The Arctic Ocean differs from other oceans globally in several ways. Stratification is largely determined by changes in salinity, with cooler fresher water overlying warmer (intruding) saltier water. Until very recently the ocean was largely isolated from the atmosphere by sea ice restricting exchange of heat and momentum across the sea surface. As much of the Arctic Ocean lies poleward of the critical latitude for the dominant tidal forcing, preventing the formation of freely propagating internal tides, the major pathway of tidal energy to ocean mixing. As such mixing between layers in the Arctic Ocean is weak.
An analogy is often drawn between the circulation in the Arctic Ocean and that in an estuary. Lateral gradients in density drive exchange through Arctic gateways with the exchange flow mediated by vertical mixing within the Arctic Ocean. Here we examine the potential impact of the recent decline sea ice extent on both the vertical mixing and the import of heat and export of freshwater through the Arctic gateways.
How to cite: Rippeth, T. P.: Arctic Ocean: mixing and exchange in a changing ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21110, https://doi.org/10.5194/egusphere-egu25-21110, 2025.
Ocean flows interacting with topography are critical for shaping large-scale circulation in polar regions such as the Arctic Ocean, where strong topographic steering shapes flow along continental slopes. Flow over sloping topography with corrugations exhibits an asymmetric response to prograde versus retrograde forcing, with stronger and more laminar flows in the prograde case (here, prograde forcing aligns with topographic wave propagation, while retrograde forcing opposes it). Previous studies attribute this asymmetry to increased topographic form stress for retrograde forcing. To further investigate these dynamics, we analyze flow responses to time-variable forcing over corrugated slopes using momentum budgets along depth-following contours. In this framework, the topographic form stress term vanishes, and vorticity fluxes across depth-contours emerge as the dominant mechanism driving asymmetries.
Preliminary results from idealized shallow water simulations reveal distinct nonlinear flow behaviors. For shorter forcing periods, the flow exhibits a cyclonic shift consistent with the "Neptune effect." For longer forcing periods, retrograde flow strength saturates, plateauing even as forcing increases. These findings build on our previous analysis of a realistic Arctic Ocean simulation, which indicated that these nonlinear effects leave an imprint on large-scale circulation. Together, they suggest that mesoscale topography-flow interactions modulate large-scale circulation and contribute to temporal variability in polar oceans under changing forcing conditions.
How to cite: Sjur, A. L. P. and Isachsen, P.-E.: Flow asymmetry over varying topography: Implications for large-scale circulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10178, https://doi.org/10.5194/egusphere-egu25-10178, 2025.
Global climate change is particularly pronounced in the Arctic regions, widely recognized as a "climatic hotspot" by the scientific community. This phenomenon, known as Arctic amplification refers to the accelerated increase in Arctic surface temperature compared to the global average. This process drives the ongoing loss of Arctic sea-ice volume and intensifies the ice-albedo feedback mechanism. Key physical drivers include the increased intrusion of warm Atlantic Water into the Arctic Ocean, which profoundly impacts biogeochemical cycles. Over the past decades, the CNR-ISP has developed marine and atmospheric observatories in the Svalbard region. These include three moorings (MDI, KIM, MAP) measuring biogeochemical parameters along the water column in the Kongsfjorden-Krossfjorden fjord system, and the land-based platform, the Amundsen-Nobile Climate Change Tower (CCT), measuring atmospheric parameters. As part of the ITINERIS PNRR project, the moorings were equipped with advanced biogeochemical sensors capable of monitoring Essential Ocean Variables, enablingthe study of seasonal and annual dynamics of suspended marine particles and nutrients. Between 2022 and 2024, contrasting environmental conditions shaped the dynamics of particulate matter and nutrients. One striking difference between the two years was the intrusion of Atlantic water observed at the end of summer in 2023 which extended to the inner Kongfjorden. Additionally, the timing of the spring phytoplankton bloom between 2023 and 2024 shifted, and also the terrestrial input from summer glacier melting exhibited significant variability. The spring phytoplankton bloom begins when PAR increases after the polar night nutrient concentrations are high due to autumn replenishment and winter water convection, and the influence of Atlantic Water on nitrate replenishment rates is evident. The timing of the spring bloom results from a complex interplay of atmospheric and marine factors. In the inner part of the Kongsfjorden, suspended matter concentrations are primary driven by glacial meltwater inputs, which contributes to low-salinity surface waters within the fjord. These findings underscore the intricate relationships between environmental changes, particle dynamics, and nutrient cycling in Svalbard.
How to cite: Paladini de Mendoza, F., Miserocchi, S., Giordano, P., Giglio, F., Mazzola, M., and Langone, L.: Seasonal particle dynamics in Kongsfjorden during two years of contrasting environmental conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19282, https://doi.org/10.5194/egusphere-egu25-19282, 2025.
The Arctic total sea ice extent has rapidly declined since the beginning of satellite observations. This decline materialized into record sea ice lows in the summers of 2007 and 2012. Those sea ice lows exhibit an important spatial heterogeneity and are likely caused by different dynamic and thermodynamic drivers of atmospheric and oceanic origins. Using the global ocean–sea ice model NEMO4.2-SI3 in the same setup but at three different horizontal resolutions (namely, 1/12°, 1/4° and 1°), we thoroughly examine the most extreme sea ice states simulated in summer by the model from a mass balance perspective. This method allows to disentangle the dominating mechanisms leading to the sea ice lows, such as dynamic redistribution and compression of sea ice in 2007, or preconditioning and excess basal melt in 2012. It also highlights the importance of processes at the ice-ocean interface to drive the evolution of sea ice at all considered temporal scales. We then compare how increased spatial resolution, allowing for the simulation of finer-scale physical processes such as ocean eddies, impacts the modelled sea ice thickness and concentration distribution, as well as the different ice mass fluxes. A particular attention is being paid to the influence of ocean heat content anomalies, as increased horizontal resolution provides a more realistic simulation of heat inflow in the Beaufort Gyre through subsurface eddies of Pacific origin. This study highlights the benefits of increased spatial resolution for realistically simulating the Arctic sea ice cover and weighs them with the associated computational cost. The decomposition of the ice mass budget into its different thermodynamic and dynamic terms puts forward the often downplayed role of the ocean in determining the interannual variability of Arctic sea ice and provides a stepping stone for further studies.
How to cite: Richaud, B., Massonnet, F., Fichefet, T., Topal, D., Barthélemy, A., and Docquier, D.: Does increased spatial resolution improve the simulation of Arctic sea ice lows in NEMO4.2-SI3?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6518, https://doi.org/10.5194/egusphere-egu25-6518, 2025.
The polar oceans, the high-latitude Earth systems, and the Earth climate system as a whole are strongly affected by the Antarctic and Greenland ice sheets. The recent developments of global climate models have allowed to accounting for the effects of the ice sheets either indirectly via parameterizations of freshwater fluxes, or via infrequent coupling between stand-alone ice sheet models and other climate models' components. The latter approach typically does not conserve mass across the model comonents. In order to address these issues, we have developed a global ocean-cryosphere model iOM that includes synchronously coupled Antarctic and Greenland ice sheets in addition to sea ice and icebergs. The results of global simulations forced by the EAR-Interim reanalysis show strong seasonal and subseasonal variability in the ice-sheet/ocean interactons, demonstrating the importance of a tight synchronous coupling between the ice sheet and the ocean model components. iOM will allow us to explore interactions and feedbacks between the polar oceans and cryosphere on the subseasonal to decadal timescales.
How to cite: Sergienko, O., Huth, A., Harrison, M., and Schlegel, N.: Impacts of synchronously coupled dynamic ice sheets in the GFDL Global Ocean Cryosphere Model iOM, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3788, https://doi.org/10.5194/egusphere-egu25-3788, 2025.
Numerical model simulations are an essential tool for assessing effects of global warming on the climate system in future greenhouse gas concentration scenarios. Commonly, these simulations cover only the next few centuries or use low-complexity models for longer periods. However, to assess the dynamics of Earth system components with long response times like the ocean or ice sheets, multi-millennial simulations with comprehensive Earth system models are essential.
Here, we present multi-millennial simulations with the complex Earth System Model AWIESM, covering an integration time beyond the typical CMIP time scale. The model runs on a multi-resolution grid with a horizontal resolution of up to 20 km in high latitudes. The model includes an interactive ice sheet for the Greenland domain. The simulations are forced with transient greenhouse gas concentrations obtained from model simulations with the Earth System Model of intermediate complexity CLIMBER-X with an interactive carbon cycle, covering overshoot scenarios that enable assessment of long-term ice sheet and ocean dynamics.
Our results reveal a scenario-dependent weakening of the Atlantic Meridional Overturning Circulation (AMOC), followed by partial recovery over the next millennium. All scenarios show sea ice-free or nearly sea ice-free summer conditions in the northern and southern hemispheres. Winter sea ice shows an asymmetric response under future warming. While Arctic winter sea ice changes are small in low- to medium-emission scenarios, Southern Ocean winter sea ice shows a large reduction even in low-emission scenarios. The Greenland ice sheet shows a continuing ice mass loss during the next millennium, even with decreasing greenhouse gas concentrations in medium-emission scenarios. The main area of ice loss is West Greenland.
These findings underscore the importance of long-term simulations with comprehensive Earth system models to understand the complex, delayed responses of key climate system components and their broader implications for the Earth system.
How to cite: Ackermann, L., Knorr, G., Willeit, M., and Lohmann, G.: Multi-millennial future warming scenarios with the comprehensive Earth system model AWIESM, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15910, https://doi.org/10.5194/egusphere-egu25-15910, 2025.
Atlantification is a major phenomenon associated with rapid changes in the Arctic Ocean, including anomalous sea-ice loss, warming and salinification of the near-surface, enhanced mixing and changes in the ecosystem structure. Despite anomalous transport of Atlantic water in the Barents Sea/Fram Strait region is among the recognized causes of Atlantification, this phenomenon remains poorly characterized in the context of the historical (1850-present) period, hence far from being fully understood.
In this contribution, we illustrate recent progress of the Italian funded project “ATTRACTION: Atlantification dRiven by polAr-subpolar ConnecTIONs in a changing climate” that aims at providing a historical perspective on Atlantification by integrating observational evidence over the last decades, paleo-reconstructions and numerical climate simulations. We show results from a multi-model ensemble of historical climate simulations contributing to CMIP6 and depict robust traits of the simulated Atlantification across models and realizations toward fingerprinting the phenomenon at the gateway of the Arctic Ocean and toward a robust definition of an index for its quantitative characterization.
How to cite: Zanchettin, D., De Rovere, F., and Rubino, A.: Atlantification in a multi-model ensemble of historical climate simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3623, https://doi.org/10.5194/egusphere-egu25-3623, 2025.
Reconstructing climate patterns from the Common Era is necessary for placing modern human-driven climate changes within the context of natural climatic variations. This is particularly relevant for the Arctic, which is warming faster than any other. This global trend is tied to rapid sea ice loss and the increasing influx of Atlantic waters into the Arctic basin, a phenomenon called "Atlantification". In this context, we reconstruct the last centuries paleoenvironmental changes in the Arctic region from sediment cores strategically located along the Barents Sea (HH1141, 74.015°N 21.071°E, -285 m; HH1181, 74.081°N 21.362°E, -298 m water depth; HH969, 76.765°N 35.831°E, -174 m water depth), and on the northern margin of the Svalbard Archipelago (KH21-234-04 (80.3531ºN 16.308ºE, -394 m water depth), based on geochronological and geochemical analyses, benthic foraminiferal data and organic biomarkers. The Age-depth are based on excess 210Pb, and are extrapolated down-core, assuming stable sediment accumulation rates (SAR) before the 20th century. The results allow us to identify two main oceanographic intervals. Pre-1900 ys CE, the dominance of Elphidium clavatum, Cassidulina reniforme, Islandiella helenae, Islandiella norcrossi, Stainforthia feylingi, Stainforthia loeblechi, together with a high concentration of biomarker (spring sea ice biomarker IP25, and alkenones), indicate cold conditions. The second interval, corresponding to the 20th century, is characterized by the presence of Adercotryma glomeratum, Trifarina angulosa, Nonionellina labradorica, Globobulimina auriculata, Melonis barleanus, Buccella frigida, documenting warm water mass inflow related to the expand incursion of Atlantic waters. Moreover, biomarker analyses provide further details of the paleoceanographic conditions showing less seasonal sea ice influence in the region and the intrusion of Atlantic waters within the Arctic domain. This work sets another milestone in our understanding of the “Atlantification” process that is crucial to forecasting the environmental changes in this region that are susceptible to heat transport through the Atlantic gateways, which affects climate and ecosystems.
How to cite: Boretto, G. M., Tesi, T., Panieri, G., Simon, M. H., Sabino, M., Nogarotto, A., De Schepper, S., Weiner, A., Hefter, J., Giuliani, S., Langone, L., Mollenhauer, G., Belt, S., and Capotondi, L.: Atlantification at the Arctic Gateway: Past and Present Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9378, https://doi.org/10.5194/egusphere-egu25-9378, 2025.
The aragonite skeletons of cold-water corals (CWCs) offer critical insights into the physico-chemical changes and dynamics of intermediate-depth water masses at high temporal resolution (e.g. sub-decadal). Previous studies have shown that variations in seawater temperature, water ventilation age, and water mass provenance can be reconstructed from measurements of skeletal Li/Mg ratios, paired U/Th and 14C, and neodymium isotopes, respectively. Notably, the solitary azooxanthellate scleractinian coral species Desmophyllum dianthus is particularly valuable due to its broad distribution, century-long lifespan, and layered skeletal growth, which facilitates the use of geochemical tracers at sub-decadal intervals.
In this study, we analysed several Desmophyllum dianthus samples collected in 2012 from the Northern Iceland Basin at depths of 570-700 m during the ICE-CTD R/V Thalassa expedition, using the Remotely Operated Vehicle Victor 6000 operated by IFREMER. Sub-samples of the coral skeletons collected along the growth axis were analysed for Li/Mg, stable isotopes (δ11B, δ18O, δ13C), U/Th, 14C and Nd isotopes, with the aim to reconstruct the physico-chemical changes of the North Atlantic intermediate water masses, specifically the Iceland-Scotland Overflow Water, Sub-Arctic Intermediate Water and Western North Atlantic Central Water, and assess how their contributions have shifted over recent decades. The Li/Mg ratios provided sub-decadal temperature records, showing variations between ~2 to ~6 °C, closely linked to changes in Nd isotopic compositions. These findings can be explained by decadal fluctuations in the North Atlantic Oscillation and East Atlantic atmospheric patterns, which influence the strength of the Atlantic Subpolar Gyre, leading to changes in the amount of warmer Subtropical Gyre-sourced water or colder Subpolar Gyre-sourced water. Additionally, our results suggest a significant reduction, by about half over the past ~70 years, of the ISOW, pointing to an increased northward transport of warm subtropical waters in recent decades. This shift may have contributed to the recent warming in the Arctic region and a notable multi-decadal weaking of the Nordic Sea overflow currents.
How to cite: Montagna, P., Brocker, K., Border, E., Rigo, M., Ragnarsson, S. Á., Valdimarsson, H., Ólafsdóttir, S. H., Therre, S., Fohlmeister, J., Trotter, J., McCulloch, M., Lausecker, M., Blaser, P., Reverdin, G., Colin, C., and Frank, N.: Seawater temperature and water mass provenance changes over the last century in the North Atlantic Ocean reconstructed from cold-water coral geochemistry , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8884, https://doi.org/10.5194/egusphere-egu25-8884, 2025.
We analyzed ostracode and foraminifera assemblages, silicoflagellates, biogenic silica, and sediment grain size from two high-resolution box cores collected in the Alaska and Canadian Beaufort Sea during the 2022 Arctic Challenge for Sustainability (ArCSII) expedition. These cores provide biennial-scale, multi-proxy records of ecological change over the past ~70 years. At BC2, located east of Barrow Canyon, faunal assemblages over the last 41 years showed three distinct ecological periods: (1) the 1980s-1990s, dominated by species indicative of stable, ice-covered conditions; (2) a shift post-2000 with warmer temperatures, longer ice-free seasons, and increased sandy sediments; and (3) a recent period (2018–2022) characterized by subarctic and Pacific-affiliated species, reflecting productive, summer ice-free waters. Similarly, at MT1 near the Mackenzie Trough, three periods were identified: (1) cold, stable conditions with high sea-ice cover (1950-1980); (2) a transition in the 1990s marked by increased productivity and longer ice-free periods; and (3) a shift (2002–2022) toward more dynamic, productive conditions, with reduced sea-ice extent and increasing Mackenzie River discharge. The faunal transitions among ostracodes, foraminifera, and silicoflagellates correspond closely with changes in ocean conditions, providing key insights into the timing of ecological responses to anthropogenic climate change. By integrating instrumental data—such as temperature, sea-ice extent, and river discharge—with the biological proxy records, we constrained the timing of when these environmental shifts began affecting biological organisms. This analysis revealed that changes in faunal composition are tightly linked to warming, sea-ice loss, and altered freshwater inputs, and underscores the complex, cascading impacts of climate change on Arctic ecosystems. These ecological shifts are also influenced by large-scale ocean-atmosphere dynamics, such as the Pacific Decadal Oscillation, which further modulate the timing and magnitude of ecological responses in the Beaufort Sea ecosystem.
How to cite: Gemery, L., Szarek, R., Suzuki, K., Addison, J., Caissie, B., Joe, Y. J., Seike, K., Yamada, K., Onodera, J., Itoh, M., and Yamamoto, M.: Ecological response to anthropogenic climate change in the Beaufort Sea: Biennial-scale evidence from proxy and instrumental records during the last ~70 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2347, https://doi.org/10.5194/egusphere-egu25-2347, 2025.
Decreasing sea-ice extent and retreating and thinning of Greenland’s glaciers are rapidly changing Arctic coastal environments by warming and freshening the sea surface and impacting light availability. In Arctic fjords, productivity is significantly influenced by the position of glacier termini, and the present retreat of the Greenland Ice Sheet will increase the number of fjords surrounded only by land-terminating glaciers in the future. This will most likely affect the productivity and ecosystem structure of coastal marine areas. To predict future cryosphere change and its impacts, it is essential to understand climate and ecosystem variability beyond the instrumental era.
Here we present a high-resolution reconstruction of coastal marine ecosystem change and its linkages to terrestrial freshwater and organic matter inputs in Young Sound fjord, Northeast Greenland, over the Holocene. The reconstructions are based on marine sediment-core proxies: organic-walled palynomorphs (including e.g. dinoflagellate cysts and pollen), sympagic and pelagic biomarkers (highly branched isoprenoids and sterols) and a set of geochemical indicators (sediment organic carbon, nitrogen, their stable isotopes, and biogenic silica). The results suggest a relatively cold early Holocene with extensive sea-ice cover and low productivity. Warmer and more variable conditions take hold after approximately 9 kyr with increasing productivity, species richness and terrestrial freshwater inputs, with colder conditions seen after approximately 3.5 kyr with high productivity coupled with higher ice-algae contribution. The results also indicate that this near-shore marine ecosystem is clearly influenced by local forcings, such as terrestrial freshwater and organic matter inputs, suggesting that the continuous melting of the Greenland Ice Sheet will affect marine productivity and ecosystem structure in Greenland’s fjord systems, with potential impacts on biodiversity and sustainability of fisheries.
How to cite: Mäkelä, M., Ribeiro, S., Pearce, C., Detlef, H., Salonen, J. S., Seidenkrantz, M.-S., and Heikkilä, M.: Marine ecosystem changes linked to climate and terrestrial freshwater inputs in a Northeast Greenland fjord over the Holocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17764, https://doi.org/10.5194/egusphere-egu25-17764, 2025.
Differences in salt content of North Atlantic surface waters drive variations in Nordic Seas' overturning circulation. These form a switchboard for changes in the oceanic heat transport to North European high latitudes, the 'Nordic Heat Pump', and for Atlantic Meridional Overturning Circulation (AMOC). We deduced changes in the Nordic Seas' overturning circulation during peak last glacial and early deglacial times (22-15 cal. ka) from two marine sediment cores with centennial-scale age resolution synchronized via radiocarbon (14C) plateau tuning. Sediment data suggest that the salinity of surface waters, advected through the Denmark Strait from the northwesternmost Atlantic, started to drop significantly near 18.4 cal. ka. This accompanied precisely an abrupt rise in bottom water temperature by up to 3.5°C and a drop in both ventilation and 14C ventilation ages of Denmark Strait overflow waters feeding the AMOC. Moreover, it paralleled a change in (detrital) Pb and Nd radiogenic isotopes suggesting that overflow waters then started to have their dominant source in the North Iceland Jet of upper North Atlantic Intermediate Water that overflows the shallow basaltic Iceland-Scotland Ridge east of Iceland. Off Norway, the salinity reduction north of Iceland went along with a fast rise in the 14C reservoir age of surface waters from ~600–1200 years up to ~2000 years and an abrupt breakdown of Nordic Seas' convection of young deep waters. Accordingly, warm Atlantic waters were replaced by slightly cooler Arctic polar waters aged like those of the East Greenland Current, inducing a breakdown of the 'Nordic Heat Pump' and start of 'Heinrich Stadial 1' as reflected by a precisely coeval cooling documented on top of the Greenland ice sheet, lasting until ~15 cal. ka. The outlined circulation changes starting near 18.4 cal. ka remind us of potential implications of the meltwater flow from West Greenland strongly enhanced today.
How to cite: Sarnthein, M. and Blaser, P.: Meltwater-induced salinity drop in Greenland Sea induced changes in AMOC and the onset of Heinrich-1 stadial 18 400 years ago – Potential analog to modern trends, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3821, https://doi.org/10.5194/egusphere-egu25-3821, 2025.
We present planktic foraminiferal and planktic stable isotope records from central and eastern Arctic Ocean sediment cores with a particular attention on the development of the structure of upper water masses during two past interglacials (here termed IG3 and IG2), in comparison to the present Holocene (IG1). The age of interglacials IG2 and IG3 is currently under discussion. While the "classic" age model based on Jakobsson et al. (2000, Geology) would relate them to marine isotope (sub)stages (MIS) 5e and 5a, latest work (e.g., Song et al., 2023, Earth Sci. Rev.; Razmjooei et al., 2023, Quat. Sci. Rev.) would assign ages of MIS 11, 9, 7 or 5.
Stable oxygen and carbon isotopes from polar planktic foraminifers Neogloboquadrina pachyderma give clues on their habitat within the upper water column which today is characterized by an ice-covered low-saline cold surface layer, underlain by high-saline warm Atlantic Water. Sediments from IG2 and IG3 containing also subpolar planktic foraminifers Turborotalita quinqueloba show oxygen isotope values of close to modern ones, indicating a similar water mass structure as today, with a transition level between freshwater-rich and Atlantic Water. Carbon isotope values are lower and may point at a higher bioproductivity due to less sea ice and a decomposition of carbon in the upper waters. Interestingly, in the sediments underneath, which are barren in T. quinqueloba but contain abundant N. pachyderma, both oxygen and carbon isotopes are significantly higher. These data can be interpreted as evidence of a strongly stratified water column, a deeper habitat of the foraminifers, a strong subsurface advection of Atlantic Water and more sea ice during the early phases of IG2 and IG3. In cases, due to a lack of carbonate microfossils this interval is not represented in all analyzed cores. We assume that near-surface salinities were below the tolerance limit of planktic foraminifers in the very early parts of IG2 and IG3, probably due to a strong influence of meltwater from disintegrating ice sheets on northern Eurasia in the preceding glacial stages. Our results reveal a two-step development of conditions in the central Arctic during previous warm intervals. In the first part, the uppermost water column (including the habitat depth of T. quinqueloba) always had very low salinties due to freshwater discharge from ice sheets on the continents. Only in the second part Atlantic Water was shoaling and allowed the occupation by shallow-dwelling T. quinqueloba. Data from the Kara Sea continental margin suggest that upper water conditions in the eastern Arctic remained under strong freshwater influence, at least throughout IG2.
How to cite: Spielhagen, R. F., Bauch, H. A., and Mackensen, A.: Atlantic Water distribution in the central and eastern Arctic Ocean during past interglacials, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6159, https://doi.org/10.5194/egusphere-egu25-6159, 2025.
A rapidly warming climate with substantial polar amplification will lead the Arctic becoming ice free during summer. An Arctic that „turns blue“, i.e. that changes from a current Arctic Ocean covered by high-albedo sea ice to a future low-albedo ice free water surface, may occur as early as the 2050s even under low emissions scenarios (Kim et al., 2023). Absence of summer sea ice will further exacerbate Arctic warming and will have ramnifications from regional to global scale (Bruhwiler et al., 2021).
The study of past warm climate states with significantly reduced prevalence of Arctic sea ice enables an integrated proxy-data and climate modelling approach. This provides a valuable out-of-sample test for climate models from which future projections are derived and may help us to better understand processes and climate patterns related to a blue Arctic.
Based on the Last Interglacial (~127,000 years ago), a time when orbital parameters caused much increased boreal high-latitude insolation forcing in particular from boreal spring to boreal autumn, the fourth iteration of the Paleoclimate Modelling Intercomparison Project (PMIP4) identified in their simulation lig127k substantial model-spread of simulated minimum annual Arctic sea ice conditions (Kageyama et al., 2020; Sime et al., 2023). To enable a better understanding of the origin of model-model discord the paleoclimate science community has proposed simulation abrupt-127k (Sime et al., in prep.) as part of the FastTrack portfolio of the seventh interation of the Climate Modelling Intercomparison Project (CMIP7). While simulation abrupt-127k inherits orbital and greenhouse gas parameters of PMIP4 simulation lig127k, its layout follows the approach of CMIP simulation abrupt-4xCO2, where the initial scientific focus is on a comparably short period (~100 model years) after model initialisation rather than on the quasi-equilibrated climate as in PMIP4 simulation lig127.
With this presentation we will outline rationale and utility of CMIP7 FastTrack simulation abrupt-127k to a) increase the model ensemble from the classical PMIP to the wider CMIP framework; b) focus on processes and feedbacks that translate modified climate forcing into Arctic climate towards refining our understanding of the apparent model-model discord found in lig127k; c) enhance analysis of simulated sea ice conditions and dynamics based on the standardized protocol for sea-ice related climate model outputs by the Sea-Ice Model Intercomparison Project (SIMIP; Notz et al., 2016).
How to cite: Stepanek, C., Sime, L. C., Diamond, R., Brierley, C., Schroeder, D., Kageyama, M., and Malmierca-Vallet, I.: The CMIP7-PMIP FastTrack abrupt-127k simulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15665, https://doi.org/10.5194/egusphere-egu25-15665, 2025.
The Last Interglacial (LIG) period approximately 130,000 to 115,000 years ago, represents one of the warmest intervals in the past 800,000 years. Here we simulate water isotopes in precipitation in Antarctica and the Arctic during the LIG, using three isotope-enabled atmosphere-ocean coupled climate models: HadCM3, MPI-ESM-wiso, and GISS-E2.1. These models were run following the Paleoclimate Modelling Intercomparison Project, phase 4 (PMIP4) protocol for the LIG at 127ka (kilo-years ago), supplemented by a 3000-year Heinrich Stadial 11 (H11) experiment run with HadCM3. The long H11 simulation has meltwater from the Northern Hemisphere applied to the North Atlantic which causes large-scale changes in ocean circulation including cooling in the North Atlantic and Arctic and warming in the Southern and Global Ocean. We find that the standard 127ka simulations do not capture the observed Antarctic warming and sea ice reduction in the Southern Ocean and Antarctic regions, but they capture around half of the warming in the Arctic. The H11 simulations align better with observations: they capture 80% of the warming, sea ice loss, and δ18O changes for both Greenland and Antarctica. Decomposition of seasonal δ18O drivers highlights the dominant role of sea-ice retreat and associated changes in precipitation seasonality in influencing isotopic values in all simulations, alongside a small common response to orbital forcing. We use the H11 and multi-model 127k simulations together to infer LIG surface air temperature (SAT) changes based on ice core measurements. Coastal sites in Greenland and Antarctica appear to have experienced less warming compared with higher central regions. The peak inferred LIG Greenland SAT increase is +2.89 ± 1.32 K at the NEEM ice core site. This is less than half the previously inferred warming. Peak inferred LIG Antarctic SAT increases are +4.39 ± 1.45 K at EDC, dropping to +1.67 ± 3.67 K at TALDICE.
How to cite: Sime, L., Sivankutty, R., Malmierca-Vallet, I., Goursaud Oger, S., LeGrande, A., McClymont, E., de Boer, A., Cauquoin, A., and Werner, M.: More modest peak temperatures during the Last Interglacial for both Greenland (and Antarctica) suggested by multi-model isotope simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8902, https://doi.org/10.5194/egusphere-egu25-8902, 2025.
The setting of a consensual climate history of the Arctic Ocean spanning the last major climatic cycles is still unachieved despite recent converging views about the chronostratigraphy of marine archives from this ocean. Under both permanent and seasonally-opened sea-ice covers, sedimentary recordings present anomalies, ranging from hiatuses under thick ice-shelf covers, during glacials, to winnowed or mixed sequences generated by deep-density currents, under seasonally freezing sea-ice conditions during interglacials or interstadials. In opposition, short, early, or late-glacial events (e.g., continental ice surging and glacial lake drainage events) may have led to the deposition of relatively thick layers occasionally with reworked material. Accordingly, time interpolation between dated layers and within these layers is misleading, and lateral sediment advection leads mixed microfossils and biomarkers records, thus to biased paleoceanography/paleoclimate inferences. Interglacial as well as glacial sequences are subsequently poorly recorded. Along ridges, erosion of fine particles by sinking brines and deep density-driven current, with redeposition in sheltered/deeper sites, further results in the mixing of fossil populations. This process and its impact on paleoecological reconstructions are well-documented by 14C records spanning the Holocene-Marine Isotope Stage 3 interval. In several cores raised from central Arctic ridges, for example, a few centimeters of mixed Holocene and Marine Isotope Stage 3 assemblages illustrate this interval. Nonetheless, the positions of the last two interglacials in deep sedimentary cores may be set with some confidence based on the relative decay of sedimentary excesses in U-series isotopes (231Pa vs 230Th) and detrital feldspar grain OSL-ages. With the complementary support of paleomagnetic records, a tentative outline of the major late Quaternary glacial/interglacial events may be proposed, as illustrated here by records from the Chukchi Sea margin. In this area, high interglacial/interstadial sea-level intervals allowed Pacific Water influx through the shallow Bering Strait, as recorded by radiogenic Nd-isotope excursions and enhanced Si-fluxes (thus high primary productivity). High sea levels also resulted in the flooding of shelves, leading to high manganese fluxes in the deep basins. These provided a cyclostratigraphic tool for the correlation of records throughout the Arctic Ocean, as documented in several studies of the last decades.
How to cite: Hillaire-Marcel, C., de Vernal, A., and Song, T.: Inserting the Arctic Ocean into the global late Pleistocene climate/ocean system: The Graal Quest?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7420, https://doi.org/10.5194/egusphere-egu25-7420, 2025.
The Arctic is currently undergoing rapid warming, which in the near future is expected to result in summers with an ice-free Arctic Ocean interior, and winters having thinner, and more mobile ice. Changes in sea-ice cover will have profound impacts on Arctic oceanography, its marine ecosystem, and ultimately on our climate from regional to global scales. To better understand what will happen in a changing future, we must look into the past. Arctic marine sediments provide a range of proxies that provide valuable palaeoceanographic, and palaeoclimatic information, documenting changes to the cryosphere. Yet, a confident interpretation of palaeoceanographic, and palaeoclimatic changes across glacial cycles of the Pleistocene is still hampered by our inability to accurately date Arctic marine sediments.
Studies conducted by Jakobsson et al. in the early 2000s transformed age-model interpretations in the Arctic following the identification of the coccolithophore Gephyrocapsa huxleyi (formerly known as Emiliania huxleyi) in a sediment core from the Lomonosov Ridge. Although G. huxleyi evolved globally ca 290 ka during MIS 8 (300-243 ka), it is generally believed that this species first appeared in the Arctic Ocean during the last interglacial period (MIS 5, 71-130 ka). The biostratigraphic datum provided by the first appearance of this species has therefore been central to much palaeoceanographic research conducted in the Arctic. However, identifying nannofossils in Arctic Ocean sediments is non-trivial, as their mineral remains are often poorly preserved or entirely absent due to unfavorable taphonomic conditions. This has led to ambiguous age estimates, as revealed by a recent study by Razmjooei et al. (2023) revising the calcareous nannofossil biostratigraphy in the Arctic, indicating that previously inferred sub-stages of MIS 5 may actually represent full interglacial periods rather than interstadials.
Recent advances using sedimentary ancient DNA (sedaDNA) now permit genome-based approaches to identify calcareous photosynthetic algae in marine sediments. We hypothesize that the sedaDNA approach may provide a “palaeogenomic biostratigraphic” age control when the conventional fossil-based approach is not usable due to poorly preserved or absent fossil remains. Given its importance in Arctic biostratigraphy, and since this is the only coccolithophore with an existing reference genome, we focus on G. huxleyi. An initial pilot study analyzing 5 samples from one sediment core from the central Arctic Ocean has previously showed positive reads for G. huxleyi in sediment layers argued to be from the last interglacial (MIS 5). Expanding on this pilot-study, we conducted a high-resolution sampling, totaling 93 sedaDNA samples, of two additional cores from the central Arctic Ocean. By integrating metagenomics with fossil, and climate proxy data, we aim to more confidently place the first appearance of G. huxleyi in the biostratigraphic framework of Quaternary Arctic marine sediments.
How to cite: Ståhl, E., Linderholm, A., and O'Regan, M.: Exploring the use of sedaDNA to provide a palaeogenomic-based biostratigraphy in central Arctic Ocean sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17627, https://doi.org/10.5194/egusphere-egu25-17627, 2025.
The Arctic is changing: sea ice is retreating and the Greenland Ice Sheet is melting. The impact of a different Arctic realm has yet to fully unfold, and extensive impacts are expected on ocean currents, stratification, marine heat waves and ecosystems. I will study past warm periods during the Quaternary, Pliocene and Miocene with focus on the Arctic. Marine heatwaves (MHWs), defined as extreme ocean warming episodes, have strengthened over the past decades. High-resolution climate models improve understanding of MHWs under global warming, but such events in the future Arctic are currently overlooked. In a high-resolution climate model, we find Arctic MHWs intensify on orders of magnitude during the warming twenty-first century, following sea ice retreat. However, with little sea ice coverage, strong interannual variability emerges, which could surpass the amplitude of former intensification. Additionally, the intensification of MHWs is linked to a substantial increase in the rate of temperature anomaly change. Cenozoic climate changes have been associated with tectonic activity and fluctuations in atmospheric CO2 levels. To explore these dynamics, we present the Holocene, Last Interglacial, Miocene and Pliocene sensitivity experiments. These experiments incorporate variations in paleogeography, ocean gateway configurations, atmospheric CO2 concentrations, and a range of ocean vertical mixing.
Ackermann, L., C. Danek, P. Gierz, and G. Lohmann, 2020: AMOC recovery in a multi-centennial scenario using a coupled atmosphere-ocean-ice sheet model. Geophysical Research Letters, 47 (16), e2019GL086810, DOI:10.1029/2019GL086810
Contzen, J., Dickhaus, T., and Lohmann, G.: Variability and extremes: statistical validation of the Alfred Wegener Institute Earth System Model (AWI-ESM), Geosci. Model Dev., 15, 1803–1820, doi:10.5194/gmd-15-1803-2022, 2022.
Gou, R., K. Wolf, C. Hoppe, L. Wu, G. Lohmann, 2025: The changing nature of future Arctic marine heatwaves and its potential impacts on the ecosystem. Nature Climate Change, https://doi.org/10.1038/s41558-024-02224-7
Lohmann, G., M. Butzin, N. Eissner, X. Shi, C. Stepanek, 2020: Abrupt climate and weather changes across timescales. Paleoceanography and Paleoclimatology 35 (9), e2019PA003782, DOI:10.1029/2019PA003782
Lohmann, G., G. Knorr, A. Hossain, C. Stepanek, 2022: Effects of CO2 and Ocean Mixing on Miocene and Pliocene Temperature Gradients. Paleoceanography and Paleoclimatology 37, (2), e2020PA003953, doi:10.1029/2020PA003953
Lohmann, G., 2020: Temperatures from energy balance models: the effective heat capacity matters, Earth Syst. Dynam., 11, 1195–1208, doi:10.5194/esd-11-1195-2020.
Hossain, A., G. Knorr, W. Jokat, G. Lohmann, K. Hochmuth, P. Gierz, C. Stepanek, and K. Gohl, 2023: The Impact of Different Atmospheric CO2 Concentrations on Large Scale Miocene Temperature Signatures. Paleoceanography and Paleoclimatology, 38 (2), e2022PA004438. DOI:10.1029/2022PA004438
How to cite: Lohmann, G.: Warm climates in the Arctic: Lessons from the past and long-term future, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19394, https://doi.org/10.5194/egusphere-egu25-19394, 2025.
The greening of previously barren landscapes in the Arctic is one of the most relevant responses of terrestrial ecosystems to climate change. Analyses of satellite data (available since ~1980) have revealed a widespread tundra advance consistent with recent global warming, but the length of the time-series is insufficient to resolve the long-term variability and the precise timing of the greening onset. Here, we measured plant-derived biomarkers from an Arctic fjord sediment core as proxies for reconstructing past changes in tundra vegetation during the transition from the Little Ice Age to modern warming. Our findings revealed a rapid expansion of the tundra since the beginning of the twentieth century, largely coinciding with the decline of summer sea ice extent, glacier retreat, and Atlantification of the eastern Fram Strait. The greening trend inferred from biomarker analysis peaked significantly in the late 1990s, along with a shift in the tundra community towards a more mature successional stage. Most of these signals were consistent with the biomolecular fingerprints of vascular plant species that are more adapted to warmer conditions and have widely expanded in proglacial areas during recent decades. Our results suggest that the greening of Arctic fjords may have occurred earlier than previously thought, improving our mechanistic understanding of vegetation-climate-cryosphere interactions that will shape tundra vegetation under future warming projections.
How to cite: Ingrosso, G., Ceccarelli, C., Giglio, F., Giordano, P., Hefter, J., Langone, L., Miserocchi, S., Mollenhauer, G., Nogarotto, A., Sabino, M., and Tesi, T.: Sea Ice Decline and Glacier Retreat Drive Greening of Svalbard in the 20th Century, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13019, https://doi.org/10.5194/egusphere-egu25-13019, 2025.
The Arctic Ocean is projected to warm twice more than the global mean in a warming 21st century, contributed by an increased solar heat input due to sea ice decrease. Here we find more solar heat input into the Arctic Ocean in a higher-resolution climate model. This is due to the impacts of Arctic marine heatwaves (MHWs), known as episodes of extreme ocean warming. The explicit consideration of MHWs, which are stronger and more realistic in higher-resolution models, increases melting of sea ice and thus solar heat input, thereby reinforcing the long-term Arctic Ocean warming. A positive feedback is identified between stronger MHWs and larger Arctic Ocean warming. We emphasize that Arctic Ocean warming is underestimated by the current generation of climate models, which generally have a too low spatial resolution to resolve Arctic MHWs. We conclude that future eddy- and storm-resolving models will provide a new perspective on the Earth system's response to past and future climate and environmental extremes.
How to cite: Gou, R., Deng, Y., Cui, Y., Qi, S., Wang, S., Wu, L., and Lohmann, G.: Underestimated future Arctic Ocean warming due to unresolved marine heatwaves at low resolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1748, https://doi.org/10.5194/egusphere-egu25-1748, 2025.
Paleoceanographic records demonstrate linkages between the increasing Pacific water flux accompanying the postglacial submergence of the shallow (~ 50 m deep) Bering Strait and the progressive warming of the Western Arctic until ca. 4000 years BP (cf. de Vernal et al. Sci. Adv. 2024). The Pacific water flux also impacts the freshwater budget of the Arctic Ocean, which ultimately plays a role in the Arctic sea ice and freshwater export rate to the northern North Atlantic. Sea-level changes thus deserve special attention from an Arctic perspective as they can considerably modify the exchanges between the Pacific and Arctic oceans. Furthermore, sea level determines the status of the Arctic shelves, submerged or not, which in turn plays a role in sea-ice production, as well as in the latent heat from the Atlantic water mass flowing northward through Fram Strait and the Barents Sea. We hypothesize that the increased freshwater inflow from the Pacific into the Arctic and the enhanced sea ice formation rates resulting from the sea level rise have played a role in the large scale cooling trend of the eastern Arctic and subarctic North Atlantic that has marked the late Holocene.
How to cite: de Vernal, A. and Hillaire-Marcel, C.: Arctic gateways, sea level and climate changes in the subpolar North Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6192, https://doi.org/10.5194/egusphere-egu25-6192, 2025.
The Late Miocene (11.63 to 5.33 million years (Ma)) has drawn attention as a potential analogue for future anthropogenic warming. During this time the global climate was warmer than present, with atmospheric CO2 concentrations at or above current levels, covering the same range as the IPCC emission scenarios. Despite its relevance for future climate scenarios, terrestrial Arctic climate variability during the Late Miocene remains poorly understood, mainly due to the scarcity of continuous, absolutely-dated proxy records.
Here we present a multi-proxy climate record derived from radiometrically dated speleothems from two caves located in eastern North Greenland (80°N). Today these caves are situated at altitudes of 604 and 660 m above sea level, in an area characterised by continuous permafrost and an annual precipitation of ca. 200 mm. Speleothem deposition provides evidence for several episodes of warmer and more humid climate conditions during the Late Miocene compared to today. We utilized dual clumped isotope thermometry to quantify these temperature changes, providing the first continental temperature record for the eastern North Greenland during the Late Miocene.
How to cite: Koltai, G., Fiebig, J., Wang, J., Cheng, H., Spötl, C., Edwards, L. R., Friedrich, L., Donner, A., Meckler, A. N., Baker, J. L., and Moseley, G. E.: Dual clumped isotopes of speleothems: unveiling Late Miocene paleotemperatures for the High Arctic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8417, https://doi.org/10.5194/egusphere-egu25-8417, 2025.
The Batagay megaslump (67.58°N, 134.77°E) in East Siberia is the largest known retrogressive thaw slump on Earth. Its approximately 55 m high headwall exposes discontinuously ancient permafrost that dates back to at least 650 ka. The permafrost preserves several paleoclimate and paleoecological proxies with distinct seasonality, e.g., ground ice and pollen.
In this study, we constrain the cryostratigraphy and chronology of the exposed permafrost based on field observations, newly obtained post-infrared infrared stimulated luminescence ages and systematic radiocarbon dating of the upper part of the sequence. To obtain seasonal climate signals, we reconstructed temperatures and precipitation from pollen and analyzed the stable isotope composition of ice wedges and composite wedges as well as pore ice from all exposed stratigraphic units.
A strongly continental climate with strong seasonal contrasts is characteristic for this region throughout glacial and interglacial periods of the Quaternary. The Lower Ice Complex with large syngenetic ice wedges (3-7 m thick, dated MIS 17/16 to MIS 13/12) indicates rather moist, cold winters and variable summers. Above an erosional unconformity, the Lower Sand unit (≤20 m) is characterized by narrow composite (i.e. ice-sand) wedges and formed under cold and dry conditions during late MIS 7 and MIS 6. Substantial warming during the Last Interglacial, i.e., MIS 5e was accompanied by permafrost degradation and the development of taiga forest, as evidenced by a woody debris layer (≤3m). The formation of the overlying Upper Ice Complex (20-25 m thick, local Yedoma Ice Complex equivalent) with huge syngenetic ice wedges started already during MIS 5, probably in MIS 5d, and ended towards the end of MIS 3. A rather cold and dry MIS 4 was followed by the coldest but moist winters of the record and variable but warmer and dry summers in MIS 3. The Upper Sand unit (≤20 m, MIS 3-2) with narrow composite wedges represents a dry climate with less cold winters than in MIS 3 and relatively warm summers. Above an erosional unconformity, the Holocene cover (≤3m) reflects the warmest and rather dry climate of the entire record. The comprehensive permafrost record of the Batagay megaslump delineates Late Quaternary seasonality variability and provides thus far-reaching paleoclimate baseline data for the East Siberian terrestrial Arctic that deserves further proxy-based and model-based validation.
How to cite: Opel, T., Fuchs, M., Andreev, A., Kizyakov, A., Wetterich, S., Meyer, H., and Herzschuh, U.: Seasonal climate signals from ground ice and pollen since the Middle Pleistocene as recorded in the ancient permafrost exposed in the Batagay megaslump (East Siberia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13346, https://doi.org/10.5194/egusphere-egu25-13346, 2025.
Our group has carried out simulations of the Labrador Sea at 1/60th and shown that very-high resolution significantly improves the model solution. That resolution, by representing the mesoscale and part of the sub-mesoscale significantly improves the simulation of boundary current system, eddies and shelf-basin exchange, with the small-scale processes combining to also improve the large-scale circulation and overturning. Given such improvements for the Labrador Sea, we now examine modelling the entire Arctic Ocean and the subpolar North Atlantic Ocean north of 53N latitude. The configuration is named ARC60. The experiment also includes an iceberg module and tidal forcing.
Here we present some of our ongoing analysis using the two very high resolution configurations and how it changes the solution compared to lower resolution simulations. We explore questions related to water formation in the Labrador Sea and Greenland melt, behavior of the Labrador Current and the Deep Western Boundary Current. We also explore the impact of Greenland runoff on driving coastal seasonal features in Melville Bay. Finally we look at eddies and small scale processes in the Arctic Ocean and Beaufort Gyre.
How to cite: Myers, P. G., Pennelly, C., and Pouneh, H.: Modelling of the Arctic Ocean and Labrador Sea at 1/60th Degree, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13443, https://doi.org/10.5194/egusphere-egu25-13443, 2025.
The Arctic is changing: sea ice is retreating and the Greenland Ice Sheet is melting. The impact of a “bluer” and “greener” Arctic has yet to fully unfold, and extensive impacts are expected on ocean currents, stratification, marine heat waves and ecosystems.
Our poster introduces the newly funded ERC Synergy Grant “Into the Blue - Resolving Past Arctic Greenhouse Climates (i2B)”. In the coming 6 years, we will study past warm periods during the Quaternary, Pliocene and Miocene with a focus on the Arctic. We will (1) document ice sheet, sea ice, ocean, and ecosystem change by analysing existing and new data as well as model results, (2) understand ocean-cryosphere feedbacks, and (3) determine the impact of a warmer Arctic on climate, ecosystems and society.
How to cite: Langebroek, P. M., Esteves, M., Knies, J., Lohmann, G., De Schepper, S., Mueller, J., Winsborrow, M., Ezat, M., and team, I. T. B.: Introducing “Into the Blue”: a new ERC Synergy Grant resolving past Arctic warm climates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15556, https://doi.org/10.5194/egusphere-egu25-15556, 2025.
The authigenic 10Be/9Be ratio retrieved from marine sediments is a promising proxy for reconstructing Arctic paleoceanography, particularly the interplay of riverine and marine influences on the extensive continental shelves and in deep basins. This study investigates the spatial variability of authigenic 10Be/9Be ratios in surface sediments from the Kara and Laptev Seas, tracing its variations from river mouths to the open ocean. Calculated 10Be/9Be ratios of the water column are compared with measured ratios in surface sediments to identify controlling factors such as reversible scavenging, co-precipitation, and water mass mixing. Results confirm that authigenic 10Be/9Be records the different water masses, with low 10Be/9Be on the shelves and increasing 10Be/9Be towards the deep sea. However, while sediments on the continental shelves faithfully capture the riverine 10Be/9Be signature, offsets emerge in deeper basins due to incomplete reversible scavenging and/or coprecipitation leading to lower authigenic 10Be/9Be in deep sea sediments compared to the local water column. This study highlights the potential of 10Be/9Be as a geochemical proxy for Arctic watermass mixing while emphasizing the complexity of interacting sedimentary and oceanographic processes influencing authigenic 10Be/9Be in Arctic Ocean sediments.
How to cite: Ollive, A., Adolphi, F., Matthiessen, J., Geibert, W., Alscher, M., Stübner, K., and Lachner, J.: Spatial variability and controls on the authigenic 10Be/9Be ratio in Arctic shelves and deep ocean sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15904, https://doi.org/10.5194/egusphere-egu25-15904, 2025.
Observations and numerical models reveal that mesoscale eddies are ubiquitous in the Arctic Ocean. These eddies are thought to play an important role in particular in the transport of heat, salt and nutrients from the shelves to the deep basins, in the modulation of the sea ice cover, and in the dynamical equilibrium of the Beaufort gyre. However, the characteristics of these eddies are poorly documented.
Here, an eddy detection and tracking method is applied to the output of a high resolution (1/12°) regional model of the Arctic - North Atlantic over the period 1995-2020 to investigate mesoscale eddies in the Amerasian Basin. Over that period, about 6000 eddies per year and per depth level are found distributed about equally between cyclones and anticyclones. On average, these eddies last 7 days, travel 5 km and have a radius of 12.4 km, with strong regional and temporal disparities that exist within the eddy population studied. Down to 250 m (i.e. the second pycnocline), eddy characteristics show a strong asymmetry between the shelf and the central basin with more numerous and larger eddies that travels longer distances with the mean flow along the shelf break. In the top 70 m, the mean characteristics of detected eddies display a strong seasonality following that of the sea ice cover. Below the first pycnocline at 70 m, the number of eddies shows little seasonality but a transient increase in response to the recent acceleration of the gyre. Deeper, within the Atlantic Waters, eddies are generated everywhere across the basin and present little interannual variability.
Finally, this eddy census helps interpret some discrepancies found between previous studies that use different datasets and approaches to examine the eddy field in the Arctic. In particular, our analysis show that the anticyclone dominance within the Beaufort Gyre that arises from the analysis of eddies from the Ice Tethered Profilers is partly due a regional sampling bias.
How to cite: Planat, N., Dufour, C., Lique, C., Rieck, J., Talandier, C., and Tremblay, B.: Characteristics of ocean mesoscale vortices in the Amerasian Basin from a high resolution pan-Arctic model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17242, https://doi.org/10.5194/egusphere-egu25-17242, 2025.
The Late Quaternary chronostratigraphic framework of the Arctic Ocean remains contentious, hindering our understanding of Arctic paleoceanographic conditions and their influence on global climate change. Recent advances in microbiostratigraphy and amino acid racemization (AAR) dating challenge the high-sedimentation rate central Arctic scenario proposed nearly two decades ago. To address this issue, U-Th analyses were performed on a Lomonosov Ridge sediment core, ICE04, whose chronostratigraphy had previously been established using AMS14C dating, lithological and mineralogical correlations, and the identification of a paleomagnetic excursion.
The Th-230 excess (230Thxs) distribution and decay downcore suggest a revised age framework. Specifically, the previously identified marine isotope stage (MIS) 3 layer can be re-assigned to MIS 3 to 6, while the MIS 4/4-5d layer extends back to MIS 7. Additionally, the 234U/238U ratio record indicates active late diagenetic processes likely driven by organic carbon decomposition. These findings highlight several key points: 1) younger organic carbon may dissolve and reprecipitate downcore due to late diagenetic processes, limiting the reliability of 14C ages derived from bulk organic carbon; 2) lithological correlations used to construct Late Quaternary chronostratigraphy can introduce significant uncertainties and may be biased by the misinterpretation of other methods, such as 14C dating; 3) dolomite peaks are recommended as reliable markers for the site-to-site correlations as they are linked to the meltwater discharge from the NW margin of the Laurentide Ice Sheet; and 4) the 1-meter-thick interval exhibiting a negative geomagnetic polarity, previously attributed to the Matuyama Chron (~780 ka) or the Laschamp (~41 ka) and Mono Lake (~35 ka) excursions, is dated to MIS 4-5d using the 230Thxs method. The revised age addresses the complexity of paleomagnetic behavior in the Arctic and underscores the need for further investigation to resolve these discrepancies.
Using the 230Thxs method, we estimate a late Quaternary mean sedimentation rate of <2 cm/ka for core ICE04, significantly lower than the previously reported rate of >4 cm/ka. These findings align with the sediment-starved deep Arctic scenario proposed prior to the 2000s, further indicating that an effort must be conducted to account for all the available data.
How to cite: Song, T., Hillaire-Marcel, C., Liu, Y., Montero-Serrano, J.-C., St-Onge, G., de Vernal, A., and Liu, J.: Revisiting Late Quaternary chronostratigraphy of the Arctic Ocean using the 230Th excess method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20470, https://doi.org/10.5194/egusphere-egu25-20470, 2025.
Modeling results and proxy data both suggest that sea-ice conditions in the Arctic Ocean were less severe during the last interglacial (MIS 5e) compared to the present interglacial (MIS 1), but spatial variability of the sea-ice cover is still poorly constrained. In this study, variations in the intensity and composition of biogenic sedimentary structures (bioturbation and trace fossils) are used to address spatial differences in sea-ice distribution between the two interglacials. The presence or absence of trace fossils and bioturbated sediment have long been used to separate interglacial and glacial and intervals in central Arctic Ocean sediment cores based on the premise that interglacial conditions with less sea ice and more open waters led to higher food flux to the benthic communities, and vice versa. However, spatial differences in sea-ice cover during the individual interglacials also led to differences in primary productivity and consequently to spatial variations in the intensity of bioturbation and the composition of trace fossils. Areas characterized by perennial sea ice and few open leads or polynyas have a lower food flux than areas close to the sea-ice margin or with abundant polynyas. Consequently, the areas with more severe sea-ice conditions display fewer trace fossils and less intensely bioturbated sediments than areas characterized by open leads, polynyas, or areas situated close to the ice margin where primary productivity is higher. The spatial pattern shows a clear decrease in bioturbation intensity and trace fossil diversity from areas today characterized by relatively open waters, towards areas characterized by thick perennial sea ice. There is also a general pattern of more diverse trace fossil communities and more intense bioturbation observed from MIS 5e sediments compared to MIS 1, suggesting that sea-ice conditions during MIS 5e were generally less severe than during the present interglacial. The application of trace fossils and bioturbation for the reconstruction of sea ice conditions is particularly viable because of the large number of cores with X-ray radiographs available from data repositories such as www.pangaea.de. The main limitation of the method comes from the generally poor age control of Arctic sediments beyond the range of radiocarbon dating.
How to cite: Löwemark, L.: A comparison of Arctic Ocean sea-ice conditions during interglacials MIS 5e and MIS 1 based on biogenic sedimentary structures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6455, https://doi.org/10.5194/egusphere-egu25-6455, 2025.
Observation-based reconstructions of Arctic sea surface temperatures in response to changing climate boundary conditions are critical to constrain climate sensitivity and evaluate the uncertainties of model simulations. On long and pre-instrumental timescales, this is only possible by employing climate proxies. Yet, most proxies of essential climate variables, such as sea surface temperatures (SST), suffer from limitations when applied to cold temperatures that characterize Arctic environments. These limitations prevent us from constraining uncertainties for some of the most sensitive climate tipping points that can trigger rapid and dramatic global climate change such as Polar Amplification, the disruption of AMOC, sea ice loss, and permafrost melting that are intrinsic to the polar regions. Here, we present a new approach to reconstructing sea surface temperatures (SST) using paired Mg/Ca - δ18Oc recorded in shells of the Arctic planktonic foraminifera Neogloboquadrina pachyderma. We show that in this proxy system, the Mg/Ca – palaeothermometry is affected by variations in seawater carbonate chemistry, which can be successfully quantified and removed from paleotemperature reconstructions allowing a reassessment of the absolute temperature and the magnitude of marine polar amplification to climate forcing on glacial-interglacial timescales. By applying this novel approach to existing records, we show that the magnitude of high latitude SST cooling during glacial periods has been underestimated and that the new estimate of SST change between the Late Holocene and the LGM exceeds model-based estimates of marine polar amplification by up to 3.0 ±1.0˚ C. Our findings open up opportunities to better constrain the oceanic carbonate system enabling a quantification of high-latitude ocean-atmosphere carbon exchange as well as to benchmark the performance of CMIP6 and future generations of climate models.
How to cite: Morley, A., de la Vega, E., Raitzsch, M., Bijma, J., Ninnemann, U., Foster, G., Chalk, T., Meilland, J., Cave, R., Büscher, J., and Kucera, M.: Reassessment and applications of the Mg/Ca - δ18Oc proxy system recorded in shells of the Arctic planktonic foraminifera Neogloboquadrina pachyderma, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19167, https://doi.org/10.5194/egusphere-egu25-19167, 2025.
The Arctic’s enhanced response to global warming, driven by sea-ice and lapse-rate feedbacks, among other processes, has significant implications for the climate system, ecosystems, and society. Known as Arctic Amplification (AA), this phenomenon accelerates permafrost thawing, influencing carbon soil emissions and hydrology. However, the physics of permafrost-related processes remain poorly understood. Additionally, Earth System Models (ESMs) exhibit significant uncertainties in projecting future Arctic hydrology, making it difficult to determine whether this region will become wetter or drier. A better representation of soil thermodynamics and hydrology within ESMs allows for assessing uncertainties related to permafrost processes. This study uses a modified version of the MPI-ESM, where soil hydro-thermodynamics is improved in permafrost regions. With the tuning of parameters in these modifications we create the WET and DRY versions of the model. This allows for evaluating how these changes affect Earth's climate and, in particular, AA until 2300. Simulations, reveal that the AA factor converges to a value of 2–3 when external forcing outperforms the influence of internal variability. Furthermore, differences in climate backgrounds and the availability of sea ice and snow result in feedback processes of different magnitudes. Thus, accurately representing Arctic hydrology is crucial to better understand and predict the region's future changes. The feedback mechanisms explored here not only shape Arctic climate, but also have the potential to affect the global climate via a series of teleconnections.
How to cite: Meabe-Yanguas, N., González-Rouco, J. F., García-Pereira, F., de Vrese, P., Martínez-Vila, A., Steinert, N. J., Jungclaus, J., and Lorenz, S.: Long term influence of changing soil hydrology in an Earth System Model on Arctic Amplification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18918, https://doi.org/10.5194/egusphere-egu25-18918, 2025.
Greenland’s west coast is highly vulnerable to the impacts of climate change, with profound implications for marine ecosystems and their services. Projections suggest significant restructuring of Arctic marine ecosystems due to ongoing sea ice decline, yet uncertainties remain regarding the biosphere-specific responses of these ecosystems. The Arctic cryosphere has undergone significant changes throughout the Holocene, with the Holocene Thermal Maximum (HTM) representing a key period of reduced sea ice and warmer conditions. These past environmental shifts provide a valuable analogue for understanding the ongoing impacts of climate warming on Arctic marine ecosystems. Understanding past climate impacts on marine species is essential for predicting future changes and informing policy decisions.
While traditional microfossil records have advanced our knowledge of past ecosystems, they are biased toward species with hard body parts and are insufficiently covered in time and space. To address these limitations, we use sedimentary ancient DNA (sedaDNA) to track HTM marine biodiversity dynamics. This method allows for the detection of a broad range of organisms, including soft-bodied species such as ciliates and jellyfish, which are not preserved in the fossil record. To enhance the taxonomic resolution of marine eukaryotes across all trophic levels, from primary producers to marine mammals, we developed custom hybridization capture probes targeting barcoding regions. This approach enables the retrieval of short DNA fragments and the assessment of postmortem damage to validate the sedaDNA signal. We employed a two-step methodology: (1) compiling databases such as GBIF and WoRMS to identify knowledge gaps in Arctic marine biodiversity, and (2) evaluating various barcoding genes (e.g., 18S, rbcL, ITS2, COI) for taxonomic resolution and reference availability. Using the SILVA-NR99 database, we focused on the V7 region of the small subunit ribosomal RNA gene as a universal marker, while applying alternative markers for groups lacking sufficient resolution. We generated 46,804 80bp-long probes targeting 11,389 species, which we tested both in silico and on marine surface sediment samples collected from 25 sites around Greenland before their application to Holocene sediment cores from western Greenland.
This approach holds great potential for identifying key marine Arctic species across trophic levels and optimizing their taxonomic resolution during the HTM, revealing ecosystem responses to warming. By providing new insights into Arctic marine ecosystem dynamics and their long-term responses to climate change, we aim to offer valuable information for developing adaptive management strategies aimed at ensuring the ecological sustainability of the region.
How to cite: Courtin, J., Ribeiro, S., and Zimmermann, H.: Sedimentary ancient DNA to unlock Arctic marine biodiversity during the Holocene Thermal Maximum, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16307, https://doi.org/10.5194/egusphere-egu25-16307, 2025.
