precipitation variability, as well as its linkage to past human civilizations. There is also potential to contribute to the recent discussion of whether the AMO is an internal oscillation or externally forced.  

How to cite: Cozadd, C., Lachniet, M., Warken, S., Li, H., and Winter, A.: Does Caribbean SST drive decadal to centennial-scale variability in the Central American Monsoon? Evidence from stalagmites from Mona Island, Puerto Rico, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8933, https://doi.org/10.5194/egusphere-egu22-8933, 2022.