Antarctic sea ice cover experienced an abrupt decline in 2016, transitioning from a record maximum state to a record minimum state. However, the drivers of this rapid retreat are currently not well understood. Therefore, it is difficult to determine whether this signals the start of a long term melting trend, as has been long anticipated by climate models, or is an isolated episode of internal climate variability. In this study, we utilise the CMIP6 archive to understand if internal climate variability could be responsible for this Antarctic sea ice anomaly, and if so what the primary atmospheric and oceanic drivers are. This involves examining composites of the tropical teleconnections, subsurface ocean heat content, and high latitude atmospheric variability preceding extreme Antarctic sea ice anomalies in CMIP6 simulations. The primary objective is to elucidate the multifaceted factors influencing these extreme events, specifically addressing the 2016-2017 sea ice retreat, with lessons for 2023’s extreme Antarctic sea ice state. Initial results indicate that such events are possible in the absence of anthropogenic emissions in some climate models, although the occurrences are considered rare. We also show that that using the limited observed record alone will underestimate the interannual variability of the Antarctic sea ice cover and therefore overestimate how rare such an anomaly would be. In fact, if we extend the observed record further back using statistical reconstructions, rapid declines of sea ice extent occurred in the early and mid 20^th century.  Our results highlight the importance of internal climate variability in the Southern high latitudes and advance our understanding of the drivers and predictability of Antarctic sea ice changes. We discuss the implications of this work for 2023’s record Antarctic sea ice anomaly.

How to cite: Chan, C. Y., England, M., Screen, J., Bracegirdle, T., and Blockley, E.: Investigating the drivers of abrupt Antarctic sea ice decline, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-810, https://doi.org/10.5194/egusphere-egu24-810, 2024.

Changes in modes of atmospheric circulation contribute to shape climate at regional scale by interacting with orography. Earth System Models (ESM) tackle the response of these modes to global warming. However, there exists considerable uncertainty regarding the magnitude and impact of the changes in modes of variability. This uncertainty is mainly due to internal variability, and inter-model variability related to the different resolution and parametrisation of physical processes in ESMs. One example of the latter is the representation of soil thermodynamics and hydrology in the Arctic. Different representations of Arctic dynamics have the potential to affect the circulation, not only locally in the Arctic, but also at mid-latitudes and the tropics via a series of teleconnections. The physical processes linking Arctic warming and sea-ice loss to lower latitude climate variability are still not well understood. This study addresses how changes in Arctic soil thermodynamics and hydrology affect the global atmospheric circulation. To do so, a modified version of the Max Plank Institute Earth System Model (MPI-ESM) was used to produce an ensemble of simulations with different set-ups of its Land Surface Model (JSBACH). These configurations consider different representation of the Arctic thermo-hydrodynamics leading to comparatively drier or wetter states. Preliminary analysis show sensitivity of atmospheric circulation to changes in the Arctic Amplification. Results are shown for a comparison of the response of extratropical (Arctic and Antarctic oscillations) and intertropical (monsoons and ENSO) modes across the ensemble of simulations.

How to cite: Martínez-Vila, A., Gonzalez-Rouco, J. F., Meabe-Yanguas, N., García-Pereira, F., Jungclaus, J., Lorenz, S., and de Vrese, P.: Atmospheric circulation sensitivity to changes in Arctic soil thermodynamics and hydrology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10074, https://doi.org/10.5194/egusphere-egu24-10074, 2024.

One significant and dangerous consequence of climate change is the growth in both the intensity and frequency of extreme weather events. The objective of this study is to examine the prevalent hypothesis that links Arctic amplification (AA) to the occurrence of cold weather extremes over the Northern Hemisphere (NH) in December–January–February (DJF). According to this hypothesis, AA alters the mid-latitude circulation, causing Rossby waves to become slower and wavier. More slow or wavy Rossby waves result in more persistent weather patterns in the mid-latitudes, potentially increasing the frequency and severity of extreme weather events.

We examine the link between AA and cold spells in the Northern Hemisphere by using idealized simulations with the Community Earth System Model (CESM) and the fifth-generation ECMWF reanalysis data (ERA5). We mimicked AA by adding a constant amount of downwelling longwave radiation (DLR) over the Arctic in the CESM slab-ocean model. Furthermore, we categorized ERA5 data into two separate periods: pre-Arctic amplification (1979–1999, Pre-AA) and post-Arctic amplification (2002–2022, Post-AA).

We computed the speed of planetary waves based on geopotential height using two different methodologies. In the first method, the speed of planetary wave zonal propagation was estimated through the utilization of a top-ridge and bottom-trough tracking algorithm. In the second method, we calculated the zonal propagation speed of planetary waves at each grid point following Takaya and Nakamura (2001). Both methods, although being fundamentally different, showed a significant reduction in DJF average zonal planetary wave speed over Northen-midlatitude during AA in both reanalysis data and idealized simulations.

The midlatitude extreme index (MEX) is used to identify cold weather extremes. On average, MEX showed a higher value for Pre-AA than Post-AA, consistent with a warmer climate in post-AA. However, the average wave speed during cold extremes is lower in Post-AA than Pre-AA.

As regard wave amplitude, based on the difference between the maximum peak and the minimum bottom of the waves in both the ERA5 data and the idealized simulations, we cannot confirm a change in the amplitude of planetary waves due to AA.

To summarize, Arctic amplification leads to a decrease in the speed of Rossby waves but little or no change in their amplitude. In addition, cold extremes are influenced by the deceleration of Rossby waves in response to warming conditions in the Arctic.

How to cite: Babaei, M., Graversen, R. G., and Stoll, J. P.: The role of atmospheric circulation in extreme cold weather events over the Northern Hemisphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12098, https://doi.org/10.5194/egusphere-egu24-12098, 2024.

Heterogeneous radiative forcing in mid-latitudes, such as those caused by aerosols, has been observed to influence the Arctic climate, although the underlying mechanisms continue to be a subject of scientific discussion. In this research, we employed Deep Learning (DL) methodologies to explore the complex response of the Arctic climate system to localized radiative forcing over Europe. We performed sensitivity experiments using the Max Planck Institute Earth System Model (MPI-ESM1.2). By applying a DL-driven clustering approach, we classified atmospheric circulation patterns within a reduced-dimensional framework, with a particular focus on Poleward Moist Static Energy Transport (PMSET) as our primary parameter of interest. Additionally, we developed a new methodology to assess the contributions of these circulation patterns to anomalies in various climatic parameters.

Our results demonstrate that anomalous negative forcing over Europe alters existing circulation patterns and their occurrence frequency without leading to the emergence of new patterns. The clusters change between the Experiment and Control runs in two main ways: variations in their frequency of occurrence and seasonal shifts between the class mean characteristics in the Experiment and Control runs. While pronounced changes in seasonal occurrence frequency can substantially contribute to the observed seasonal anomaly, even subtle alterations in the seasonal differences between class mean characteristics can profoundly affect the class's contribution to the anomaly, especially if that cluster occurs with a high frequency.

We identify changes in the circulation pattern with the high-pressure system over Scandinavia as a key driver for reduced sea ice concentration (SIC) in the Barents-Kara Sea in autumn through enhancing the PMSET. The alterations in this circulation pattern also impact the dynamics of the middle atmosphere. However, its influence is relatively minor compared to other circulation patterns that are analogous to the various phases of the North Atlantic Oscillation (NAO). 

These results shed light on the complex interactions between diverse atmospheric circulation patterns and climatic variables, revealing the underlying mechanisms responsible for the anomalies observed across different seasons. Notably, a complex interplay of different circulation patterns, particularly those mirroring the distinct phases of the NAO, plays a crucial role in dictating wave propagation and the dynamics within the stratosphere. While our study did not specifically investigate the stratospheric pathway, our findings highlight that regional negative radiative forcing over Europe can lead to changes in both Arctic climatic parameters and the dynamics of the stratosphere.

How to cite: Mehrdad, S., Handorf, D., Höschel, I., Karami, K., Quaas, J., Dipu, S., and Jacobi, C.: A Physics-informed Deep Learning Based Clustering to Investigate the Impact of Regional European Radiative Forcing on Arctic Climate and Upper Atmospheric Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16391, https://doi.org/10.5194/egusphere-egu24-16391, 2024.

The Arctic region is particularly sensitive to global warming due to snow and sea ice dynamics, as well as to the strong positive feedback mechanisms that amplify Arctic warming response to forcing, such as ice-snow-albedo feedback or lapse-rate feedback. The presence of permafrost makes the Arctic also relevant for global climate, since Arctic soils contain large quantities of carbon with radiative feedback implications. Improved representation of the physical processes in frozen soils  and considering different model variants allows for assesing uncertainties in permafrost related processes. In this study several experiments with different set-ups of the Arctic thermo-hydrodynamics will be analyzed in order to understand how different parametrizations in permafrost areas affect Earth’s climate and in particular the surface temperature in the Arctic. Those set-ups also account for different vertical discretizations of the land model. The different model configurations lead to relatively different climate background states in the Arctic, with the different vertical discretization set-ups playing a minor role. A positive sea-ice-snow-albedo feedback is shown to enhance the warming signal under a climate change scenario. The magnitude of the feedback depends on the background state and available snow and sea-ice. By assessing the Arctic amplification ratio (AA) we conclude that all configurations show considerable (internal) AA variabillity in the 20th and the first quarter of the 21st century, but end up converging to a factor of 2-3 times larger warming in the Arctic regions than globally by the end of the century. This suggests that high AA values recently found in observations are related to internal variability.

How to cite: Meabe-Yanguas, N., González-Rouco, J. F., García-Pereira, F., Steinert, N., de Vrese, P., Jungclaus, J., and Lorenz, S.: Surface air temperature sensitibily to changes in land surface model thermodynamics and hydrology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10111, https://doi.org/10.5194/egusphere-egu24-10111, 2024.

From a combination of the operational system of reindeer herding and meteorological seasonality, we developed a range of climate indices reflecting critical events in the reindeer herding year that influence the success of this livelihood. These critical events can be described as combinations of specific meteorological conditions, and therefor rendered as equations we can compute from climate model output, creating a capability for analysing different projections of the future and delivering relevant information on climate change to reindeer herding communities.

For this purpose, we can use a wealth of different global and regional climate projections, with distinct advantages and disadvantages (e.g. model resolution, different greenhouse gas futures, high number of models in the ensemble for uncertainty estimates, process representation, availability of variables). For example, the CMIP6 ensemble enables the analysis of a broad range of greenhouse gas futures from a wide variety of models, allowing us to assess scenario uncertainty, but it is limited by its coarse spatial resolution. On the other hand, the PolarRES ensemble has a higher spatial resolution but is only available for one RCP/greenhouse gas future. The PolarRES ensemble consists of regional climate simulations generated by multiple regional climate models that dynamically downscale CMIP6 global climate simulations selected using a novel storyline approach. Both ensembles provide hindcast simulations that allow us to evaluate the ensemble performance with regard to the climate indices we defined.

This study uses these simulations to evaluate and compare model performance to understand the potential and limitations of future projections of specific climate indices relevant for reindeer herding. We use in-situ based observations from the data set Global Summary of the Day to evaluate onset and end of the continuous freezing period, hot summer days, thawing days in autumn and freeze-thaw cycles in both spring and autumn.

How to cite: Matthes, H., Eronen, J. T., Fettweis, X., Forbes, B. C., Gilbert, E., Habeck, J. O., Horstkotte, T., Istomin, K., Komu, T., Landgren, O., Landwehrs, J., Laptander, R., Mooney, P., Mottram, R., van Dalum, C., van den Berg, W. J., Rasmus, S., Rinke, A., and Tømmervik, H.: Evaluating the PolarRES regional models using tailor-made climate indices for Arctic reindeer herding communities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12738, https://doi.org/10.5194/egusphere-egu24-12738, 2024.

The strongly warming and wettening Arctic exhibits considerable temporal interannual and decadal variability. A conclusive transition point to a new climate state – the time of emergence (ToE) – occurs when the forced signal exceeds natural variability. Uncertainties in model-simulated climate trends and variability, as well as in methods, have thus far resulted in diverging estimates of Arctic ToE. Here we use a detailed, robust method applied to state-of-the-art climate model projections to show that in most seasons Arctic sea ice thickness emerges first (2038-2043), followed by surface air temperature (2037-2053) and sea ice cover (2050-2074). Since precipitation/rainfall variability is comparatively high, these variables emerge relatively late (after 2080). Autumn generally exhibits the earliest ToE-values due to strong sea ice retreat and associated warming and surface evaporation. Spatial variations in Arctic trends and variability cause ToE for temperature and sea ice thickness to emerge first in the Central Arctic, whereas for sea ice cover and rainfall this primarily occurs in the North Atlantic – Barents Sea region. Evidently, parts of the Arctic are close to entering a new climate state in terms of temperature and sea ice changes, with wide-ranging, long-term and possibly irreversible consequences for vulnerable Arctic ecosystems and human activities.

How to cite: Bintanja, R., Tsakali, N., Skyllas, N., and Kolbe, M.: The time of emergence of Arctic warming, wettening and sea ice melting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1246, https://doi.org/10.5194/egusphere-egu24-1246, 2024.

Planktonic foraminifera tests are commonly used in geochronology and palaeoceanographic reconstructions as micropaleontological and geochemical proxies. In the high latitude North Atlantic and Arctic, the polar specialist Neogloboquadrina pachyderma is the most common planktonic foraminifera and is known for its morphological plasticity, resulting in the identification of at least 5 morphotypes within a single genotype. The significance of its morphological variability remains uncertain, with hypotheses linking it to ecological/environmental differences, and/or life history stages. However, N. pachyderma morphotype analysis has been largely limited to sediment studies, lacking a systematic exploration of water column populations. Here, we explore this question using a novel supervised machine learning (SML) and automated image processing (AutoMorph software) approach to acquire large morphometric data sets on populations of Central Arctic N. pachyderma from 8 paired plankton net and sediment (box-core) sample sets. This study addresses the ability of SML to discern the established morphotypes and whether alternative morphological models can better represent the morphological diversity. Additionally, this study explores how morphologic variability in living N. pachyderma populations compare with their sedimented counterpart.

The results, based on approximately 15.000 N. pachyderma morphotypes, represents the largest data set for a single planktonic foraminifer species and the largest study of this kind based on water column populations in the Arctic Ocean. The highest specimen abundance was found in the upper 100m. Preliminary findings indicate a dominance of small (55-120µm) N. pachyderma specimens, assumed to be juveniles, whereas the sediment assemblage is dominated by heavily encrusted, larger morphotypes. The water column and sediment assemblages are mismatched, potentially due to the much narrower time window recorded in the water column compared to the annual-millennial timescale in the sediments. This study provides new insights into how ecology and life history of N. pachyderma translates to test morphology – a crucial aspect for taxonomy and geological studies.

How to cite: Weitkamp, T., Hsiang, A., Bird, C., Vermassen, F., Darling, K., and Coxall, H.: Identifying modern Neogloboquadrina pachyderma morphotypes from the Central Arctic Ocean through supervised machine learning – a comparison between water column and seafloor sediment populations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-993, https://doi.org/10.5194/egusphere-egu24-993, 2024.

Sea ice and ice sheets are highly sensitive to climate change in the Arctic, which shows an amplified response to global warming. To better understand the environmental changes and feedback processes associated with Arctic sea-ice decline and continental ice mass loss in a warmer-than-present world, it is urgent to investigate records of past warm periods.

Here, we present the first results of two sediment cores from the Baffin Bay recovered during the Expedition MSM111 in 2022. A 43-cm-long multicore on top of a 17-m-long gravity core (GeoB25212-1 and -3) was recovered from the continental slope west of Greenland (68°47.621’, 59°59.426’, water depth: 1505 m). According to a first stratigraphic interpretation, these cores contain a Holocene sediment succession and a high-resolution record of the last glacial cycle including Marine Isotope Stage 5e (MIS 5e) (Kucera et al., 2023).

Sediment samples taken from the mentioned cores are investigated for lipid biomarkers. Variations in the concentration of IP25, a well-established proxy for seasonal sea ice in the Arctic Ocean (Belt et al., 2007), point to distinct changes in the presence of sea ice in Baffin Bay. The joint analysis of IP25 and open-ocean biomarkers, such as brassicasterol and dinosterol, allows to draw more quantitative conclusions on paleo sea-ice conditions (Müller et al., 2011). Furthermore, alkenones and glycerol dialkyl glycerol tetraethers enable the reconstruction of sea-surface temperatures, while changes in terrestrial influx are deduced from biomarkers such as n-alkanes, ß-sitosterol, and campesterol. The terrigenous biomarker data will be complemented by mineralogical investigations to gain more information on the provenance of the sediments. X-ray fluorescence scanning data further provides additional information on paleoproductivity changes, biogeochemical processes, etc.

The first results of our investigations show that sea-ice conditions were highly variable. Throughout the Holocene, the presence of IP25 demonstrates that seasonal sea ice was present in Baffin Bay. However, intervals with low open-water biomarker concentrations indicate that the relatively stable climate conditions were disrupted by three cold events leading to more severe sea-ice conditions. Most interestingly, we observe elevated IP25 and sterol concentrations during the stratigraphic youngest Baffin Bay Detrital Carbonate (BBDC) event, probably BBDC 0, that was identified based on elevated calcium, dolomite, and calcite contents. By contrast, the following BBDC layer, probably BBDC 1, does not show significant changes in biomarker concentrations, leading to the conclusion that conditions during BBDC 0 were special.

Ongoing analyses focus on the last interglacial (MIS 5e) and will provide information on similarities and differences in the sea-ice conditions compared to the Holocene warming.

References

Belt et al., 2007. Organic Geochemistry 38 (1), 16-27.

Kucera et al., 2023. MARIA S. MERIAN-Berichte.

Müller et al., 2011. EPSL 306 (3-4), 137-148.

How to cite: Mikler, M., Müller, J., Faust, J. C., Vogt, C., and Kucera, M.: Holocene to Eemian sea ice and terrigenous influx variations in Baffin Bay – a lipid biomarker study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14777, https://doi.org/10.5194/egusphere-egu24-14777, 2024.

The Last Glacial Maximum (LGM) represents a critical period in Earth's history, and understanding the dynamics of the Greenland Ice Sheet (GrIS) during this time is pivotal for predicting its response to present and future climate change. Accurate reconstructions of the LGM ice sheet margin rely on marine limit and relative sea level data, which provide valuable insights into past ice sheet behavior. However, current databases of Greenland marine limits and relative sea levels are incomplete or not readily accessible, hindering scientific progress and impeding collaboration among researchers.

Here, we develop an online, open-access database hosted by the Geological Survey of Denmark and Greenland (GEUS) that consolidates all available information on the deglacial marine limit and relative sea level data from Greenland. The data is recorded in the HOLSEA format and includes realistic reporting of errors. The collected data comprises over 3,000 distinct data points, sourced from more than 120 publications and literature entries. These field observations span over 140 years, reflecting the evolution of measurement techniques and a growing comprehension of marine deposit and relative sea level features. By mining all existing databases, original publications, and unpublished data, this new database will provide researchers with a centralized and up-to-date resource for investigating the LGM ice sheet and subsequent deglaciation history.

In the future, the database will undergo regular updates to incorporate new findings and adhere to international standards for reporting marine limit and relative sea level data. This initiative forms the baseline for validating reconstructions of the past behavior of the GrIS contributing to more accurate predictions of its future response to changing climatic conditions.

How to cite: Luetzenburg, G., Funder, S. V., Woodroffe, S., and Kjeldsen, K. K.: An Open-Access Repository of Holocene Marine Limit and Relative Sea Level Data for all of Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7166, https://doi.org/10.5194/egusphere-egu24-7166, 2024.

Grain size end-member (EM) modeling is a statistical method employed to identify and quantify dominant grain size distributions in marine sediments, contributing to a comprehensive understanding of sediment transport and deposition mechanisms. Despite its utility in various marine sediments, the application of this modeling approach to glacimarine fjord sediments in polar regions remains relatively unexplored.

This study investigates the grain size distributions of glacimarine sediment cores collected from the Wijdefjorden and off Kongsfjorden in the Arctic Svalbard archipelago. By integrating grain-size EMs with lithologic and acoustic facies, we delineate distinct EM groups associated with specific depositional processes and environments. This study shows that Svalbard fjord systems underwent significant depositional changes influenced by glacial retreat during the last deglaciation to the early Holocene, coinciding with enhanced Atlantic Water inflow. Conversely, the late Holocene noticed reduced Atlantic Water inflow, aligning with glacial advances, and resulted in notable changes in depositional environments. This study underscores the efficiency of EM modeling as a valuable tool for comprehending grain size distributions and reconstructing depositional processes in glacimarine sediments within the fjord complex systems of Svalbard. Consequently, this approach enhances our understanding of the interconnected dynamics involving climate change, glacier dynamics, and oceanic forcing in glaciated polar environments throughout past glacial-interglacial climate changes.

How to cite: Nam, S.-I., Ahn, Y., Joe, Y. J., Jang, K., Kim, D., Kim, J.-H., Son, Y. J., Forwick, M., Knies, J., and Hong, S.: Depositional and paleoenvironmental changes in Arctic Svalbard fjords during the last deglaciation: Insights from Grain Size End-Member Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13956, https://doi.org/10.5194/egusphere-egu24-13956, 2024.

Sulfide weathering plays a crucial role in driving the long-term carbon cycle on Earth, and thus its historical reconstruction is essential for a better understanding of the global carbon-climate feedback. In this study, we analyzed the abundance of rare earth elements (REE) within authigenic Fe-(oxyhydr)oxide phases in glacimarine sediments retrieved from the continental shelf offshore northern Svalbard, spanning over the last 16,300 years, to evaluate their potential as a novel tracer of sulfide weathering in source areas. The shale-normalized REE concentrations mostly showed strong mid-REE enrichment patterns over the entire period, characterized by a concavity index (CI) greater than 2.5. Such a high CI value distinctly deviates from typical measurements in authigenic phases of global marine/river sediments (1.0 < CI < 2.5) and exclusively occurs in acid mine drainage, minesoil leachates, or some authigenic river sediments known to be affected by intense sulfide weathering. In this context, we argue that the pronounced mid-REE enrichments with CI > 2.5 observed in northern Svalbard have resulted from prevailing sulfide oxidation linked to glacial weathering. This finding underscores a new approach of REE signatures in the authigenic phases of marine sediments for the past reconstruction of sulfide weathering over the geological time scale.

How to cite: Jang, K., Bayon, G., Pourret, O., Joe, Y. J., Kim, J.-H., Byun, E., Forwick, M., León, R., and Nam, S.-I.: Tracing glacial weathering and pyrite oxidation using rare earth elements in sedimentary iron oxides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14192, https://doi.org/10.5194/egusphere-egu24-14192, 2024.

Six gravity cores (GC) and four sea-floor drill rig (MeBo) cores from water depths of ~1800–1400 m have been successfully collected off the outer Disko Bay fan in eastern Central Baffin Bay during the research expedition MSM111 in 2022. These sediment cores provide an up to 125 m long (MeBo 14, 20 and 23) record potentially reflecting the late- and mid-Pleistocene dynamics of the Western Greenland ice sheet. Besides the presence of a few turbiditic sequences a continuous sedimentation is well supported by the parasound seismostratigraphy as well as by lithostratigraphic log correlation based on X-ray Fluorescence (XRF) and magnetic susceptibility (MS). Establishing a chronostratigraphy of the Baffin Bay glaciomarine sediments is, however, challenging as e.g., carbonate dissolution impedes reliable foraminiferal δ¹⁸O stratigraphy.

Here, we present our preliminary chronostratigraphic framework established by combining three stratigraphic tools: radiocarbon ages, relative paleointensity (RPI), and characteristic basin-wide detrital carbonate layers (BBDCs). BBDCs represent periods of elevated terrigenous deposition in response to increased meltwater discharge that can be well identified by XRF Ca/Ti. The GC 12&22 and MeBo 14&20 cores contain rhythmic alterations between sandy-rich detrital carbonate layers and clayish layers, which are clearly represented by Ca/Ti and MS data. Intriguingly, these cyclic alterations also display significant correlation with marine isotope stages (MIS), where higher Ca/Ti and MS values correspond to warmer periods. We thus estimated that our 125-m composite core lasts until MIS 16 or ~700 ka. This long duration is also partly supported by our RPI data from MeBo 20&23. Nevertheless, two major difficulties were encountered: (1) RPI data of GC 24&21 do not reveal an unambiguous match with global RPI reference stacks and/or regionally established RPI records, probably due to condensed sedimentation of these two deeper gravity cores; and (2) recurring BBDCs of the studied cores can be interpreted as high-frequency events reflecting the intrinsic dynamics of the North American Arctic-ice sheet complex, or, alternatively as glacial-interglacial cycles. In order to solve the current chronostratigraphy controversy between a Late Pleistocene age or of deeper mid-Pleistocene age, further carbon-14 ages from the condensed GC24 and collect RPI data from the more expanded MeBo 14 will be obtained.

How to cite: Zhang, Y., Faust, J., Römer-Stange, N., von Dobeneck, T., and Kucera, M.: Chronostratigraphy of glaciomarine sediments off the West Greenland Shelf: a key to the understanding of the Quaternary evolution of the Greenland ice sheet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4326, https://doi.org/10.5194/egusphere-egu24-4326, 2024.

Heinrich events are characterised by the collapse of ice-sheets surrounding the North Atlantic, with Hudson Strait suggested as the prominent source region. Cryosphere-ocean interactions during stadial periods of the last glacial interval have been proposed as a potential trigger for ice-sheet collapse. Extensive sea-ice cover in the Labrador Sea, in combination with a reduced overturning circulation in the North Atlantic, might have caused the build-up of a subsurface heat reservoir by preventing the release and downward mixing of heat in the water column. Increased subsurface heat then caused/supported the destabilisation of the Laurentide ice sheet.

We present high-resolution records of sea-ice and subsurface temperatures in the outer Labrador Sea at IODP Site U1302/03 between 30 and 60 ka. The sea-ice record suggests that an extensive sea-ice cover established in the outer Labrador Sea around 0.8-0.9 kyr prior to the arrival of ice-rafted debris associated with Heinrich events. Subsurface temperatures also increase prior to the onset of Heinrich events, although the exact timing needs to be confirmed. As such, the sea-ice and subsurface temperatures support cryosphere-ocean interactions prior to the onset of Heinrich events.

How to cite: Detlef, H., Mørk Jensen, M., Andreasen, R., Glasius, M., Seidenkrantz, M.-S., and Pearce, C.: Sea-ice and subsurface temperatures in the outer Labrador Sea across four Heinrich events during MIS 3, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14848, https://doi.org/10.5194/egusphere-egu24-14848, 2024.

Deep-sea sediment cores from the Arctic Ocean are excellent archives suitable for the reconstruction of deglacial events on circum-Arctic continents and the associated enhanced export of freshwater to the North Atlantic. Here we present new records from a long large-volume sediment core obtained on the NE Greenland continental margin at 81.2°N where the shelf is particularly narrow. The site is perfectly located to monitor the export of freshwater and ice from the Arctic Ocean to the Greenland Sea using data on ice-rafted debris (IRD) and the stable isotope composition of planktic and benthic foraminifers in the sediments. The records from our new core hold evidence of a number of strong freshwater export events in the last 200 ka. Several events correlate in time with extreme discharges from large lakes which had developed south of the ice sheets on northern Eurasian shelves in MIS 6, 5b and 4. Using published data from the Greenland Sea and the North Atlantic, we can show that freshening events in the Arctic and the Nordic Seas correlate with weakenings of the Atlantic meridional overturning circulation (AMOC). We propose that enhanced Arctic Ocean freshwater export triggered (or contributed to) decreased deepwater renewal in the Greenland Sea and had severe consequences for the strength of the global ocean circulation.

In addition to the Arctic Ocean freshwater events our new records reveal a number of probably minor events of iceberg melting and intermediate water freshening which we associate with the history of continental ice on North Greenland and in particular in the Wandel Sea. We propose that the repeated ice expansion and retreat in this area released dense plumes of fine-grained sediment and low d18O-water which spread along the continental slope. This may have happened in MIS 6, 5d, and 4. For the last 50 ka, our records suggest an ice retreat on North Greenland at 50-40 ka and a stepwise readvance of the ice front at 35-25 ka.

How to cite: Spielhagen, R. F., Zehnich, M., Bauch, H. A., and Kuhnert, H.: Arctic Ocean freshwater export events and possible linkages with AMOC weakenings in the last 200 ka, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8688, https://doi.org/10.5194/egusphere-egu24-8688, 2024.

Marine sediments provide invaluable records of past climate variations. However, dating these sediments with classical dating methods is challenging in the Arctic Ocean because of the lack of foraminifera, their poor preservation, and the extremely low sedimentation rates. Yet, understanding the history of the Arctic Ocean is of great importance for assessing its potential response to the current fast warming of these high latitudes.

Recently, Geibert et al. (2021) proposed that during some glacial periods, the Arctic Ocean might have been filled with freshwater. This hypothesis, which has potentially far-reaching implications, can explain intervals of low ²³⁰Th-excess and low ¹⁰Be concentration in Arctic sediments but is strongly debated (Spielhagen et al., 2022; Hillaire-Marcel et al., 2022). This hypothesis posits that during these freshwater intervals, primary input fluxes originated from Arctic rivers rather than the North Atlantic.

To test this theory, we assess the ¹⁰Be/⁹Be ratio in sediments that correspond to the freshwater intervals. Since the ¹⁰Be/⁹Be ratio differs systematically between North Atlantic and riverine waters, this proxy used as a water mass tracer can give novel insights into the Quaternary history of the Arctic Ocean. We discuss our results in the light of the hypothesis by Geibert et al. and evaluate the use of ¹⁰Be/⁹Be as a dating and correlation tool of Arctic Ocean sediments contributing to the ongoing chronostratigraphic investigations in the Arctic Ocean.

Geibert, Walter, et al. "Glacial episodes of a freshwater Arctic Ocean covered by a thick ice shelf." Nature 590.7844 (2021): 97-102.

Spielhagen, Robert F., et al. "No freshwater-filled glacial Arctic Ocean." Nature 602.7895 (2022): E1-E3.

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How to cite: Ollive, A., Adolphi, F., Geibert, W., Matthiessen, J., Lachner, J., and Stübner, K.: 10Be/9Be in Arctic Ocean Sediments: Another clue towards a fresh Arctic hypothesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5768, https://doi.org/10.5194/egusphere-egu24-5768, 2024.

The excess freshwater in the Arctic due to global warming is causing a weakening the Atlantic Meridional Overturning Circulation (AMOC). The question of how the climate change will impact the stability of the AMOC, however, remains unclear. We address this uncertainty through a series of ensemble simulations (100 members) using freshwater hysteresis experiments, aiming to elucidate potential changes in AMOC stability across different interglacials. Our findings suggest that future increases in anthropogenic CO₂ emissions will bolster the AMOC's resistance to excess freshwater, though it exhibits less resilience compared to past interglacials. In future climate scenarios, warmer conditions lead to a notable delay in sea ice expansion, which aids in the preservation of deep water formation and AMOC strength. Concurrently, an intensification of freshwater convergence in the North Atlantic acts as a dampening factor during AMOC recovery under warmer climate background. The influence of orbital parameters on AMOC stability across different interglacials is found to be relatively minor. These results underscore the importance of considering background climate conditions, particularly CO₂ concentrations, when investigating future AMOC changes and making comparisons to past AMOC dynamics.

How to cite: Liu, W., Shi, F., Zhang, X., and Yin, Q.: Different AMOC Stabilization between Past Interglacials and Future, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3767, https://doi.org/10.5194/egusphere-egu24-3767, 2024.