This session focuses on physical, microbiological and chemical oceanographic trends in polar regions in response to past and present climatic changes and other anthropogenic impacts. We particularly encourage submissions focusing on elemental isotope budgets but also welcome contributions that explore elemental concentrations, (bio)geochemical models, plankton assemblages and physical oceanography including, but not limited to, water mass movements and meltwater input, advancing predictions of polar ocean development.
Hydrothermal venting along mid-oceanic ridges alters deep ocean water masses around the globe. These vent systems supply geothermal heat and various biogeochemical properties to water masses close to the bottom. In the Arctic, the influence of hydrothermal venting is largely unknown, and whether it should be considered in relation to other processes that modify the highly isolated deep water masses.
We present new results from the expedition PS 137 on water masses and the flux associated with the Aurora Vent Site at the Gakkel Ridge, 82.9° N, the only system in the Arctic Ocean to have been visited twice. Utilising CTD observations including physical and biogeochemical data, we assess the dimensions of the hydrothermal plume and estimate the heat flux. A spatially restricted plume core with a horizontal extent of less than 1000 m but a large rise height of 1200 m above the seafloor results in an estimated heat flux of approximately 180 MW.
A comparison with the observations made in 2014 reveals that the plume exhibits a comparable height, suggesting a constant heat flux over the period. Furthermore, the combined helium isotope measurements indicate that water masses on a larger scale at the Gakkel Ridge are also influenced by hydrothermal systems.
How to cite: Mette, J., Walter, M., Sültenfuß, J., and Mertens, C. and the R/V Polarstern PS137 Science Team: Hydrothermal Plumes in the Arctic Ocean -The Aurora Site at Gakkel Ridge, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1071, https://doi.org/10.5194/egusphere-egu26-1071, 2026.
Dissolved oxygen is a key indicator of ocean health and is being altered by climate-driven warming. The Arctic–subarctic system is warming at an exceptional pace due to Arctic amplification, but how this rapid warming translates into basin-wide oxygen change is still not well constrained. Using observations of Atlantic Water (AW) pathways, we find that the Atlantic inflow exerts a leading control on recent deoxygenation in the Arctic Ocean. Oxygen declines are detected in the upper eastern Arctic and in the intermediate layers of the western Arctic at rates of −0.41 ± 0.17 to −0.47 ± 0.07 μmol kg−1 yr−1, approximately six times the global mean. We identify amplified warming in Arctic gateway regions as the dominant driver, primarily through a strong reduction in oxygen solubility. The resulting low-oxygen signal is then propagated into the interior Arctic by rapid subduction and circulation of AW, extending the impact to deeper layers and increasing risks to Arctic marine ecosystems. These results emphasize that warming Atlantic inflow is central to shaping Arctic oxygen dynamics; continued temperature rise is therefore expected to sustain and potentially strengthen ongoing deoxygenation, calling for heightened attention and broader monitoring across the Arctic.
How to cite: Wu, Y.: Arctic amplification–driven warming of Atlantic inflow intensifies oxygen loss across the Arctic Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2655, https://doi.org/10.5194/egusphere-egu26-2655, 2026.
Reconstructing past ocean-cryosphere interactions can provide crucial insight to the ongoing rapid climate change in the polar regions and beyond. However, there are large uncertainties in existing proxies commonly used in downcore reconstructions, including a lack of low-temperature (<9°C) culture-based Mg/Ca-temperature calibrations for planktic foraminifera. In the polar oceans the foraminiferal assemblage is not diverse and commonly dominated by Neogloboquadrina pachyderma, yet there is limited understanding of non-thermal influences on this proxy in this species. N. Pachyderma also precipitates a thick low-Mg/Ca crust over its inner higher Mg/Ca lamellar calcite, that contributes to uncertainties and inaccuracies in high-latitude palaeotemperature reconstructions.
To address this, we cultured N. pachyderma across a 2 to 9°C temperature range, at a range of salinities (29.8–36.6), and carbonate chemistry conditions with both co-varying and decoupled pH (7.65–8.4) and [CO32-] (64–243 µmol/kg) and analysed their trace element composition using Laser Ablation Inductively Coupled Plasma Mass Spectrometry.
We present a new method that distinguishes the crust and lamellar calcite using trace element profiles from both cultured and fossil shells. This allowed us to show distinct geochemical signals in the crust and lamellar calcite of laboratory-grown N. pachyderma, including lower Mg/Ca, Na/Ca, and B/Ca in the crust compared to the lamellar calcite. We present new Mg/Ca-relationships, with independent calibrations for the crust and lamellar calcite. The temperature calibrations extend the lower range of culture-based Mg/Ca-calibrations down to 2°C. Furthermore, we show significant and opposing pH and [CO32-] influences on Mg/Ca when these variables are decoupled and no statistically significant influence of salinity on Mg/Ca. Crust and lamellar calcite element/Ca are found to have different sensitivities to changing environmental conditions. Our results also show that environmental conditions control the crust-lamellar proportions and shell thickness which has implications for both downcore reconstructions and ongoing ocean acidification and warming.
Overall, our findings suggests that the crust and lamellar calcite precipitate via contrasting biomineralisation strategies and/or varying precipitation rates, leading to distinct geochemical compositions and different sensitivities to changing environmental conditions. We propose that distinguishing the two components and applying Mg/Ca-environmental relationships with separate calibrations for the crust and lamellar calcite will substantially reduce uncertainties in high-latitude palaeoceanographic reconstructions. We are now in the process of applying these methods and relationships to Quaternary sediment records from the central Arctic Ocean and the Nordic Seas.
How to cite: Westgård, A., Ezat, M. M., Sykes, F. E., Meilland, J., Chalk, T. B., Milton, J. A., Chierici, M., Knies, J., and Foster, G. L.: Improving polar ocean temperature reconstructions with crust-lamellae specific Mg/Ca-temperature calibrations and improved understanding of its non-thermal forcers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6726, https://doi.org/10.5194/egusphere-egu26-6726, 2026.
Phaeophyta (i.e., brown seaweeds) are significant primary producers in high-latitude environments, serving as a key nutritional source to fauna and carbon sink. Despite being the dominant biomass source in polar regions, they have largely been overlooked in carbon assessments, trophic ecology, and biogeochemical studies. Our understanding of how these ecosystems will respond to climate change is limited, based on a handful of studies that are primarily Arctic focussed. Stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of macroalgae has often been used as a tool to assess nutrient sources, energy transfer and photosynthetic mechanism but has rarely been applied to polar macroalgae. The rapid environmental change in both poles has the potential to shift the isotopic baseline. Our current understanding is poor, to our knowledge only 28 studies have published biogeochemical assessments of Antarctic macroalgae, half of which are from the South Shetland Islands in the northern West Antarctic Peninsula. Yet biogeochemical data can provide a wealth of information regarding nutrient source changes, light dynamics, productivity and nutritional quality. Larger species, such as Himantothallus grandifolius (Antarctic) or Saccharina latissima (Arctic) can provide seasonal or even multi-annual data through incremental stable isotope analysis along macroalgal blades. Changing productivity rates can be tracked through δ13C values, fluctuating due to sea ice break out, carbon demand and growth requirements. Over 20 specimens of H. grandifolius and Arctic kelps have been collected over several field trips to the Antarctic Peninsula, East Greenland coastline and Svalbard for δ13C and δ15N analysis; forming the largest biogeochemical dataset for polar macroalgae to date. Large variations > 15 ‰ were recorded for the Antarctic species H. grandifolius from a single organism, a significant variation when considering trophic level shifts are on a scale of ~ 3–5 ‰. Cyclical trends in productivity were also identified in several specimens with wider implications for shifting isotopic baselines of primary producers in response to environmental change on seasonal and multi-year time scales. Strong seasonal responses in δ13C are linked to sea ice and fluctuating light conditions with increased run off through glacial melting. Nitrogen was found to vary between sub-tidal and inter-tidal species, as well as incrementally along blades of larger species. New nitrogen sources may be introduced to remote polar regions as increased tourism increases the risk of wastewater and pollutant inputs to these fragile ecosystems. Macroalgae could become an ideal tracer in coastal environments where nutrient sources can be assessed at varying time scales.
Our incremental approach provides high resolution isotopic data with the capacity to generate seasonal to multi-year records from an understudied ecosystem. Polar environments are set to change in unprecedented ways, the shifting isotopic baseline has repercussions for the wider food web, ecosystem structure and functioning that macroalgae play a key role in.
How to cite: Alldred, F. and Gröcke, D.: Stable isotope analysis of polar seaweeds: Assessing productivity and response to environmental change on seasonal and multi-annual time scales, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-722, https://doi.org/10.5194/egusphere-egu26-722, 2026.
The Southern Ocean is a major sink for atmospheric carbon dioxide and critical to the current and future carbon cycle. This net annual CO2 flux reflects the balance between strong seasonal variability characterized by opposing periods of winter outgassing and summer uptake. Using a simple framework, we evaluate how model biases in both the amplitude and timing of dissolved inorganic carbon (DIC) and total alkalinity (TA) and in the amplitude of sea surface temperature (SST) impact simulated pCO2. We examine seasonal CO2 fluxes and pCO2 south of the Subantarctic Front in 42 Earth System Model and three state estimate simulations. Only 11 of the 45 simulations have a seasonal pCO2 cycle with a correlation of ≥0.7 to observed pCO2, while 26 have a correlation of <0. Four of the well-correlated models accurately represent the seasonality of SST, DIC, and TA, while TA biases compensate for DIC or SST biases in the other seven. DIC and SST amplitude biases are related to mixed layer (MLD) biases, with shallow MLDs, especially in the summer, correlated with larger amplitude DIC and SST cycles than observed. The amplitude of seasonal Net Primary Production is correlated to DIC and TA timing. We provide input on the main adjustments needed to correct the simulated pCO2 seasonality in each of the evaluated models. These findings highlight the difficulty and importance of capturing the seasonal processes influencing the carbonate system to correctly model and predict the Southern Ocean carbon sink and its response to a changing climate.
How to cite: Bushinsky, S., Arteaga, L., Fassbender, A., Hauck, J., Mazloff, M., Cerovečki, I., Landschützer, P., Rödenbeck, C., Danek, C., Romanou, A., Lerner, P., Gray, A., and Schlunegger, S.: Nonlinear Interactions of Timing and Amplitude Biases in Modeled Southern Ocean pCO2: The Roles of Dissolved Inorganic Carbon, Total Alkalinity, and Sea Surface Temperature, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19010, https://doi.org/10.5194/egusphere-egu26-19010, 2026.
Global climate change is concurrently and profoundly altering the ocean’s physical and biogeochemical environment. The intermediate water in the South Atlantic and Indian Oceans, which together constitute a critical component of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), lies at the heart of these changes. The intermediate layer of the South Atlantic is ventilated by two primary sources: relatively fresher and younger waters (characterised by low Apparent Oxygen Utilization, AOU) originating from the Pacific Ocean, and saltier and older waters advected from the Indian Ocean via the Agulhas System. However, the extent to which the intrusion of saline, older Indian Ocean waters via the Agulhas System modulates the stability of the AMOC’s upper limb remains poorly understood. Specifically, the temporal variability and long-term contribution of the Indian Ocean waters to the South Atlantic intermediate layer remains a knowledge gap.
Here, we focus on observational evidence of and investigate the underlying mechanisms driving the influence of Indian Ocean intermediate waters on the Atlantic Ocean in a warming climate. We examine AOU-salinity covariability across decadal to multi-decadal time scales within South Atlantic intermediate water. This analysis integrates high-quality observational databases of temperature, salinity, dissolved oxygen, and water age, as well as repeat hydrographic sections, allowing us to link their observed variability to changes in circulation and mixing, while considering oxygen disequilibrium effects and the influence of the biological carbon pump in changing AOU.
We find an increasing influence of Indian Ocean water in the South Atlantic at the intermediate layer over the past 30 years. The most strongly impacted regions are identified. In addition, we quantify the impact of Indian Ocean influence on the South Atlantic and show that this signal has become progressively detectable over the past 30 years, but has not yet exceeded the level of internal variability, indicating an ongoing ‘Indianization’ of the South Atlantic intermediate layer. We identify the underlying mechanisms related to the increasingly positive phase of the Southern Annular Mode (SAM) and an associated multidecadal increase in Agulhas leakage. Finally, we will discuss the potential implications of this phenomenon for the long-term stability of the AMOC.
How to cite: Tan, Z., McDonagh, E., Speich, S., Florindo Lopez, C., Davila Rodriguez, X., and Jeansson, E.: Growing Influence of Indian Ocean Waters in the South Atlantic Intermediate Layer over the last 30 years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6434, https://doi.org/10.5194/egusphere-egu26-6434, 2026.
The Southern Ocean (SO) is of major importance in shaping climate transitions due to its substantial potential in storing carbon in the deep ocean and its release to the atmosphere most dominantly during glacial terminations. Through wind driven upwelling of deep waters and high latitude deep water formation, the SO acts as a gateway between the surface ocean and its interior. With the Antarctic Circumpolar Current (ACC), the world’s largest current system, the SO connects all three major basins of the global ocean and therefore integrates and responds to climate signals across the globe. Additionally, the SO exerts a major influence on the Antarctic Ice Sheet and partly controls its mass balance.
The evolution of deep-water formation and export, as well as its interplay with the ACC and the Antarctic Ice Sheet are important factors that are still poorly constrained. We present a largely isotope geochemical based high-resolution multi-proxy reconstruction of IODP Site U1537 to examine these interplays in the southern Scotia Sea. The Scotia Sea is a key area in the SO, where newly formed well ventilated Weddell Sea Deep Water (WSDW) is admixed into and entrained underneath the ACC.
Sedimentation in this area is mainly modulated by the strong ocean currents, as seen by extremely high sediment focusing throughout. Detrital neodymium (Nd) as well as authigenic and detrital lead (Pb) isotope compositions in Southern Ocean sediments provide insights into sediment sources, which can be clearly identified due to the distinct crustal ages of East and West Antarctica and its surrounding areas. Sediments at Site U1537 are dominantly sourced from the Antarctic Peninsula and the Weddell Sea region. The sediment provenance investigations are additionally complemented by K’-Ar analyses on the <63 µm fractions of the sediment samples, providing average age information. All of our obtained isotopic records reveal substantial variations during glacial-interglacial transitions.
Site U1537 provides evidence for low bottom water oxygenation (derived from authigenic uranium) and likely no WSDW export into the Scotia Sea during the Last Glacial Maximum. The data further suggests early deglacial pulses of WSDW export. We advocate that these pulses might be a considerable contributor to the reestablishment of interglacial-type deep ocean ventilation and AMOC conditions. A substantial increase in current-shelf interaction along the Antarctic margin in the Pacific sector is seen during MIS5e. Taken together, our multi-proxy approach highlights the complex sedimentation regime in the Scotia Sea and provides new paleoceanographic insights towards the circulation and frontal dynamics as a function of climatic boundary conditions at submillennial-scale resolution.
How to cite: Hallmaier, M., Gutjahr, M., Hemming, S. R., Lippold, J., Weber, M. E., and Eisenhauer, A.: Climate state dependent sedimentation dynamics in the southern Scotia Sea during the last four glacial cycles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-506, https://doi.org/10.5194/egusphere-egu26-506, 2026.
The Fram Strait is a unique deep-sea gateway connecting the Arctic Ocean to the North Atlantic. Under modern conditions, the eastern Fram Strait remains largely ice-free due to the influx of warm Atlantic water via the West Spitsbergen Current (WSC). Conversely, the western Fram Strait is characterized by the export of cold, fresh Arctic water masses and sea ice from the central Arctic Ocean via the East Greenland Current (EGC), thereby impacting the North Atlantic thermohaline circulation. Paleoceanographic records, however, suggest radical departures from this oceanic regime during glacial periods (Geibert et al., 2021; Nørgaard-Pedersen et al., 2003).
Here, we present a high-resolution record of oceanographic conditions during Marine Isotope Stage (MIS) 6 using a sediment core KH14-GPC02, recovered from the eastern Fram Strait (77° 31' 22.7994" N, 8° 24' 4.9674" E) during Expedition CAGE19-3 in 2019. Core KH14-GPC02 was analyzed for biomarker lipids, e.g., highly branched isoprenoids, sterols, and glycerol dialkyl glycerol tetraether lipids, providing the first complete, high-resolution records of sea-ice conditions and ocean temperature during the penultimate glacial maximum from this climatically critical region.
Our results reveal a two-phased evolution of sea-ice conditions in the eastern Fram Strait. Early MIS 6 was dominated by a marginal sea-ice cover with significant seasonal variability, as evidenced by high concentrations of the sea-ice biomarker IP25 and open-ocean biomarkers. From ~165 ka onward, however, a sharp decline in IP25 and open-ocean biomarkers signals a shift to perennial ice cover. To investigate the climatic drivers of this environmental transition, we conducted simulations with the complex Earth system model AWI-ESM. While lowered summer insolation and the closure of the Canadian Arctic Archipelago gateways contribute to regional cooling during glacial climates in the Fram Strait and Nordic Seas (e.g., Lofverstrom et al., 2022), our simulations demonstrate that these factors alone are insufficient to explain the perennial ice cover in the eastern Fram Strait during late MIS 6. Instead, we propose that the closure of the Denmark Strait, driven by ice‑sheet expansion, acted as a critical threshold to explain the heavy sea-ice cover in eastern Fram Strait during late MIS 6. This geographic blockage not only halted sea‑ice export through the Denmark Strait but also diminished the inflow of warm Atlantic water, fundamentally altering sea‑ice dynamics in the Arctic-Atlantic gateway. Our findings highlight the crucial – but often underestimated – role of oceanic gateways in regulating Arctic sea-ice extent during extreme glacial climates.
References
Geibert, W. et al., 2021. Nature 590, 97-102.
Lofverstrom, M. et al., 2022. Nature Geoscience 15, 482-488.
Nørgaard-Pedersen, N. et al., 2003. Paleoceanography 18, 1063.
How to cite: Mikler, M., Song, P., Knies, J., Lohmann, G., Ahn, Y., Nam, S.-I., and Müller, J.: A trapped East Greenland Current: Sea ice expansion during late MIS 6 in the eastern Fram Strait, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11521, https://doi.org/10.5194/egusphere-egu26-11521, 2026.
Deep-water formation plays a crucial role in global climate, yet it is absent in the modern North Pacific. However, the existence of North Pacific Deep Water (NPDW) formation during the Pliocene and its impact on the marine carbon cycle remain controversial. Here, we present high-resolution sedimentary records of authigenic neodymium isotope composition(εNd), barite accumulation rates (BAR), and barite barium (Ba) isotope compositions (δ138Babarite) from ODP Site 882 in the subarctic Northwest Pacific.
Our results reveal pronounced shifts in εNd and Ba-proxy records synchronous with the intensification of Northern Hemisphere Glaciation. Specifically, across the ~2.73 Ma interval, seawater εNd values decrease from +0.2 to -1.4, marking a shift from northern-sourced NPDW to southern-sourced Pacific Deep Water (PDW). This circulation collapse was accompanied by elevated BAR and δ138Babarite values, indicating a transient peak in export production. Intriguingly, this productivity pulse is decoupled from biogenic opal accumulation, which declines during the same interval. We propose that the cessation of NPDW formation allowed the upwelling of nutrient-rich PDW. This process fueled a transient increase in export production but partly drove the ecosystem from a silicate-replete to a silicate-limited regime, or reduced nutrient burial efficiency.
In contrast to the dynamic Late Pliocene, our new data from the Early Pliocene (~4.3–3.6 Ma) show relatively stable εNd and Ba-proxy records. These findings challenge previous hypotheses of an Early Pliocene circulation transition derived from Japan Sea records, suggesting that open ocean circulation in the subarctic Pacific remained stable prior to the onset of major glaciations. Our study highlights the critical role of physical circulation thresholds in regulating the efficiency of the biological carbon pump and nutrient inventory in the North Pacific.
How to cite: Chu, Y., Zhang, R., Li, X., Xie, R., Yao, W., and Xu, A.: Evidence for Pliocene North Pacific Deep Water Formation and Its Paleoproductivity Imprints, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8271, https://doi.org/10.5194/egusphere-egu26-8271, 2026.
Polar ocean ecosystems are a key source of nutrients such as nitrogen (N) and phosphorus (P) to the rest of the world’s oceans. Climate change is already altering many processes affecting elemental cycling at the poles, but interruption of polar nutrient export could suppress global primary productivity and fisheries by around a quarter over multi-century timescales. It is thus essential to constrain both the mechanisms and variability of these fluxes, and their global implications.
The Arctic specifically exports an excess of P relative to N, equivalent to ~90% of the net phosphate flux to the Atlantic at 47°N, and supporting a significant fraction of North Atlantic N-fixation. Of the gateways into the Atlantic, Davis Strait has the strongest net southwards transport. A mooring array has been tracking volume and freshwater transports there since 2004, yet biogeochemical transports remain poorly quantified. To move towards addressing this gap, two autonomous water samplers were deployed at the western boundary of Davis Strait; targeting the P*-rich core of the Baffin Bay outflow (~100db) enabled the monitoring of nutrient transport of waters being exported into the North Atlantic, and the variability in their N:P relationship.
Deployed in Ocober 2022, samples were collected at ~2 week intervals and analysed for inorganic and organic nutrients, oxygen isotopes and pH, forming the first two years of a dedicated biogeochemical time series of the western boundary outflow.
Initial results show substantial chemical variability across all measured parameters, with a clear seasonal cycle in salinity-normalised nutrients and oxygen isotopes. When combined with velocity fields then concentration difference drive varialbity in the transports. While temperature and salinity also vary strongly on seasonal (and shorter) timescales, their cycles showed some temporal offsets, suggesting different underlying forcing mechanisms. Differences between the slope and off slope sites (a stronger amplitude in both concentrations and transports closer to the shelf)also highlight spatial structure in the exported water masses.
Across the Straits then preliminary P* transport estimates underscore the dominant role of the western core in total nutrient export through Davis Strait. Early indications are of longer-term changes in N:P ratios in the outflow. Ongoing work will further refine transport estimates and assess implications for Arctic–Atlantic nutrient connectivity.
How to cite: Brown, P., Mawji, E., Painter, S., Lenetsky, J., Gabriel, C.-E., Martin, A., Azetsu-Scott, K., and Lee, C.: Variability in biogeochemical Arctic outflow through Davis Strait, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14945, https://doi.org/10.5194/egusphere-egu26-14945, 2026.
The Southern Ocean (SO) plays a crucial role in connecting all the world's oceans through the Antarctic Circumpolar Current (ACC). Global ocean circulation is also affected by processes in the Southern Ocean that change the density and subduction rate of water. Argo has provided consistent and basin-wide coverage of this region over the past two decades, enabling analyses not possible with the sparse and episodic ship-based observations available earlier. This study uses the Argo float dataset collected between 2004 and 2025 along the ACC. The data was gridded and processed using the pseudoeulerian approach; the full dataset and decadal differences were obtained for 18 sections of the SO. We will present the spatial variability of water masses in the Southern Ocean, highlighting their decadal and interannual variability and the associated large-scale spatial gradients relevant to Southern Ocean dynamics. The use of Argo float observations provides unprecedented details for examining the spatial and temporal evolution of density patterns resulting from salinity and temperature changes, with important implications for global ocean circulation and climate.
How to cite: Amaral Wasielesky, A., Menna, M., Mauri, E., Rubino, A., Martellucci, R., and Bowen, M.: Changes in the Southern Ocean over the last two decades from Argo float measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8433, https://doi.org/10.5194/egusphere-egu26-8433, 2026.
Antarctic Intermediate Water (AAIW) is a fundamental component of the global overturning circulation and a key determinant of the pycnocline structure. It is produced in the high-latitude Southern Ocean, where interactions between the ocean, atmosphere, and sea ice strongly shape its physical characteristics. From the late twentieth century through 2015, Antarctic sea ice underwent a sustained expansion of roughly 3% per decade. This prolonged growth enhanced the seasonal meltwater supply, increased surface stratification, and contributed to a gradual freshening of AAIW, whose effects were observed in the subtropical basins. Beginning in 2016, this pattern shifted abruptly. A sequence of unprecedented annual sea-ice losses signalled a rapid transition away from the earlier expansion phase. By combining Argo float measurements with satellite observations and reanalysis data, we demonstrate that this regime change is already affecting the properties of intermediate-depth water masses throughout the Southern Hemisphere. Our analysis indicates that, since 2016, the contribution of sea-ice meltwater has declined at a rate of up to 36 mSv per decade, a stark contrast to the pre-2015 increase of about 14 mSv per decade. This reduction in freshwater input has driven a concurrent increase in the density and salinity of AAIW, with core salinity rising by approximately 6×10-3 g kg-1 per decade. Together, these trends point to an emerging, hemispheric-scale adjustment of Southern Ocean–sourced water masses.
How to cite: Mishra, K., Gayen, B., and Naveira Garabato, A. C.: Reversal of Antarctic Intermediate Water trends triggered by sea ice decline, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21652, https://doi.org/10.5194/egusphere-egu26-21652, 2026.
The Southern Ocean plays a central role in the global climate system by regulating large-scale circulation, facilitating interbasin exchange, absorbing large amounts of anthropogenic heat and carbon and influencing Antarctic Ice Sheet stability. Yet, observational data, including rare earth element measurements such as neodymium (Nd) isotopes and samarium (Sm), have so far remained sparse in the Indian sector and along the East Antarctic continental margin, thereby limiting our understanding of circulation, water mass transformation, and sediment-ocean interactions in a changing climate.
Water masses in the Southern Ocean are traditionally characterized using hydrographic parameters (e.g., potential temperature, salinity, neutral density). During physico-chemical weathering along the East Antarctic margin, old continental crust supplies a distinctly unradiogenic neodymium isotope signature (low εNd) to regional shelf waters that interact with more radiogenic Antarctic Circumpolar Current waters (higher εNd) further north. This isotopic difference makes neodymium isotopes an especially powerful tracer of regional circulation and mixing along the East Antarctic continental margin. We present the first high-resolution dataset of dissolved εNd, together with Nd and Sm concentrations, from the Indian sector of the Southern Ocean. Gridded water column samples in conjunction with bottom water samples extracted from multicorer sediment supernatants, collected during expedition EASI-2 onboard RV Polarstern (Dec 2023–Feb 2024), provide a meridional transect from the Denman Glacier front (~66°S) to ~45°S along 100°E. Combined with hydrographic observations, this dataset provides a detailed framework for examining water mass structure, mixing, and regional boundary fluxes along the transect.
Away from direct Antarctic continental influences, the εNd distributions show largely conservative behavior in intermediate to deep waters and allow clear identification of major Southern Ocean water masses. A striking feature is the persistence of a remnant North Atlantic Deep Water εNd signal within lower Circumpolar Deep Water, highlighting long-range interbasin connectivity. Near the Denman Glacier, warm and radiogenic modified Circumpolar Deep Water (mCDW) intrudes onto the continental shelf, evident in both physical properties and εNd signatures below ~400 meters water depth. As seen in earlier studies, a pronounced mCDW tongue was observed to reach close to the Denman Glacier front, with associated high basal melt rates evident from potential temperature and salinity in sampled local East Antarctic shelf waters.
Nd and Sm concentrations increase linearly with depth north of the Polar Front, but exhibit substantial enrichment south of the front, reflecting deep-water upwelling, biogenic scavenging, and a latitudinally gradual boundary exchange. Pronounced variations in εNd and rare earth element concentrations in bottom waters point to substantial benthic additions in the southern reaches of the transect driven by weathering inputs from ambient terrigenous sediments, whereas particle-related scavenging appears to dominate offshore.
This study closes a critical observational gap in the Indian sector of the Southern Ocean and provides new constraints on the present-day circulation, water mass structure, and the influence of Antarctic crustal and benthic Nd additions, while demonstrating the value of εNd as a tracer in modern and paleoceanographic contexts.
How to cite: Ehnis, M., Gutjahr, M., Menzel, D., Huang, H., Creac'h, L., Oetjens, A., Rieke, O., Herraiz Borreguero, L., Janout, M., Rickli, J., Frank, M., Tippenhauer, S., and Lippold, J.: Neodymium Cycling and Water Mass Structure in the Indian Sector of the Southern Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10619, https://doi.org/10.5194/egusphere-egu26-10619, 2026.
Anthropogenic climate change is accentuated at high latitudes due to Polar Amplification, a process driven by interactions and feedback mechanisms among terrestrial, atmospheric, and oceanic systems. Arctic sea ice is in rapid decline while Antarctic sea ice has experienced recent extreme lows after relative stability, with global climatic and ecological responses and impacts. Multiple proxies have been developed for past sea ice reconstructions to assess modern trends and aid future forecasting. These include microfossil assemblages (dinocysts, foraminifera, ostracodes) and biomarker concentrations derived from ice-edge and open-water diatoms. Two sea ice biomarkers, IP25 (Ice Proxy with 25 carbon atoms) and IPSO25 (Ice Proxy for the Southern Ocean with 25 carbon atoms), can be used to produce semi-quantitative reconstructions of past sea ice extent when combined with phytoplankton derived biomarkers (e.g. phytosterols brassicasterol and dinosterol). However, there gaps remain in understanding past sea ice states and the critical processes that drive change, including at critical transitions that may provide insight into current and predicted future warming. We present an overview of synthesised sea-ice proxy records spanning key periods characterised by lower and higher than pre-industrial CO₂ background states: the Mid-Holocene (6ka; 8.2–4.2 ka BP), the Last Glacial Maximum (LGM; 21ka; ~ 19–23 ka), the Last Interglacial (LIG; 127ka; ~130–115 ka BP), and the Mid Pliocene Warm Period (mPWP: 3.264–3.025 Ma). These syntheses are feeding into model-data integration as a key component of the EU Horizon project Past-to-Future (P2F), which aims to radically advance our knowledge of past climatic conditions to better understand Earth’s climate response to different kinds of forcing. A better understanding of past sea ice states and stronger data–model integration are essential for improving our ability to anticipate the future trajectory of sea ice and its cascading effects on global climate.
How to cite: Hole, G. M., Kjær, H. A., Andreasen, N., and McClymont, E.: Defining the States and Variability of Sea Ice via Marine Proxy Data Synthesis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13232, https://doi.org/10.5194/egusphere-egu26-13232, 2026.
The Northern Antarctic Peninsula (NAP) marine ecosystem is experiencing rapid environmental changes, yet the evolving relationships among atmospheric forcing, sea ice dynamics, and primary productivity remain poorly understood. This study investigates the interannual variability of summer chlorophyll-a (Chl-a) concentration and its physical drivers over the past two decades (2001–2024), utilizing multi-source satellite data and atmospheric reanalysis products. We identify a significant regime shift in climate-ecosystem interactions occurring around 2014.
Since 2014, major climate modes have shown concurrent trends: the Southern Annular Mode (SAM) accelerated towards a positive phase, while the Interdecadal Pacific Oscillation (IPO) shifted towards a negative phase. These combined trends led to a significant deepening of the Amundsen Sea Low (ASL), resulting in intensified regional winds (r=−0.79, p<0.01). This change in atmospheric circulation coincided with a rapid retreat of sea ice, marked by a significant increase in Ice-Free Days (IFD) in the NAP after 2014.
The significant change in climatic and physical conditions fundamentally altered the biological response patterns. Prior to 2014, the correlation between climate indices and summer Chl-a concentrations was weak, likely limited by the presence of sea ice cover. However, under low sea ice conditions after 2014, this association was notably strengthened. The correlation between the spring SAM index and summer Chl-a increased from 0.39 to 0.58 (p<0.1). The retreat of sea ice exposed the surface ocean directly to atmospheric forcing, enhancing the availability of irradiance and wind-driven vertical mixing. The enhanced mixing can facilitate the replenishment of limiting nutrients (e.g., iron) to the euphotic zone, thereby sustaining summer phytoplankton blooms. These findings suggest that the NAP ecosystem has entered a new state where productivity is tightly coupled with atmospheric dynamics.
How to cite: Ye, S., Zhang, Z., and Uotila, P.: Synergistic Climate Modes Drive a Regime Shift in Physical-Biological Coupling in the Northern Antarctic Peninsula Region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18273, https://doi.org/10.5194/egusphere-egu26-18273, 2026.
Antarctic krill populations exhibit substantial interannual fluctuations with highly variable success in the survival of larvae to the juvenile stage. Understanding connectivity between spawning hotspots and the areas where larvae successfully develop into juvenile populations is essential for predicting population dynamics and informing fishery management, yet the drivers of krill connectivity variability across the Southern Ocean remain poorly quantified.
This project uses Lagrangian particle tracking simulations to investigate krill larval connectivity patterns over 30 years (1993-present) based on high-resolution ocean circulation model outputs. We release over a billion virtual larvae throughout the spawning season across known spawning grounds and track their drift to quantify: (1) the variability of natural connectivity among populations, (2) how spawning timing influences dispersal success, and (3) which large-scale climate patterns (SAM, ENSO, ACC variability) drive strong versus weak connectivity years.
Network analysis identifies critical source populations that supply multiple recruitment areas and vulnerable sink populations dependent on external larval input. This connectivity baseline is essential for distinguishing natural fluctuations from climate-driven changes in future projections.
Results will inform the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) by revealing which populations require protection and identifying critical hubs that sustain networks of connected krill populations. The Lagrangian model framework and open-source outputs will provide a foundation for subsequent climate change projections examining how changes in Southern Ocean circulation may alter connectivity patterns by 2050-2100.
How to cite: Gourgue, O., Barbut, L., Barthélémy, A., Dulière, V., Fichefet, T., Hanert, E., Lacroix, G., Massonnet, F., Richaud, B., Schön, I., Sylvester, Z., and Van de Putte, A.: Antarctic krill connectivity: a Lagrangian modeling framework to understand Southern Ocean population dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8075, https://doi.org/10.5194/egusphere-egu26-8075, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 1a
EGU26-15143 | ECS | Posters virtual | VPS20
Holocene Sea Ice and Organic Matter Dynamics in the Southern Chukchi Sea Revealed by Lipid BiomarkersTue, 05 May, 14:21–14:24 (CEST) vPoster spot 1a
Arctic sea ice plays a critical role in regulating global climate and marine primary production, yet long-term records documenting its natural variability remain sparse in the Pacific sector of the Arctic Ocean. This limitation hampers our ability to establish a regionally coherent understanding of how sea ice responds to climatic and oceanographic forcing on centennial to millennial timescales. Here, we present a new biomarker-based reconstruction of Holocene sea ice and environmental change from the southern Chukchi Sea, north of the Bering Strait.
A 519-cm sediment core (SKQ-VC29) was recovered using a vibracorer and spans the last ~8.6 kyr, based on 17 AMS radiocarbon dates from shells and terrestrial macrofossils. Downcore concentrations of highly branched isoprenoids (HBIs) and sterols were quantified to reconstruct sea-ice conditions, marine productivity, and terrestrial organic matter (OM) inputs. Seasonal sea ice presence is inferred from IP25, a mono-unsaturated HBI produced by sea-ice diatoms, while open-water conditions and phytoplankton productivity are tracked using HBI III, brassicasterol, and dinosterol. These proxies are combined using the PIP25 index to provide a semi-quantitative reconstruction of sea-ice cover. Terrestrial inputs are assessed using vascular-plant sterols (campesterol and β-sitosterol), alongside bulk δ¹³C and C:N ratios.
The record indicates predominantly open-water conditions during the early to mid-Holocene, followed by the reappearance of seasonal sea ice at ~2.5 kyr BP—substantially later than in more northerly Arctic records. This delayed signal suggests that Neoglacial sea-ice expansion in the Pacific Arctic was spatially heterogeneous. Bulk OM proxies and declining β-sitosterol concentrations indicate a progressive reduction in terrestrial OM delivery through the Holocene, while marine productivity remains relatively stable. A pronounced shift at ~4 ka BP marks reduced organic carbon accumulation and broader environmental reorganization.
Together, these results improve spatial coverage of Holocene sea-ice reconstructions in the Pacific Arctic and highlight the complex, regionally variable nature of sea-ice evolution in a climatically sensitive gateway region.
How to cite: Jin, K., de Vernal, A., Pickart, R. S., Chen, M., Otiniano, G., and Porter, T.: Holocene Sea Ice and Organic Matter Dynamics in the Southern Chukchi Sea Revealed by Lipid Biomarkers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15143, https://doi.org/10.5194/egusphere-egu26-15143, 2026.
