Orals: Tue, 5 May, 14:00–18:00 | Room 0.31/32
Regions of Antarctica were most recently ice-free during the Miocene Climatic Optimum (MCO, ~17-14 Ma). During this warm interval, the East Antarctic Ice Sheet (EAIS) exhibited highly dynamic behavior and episodic wide-scale retreat associated with global sea level rise. During the subsequent Middle Miocene Climate Transition (MMCT), the EAIS expanded and stabilized with contemporaneous global cooling. However, little is directly known about drivers of EAIS behavior during the Miocene due to a lack of continuous, high-resolution climate records near Antarctica. Here, we present multi-proxy (Uk’37 and TEX86) biomarker records of sea surface temperatures (SSTs) from Ocean Drilling Program (ODP) Site 1165 in the polar Southern Ocean to constrain ocean-ice sheet interactions in the Prydz Bay region of East Antarctica throughout the Miocene. Our records span 5 to 19 Ma, with orbital-resolution data (5 kyr) during the MMCT from 13.2 to 15.1 Ma. We find peak SSTs during the MCO up to 18°C warmer than modern as well as polar-amplified cooling synchronous with the establishment of permanent Antarctic glaciation and broader global cooling during the MMCT (13.8 Ma) and Late Miocene (6-8 Ma). Comparison of our high-resolution SST record and ice rafted debris at the same site shows that ice rafting disappeared when SSTs warmed above 12°C, demonstrating the vulnerability of the marine ice margin to ocean warming. However, comparison with global benthic oxygen isotope records indicates that terrestrial-based ice volume exhibited threshold behavior as transient cooling during the MMCT crossed a tipping point for terrestrial ice sheet growth and stabilization, which subsequent warming was not sufficient to reverse. These results constrain the EAIS response to elevated greenhouse gas concentrations during the past global warmth of the Miocene, with implications for potential future long-term behavior of Earth’s largest ice sheet.
How to cite: Nirenberg, J. and Herbert, T.: East Antarctic ocean-ice sheet interactions during Miocene warmth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6070, https://doi.org/10.5194/egusphere-egu26-6070, 2026.
West Antarctica’s transition to its first extensive glaciation likely post-dated the establishment of the East Antarctic Ice Sheet (EAIS) by more than 10 million years, yet the timing and nature of West Antarctic Ice Sheet (WAIS) development have remained poorly constrained due to the absence of reliable sediment records. Newly recovered sediment sequences drilled with the seafloor drill rig MARUM-MeBo70 during RV Polarstern Expedition PS104 from the eastern Amundsen Sea Embayment were explored using multi-proxy sediment analyses alongside biostratigraphic and isotopic dating methods. These revealed ice-proximal terrigenous and diatomaceous diamictites as well as diatomaceous mudstones indicating the advance of a substantial WAIS to these drill sites already prior to the Oligocene–Miocene transition (~23 million years ago). Coupled climate-ice sheet modelling simulates the growth of a distinct WAIS separated from the EAIS, which expanded far into basins below sea level. Therefore, our new sedimentary data validate these model results and demonstrate that extensive WAIS expansion to the coast occurred several million years earlier than previously thought.
How to cite: Klages, J. P., Hillenbrand, C.-D., Bickert, T., Bauersachs, T., Salzmann, U., Titschack, J., Bohaty, S. M., Müller, J., Frederichs, T., Knahl, H. S., Lohmann, G., Ehrmann, W., Freudenthal, T., Larter, R. D., Hochmuth, K., van de Flierdt, T., Reinardy, B. T. I., Eisenhauer, A., Knorr, G., and Pälike, H. and the Science Party of Expedition PS104: Marine-terminating West Antarctic Ice Sheet during the latest Oligocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1740, https://doi.org/10.5194/egusphere-egu26-1740, 2026.
Ice sheets on West and East Antarctica presumably react considerably different to changing climatic conditions – today, in the future, and also when initiated. Large-scale East Antarctic glaciation preceded West Antarctica’s likely by more than 10 million years. However, the precise timing and nature of West Antarctic Ice Sheet (WAIS) evolution still remain largely speculative. Drilled sedimentary sequences from the Amundsen Sea Embayment of West Antarctica revealed evidence for marine-terminating glaciers already before the Oligocene-Miocene transition (~23 million years ago). For contextualizing this result, we coupled climate and ice sheet simulations using recent topography reconstructions for this critical climate transition and applying different CO2 forcings.
Our 280 ppm CO2 model results, i.e., closely resembling CO2 reconstructions for the latest Oligocene, reveal separate WAIS nuclei that evolved independently from the East Antarctic Ice Sheet. They were fuelled by increasing near-coastal precipitation and eventually expanded into West Antarctic marine basins as well as towards East Antarctic ice, which advanced from the Transantarctic Mountains. Our data-validated simulations emphasize the importance of considering both comprehensive climate information and bedrock topography for understanding initial West Antarctic glaciation – knowledge that is crucial not only for a better understanding of WAIS’s initiation, but also for assessing its future fate.
How to cite: Knahl, H. S., Klages, J. P., Hillenbrand, C.-D., Hochmuth, K., Bauersachs, T., Salzmann, U., Bickert, T., Titschack, J., Bohaty, S., Müller, J., Frederichs, T., Larter, R., van de Flierdt, T., Reinardy, B., Pälike, H., Kuhn, G., Gohl, K., Knorr, G., Lohmann, G., and Science Party of Expedition PS104, T.: Simulating the onset and evolution of West Antarctic glaciation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4989, https://doi.org/10.5194/egusphere-egu26-4989, 2026.
In Antarctica, ocean currents and ice sheet dynamics affect sediments, their erosion, transport and deposition, and the sedimentological record represents a precious natural archive of the past climate. The study of the mineralogical composition of modern sediments can be conducted by applying the most modern techniques of preparation and analysis of individual grains. The sediments studied were collected from a box-core (BC-08) within the PNRA ODYSSEA project, near the U1523 IODP site and considered as a valid present analogue of the site itself. The sampling site is on the edge of the Iselin Bank, under the influence of the Antarctic Slope Current, and records both along-slope circulation and inputs from the continent. Heavy minerals were concentrated in the 5-500 microns grain size window and the entire suite of heavy minerals was quantified. A specific protocol for silt and sand was applied separating heavy grains, calculating the percentage of minerals with density greater than 2.90 g/cm3, in different samples and describing the suite of minerals as a proxy of the source rocks in an interval of time from 14.000 yrs. BP to modern sediments. Combining optical microscopy and Raman spectroscopy, a high-resolution study of different species and varieties in groups of minerals was achieved, allowing a more detailed characterization of different magmatic and metamorphic sources. During point counting, the surficial texture of each single grain was described, highlighting how corrosion features in polar environments are common and could be used as an independent proxy identifying tendencies and changes in climate effects on sediments through time. Clinopyroxenes are the best candidate to record the degree of corrosion, due to their crystalline structure and chemical instability in the geological record. From Late Pleistocene to the Holocene, a clear trend and increasing in the weathering indices suggest a direct link with warming and production of brines, involved in the chemical dissolution of unstable silicates in sediments. The amount of sediment used was small, between 8-13 g. The percentage of heavy minerals in the 7 samples analysed remains almost constant throughout the time interval considered, varying between 2.2 and 2.7%, with the lowest amount in the most recent time. The pyroxene corrosion index varies through time, from 29% at the depth of 10-11 cm and it increases regularly up to 50% in the most recent sample, indicating a progressive effect of dissolution of unstable minerals in modern sediments. The mineralogical composition is characterized by a wide range of 35 minerals, associated with magmatic (pyroxenes and olivine) and metamorphic (amphiboles, epidote, garnet) source rocks around the Ross Sea. Detailed study of mineralogical assemblages in silt to medium sand represents a new tool for quantitatively demonstrating the effects of climate change recorded by sediments.
How to cite: Andò, S., Rabassi, M., Barbarano, M., Pastore, G., De Santis, L., Torricella, F., Zurli, L., Perotti, M., Lucchi, R. G., Colizza, E., Caburlotto, A., Gales, J., McKay, R., Rebesco, M., and Ferrante, G. M.: High-resolution heavy mineral analysis of marine sediments in the Ross Sea, Antarctica, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19647, https://doi.org/10.5194/egusphere-egu26-19647, 2026.
East Antarctica experienced a dramatic transformation in hydroclimate during the Miocene, from warm and wet conditions during the Miocene Climatic Optimum (MCO, ~14-17 Ma) to the establishment of polar desert conditions with cooling and ice sheet expansion during the Middle Miocene Climate Transition (MMCT, ~13.8 Ma) and late Miocene cooling interval (~6-8 Ma). During Miocene warmth, retreat of Antarctic ice sheets allowed for the rise of vascular plant ecosystems on Antarctica, which preserved information on terrestrial hydroclimate through their epicuticular waxes. Here, we investigate molecular biomarkers of plant waxes from East Antarctica preserved in the polar Southern Ocean at Ocean Drilling Program Site 1165. We quantify the isotopic composition of long-chain n-alkanoic acids, providing a record between 5 and 19 Ma. In addition, we present high-resolution (5 kyr) data between 13.2 and 15.1 Ma which span the expansion of the East Antarctic Ice Sheet during the MMCT.
Comparison of plant wax isotopes (δD) with Uk’37, a sea surface temperature (SST) proxy, that we measured in the same samples constrains interactions between polar Southern Ocean temperatures and East Antarctic terrestrial hydroclimate throughout the Miocene. Our records reveal a timescale-dependent relationship between SSTs and plant wax δD, with opposing isotopic responses to temperature forcing on orbital versus longer timescales. Our results demonstrate a complex response of Antarctic precipitation isotopes during the Miocene, with plant wax δD not only reflecting temperature changes, but also changes in vapor transport to Antarctica, aridity, and/or ecology. We conclude that our plant wax constraints on Antarctic precipitation isotopes have broader implications for the past isotopic composition of the East Antarctic Ice Sheet and the resulting deconvolution of global benthic δ18O into temperature and ice volume components during the Miocene.
How to cite: Nirenberg, J., Ibarra, D., and Herbert, T.: Coupled Southern Ocean temperatures and East Antarctic hydroclimate during Miocene global warmth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15222, https://doi.org/10.5194/egusphere-egu26-15222, 2026.
The Antarctic Circumpolar Current (ACC), Earth's largest ocean current, regulates global ocean circulation, Antarctic Ice Sheet stability, and the carbon cycle. Previous investigations have typically assumed uniform ACC variability across the Southern Ocean over Pleistocene glacial-interglacial cycles, yet proxy records show conflicting responses on orbital timescales. Here, we reconstruct the spatiotemporal variability of ACC strength over the past one million years using sortable silt mean grain size from a transect of six sediment cores in the South Indian Ocean, complemented by a synthesis of existing records from all Southern Ocean sectors. Our results reveal a persistent zonal asymmetry in ACC strength on glacial-interglacial and obliquity timescales. The Indian and Pacific sectors of the Southern Ocean exhibited anti-phased changes on both glacial-interglacial and obliquity timescales: during glacial and low-obliquity intervals, the ACC intensified in the Indian sector but weakening in the Pacific sector, with the pattern reversing during interglacials and high-obliquity periods. Proxy-model integration indicates this asymmetry is likely driven by sector-specific responses to shifts and intensification of the Southern Hemisphere westerly winds, bathymetric steering, sea-ice extent and meridional density gradients. These findings link ACC dynamics to interbasin exchange, ice sheet variability and the carbon cycle, providing insights into past and ongoing climate change.
How to cite: Wu, S., Mazaud, A., Michel, E., Erb, M. P., Stocker, T. F., Amsler, H. E., Le Tallec--Carado, P., Lamy, F., and Jaccard, S. L.: Zonally asymmetric variability of the Antarctic Circumpolar Current strength on orbital timescales , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15782, https://doi.org/10.5194/egusphere-egu26-15782, 2026.
From orbital (10 to 100 thousand years or kyr) to millennial (1 to 10 kyr) timescales, the Southern Ocean is thought to substantially modulate global climate and ocean variability by affecting global heat, salt, and nutrient distribution and the processes influencing storage and outgassing of atmospheric CO2. The millennial-scale variability remains underexplored, as little high-resolution records are available. This variability is unknown across the Mid-Pleistocene Transition (MPT), a period when Earth´s ice ages lengthened and intensified between ~1,250 and ~750 kyr ago (ka). We take advantage of the unique location of IODP Site U1539 in vicinity of the present subantarctic front. This location is characterised by unusual high sedimentation-rates (~10-50 cm/kyr), mainly because Site U1539 is reached by the northerly extended opal belt during glacials with high diatom deposition. This unique setting provides a high-resolution pelagic sediment archive in an area with strong oceanographic gradients. We reconstructed and present sea-surface temperature, primary productivity, opal content, and current strength over the past 1,400 ka at an unprecedented resolution.
How to cite: Rigalleau, V., Lamy, F., Ruggierri, N., Sadatzki, H., Arz, H. W., and Winckler, G.: Orbital and millennial-scale upper ocean dynamics in the Pacific Southern Ocean since the Mid-Pleistocene Transition , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1668, https://doi.org/10.5194/egusphere-egu26-1668, 2026.
Paleotemperature records from Antarctica and the Southern Ocean show a millennial variability in addition to the glacial-interglacial variability over the last glacial cycle. This millennial variability is the Southern Hemisphere counterpart of the Northern Hemisphere abrupt variability via the thermal bipolar seesaw, a concept describing the meridional heat transport leading to opposite temperature changes between both hemispheres. However, the thermal bipolar seesaw is typically studied from the atmospheric perspective using temperature records from ice cores in Greenland and Antarctica. While the thermal bipolar seesaw model was recently revisited using oceanic temperature records from the Iberian Margin (Davtian and Bard, 2023 PNAS https://doi.org/10.1073/pnas.2209558120), oceanic temperature records from the Southern Ocean remain to be considered.
We generated oceanic temperature records over the last 160 kyr using novel organic proxies (e.g., RI-OH′ and TEX86OH) from three deep-sea sediment cores located in the Southern Indian Ocean (cores MD11-3353, MD11-3357, and MD12-3394). We assessed the paleothermometric potential of the novel organic proxies and accuracy of preliminary temperature reconstructions by comparing them with a more established organic proxy (TEX86L) at the same Southern Indian Ocean sites, as well as with Antarctic temperatures and modern oceanic temperatures. All novel organic proxies, except %OH, show a glacial-interglacial variability. TEX86OH best shows the Antarctic-like millennial variability, notably at the MD12-3394 site with the highest-resolution temperature records. At the MD11-3357 site north of the Subantarctic Front, global calibrations yield more realistic temperature reconstructions with TEX86OH (from 5 to 12 °C) than with RI-OH′ (from 0 to 7 °C), possibly due to a stronger water depth effect on RI-OH′ than on TEX86OH coupled to bottom waters colder by roughly 9–10 °C than surficial waters. At the MD11-3353 and MD12-3394 sites south of the Subantarctic Front, regional calibrations of RI-OH′ and TEX86OH yield more consistent and more accurate temperature reconstructions (from –2 to 5 °C for RI-OH′ and from –1 to 5 °C for TEX86OH) than do global calibrations of these proxies (from –2 to 4 °C for RI-OH′ and from 0 to 8 °C for TEX86OH), as RI-OH′ and TEX86OH show reduced thermal sensitivity below 5 °C. At the MD12-3394 site, millennial warming amplitudes based on TEX86OH reach 1.5–2.0 °C for the most pronounced Antarctic-like warming events.
We then revisited the classical thermal bipolar seesaw model by comparing reconstructed Southern Ocean temperatures with simulated Southern Hemisphere temperatures. We selected the TEX86OH record from core MD12-3394 and a Southern Hemisphere temperature record simulated with two independent organic proxies (RI-OH′ and UK′37) from the southern Iberian Margin (core MD95-2042; Davtian and Bard, 2023). Despite the limited amplitude of Southern Ocean millennial warming events, our data-model comparison shows that to revisit the thermal bipolar seesaw model from the oceanic perspective is feasible by considering temperature records from the Southern Ocean and Iberian Margin. However, our study also demonstrates the need for high-resolution (200 to 500 years) oceanic temperature records from multiple sectors and sites in the Southern Ocean, including with the tested novel organic proxies.
How to cite: Davtian, N., Bard, E., and Martínez-García, A.: Revisiting the thermal bipolar seesaw model from the oceanic perspective by considering novel organic proxies from the Southern Indian Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19334, https://doi.org/10.5194/egusphere-egu26-19334, 2026.
The climate of the last glacial period was shaped by two dominating signals of glacial climate variability known as Dansgaard-Oeschger cycles and Heinrich events. Typically, these two modes of millennial-scale glacial climate variability are associated with dramatic, periodic climate changes in the northern hemisphere. Specifically, Heinrich events have been linked to instabilities of the Laurentide ice sheet. The discovery of Heinrich events has largely been based on the presence of repeated ice-rafted debris horizons in sediment cores from the North Atlantic. While similar geologic signatures have been found in sediment cores of the Southern Ocean, the hypothesis that the Antarctic ice sheet may have undergone similar millennial-scale episodes of instability has gained little attention in the scientific community. Here, we use a simulation of the period from 56,000 – 10,000 years before present with a novel climate-ice sheet-iceberg-solid earth model to explore the climatic response of southern hemispheric Heinrich events (SHEs). Our results reveal the global climatic fingerprint of SHEs. In addition, our simulated climate response reconciles three independent sources of proxy observations that have hitherto been interpreted in isolation. Overall, our model results suggest that the Antarctic ice sheet may have played a much more prominent role in shaping glacial climate variability than previously thought.
How to cite: Schannwell, C., Mikolajewicz, U., Kapsch, M. L., and Six, K. D.: Southern hemispheric Heinrich events as source of glacial climate variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5900, https://doi.org/10.5194/egusphere-egu26-5900, 2026.
Reconciliation of the southern and northern mechanisms of abrupt climate change is challenging, but the Southern Westerly Winds (SWW) variability stands with a main role in deciphering interhemispheric teleconnections. Normally focused as a polar interhemispheric debate, the southern middle latitudes are usually ignored in the millennial scale climate oscillations problem, despite they record the mobility of northern margin of SWW precipitation bearing belt in association with Antarctic and Southern Ocean variability. The SWW plays a central role for redistributing the Southern Ocean – atmosphere heat interchange globally through their role in atmospheric CO2, Antarctic circumpolar circulation and meridional overturning Circulation (AMOC) intensity in association with Southern Ocean front’s location. Nonetheless, we lack fundamental understanding of the SWW variability through the last glacial cycle and their linkage to the global climate system. Here, we produced a luminescence chronology in the paleodune and paleosol record of Ventanas II in the SE coastal Pacific (Chile, 32ºS) that track the latitudinal variability of the SWW in association with the high-latitude oscillations. Our findings consistently show dune morphogenesis occurs tied to Antarctic Isotope Maxima (AIM) interstadials that disrupt the otherwise stable southern glacial humid climate mode encompassed by long duration (multi-millennial) soil development. This record provides better insights into the interhemispheric mechanisms of climate change and the role of the SWW in driving the observed climate patterns during the ice age.
How to cite: García, J.-L., Pfeiffer, M., Luethgens, C., Quilamán, A., Opazo, M., and Tapia, C.: Dune morphogenesis in the SE Pacific record south shifted southern westerlies during the Antarctic Isotope Maxima (AIM) interstadials, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5935, https://doi.org/10.5194/egusphere-egu26-5935, 2026.
Glacials and interglacials characterized the Quaternary period and were caused by global and regional climate fluctuations. The advances and retreats of glaciers in New Zealand’s Southern Alps during the Late Quaternary can be attributed to global climate fluctuations in conjunction with the adjacent surface ocean dynamics and interactions with the southern westerly wind belt. Several studies have been conducted to better understand the role of New Zealand’s climate in the Quaternary ice age cycles, mostly focusing on the last glacial period that is well covered by regional climate archives. However, marine sediment cores can be used as continuous archives for glacier fluctuations over several of the past glacial-interglacial cycles. The present study investigates the glaciation history of New Zealand’s South Island over the last 200,000 years and its interaction with paleoceanographic changes of the adjacent Southeast Tasman Sea. South of New Zealand, Solander Trough is located under the Subtropical Frontal Zone (STFZ) that separates warm subtropical waters from cold subantarctic waters. During glacial periods, the STFZ shifted equatorward. Core SO290-17-1 from Solander Trough was dated using oxygen isotopes from benthic foraminifera as well as paleo- and rock-magnetic measurements in combination with x-ray fluorescence (XRF) core scanning data and aligning them to a well-dated neighboring sediment core (TAN1106-28; Toucanne et al., 2026) covering the last glacial period. n-alkane biomarkers were used to investigate terrigenous input and vegetation changes, whereas C37 alkenones (UK’37) were used to estimate sea-surface temperatures (SST). These data are compared to the Ti/K ratio and terrigenous Nd isotope compositions (expressed as ɛNd) of the sediments as proxies for the source of the terrigenous material and hence glacier fluctuations. The concentration of n-alkanes increases during glacial periods indicating terrestrial organic matter input. The Ti/K ratio shows a similar pattern and indicates compositional changes of the terrigenous fraction that are also seen in ɛNd and suggest that during these phases, extensive glaciation occurred in the Southern Alps. The SST anti-correlates with those glacier advances and follows an Antarctic pattern. Changes in SST of ~12°C can be observed between glacial and interglacial periods together with a short-term, millennial variability. Compared to Patagonia, the SST changes more abruptly and with a higher magnitude. Our preliminary results indicate glacier advances during MIS 5b and 5d, which are consistent with the dominance of beech forests from pollen records during these cooler intervals. Furthermore, our data indicate large glacier fluctuations during MIS 6 with three major expansion phases at ~137 ka, ~157 ka and ~178 ka and even more frequent phases of glacier expansions on a millennial scale.
References
Toucanne, S., Vázquez Riveiros, N., Soulet, G., Blard, P.-H., Migeon, A., Rigalleau, V., Roubi, A., Cheron, S., Boissier, A., Menviel, L., and Bostock, H.: Synchronous bipolar retreat of mid-latitude ice masses during Heinrich Stadials, Nat. Geosci., 1–6, https://doi.org/10.1038/s41561-025-01887-x, 2026.
How to cite: Krüger, H., Kaiser, J., Toucanne, S., Lamy, F., Lembke-Jene, L., Nowaczyk, N., Pahnke, K., and Arz, H. W.: Millennial-scale glacier fluctuations in southern New Zealand during the past 200 ka, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13595, https://doi.org/10.5194/egusphere-egu26-13595, 2026.
Atmospheric mineral dust is an important component of the global climate system. It influences the Earth’s radiative budget and supplies (micro)nutrients like iron (Fe) to the ocean. The Southern Ocean is a critical region where dust-Fe input enhances primary productivity and thus oceanic uptake of atmospheric CO₂. The climate impact of dust-Fe depends on its total amount and partial solubility of the dust particles releasing Fe to the surface ocean, and the latter critically depends on the rock composition and environmental conditions in the source regions. However, these dust properties are particularly poorly constrained for the Pliocene and Pleistocene time period. Here we present radiogenic neodymium, strontium and lead isotope compositions paired with element concentration data of the dust fraction extracted from marine sediments of IODP Expedition 383 Sites U1540 and U1541 in the subantarctic South Pacific to trace dust provenance and chemical maturity. Our data reveal systematic shifts in the origin and chemical maturity of dust particles from orbital to millennial time scales during major climate transitions of the last four million years. Notably, there is an increase in South American dust contributions from ~40% to 60% across the Northern Hemisphere Glaciation, and from ~30% to 65% during the Mid-Pleistocene Transition. These pronounced changes in dust provenance correspond with shifts toward more pristine mineral compositions of the dust fraction reaching the South Pacific. Tracers of export production such as opal flux indicate a high sensitivity of South Pacific carbon export to the chemical maturity of the dust particles rather than the total dust-Fe input, amplifying export production during the Mid-Pleistocene Transition and across Northern Hemisphere Glaciation.
How to cite: Krishnamurthy, K., Pahnke, K., Longman, J., Basak, C., Kapuge, I. U., Lamy, F., Winckler, G., and Struve, T.: Properties and impact of South Pacific dust over the last four million years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20610, https://doi.org/10.5194/egusphere-egu26-20610, 2026.
Southern Ocean deep water mass dynamics, their interaction with the upper ocean and atmosphere in the Subantarctic Zone, are key components in Pleistocene climate change on orbital to (sub-)millennial timescales. Variations in ventilation and biogeochemical characteristics of bathyal and abyssal water masses, as well as changes in the stratification between those deep and mesopelagic waters play a major role in the marine carbon cycle and hence atmospheric CO2 concentrations on geological timescales. The realisation of IODP Expedition 383 DYNAPACC to the subantarctic South Pacific closed a critical gap in available sedimentary records from the high-latitude Southern Hemisphere, in particular for the Pacific. We use those sites in combination with piston cores from R/V Polarstern campaigns to study changes in water mass patterns and their physical and chemical signatures in the Subantarctic Zone and northern section of the ACC across the last 1.2 Ma BP. We measured benthic and planktic foraminiferal oxygen and carbon isotopes to reconstruct physical and ventilation characteristics, with one focus on Lower Circumpolar Deepwater (LCDW) at the intersection to Antarctic Bottom Water (AABW). Our results provide an abyssal δ18O and δ13C South Pacific water mass signature over last 1.4 Ma BP with with suborbital- to millennial-scale resolution, allowing to differentiate different CDW, AABW source waters and their subsequent mixing. Complementary XRF scanning-derived Zr/Rb ratios are used to relate observed variations to abyssal bottom current strength changes in the Antarctic Circumpolar Current domain. Observed offsets between Ross Sea-derived AABW and our sites imply mixing with other source waters and higher glacial isolation from proximal Antarctic bottom water sources than previously thought.Generally, glacial epibenthic δ13C minima correlate with Antarctic CIrcumpolar Current strength reductions. Suborbital- to millennial-scale δ13C changes vary in phase with atmospheric CO2 changes as recorded in the EPICA Dome C ice core back to 800 ka BP, implying a critical role of the bathyal to abyssal Pacific Southern Ocean in the Pleistocene marine carbon cycle.
How to cite: Lembke-Jene, L., Ruggieri, N., Iwasaki, S., Rigalleau, V., Venancio, I. M., Arz, H. W., and Lamy, F.: Orbital- to Millennial-scale Changes in Pacific Circumpolar Deepwater Circulation and Ventilation During the Pleistocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21067, https://doi.org/10.5194/egusphere-egu26-21067, 2026.
Antarctic Bottom Water (AABW) is a critical component of the global meridional overturning circulation, driving abyssal ventilation, heat storage, and carbon sequestration on centennial to millennial timescales.Despite its importance, the mechanisms governing AABW formation across different climate states remain poorly understood. Here we investigate AABW production during five paleoclimate periods including preindustrial (PI), mid-Holocene (MH), Last Interglacial (LIG), Last Glacial Maximum (LGM), and Marine Isotope Stage 3 (MIS3) using the AWI-ESM coupled climate model. Through water mass transformation (WMT) analysis and surface buoyancy flux decomposition using the xbudget framework, we quantify the relative contributions of thermal (longwave, shortwave, sensible, and latent heat) and haline (sea ice and precipitation-evaporation-runoff) forcing to AABW precursor water formation.Our results reveal a fundamental shift in formation mechanisms between climate states: during interglacial periods (PI/MH/LIG), heat fluxes dominate AABW precursor water production, whereas glacial conditions (LGM/MIS3) exhibit enhanced sea ice-driven transformation. Surface flux decomposition reveals that glacial conditions paradoxically reduce ocean heat loss despite colder atmospheric temperatures, as expanded sea ice insulates the bulk ocean while concentrating brine rejection. Ideal age tracer simulations demonstrate that AABW ventilation ages during LGM/MIS3 exceed preindustrial values by approximately 1,500 years, consistent with paleoceanographic proxy reconstructions. The LIG Ross Sea exhibits anomalously young ventilation ages attributed to reduced sea ice and enhanced thermal forcing.
How to cite: Shi, X., Liu, J., Yang, H., and Werner, M.: Antarctic Bottom Water Formation Mechanisms Across different Periods: Insights from Water Mass Transformation Analysis Using AWI-ESM, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21934, https://doi.org/10.5194/egusphere-egu26-21934, 2026.
The Southern Ocean plays a key role in regulating atmospheric CO₂ through ocean circulation, sea-ice dynamics, and biological carbon sequestration. However, the response of biological productivity south of the Antarctic Polar Front (APF) to millennial-scale climate variability during the Last Glacial Period remains incompletely understood, largely due to the scarcity of high-resolution records from this region. Here we present a multiproxy reconstruction of biological productivity and paleoceanographic conditions over the past ~26 kyr based on sediment core KH-19-6-PC07 recovered from the eastern South Sandwich Islands region.
We combine geochemical proxies (total organic carbon, Br/Ti, and Si/Ti ratios), stable nitrogen and carbon isotopes, diatom assemblage data, and grain-size analyses with a dust-correlated age model. The age model is supported by radiocarbon dating of acid-insoluble organic carbon and geomagnetic relative paleointensity. The results indicate persistently low biological productivity and seasonally extensive sea-ice cover between 26 and 24 ka. During this interval, diatom assemblages are dominated by taxa associated with cold, sea-ice-influenced conditions, consistent with reduced nutrient availability and limited light conditions.
In contrast, Antarctic Isotope Maximum 2 (AIM2; ~24–23 ka) is characterized by a marked increase in diatom productivity, a decline in δ¹⁵N values, and major shifts in diatom community composition. These changes are accompanied by an abrupt retreat of both summer and winter sea-ice margins, suggesting enhanced nutrient supply and reduced nutrient utilization efficiency under more open-water conditions. A transient dominance of Thalassiothrix antarctica further points to the development of strong surface-water stratification following rapid sea-ice melt.
Comparison with nearby sedimentary records from the Scotia Sea and the eastern Weddell Sea shows that, despite comparable or higher diatom concentrations, KH-19-6-PC07 consistently records lower abundances of sea-ice-associated diatom taxa. This pattern suggests relatively warmer surface conditions in the eastern South Sandwich Islands region during the investigated interval. We propose that these regional characteristics reflect intensified heat and nutrient supply linked to changes in ocean circulation, potentially associated with poleward shifts or enhanced meandering of the southern boundary of the Antarctic Circumpolar Current along the South Sandwich Trench. Overall, our results highlight pronounced spatial heterogeneity in Southern Ocean surface conditions during millennial-scale climate events and emphasize the importance of ocean circulation and bathymetric influences in modulating biological productivity south of the APF during the Last Glacial Period.
How to cite: Ikehara, M., Osanai, A., Kato, Y., Itaki, T., Obrochta, S. P., Yamazaki, T., and Yamaguchi, A.: Millennial-scale variability in biological productivity south of the Antarctic Polar Front during the last glacial period, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6216, https://doi.org/10.5194/egusphere-egu26-6216, 2026.
Marine Isotope Stage 11 (MIS 11; ~424–374 ka) was an exceptionally long and warm interglacial, characterized by a ~30 kyr plateau in atmospheric CO2 that remains poorly understood. Here we present new multiproxy evidence from the Pacific sector of the Southern Ocean indicating that MIS 11 operated under a distinct mode of carbon cycling dominated by intermediate-water processes. Stable isotope and Mg/Ca records from 54ºS and 45ºS reveal a pronounced δ13C enrichment in thermocline waters, contrasted by a muted surface expression at 54°S, indicating strong vertical decoupling in the transmission of ventilation signals. We interpret this pattern as consistent with enhanced ventilation and export of Antarctic Intermediate Water (AAIW), which efficiently transmitted high-δ13C signals into the Pacific thermocline, while anomalously warm and saline Subantarctic Mode Water (SAMW) at the surface limited the upward expression of these signals. Hydrographic reconstructions further indicate an unusual density structure during MIS 11, with buoyant surface waters overlying denser intermediate waters and enhanced advection within the Antarctic Circumpolar Current. Together, these findings support a circulation-driven mechanism in which intermediate waters facilitated subsurface carbon sequestration while muted surface feedbacks limited CO2 drawdown, providing a coherent explanation for the prolonged stability of atmospheric CO2 during MIS 11. This intermediate-water–dominated carbon-cycling mode highlights how prolonged warm interglacials may operate under ocean–carbon states distinct from shorter interglacials.
How to cite: Tapia, R., Nuernberg, D., Lamy, F., and Tiedemann, R.: Subantarctic hydrography and intermediate-water carbon sequestration during MIS 11, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5325, https://doi.org/10.5194/egusphere-egu26-5325, 2026.
The rise in atmospheric CO₂ during the last deglaciation has been attributed to carbon release from the deep ocean, establishing the ocean interior as the dominant reservoir modulating glacial–interglacial CO₂ variability. In contrast, the processes by which carbon was sequestered in the ocean during periods of declining atmospheric CO₂ remain poorly constrained. In particular, three irreversible CO₂ drawdown events since the last interglacial (MIS 5d, MIS 4, and MIS 2) represent critical intervals for understanding how the ocean stored carbon over multi-millennial timescales. Here we reconstruct vertical profiles of carbonate ion concentration ([CO₃²⁻]) from deep-sea sediment records in the South Pacific, located at the junction of the Pacific and Atlantic deep-water pathways. Millennium-scale measurements of carbonate dissolution reveal distinct depth-dependent [CO₃²⁻] changes that correspond to variations in the Atlantic Meridional Overturning Circulation (AMOC) and the Antarctic Circumpolar Current (ACC). The results reveal that during periods of CO₂ drawdown, the South Pacific developed a pronounced two-layer structure, reflecting the contrasting influences of bathypelagic carbon accumulation and abyssal ventilation. By integrating our new records with existing datasets from the equatorial Pacific to Atlantic, we show that each of the three irreversible CO₂ drawdown events was characterized by carbon storage in different oceanic basins and depth ranges. These findings reveal that distinct circulation regimes of the AMOC and ACC governed deep-ocean carbon sequestration during glacial intensification, which advance our understanding of how the deep ocean regulates atmospheric CO₂.
How to cite: Iwasaki, S., Kimoto, K., Lembke-Jene, L., Venancio, I. M., Irino, T., Kobayashi, H., and Lamy, F.: Two-Layered South Pacific Carbon Reservoirs and Deep-Water Export to the Atlantic During CO₂ Drawdowns Since the Last Interglacial, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15499, https://doi.org/10.5194/egusphere-egu26-15499, 2026.
Posters on site: Wed, 6 May, 10:45–12:30 | Hall X5
Ice-sheet models that underpin current projections of future sea-level change often calibrate sensitivity to changes in climate using palaeo-ice volume estimates for the Mid-Pliocene Warm Period (MPWP; ∼3 Ma), the most recent interval with climatic conditions approximating those expected in the near future. The ice-sheet model runs used in these calibrations generally assume MPWP bedrock topography equal to that of the present day. Bedrock topography is a major control on ice-sheet volumes predicted by these models, since marine-based regions are highly susceptible to runaway destabilisation. However, dynamic topography (DT; i.e., topography supported by convectively generated stresses) is likely to have evolved substantially over the past ∼3 Ma, invalidating this assumption. To our knowledge, no study has yet assessed this impact on Greenland’s MPWP equilibrium ice volume, while only one study has done so for the Antarctic Ice Sheet (AIS) using relatively low-resolution seismic tomography to predict mantle flow patterns.
This study aims to more accurately quantify DT impacts on Pliocene ice-sheet stability at both poles using high-resolution seismic tomographic and geodynamic models. Existing DT predictions and observations of present-day DT are compared, finding generally good agreement, though a +0.8 km offset in observed values is seen across the North Atlantic region. This feature can be explained by invoking isostatic elevation of melt-depleted oceanic mantle lithosphere resulting from longstanding interaction between the Iceland plume and North Atlantic mid-ocean ridge spreading centres. Improved correlations between shear-wave velocity (VS) and residual depth anomalies motivate incorporation of a higher-resolution Antarctic seismic tomographic mantle model into DT predictions by merging it in temperature space with a lower resolution global model. The resulting mantle convection simulations and reconstructions of post-MPWP DT change enable more accurate prediction of Pliocene bedrock topography. Ice sheet models are run on both DT-corrected MPWP topography and present-day topography, showing differences in steady-state ice volume of ∼1.8 m sea-level equivalent (SLE), with complete loss of the Ross Ice Shelf occurring in the former. This substantial DT-related component of observed MPWP sea-level excess suggests existing estimates of climatically controlled AIS contributions need to be lowered, reducing inferred ice-sheet sensitivity. Recalibrating existing sea-level projections accordingly reduces predicted end-of-century Antarctic contributions to future sea level change by 45%. Ice sheet models are also run under a representative Pliocene climate to verify whether this bedrock-topography driven equilibrium ice volume difference is independent of climatic forcing, as suggested by recent palaeo-ice-sheet modelling work.
How to cite: Broadley, L., Richards, F., and Hazzard, J.: Impact of Late Neogene Dynamic Topography on Antarctic and Greenland Ice-Sheet Stability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12164, https://doi.org/10.5194/egusphere-egu26-12164, 2026.
Hole U1524A from IODP Expedition 374 provides a new record of sedimentary cycles on the Ross Sea continental slope over the past 1.5 Ma. A robust stratigraphic framework for the upper 51.13 m of Hole U1524A is established using diatom biostratigraphy, paleomagnetic data, volcanic ash layers, and geochemical (Zr/Rb) records. On the continental slope, opal cannot be directly used as a proxy for productivity, as it is more strongly influenced by reworking processes. Further reconstruction of surface ocean conditions based on diatom assemblages reveals a sedimentary pattern characterized by gradual WAIS expansion during glacial periods, with extensive sediment transport to the lower continental slope, and by enhanced ASC and southward CDW intrusion during interglacials, causing substantial ice-shelf melting and IRD input. Changes in surface ocean conditions began around ~1 Ma. Prior to the early MPT (~1.5-1.0 Ma), glacial-interglacial variability was relatively mild and open ocean conditions prevailed. Subsequently, long-term cooling led to progressively greater sea ice extent and longer sea ice seasons even during interglacials, likely driven by declining atmospheric CO₂. This promoted longer sea ice seasons, enhanced upper-ocean stratification, increased carbon storage, and expansion of the Antarctic Ice Sheet. Following the MPT (post ~0.7 Ma), glacial-interglacial cycles were characterized by stronger oscillations. Diatom records from U1524 also provide evidence supporting WAIS retreat after the MPT. These findings highlight the critical role of surface ocean environmental changes and oceanic forcing in regulating Antarctic ice sheet dynamics and carbon storage, with implications for future ice-sheet stability in a warming climate.
How to cite: Li, Q., Xiao, W., Wang, R., and Esper, O.: Middle Pleistocene West Antarctic Ice Sheet variability in the Ross Sea inferred from diatom assemblages, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10239, https://doi.org/10.5194/egusphere-egu26-10239, 2026.
Antarctic ice-core records reveal that over the past 800 000 years (800 kyr), atmospheric pCO₂ closely tracked global climate variability on orbital timescales, declining progressively to ~180 ppm during glacial periods and increasing rapidly by 50–100 ppm during glacial terminations. The Southern Ocean is widely recognized as a key regulator of atmospheric pCO₂ at these timescales, owing to its strong influence on global air–sea CO₂ exchange through coupled physical and biological processes. In particular, the marine biological pump plays a central role: while the production and export of organic carbon reduce surface-ocean and atmospheric pCO₂, the formation and export of biogenic carbonate increase surface-ocean pCO₂ and may partially offset this drawdown. Consequently, variations in the balance between organic and inorganic carbon export—commonly expressed as the export rain ratio—exert a first-order control on atmospheric pCO₂. Although this ratio is relatively well constrained in the modern ocean, its past variability remains poorly documented.
Here, we reconstruct glacial–interglacial changes in the rain ratio across the Southern Ocean using a combination of micropaleontological (coccoliths and foraminifera) and geochemical (CaCO₃, total organic carbon (TOC), δ¹³C, C/N) records from sediment core MD04-2718 (1428 m water depth; 48°53.31′S, 65°57.42′E), located in the Polar Front Zone (PFZ, Indian sector), complemented by published records from the Subantarctic Zone (SAZ). We show that sedimentary CaCO₃ primarily reflects the export of biogenic carbonate by calcifying phytoplankton and zooplankton, whereas TOC records the export of phytoplankton-derived organic carbon. Accordingly, TOC/CaCO₃ ratios provide a robust proxy for past variations in the rain ratio.
Our results indicate higher rain ratios during glacial periods, driven by enhanced organic carbon export associated with increased diatom productivity, as colder conditions and intensified iron-rich dust inputs prevailed. In contrast, lower rain ratios during interglacials reflect strengthened carbonate export, as warmer conditions and enhanced macronutrient supply from reinvigorated Southern Ocean upwelling, favored coccolithophore and foraminifera productivity. These patterns further suggest that glacial northward migration of the polar front system, combined with reduced sea-surface temperatures and expanded sea-ice cover, promoted an equatorward retreat of coccolithophores and a northward expansion of diatom-dominated ecosystems, with opposite trends during interglacial periods. Because increases in rain ratios generally coincide with declining atmospheric pCO₂, our results support a role for glacial–interglacial rain-ratio dynamics in the SAZ–PFZ — driven by shifts between silica- and carbonate-producing phytoplankton communities — in modulating the global carbon cycle.
How to cite: Wang, Y., Duchamp-Alphonse, S., Sépulcre, S., Brandon, M., Michel, E., Pige, N., Crosta, X., Etourneau, J., Lowe, V., Bartolini, A., Bassinot, F., Isguder, G., Richard, P., Manssouri, F., Nouet, J., Jardillier, L., and Jaccard, S.: Polar Front System variability and its control on export rain ratio over the past 800 ka: implication for atmospheric pCO2 changes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11611, https://doi.org/10.5194/egusphere-egu26-11611, 2026.
Recent work indicates that the Southern Ocean underwent major reorganisation during the Late Miocene, culminating in the establishment of a modern-like Antarctic Circumpolar Current (ACC). Understanding how changes in ACC dynamics interact with Antarctic ice-sheet behaviour is essential for constraining past ocean–ice feedbacks and for assessing the sensitivity of marine-based sectors of the Antarctic Ice Sheet to future warming. Here, we present new mean sortable silt records from ODP Site 1192 in the South Atlantic Ocean and ODP Site 744 in the South Indian Ocean, both located along the main pathway of the ACC and spanning the past ~18 million years. These records are combined with neodymium isotope compositions (εNd) of fine-grained (<63 μm) detrital sediments from ODP Site 1165, situated on the continental rise off Prydz Bay, East Antarctica, providing complementary constraints on ACC strength, sediment transport, and ice-sheet dynamics. Our results indicate that the development of a vigorous, modern-like ACC during the Late Miocene coincided with a major reorganisation of the ice sheet in the Prydz Bay sector, marking a transition toward a more dynamic ice-sheet state. Overall, our data suggest that oceanic forcing became increasingly important following the establishment of modern-like ACC conditions, highlighting intensified ocean–ice interactions since the Late Miocene.
How to cite: Evangelinos, D., van de Flierdt, T., Pena, L., Paredes, E., Cacho, I., and Escutia, C.: Intensified coupling between the East Antarctic Ice Sheet and the Antarctic Circumpolar Current during the Late Miocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12944, https://doi.org/10.5194/egusphere-egu26-12944, 2026.
The continental margin of the Wilkes Subglacial Basin (WSB) in East Antarctica presents a complex morphology, with overdeepened basins and articulated sedimentary architectures, which reflect an evolutionary history controlled by interactions between ice-sheet dynamics, ocean circulation, isostatic response, and sedimentary processes. The existing marine seismic data suggest a dynamic history of ice-sheet advances and retreats, with episodes of submarine continental-slope instability. The study focuses on the role of glacio-isostatic adjustment (GIA) in controlling the morphological changes of the Wilkes continental margin during the Late Pleistocene. To achieve this objective, we use a combination of two GIA models, TABOO (Spada et al., 2003) and the Sea-level Equation Solver SELEN4 (Spada et al., 2019) to reconstruct the temporal evolution of uplift and subsidence along the WSB continental margin. TABOO allows us to compute the general response of a spherically symmetric, incompressible, Maxwell viscoelastic and self-gravitating Earth to ice loads. SELEN4 solves the sea-level equation for a 1D spherically symmetric Earth with linear viscoelastic rheology, taking into account the migration of shorelines and the rotational feedback on sea level. Recent seismic tomography studies suggest that the lithosphere is thinner than previously thought in this sector and this also suggests that the mantle beneath could be less viscous than usually prescribed in ice-sheet models (Hansen et al., 2025). We set up idealised simulations of the WSB to understand the sensitivity of its continental margin to ice surface loads and rheological variations of the lithosphere and the Earth’s mantle. This work aims to highlight the role that GIA played in the morphological evolution of the WSB continental margin and the consequent influence on ice-sheet stability and on its potential contribution to global sea level during deglaciation phases.
How to cite: Di Pauli, M., De Santis, L., Colleoni, F., Stocchi, P., and Petrini, M.: Numerical modeling of the past stability of the Wilkes Subglacial Basin (East Antarctica) continental margin: interplay between glacio-isostatic adjustment and ice-sheet dynamics. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13570, https://doi.org/10.5194/egusphere-egu26-13570, 2026.
The Southern Ocean’s frontal system controls nutrient availability and sea-ice extent in the region, thus participating in the regulation of biological productivity and the export of carbon to the deep ocean. Sedimentary evidence indicates that latitudinal migrations of frontal boundaries accompanied glacial-interglacial transitions, with implications for spatial patterns of export production. Here, we present new biostratigraphic, geochemical, and sedimentological results of a sediment core transect along 100°E from the Antarctic coast to the Southeast Indian Ridge from the expedition PS140 of R/V Polarstern to address Pleistocene dynamics of oceanic fronts within the Antarctic Circumpolar Current, changes in sea surface water temperatures, sea-ice extent, and surface water productivity. A profile of eight piston cores was retrieved, comprising three sediment cores from the Seasonal Ice Zone (SIZ) and Permanent Open Ocean Zone (POOZ) south of the Antarctic Polar Front, and five sediment cores from the Polar Frontal Zone (PFZ) to the Subantarctic Zone (SAZ). Our stratigraphic framework is based on a combination of lithostratigraphic correlations, benthic foraminiferal oxygen-isotope data, and the tuning of dust records from our cores to Antarctic reference records. We also obtained planktic radiocarbon dates for younger sections. We use XRF-scanning-based element ratios, magnetic susceptibility, GRAPE densities, and bulk inorganic geochemistry data to reconstruct changes in export production and terrigenous sediment delivery via dust and ice transport. Major lithologies in the SIZ and POOZ are mainly diatom oozes with minor terrigenous components. The multiproxy data from the PFZ to the SAZ indicate a transition from biosiliceous to calcareous sediments. The northernmost cores of the transect are characterized by alternating sequences of foraminifera-bearing nannofossil ooze and diatom ooze. These alterations are likely derived from lateral migrations of the subantarctic frontal system and may reflect the frontal movement during glacial-interglacial changes. Our findings serve as the basis for ongoing and upcoming studies that will generate complementary paleoceanographic and paleoclimatic information in this to date poorly studied region of the Southern Ocean.
How to cite: Amezcua Montiel, A., Esper, O., Otto, D., Lamy, F., Gutjahr, M., Mollenhauer, G., and Lembke-Jene, L.: Subantarctic Indian Ocean export production and frontal dynamics over the last glacial-interglacial cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15766, https://doi.org/10.5194/egusphere-egu26-15766, 2026.
The Southern Ocean (SO) and Antarctica are intrinsic to the Earth´s climate system. While the oceanic firewall of the Antarctic Circumpolar Current (ACC) frontal system is presently mitigating ocean warming and enhancing ice-sheet stability in Antarctica, it is beginning to weaken and its future is uncertain. With few exceptions, instrumental and satellite-based climate records in the SO and Antarctica do not exceed the past 50 years and are thus too short to place the recent anthropogenic global warming-induced SO changes in the context of natural climate variability.
It has long been recognized that the distribution of biogenic and terrigenous sediments in the SO closely reflects the meridional character of the ACC, which critically links the climatic gradients between glaciated Antarctica and the subtropics (e.g., Diekmann, 2007; Keany & Kennet, 1972). The most prominent SO sedimentation pattern is the circumpolar occurrence of diatomaceous oozes, formed of the amorphous opaline silica (Si) remains of marine micro algae. This so-called opal belt (Lisitzin, 1971) is the largest sink of biogenic Si in the world ocean (Chase et al., 2015). Opal contents in the SO are maximal in the vicinity of the Polar Front and decrease towards Antarctica, the latter being largely controlled by increasing sea-ice cover (Chase et al., 2015). Today, the opal belt in the Polar Frontal Zone roughly corresponds to the modern oceanic firewall, i.e. the limit between substantial surface ocean warming to the north and dampened surface warming to the south. North of the Subantarctic Front, an abrupt shift occurs to predominantly calcareous sediments, composed of carbonate skeletal remains built by planktic and benthic foraminifera and marine algae (coccolithophorids).
We assess past changes in sediment budgets across the ACC fronts, and assess four-dimensional variations of ACC circulation across different climate states. This is done through sediment echosounder records, calibrated with down-core sediment records along the cross-frontal transects. These data allow to obtain geographically extensive estimates of changes in the position and latitudinal distribution of major oceanic sediment types occurring at the SO firewall.
At the present stage, we focus on ACC fluctuations and frontal shifts on cross frontal transects from selected regions in SW Pacific SO domain, where previous expeditions provide sediment echosounder profiles and sediment cores. However, future research requires the integration of additional core material, and a denser grid of sediment echosounder data in different SO sectors in order to capture expected zonal heterogeneities of ACC strength changes and frontal shifts on a hemispheric scale. For this purpose, substantial coordination efforts and collaboration with international partners is required.
Diekmann B (2007) Sedimentary patterns in the late Quaternary Southern Ocean. Deep Sea Research Part
Keany J, Kennett JP (1972) Pliocene-early Pleistocene paleoclimatic history recorded in Antarctic-Subantarctic deep-sea cores. Deep Sea Research and Oceanographic Abstracts, 19(8):529–548.
Lisitzin AP (1971) Distribution of siliceous microfossils in suspension and in bottom sediments, in The Micropaleontology of Oceans, edited by B. M. Funnell and W. R. Reidel, pp. 173–195, Cambridge Univ. Press.
Chase Z, Kohfeld KE, Matsumoto K (2015) Controls on biogenic silica burial in the Southern Ocean. Glob. Biogeochem. Cycles 29:1599-1616.
How to cite: Lamy, F., Lembke-Jene, L., Miramontes, E., Schwenk, T., Gebhard, C., and Arz, H. W.: Southern Ocean sediment records reveal future scenarios of the circum-Antarctic frontal system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17683, https://doi.org/10.5194/egusphere-egu26-17683, 2026.
The fate of the Antarctic Ice Sheet (AIS) under climate warming remains highly uncertain. Geological evidence from the warm Miocene Climatic Optimum (MCO, ~17–14.7 Ma) are still limited to few circum-Antarctic records, but they generally suggest a substantial AIS retreat and reduced or absent sea-ice. Yet the magnitude and temporal variability of the cryosphere dynamics within the generally warm MCO remain poorly constrained. Here, we present marine and terrestrial palynological results from sediments drilled at Site U1521 on the outer shelf of the central Ross Sea during International Ocean Discovery Program (IODP) Expedition 374 spanning portions of the interval ~ 17.3 to ~ 14.5 Ma. Dinoflagellate cysts and other aquatic palynomorphs, including brackish-water algae, indicate phases of progressive cryosphere melting, related to marine-terminated ice to fully open-ocean conditions, punctuated by ephemeral ice re-advances including both sea-ice and land-ice during the interval 16.3 to 15.8 Ma. Terrestrial palynomorphs reflect a generally warming trend, but alternating cooling and warming conditions on the hinterland, closely coupled to ice and ocean dynamics. Despite the fluctuations, persistent vegetation implies a vigorous hydrological cycle, consistent with enhanced moisture delivery under a generally warm climate. In addition, we conducted marine palynological analyses at unprecedented millennial-scale resolution in two intervals of the MCO (~ 16.2 Ma and ~ 16 Ma) where such resolution could be achieved. During the first interval dinoflagellate cysts suggest stepwise changes towards more open-ocean conditions interrupted by transient cooling events (with sea-ice presence) and generally high productivity. In contrast, the interval ~ 16 Ma is characterized by persistent open-ocean condition and low productivity.
How to cite: Sangiorgi, F., Hou, S., Sriwichai, M., and Prebble, J.: Central Ross Sea cryosphere and ocean variability during the early and middle Miocene: palynology from IODP 374 Site U1521, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16892, https://doi.org/10.5194/egusphere-egu26-16892, 2026.
The Amery Ice Shelf, the third largest ice shelf at the head of Prydz Bay, and one of the four regions where Antarctic Deep Waters form, is reported as one of the most stable portions of the East Antarctic Ice Sheet (EAIS). Yet, its response to future warming remains uncertain. The Miocene Climatic Optimum (MCO, ~17–15 million years ago) is the warmest period of the past 23 million years, with global temperatures 3–8°C above modern and pCO2 of 400–600 ppm, similar to end-century projections. It therefore provides a valuable opportunity to investigate EAIS stability under warm conditions. Here, we present a combined lipid biomarker, palynology and XRF record from ODP Site 1165, offshore Prydz Bay, spanning ~16.3-16 Ma at an unprecedented millennial-scale resolution, crucial for understanding the near-future EAIS conditions in a warmer world. Interestingly, the record shows recurrent pulse-like intense organic matter oxidation events associated with elevated proportions of reworked and oxidation-resistant in situ dinoflagellate cysts as well as ice-rafted debris (IRD). IRD presence in this record was previously interpreted as evidence for deglaciation. However, deglaciation, meltwater and subsequent stratification are somewhat in contrast with seafloor oxidation.
Oxidation events at the seafloor may rather be linked to oxygen-rich deepwater associated with EAIS and sea ice dynamics at location, or other processes we are investigating. Excluding the interval where organic matter oxidation is recorded, the remaining record indicates relatively stable seawater conditions. Specifically regarding sea water temperature (SST) based on glycerol dialkyl glycerol tetraethers (GDGTs)-based SST proxy (TEX86) and alkenone-based SST proxy both suggest SSTs around 9-16°C, although hydroxylated-GDGTs suggest much lower SSTs around 4-9°C. Furthermore, the occurrence of plant-derived fatty acids and pollen-spore assemblages indicate a sustained woody-tundra vegetation and an intensified hydrological cycle on the hinterland than modern throughout the record.
How to cite: Hou, S., Nierop, K. G. J., Leenarts, G., Nirenburg, J., Herbert, T., Kulhanek, D., Peterse, F., Bijl, P. K., and Sangiorgi, F.: Millennial-timescale East Antarctic Ice Sheet variability and recurrent seafloor oxidation pulses during the Miocene Climatic Optimum at Prydz Bay, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17809, https://doi.org/10.5194/egusphere-egu26-17809, 2026.
Sediment core SO290-33-2 from the Lord Howe Rise (Tasman Sea) provides a unique archive to investigate long-term changes in sea surface temperatures (SST) and aeolian dust input from Australia over multiple glacial–interglacial cycles. Owing to its location outside major fluvial influence from New Zealand and Australia, the sediment record is dominated by biogenic carbonate, with minor climatically sensitive terrigenous contributions.
The age model is based on benthic foraminiferal δ¹⁸O stratigraphy, allowing identification of nearly all Marine Isotope Stages back to ~580 ka. Sedimentation rates range from ~0.5 to 2.2 cm kyr⁻¹.
Alkenone-based SST reconstructions reveal pronounced glacial–interglacial variability with amplitudes of ~5–6 °C, particularly after the Mid-Brunhes Transition. Interglacial SSTs average ~24 °C, with peak values of up to 25 °C during the last interglacial (MIS 5e), while glacial minima reach ~17 °C during MIS 10. The pattern of SST variability broadly resembles temperature changes recorded in the EPICA Dome C ice core, although reduced pre–Mid-Brunhes amplitudes reflect relatively warm glacials rather than cooler interglacials (as documented in the ice core).
Dust input is assessed using n-alkane mass accumulation rates and lithogenic content derived from XRF core-scanner dataand geochemical calibrations. Both proxies show enhanced dust fluxes during glacial periods and closely follow Antarctic ice-core dust records, supporting an Australian aeolian origin for terrigenous material at the site. Compared to Subantarctic South Pacific records, glacial dust fluxes at the Lord Howe Rise are lower, likely reflecting its location near the northern margin of major Australian dust source regions, whereas more distal Pacific sites integrate dust input from multiple sources within and outside of Australia.
How to cite: Ruggieri, N., Lamy, F., Lembke-Jene, L., van der Does, M., Pahnke, K., Struve, T., and Arz, H. W.: Changes in sea surface temperatures and dust input at the Lord Howe Rise (Tasman Sea) over the past 580 , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18006, https://doi.org/10.5194/egusphere-egu26-18006, 2026.
Biomarkers and dinoflagellate cyst assemblages are valuable proxies for reconstructing palaeoceanographic conditions and past ocean-ice interactions in polar regions. However, in the modern Southern Ocean, the sparse and uneven distribution of surface sediment samples of these proxies limits our ability to fully evaluate their oceanic and environmental affinities. This is particularly problematic in the West Antarctic region, where upwelling of Circumpolar Deep Water (CDW) onto the continental shelf influences the dynamics and stability of the West Antarctic and Antarctic Peninsula ice sheets. Because these ice sheets could together, if destabilised, contribute an equivalent of 4.5 m to global sea-level rise, better tools for reconstructing CDW and its interactions with the ice sheets are needed. Here we expand the surface sediment database for this region by analysing dinoflagellate cyst assemblages and organic geochemical biomarkers (isoGDGTs, OH-GDGTs, di-unsaturated highly branched isoprenoids) in a new set of 80+ surface sediment samples. We constrain the relationships between dinoflagellate cyst assemblages and surface oceanographic conditions, IPSO25 and sea ice occurrence, and assess TEX86 and TEX86OH as potential proxies for CDW-influenced (sub)surface ocean temperatures. Our refined transfer functions are then used to generate a new GDGT-based temperature record covering 2.5–0.6 million years from IODP Site U1537 in the Scotia Sea’s “Iceberg Alley”. Together, these expanded proxy calibration datasets and their down-core application contribute new insights into past ocean-ice interactions, knowledge vital for understanding future cryosphere and sea level changes.
How to cite: Steinsland, K., Koene, B., Sangiorgi, F., Peterse, F., Hillenbrand, C.-D., Larter, R., Allen, C., Jasper, C., D'Andrea, W. J., Raymo, M. E., Guitard, M., and Bijl, P. K.: Expanding surface sediment proxy calibration to improve reconstructions of ocean-ice interactions in West Antarctica, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18376, https://doi.org/10.5194/egusphere-egu26-18376, 2026.
The Southern Ocean represents a carbon sink and also one of the few regions where deep water formation is triggered, because of cold temperatures and brine release consequent to sea-ice formation. Several paleoclimate studies have underlined its crucial influence to explain a shoaled AMOC (Shin et al., 2003, Klockmann et al., 2016, Marzocchi and Jansen, 2017) and a lower CO2 concentration (Ferrari et al., 2014, Stein et al., 2020) at the Last Glacial Maximum, when the Southern Ocean sea ice was more extensive and seasonal (Gersonde et al., 2005, Roche et al., 2012). Considering that a majority of PMIP models simulate a too deep and intense AMOC at the LGM (Muglia and Schmittner, 2015, Sherriff-Tadano and Klockmann, 2021), in contrast with paleotracer reconstructions, Marzocchi and Jansen (2017) suggest largely attributing this discrepancy and the large intermodel spread to "differing (and likely insufficient) Antarctic sea-ice formation". In Lhardy et al. (2021), we show that the iLOVECLIM model of intermediate complexity produces at the LGM a very deep and intense NADW overturning cell, in addition to model-data disagreements in the Southern Ocean sea ice (such as an underestimated seasonal range).
We propose investigating the link between these biases thanks to sensitivity tests with a modified wind stress and a parameterisation of the sinking of brines (Bouttes et al., 2010) in the iLOVECLIM model. Wind stress, convection in the Southern Ocean, and sea-ice seasonality seem broadly related in the simulations, with reduced wind stress leading to less convection and an enhanced sea-ice seasonality in the Southern Ocean, in better agreement with proxy data. However, experiments with a modified wind stress do not lead to a water mass distribution in good match with δ13C data (Peterson et al., 2014), contrary to simulations with a parameterised sinking of brines. These results thus do not support the systematic attribution of the deep and intense AMOC to an insufficient sea-ice cover in the Southern Ocean, but rather underline the importance of model representation of convection processes.
How to cite: Lhardy, F.: Exploring the links between model biases in Southern Ocean sea ice and deep ocean circulation in glacial simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19500, https://doi.org/10.5194/egusphere-egu26-19500, 2026.
Diatoms are photosynthetic siliceous algae and major contributors to the marine biological pump. Their fossil record provides insight into the environmental conditions that alter its performance, particularly during major climatic events. Defining the past oceanographic settings that favored diatom productivity improves the understanding of the biological pump efficiency and can ultimately enhance climate projection accuracy.
Nowadays, due to its rich silica waters, the Southern Ocean (SO) offers optimal conditions for diatom production, whereas diatoms are in general poorly or not even preserved in the North Atlantic sediments. During periods when the Atlantic Meridional Overturning Circulation (AMOC) was disrupted, such as during Heinrich events, the adjustment of ocean currents may have allowed silica-rich waters from the Southern Ocean to reach the North Atlantic, enhancing diatom productivity. Diatoms records for the last 40 000 years from the subtropical North Atlantic and the Drake passage will be compared to evaluate the possible leaking of southern sourced water and its impact on the efficiency of the biological pump will be discussed.
How to cite: Gil, I., McManus, J., Abrantes, F., and Keigwin, L.: Exploring the Relationship Between Diatom Productivity and AMOC Variability Over the Past 40,000 Years: records from the Drake Passage and the Subtropical North Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20894, https://doi.org/10.5194/egusphere-egu26-20894, 2026.
The Mid-Pleistocene Transition (MPT), from ~ 1.2 to 0.6 million years is characterized by glacial interglacial cycles periodicity shifting from 41 kyr to ~100 kyr with larger amplitude variations (Pisias et Moore, 81; Imbrie et al., 93). This transition cannot be explained as a direct consequence of the astronomical forcing. Among the different mechanisms that has been suggested to explained this change in periodicity, a number involve a long-term decrease in atmospheric carbon, linked to greater carbon sequestration in the ocean. Various processes may have caused this carbon sequestration in the ocean (Paillard, 207; Willeit et al., 2019), including ocean temperature decrease, increased productivity in the Southern Ocean (Martinez-Garcia et al., 2011), and changes in deep ocean circulation (Raymo et al., 1997, Peña et Goldstein, 2012, Hasenfratz et al., 2019). For some processes, reconstructions indicate different timings, with mean surface temperature decrease occurring before 1.2 Myr (Snyder 2016) while ocean circulation changes started after 0.95 Myr (Raymo et al., 1997, Peña et Goldstein, 2012, Hasenfratz et al., 2019). Here we present the evolution of CO32- concentration along the MPT, in the Pacific sector of the Southern Ocean, that is linked to carbon accumulation. This record has been reconstructed from benthic foraminifera B/Ca ratio (Yu and Elderfield, 2007) from 1.25 to 0.45 Myr. While the two records from the Atlantic Ocean, North (Sosdian et al. 2018) and South (Farmer et al., 2019), indicate a reduction in CO32-, thus an increase in carbon accumulation, starting with the deep Atlantic Ocean circulation change at ~0.95 Myr (Raymo et al., 1997, Peña et Goldstein, 2012), these new South Pacific data indicate a delayed decrease by ~100kyr in agreement with a Pacific tropical record (Qin et al., 2022) obtained from changes in normalized weights of planktic foraminifera. This different timing, even within the Southern Ocean, questions the role of the balance between the dissolution/accumulation of carbonates between the Atlantic and Pacific basins.
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How to cite: Michel, E., Gray, W., Rebaubier, H., Richard, P., Manssouri, F., Fries, M., Gottschalk, J., Lamy, F., and Winckler, G. and the IODP 383 scientits: Southern deep ocean carbon chemistry changes along the mid-Pleistocene transition evidenced an increase in carbon storage starting from stage 22, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22988, https://doi.org/10.5194/egusphere-egu26-22988, 2026.
The Bellingshausen Sea sector frames the eastern part of the West Antarctic Ice Sheet (WAIS). Between 83 and 89°W the Bellingshausen Sea margin is characterised by the 150 km wide Belgica Fan, a large trough mouth fan extending from the shelf break into the deep sea to about 3000 m water depth. Sedimentary material from the hinterland has been transported to the Belgica Fan via the Belgica Trough, a major glacial morphological feature on the Bellingshausen Sea shelf. Thus, the fan constitutes an important archive of the WAIS dynamics of this sector. Still, little is known about the development of the fan and the potential to unlock this sedimentary archive.
A recently collected set of seismic reflection data has been analysed and interpreted with the aim to reveal the formation of the fan and decipher the glacially controlled transport, deposition and erosion processes. A seismic link to ODP Leg 178 Sites 1095 and 1096 enables the age dating of prominent reflections and seismic units. The fan is underlain by several basement highs. The lowermost two seismic units (M6, > 25 Ma, and M5, 25-15 Ma) fill and level the basement relief. Unit M4 (15-9.5 Ma) shows erosive structures such as channels and mass transport deposits in its upper part. These occur mainly in the far west and east of the fan. This erosion appears intensified in the lower part of unit M3 (9.5-5.3 Ma). In units M2 and M1 the erosional features are localised in the western and distal part of the fan.
These observations indicate an increased input of material following the mid-Miocene Climatic Transition pointing towards the beginning of an expanding, shelf-crossing WAIS in the Bellingshausen Sea sector.
How to cite: Uenzelmann-Neben, G. and Gohl, K.: The Belgica Fan, Bellingshausen Sea, documents dynamics of the West Antarctic Ice Sheet, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3347, https://doi.org/10.5194/egusphere-egu26-3347, 2026.
