The Circumpolar Deep Water (CDW) is one of the key components of the global climate system and Antarctic cryosphere. However, the variability of the CDW in the Indian sector of the Southern Ocean over glacial-interglacial climate cycles is still unknown due to a lack of knowledge of deep-water geochemistry. The new records of δ¹⁸O and δ¹³C in benthic foraminifer from Del Caño Rise (DCR-1PC and DCR-2PC) characterized the δ¹³C composition of CDW in the Indian sector of the Southern Ocean. During the glacial periods, the South Indian has lower δ¹³C values, representing the influence of a more southern water mass, perhaps a glacial Antarctic Bottom Water (AABW). A comparison with published South Atlantic (ODP 1090) and South Pacific (PS 75/59) deep water records suggests a continuous water mass exchange throughout the past 500 ka. Almost identical glacial-interglacial δ¹³C variations imply a common deep-water evolution in all basins, suggesting persistent CDW exchange and homogenization. A much lower δ¹³C signal was observed at the deeper Cape Basin (ODP 1089, RN13-229), which was influenced by strong AABW originating from the Weddell Sea during the glacial periods. The anomalous heavier values (> 0.5‰) were recorded at DCR-1PC during the MIS 5 (~97 ka and ~83 ka), suggesting the strong influence of the North Atlantic Deep Water (NADW). 

How to cite: Ikehara, M.: Circumpolar Deep Water variability in the Southern Ocean during the past 500 ka, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3529, https://doi.org/10.5194/egusphere-egu25-3529, 2025.

The atmospheric CO₂ content has been discussed as one of the major factors influencing global climate. In the framework of the deep ocean forming the main reservoir of carbon dioxide, the Southern Ocean plays a crucial role in partitioning carbon between the atmosphere and the deep ocean. The processes resulting in the variability of atmospheric CO₂ and carbon uptake in the deep ocean have not yet been fully identified. Sedimentary structures imaged with seismic reflection data are interpreted regarding direction and intensity of pathways of deep/bottom water masses to contribute to the knowledge on potential locations of carbon subsidence. Under the assumption that the general circulation scheme has been similar during the Neogene, i.e., driven by gyres, the positions and sizes of palaeo-gyres have been reconstructed, which were then interpreted regarding the intensity of carbon uptake. This has been compared with published reconstruction of warming/cooling trends of the global climate. While the method applied is equivocal it links observed sedimentary structures with the development of gyres thus potential sports of carbon uptake. This way the presented reconstruction provides pieces to the climate variability puzzle, which can be tested using numerical simulation.

How to cite: Uenzelmann-Neben, G.: Neogene circulation in Princess Elizabeth Trough, Southern Ocean, driven by gyres?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1189, https://doi.org/10.5194/egusphere-egu25-1189, 2025.

Understanding Southern Ocean-Antarctic Ice Sheet (AIS) interactions in the geological past is crucial for evaluating the sensitivity of the ice sheet to ocean forcing during future climate warming and predicting its contribution to future sea-level rise. Geological evidence indicates the onset of a modern-like strong Antarctic Circumpolar Current (ACC) in the Late Miocene (~10 million years ago). However, the response of the East Antarctic Ice Sheet to these changes remains poorly constrained. In this study, we present neodymium and strontium isotope compositions of fine-grained (<63 μm) detrital sediments from Ocean Drilling Program (ODP) Site 1165, located on the continental rise off Prydz Bay. These records trace changes in sediment provenance from the Middle Miocene to the present, offering insights into how erosion by Antarctica’s ice sheets in the Prydz Bay sector has evolved over time. Our data reveal that the ice sheet in the Prydz Bay sector crossed a tipping point in the Late Miocene, becoming highly dynamic. Our preliminary findings suggest that this significant shift in the East Antarctic Ice Sheet's evolution may be linked to the emergence of the modern ACC, indicating major ocean-ice interactions in the Late Miocene.

How to cite: Evangelinos, D., van de Flierdt, T., Pena, L. D., Paredes, E., Cacho, I., and Escutia, C.: East Antarctic Ice Sheet–Southern Ocean Interactions in Prydz Bay region from the Middle Miocene to the Present, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12620, https://doi.org/10.5194/egusphere-egu25-12620, 2025.

The Southern Ocean, especially the Subantarctic region, plays a critical role in anthropogenic carbon uptake, heat exchange, and nutrient transfer between high and low latitudes. Pronounced past changes in surface ocean properties, particularly sea surface temperatures (SSTs), reflect this region’s exceptional sensitivity to external and internal forcings over millennial and orbital timescales. This underscores its importance in understanding past and future climate change and its key role as major link between Antarctica and the low latitudes.

Accurate reconstructions of past SSTs are crucial for understanding past climate dynamics and validating models for future projections. To achieve this, various temperature proxies based on physical, chemical, and biological properties preserved in marine sediments have been developed. However, all proxies carry uncertainties due to environmental factors that may bias the signals archived in the sedimentary record. A multiproxy approach helps to mitigate these uncertainties, providing a more robust and comprehensive interpretation of past climate conditions.

This study presents a high-resolution SST reconstruction from IODP Expedition 383 Site U1539 and pre-site survey PS75/054 in the Subantarctic South Pacific, near the modern Subantarctic Front (SAF), using three different temperature proxies: a diatom transfer function and two organic proxies based on coccolithophorid alkenone lipids (U^K’₃₇) and archaeal glycerol dialkyl glycerol tetraether (GDGT) lipids (TEX₈₆). This location is characterized by unusually high sedimentation-rates (~10-50 cm/kyr), mainly because the northerly extended opal belt reaches Site U1539 during glacials with high diatom ooze deposition.

Our record spans the last 150 ka with a centennial to millennial resolution. The general temperature pattern follows the overall glacial/interglacial succession. The alkenone SSTs range from minimum values approaching zero around the Last Glacial Maximum to ~10°C in MIS 5e (and 6-7°C during the Holocene equivalent to modern austral summer SST). These exceptionally high glacial/interglacial amplitudes are much less pronounced in the diatom summer SST reconstruction with an amplitude of only~3-4°C. Much higher SSTs are shown by the TEX₈₆ with equally maximum values during MIS 5e (absolute SST higher than the alkenone SST). However, the TEX₈₆ temperature record shows very high amplitudes at millennial time-scales. Within dating uncertainties, these changes follow the Antarctic temperature pattern as recorded in ice-core.

We are discussing the palaeoceanographic implications of our SST records and potential reasons for the partial mismatches of the different SST proxies. These include varying seasonality sensitivity, depth habitat, and SST calibration and transfer function uncertainties.

How to cite: Ruggieri, N., Jaeschke, A., Hefter, J., Rigalleau, V., Lembke-Jene, L., Esper, O., Mollenhauer, G., Winckler, G., and Lamy, F.: Multi-proxy reconstruction of sea surface temperatures in the Pacific Southern Ocean over the last glacial-interglacial cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18659, https://doi.org/10.5194/egusphere-egu25-18659, 2025.

The intensification of Northern Hemisphere Glaciation at ~2.7 Ma ago, known as the significant iNHG event during the late Pliocene, has marked a prominent transition of Earth’s climate from uni-polar to bi-polar ice sheets. Here, we present proxy records from the deep sea sediments of Ocean Drilling Program Site 1123 in the South Pacific (41°47´S，171°30´W，water depth 3290 m), covering a time span of approximately 3.5 to 1.7 million years, aiming to reveal the South Pacific deep circulation and ocean carbon reservoir changes during this period. After careful rinsing of the sediment samples, we selected benthic foraminifer C. Wuellerstorfi and G. Mundulus for B/Ca ratio and fish tooth εNd isotope analysis, with a temporal resolution of approximately 3 to 10 thousand years, totaling 112 sediment samples.

Our results show that the eNd of ODP Site 1123 rapidly shifted towards negative values by approximately 2 units during the iNHG period. Meanwhile, the deep-water △[CO₃^2-] reconstructed using the B/Ca ratio of benthic foraminifera exhibited a positive shift at around 2.9 Ma and then a negative shift at around 2.7 Ma. We interpret that the positive shift in △[CO₃^2-] at ODP Site 1123 at ~2.9 Ma might be caused by the weakening of the Antarctic Circumpolar Current (ACC), which reduced the upwelling in the Southern Ocean and thereby caused a shift of the major source of the water mass bathing this site from the north with more negative carbonate ion concentrations to that in the south with more positive carbonate ion concentrations. The enhanced northward expansion of southern sourced water in the deep Pacific Ocean could result in a decrease in the Pacific carbon reservoir. We further hypothesize that the enhanced input of sub-Antarctic dust during the iNHG period had great potential for increasing the iron fertilization effect, thereby strengthening the biological pump in the sub-Antarctic region. This process had resulted in an increase in the carbon storage and a more negative carbonate ion concentration in the southern sourced water flowing into the Pacific Ocean, ultimately causing the negative shift in △[CO₃^2-] at ODP Site 1123 and enhancing carbon storage in the Pacific Ocean. Our results demonstrate that the Pacific Ocean had played a great role in the decline of the atmospheric pCO₂ and finally contributed to the final formation of the iNHG event.

How to cite: Xu, J., Ma, Y., and Tian, J.: Synergic Variations of the South Pacific Deep Circulation and Carbon Reservoir During the Late Pliocene Intensification of the Northern Hemisphere Glaciation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2567, https://doi.org/10.5194/egusphere-egu25-2567, 2025.

The Earth's climate transitioned significantly from the mid-Piacenzian Warm Period (mPWP, 3.3–3.0 Ma) to the intensified Northern Hemisphere Glaciation (iNHG, 3.0–2.7 Ma). The Southern Ocean, a major CO₂ sink, played a pivotal role in this shift by regulating CO₂ through ocean ventilation. While most research focuses on the Northern Hemisphere, this study investigates planktonic foraminiferal assemblages, stable isotopes, trace metals, and sedimentary records from the Subantarctic Pacific to explore the Southern Hemisphere’s contribution.

Three intervals are identified: mPWP (3.3–3.0 Ma), iNHG (3.0–2.7 Ma), and the Subantarctic-dominant interval (<2.7 Ma). Key planktonic foraminiferal groups include Neogloboquadrina pachyderma (cold-water indicator), Globoconella spp. (thermocline indicators, G. puncticulata and G. inflata), and Globigerina bulloides (nutrient-enrichment indicator). During the mPWP, thermocline species dominated (90%). The faunal assemblage underwent a transition during the iNHG, with a 40% decline in Globoconella spp. and accompanied growth of N. pachyderma. By the Subantarctic-dominant interval, N. pachyderma increased (~90%), reflecting expanded cold-water conditions. G. bulloides rose by 30% at the end of the mPWP and fluctuated with glacial-interglacial (G/IG) cycles, peaking during interglacials (~25% higher). These shifts suggest destratification at the mPWP’s end and higher surface productivity during the Subantarctic-dominant interval, supported by increased planktonic foraminiferal accumulation rates.

Sedimentary analysis reveals a long-term decrease in CaCO₃ content (90% reduction) and a slight increase in total organic carbon (TOC) content, showing a 1% growth throughout the research interval. Additionally, ice-rafted debris (IRD) production exhibits a pronounced increase, reaching a maximum of 200 pieces/cm²·kyr during the Subantarctic-dominant interval, and demonstrates a long-term upward trend throughout the research interval. This rise in the IRD aligns with the increased abundance of the cold-water species N. pachyderma, suggesting an expansion of sea ice and ice sheets.

Stable isotope records reveal long-term environmental changes. δ¹³C values decreased during the mPWP and stabilized during the iNHG but became G/IG-dominant in the Subantarctic-dominant interval, with lower values in glacial periods likely due to increased Circumpolar Deep Water (CDW) input. δ¹⁸O records suggest a cooling trend (over 1‰) throughout the interval, showing G/IG variability in N. pachyderma and Globoconella spp. during the Subantarctic-dominant period. The δ¹⁸O_seawater derived from planktonic foraminifera generally exhibits a long-term increasing trend from -0.5‰ to 2‰, with glacial periods showing approximately 1‰ higher δ¹⁸O_seawater compared to interglacial periods.

Mg/Ca-derived temperatures show complex patterns. While N. pachyderma Mg/Ca ratios reveal strong G/IG fluctuations (~6°C) during the Subantarctic-dominant interval, G. puncticulata exhibits a long-term cooling (~6°C) since the iNHG. G. inflata mirrors these trends, and G. bulloides shows a 2°C decline. These data highlight N. pachyderma’s sensitivity to sea-ice expansion and the thermal stability preferences of G. bulloides.

Overall, stable ocean stratification and minimal sea ice characterized the mPWP, underpinned by a well-stratified thermocline. Since the iNHG, frontal system shifts, destratification, and increased CDW upwelling have enhanced nutrient availability and phytoplankton photosynthesis, boosting CO₂ sequestration. By 2.55 Ma, the Subantarctic Pacific emerged as a critical CO₂ sink, driven by Pleistocene G/IG cycles and contributing significantly to global CO₂ storage.

How to cite: Wu, L.-P., Lo, L., Shen, C.-C., Löwemark, L., Wu, P.-T., and Mii, H.-S.: Evidence of significant destratification of the Subantarctic Pacific during the past 3.3-2.4 million years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3002, https://doi.org/10.5194/egusphere-egu25-3002, 2025.

The Southern Ocean (SO) is a key area for global climate. It connects the deep water with the surface through upwelling. The deep SO, storing a large amount of carbon during the glacial period and releasing CO₂ during the deglacial period, is critical for the carbon cycle on orbital-millennial timescales.

In the Southwest Pacific (SWP), there are many reconstructions of deep water, however, these reconstructions primarily rely on carbon and oxygen isotopes, which cannot effectively distinguish the North Pacific Deep Water (NPDW) and the Circumpolar Deep Water (CDW). Neodymium isotopes (ε_Nd) of seawater is dominated by the crustal sources, which is spatial heterogeneous, enabling its wide application as water mass traces. However, the available data in the SWP is not enough to resolve spatial complexity and evolution mechanisms of water masses, especially at the depth of NPDW and UCDW (Upper CDW).

Here, ε_Nd on planktonic foraminifera are used to investigate the evolution of deep-water masses in SWP since 30 ka BP on core MD97-2115 (43° 6' 30" S, 171° 29' 7.8" W, 2160 m water depth), which is located on the east Chatham Rise.

The ε_Nd results show an increase from -4.5 to -3.8 between 30 ka BP and 21 ka BP, followed by a positive shift to -4.7 at 19 ka BP. After 19 ka BP, the values remain relatively stable around -5.

These values agree well with modern NPDW seawater ε_Nd value in Southwest Pacific Basin, ranging from -4 to -5. Comparison with nearby ε_Nd records suggests a persistent influence of NPDW in the eastern Chatham Drift since 30 ka BP. However, the mechanism of the shift around 19 ka BP needs further investigation.

How to cite: Tang, X., Siani, G., and Colin, C.: The evolution of deep water in the Southwest Pacific Ocean since 30 ka BP, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5120, https://doi.org/10.5194/egusphere-egu25-5120, 2025.

During the last glacial period, millennial-scale iceberg discharges in the North Atlantic, known as Heinrich Events (HEs), could have shifted the Southern Hemisphere Westerly Wind Belt (SWW) poleward and potentially led upwelling-driven CO₂ outgassing from the Southern Ocean. However, direct evidence of SWW poleward shift in response to HEs remains limited. Based on detrital elements, minerals, and grain-size records in well-dated sediment cores, MR16-09 PC02 (46°04.23′S, 76°32.10′W, 2793 m water depth) and PC03 (46°24.32′, 77°19.45′, 3082 m water depth), from off western Patagonia at ~46°S, we found abrupt onsets in the discharge of coarse silt-sized detritus during the latter half of each HEs (HE 3, 4, 5, 5a, and 6) originating from the Patagonian Batholith located in the coastal area of western Patagonia. Such abrupt discharges are unique events south of ~46°S and probably reflect the extension of glacial erosion into the western fjords related to a pronounced positive anomaly in the glacial accumulation/ablation mass balance of the western-central Patagonian ice sheet. Our climate model (MIROC4m) hosing experiment in the North Atlantic suggests the SWW and precipitation belt began shifting poleward hundreds of years after the onset of HE, which is consistent timing with our proxy data. Thus, increased precipitation south of 46°S following the poleward-SWW shift most likely generated detritus discharges. These findings provide critical evidence of abrupt climate changes propagating from the North Atlantic to the southern midlatitudes via the large-scale reorganization of the atmospheric and ocean circulations.

How to cite: Kasuya, T., Nagashima, K., Hasegawa, H., Okazaki, Y., Kuniyoshi, Y., Abe-Ouchi, A., Iwasaki, S., Arz, H. W., Hagemann, J. R., Harada, N., Murayama, M., Lange, C. B., and Lamy, F.: Poleward shift in Southern Westerlies triggered by iceberg discharge in the North Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7778, https://doi.org/10.5194/egusphere-egu25-7778, 2025.

Marine terminating ice sheets and glaciers influence the chemical, biological and physical dynamics of adjacent marine systems. For example, changes in ice extent affect sedimentation rates along glaciated coasts, as well as drive shifts in marine productivity linked to stratification and nutrient delivery. These changes can affect the redox conditions and storage of organic carbon in shelf sediments. Therefore, glacial retreat due to modern climate warming could potentially have major impacts on marine productivity, sedimentation and carbon cycling in the Southern Ocean and other high latitude areas. To study the effects of warming on diagenetic processes and sedimentation dynamics, we analyzed core samples from IODP Expedition 383 Site U1542, collected close to the southern Chilean Margin, a region of rapid sedimentation rates that is linked to the Southern Ocean via the Cape Horn Current and the Drake Passage. This site provides a high-resolution record of changes at the western maximum extent of the Patagonia Ice Sheet (PIS), which was dominant in this setting during the last glacial period. Preliminary results from this Site indicate 7 distinct intervals of short-term warming events (1-5 kyr) between 20 and 60 kyr. We analyzed samples spanning these warming events for total organic carbon, grain size, and Fe minerology, and compared results with records of trace metal (e.g., Mn and Ni) contents from X-ray fluorescence (XRF) analysis. Preliminary results indicate that when the PIS retreated during short-term warming events, the redox conditions in the sediment shifted, becoming more reducing as indicated by trace metal contents and Fe minerology, and the organic carbon content in the sediment increased. In addition, larger grain sizes during warm periods suggest a possible decrease in fine glacial flour input with the retreat of the ice sheet. Overall, this study disentangles signals reflecting diagenetic, benthic redox and sedimentological changes driven by changes in glacial input. This research ultimately aims to improve our understanding of how a marginal marine system responded to climatic warming and ice sheet loss, serving as a potential analog for future loss of modern ice sheets.

How to cite: Herbert, L. C., Brion, E., Wehrmann, L. M., Rigalleau, V., Arz, H. W., Winckler, G., and Lamy, F.: Benthic responses to warming and ice retreat on the Chilean Margin during the Last Glacial Period, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14444, https://doi.org/10.5194/egusphere-egu25-14444, 2025.

The Southern Ocean plays a critical role in the Earth system, both for the uptake of anthropogenic carbon and for the exchange of heat and nutrients between high and low latitudes. This is particularly valid for the Subantarctic Southern Ocean where atmosphere-ocean-cryosphere interactions and teleconnections between high and low latitudes play an important role in past and future climate change providing the major link between Antarctica and the low latitudes. In general, atmosphere-ocean interactions within the Southern Ocean are believed to control sea ice cover, upper ocean stratification, biological nutrient utilization, and exposure rates of CO₂-enriched deep water. Thus, they have been considered to play a key role in explaining the variability in atmospheric CO₂ concentrations, which are controlled by biogeochemical and physical processes.

Beyond information from continental margin records, little is known on millennial-scale variability in the pelagic Southern Ocean. High resolution sediment archives reaching back various glacial/interglacial cycles have not been explored so far. This includes the time span beyond the reach of the presently available ice-cores and will likely be critical for evaluating the extended time-interval of the ongoing European Beyond EPICA – oldest ice (BE-OI) ice core drilling initiative. Our project focuses on high resolution paleoceanographic reconstructions (biomarker-based sea surface temperatures, biogenic opal, Antarctic Circumpolar Current strength, ice-rafted detritus) of upper ocean dynamics at Expedition 383 IODP Site 1539 in the subantarctic South Pacific in vicinity of the modern Subantarctic Front (SAF). This location is characterized by unusually high sedimentation-rates (~10-50 cm/kyr), mainly because Site U1539 is reached by the northerly extended opal belt during glacials with high diatom ooze deposition. This unique setting provides a high-resolution pelagic sediment archive in an area with strong oceanographic gradients (close to the SAF with strong dynamics of SST, ACC strength, and the influence of the opal belt).

We expect that high resolution records from IODP Expedition 383 Site U1539 could substantially enhance our understanding of sub-orbital climate variations and potential tipping points in the Southern Ocean and their link to the marine carbon cycle and Antarctic ice-sheet stability.

How to cite: Lamy, F., Rigalleau, V., Ruggieri, N., Lembke-Jene, L., Arz, H. W., Mollenhauser, G., and Winckler, G.: Orbital and millennial-scale upper ocean dynamics in the Pacific Southern Ocean since the Mid-Pleistocene Transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18501, https://doi.org/10.5194/egusphere-egu25-18501, 2025.

IODP Site U1537 is located in a contourite deposit in the Dove Basin of the southeastern Scotia Sea, in 3,713 meters of water. It consists of alternating diatom oozes and silty clays, with variable amounts of sand to gravel-sized clasts delivered as IRD.   Shipboard track measurements, weight percent ice-rafted detritus (IRD), ⁴⁰Ar/³⁹Ar hornblende and biotite age (provenance), and split core XRF elemental measurements were collected and examined to study Antarctic ice-sheet dynamics between 1.75 and 3.35 Ma, the Plio-Pleistocene transition. 

            The highest and most variable amounts of IRD (from 0 to >0.4 g/cm²/ky) are in the earliest part of the study before 3.24 Ma. Between 3.24 and 2.4 Ma, with the exception of one sample, IRD comprises < 0.2 g/cm²/ky of the sediment. Between 2.4 and 2.1 Ma, IRD form < 0.05 g/cm²/ky, and from 2.1 Ma to the end of the study, they return to values of < 0.1, g/cm²/ky. With the exception of the lowest IRD interval (2.4 and 2.1 Ma), ⁴⁰Ar/³⁹Ar ages of biotite and hornblende grains are sourced from both East and West Antarctica, with the majority being between about 400 and 600 Ma old, broadly corresponding to the Pan-African event, and the assemblage of Gondwana.

            The 300,000-year, diatom-rich, low IRD interval between 2.4 and 2.1 Ma is unique in that all of the grains, except one, came from West Antarctica. Other Antarctic sites such as IODP Site U1361 (Wilkes Land), and ODP Site 1011 (northwest tip of the Antarctic Peninsula), also have their lowest IRD values during this time interval. We propose that this was a warmer time interval and that icebergs from East Antarctica either melted before reaching the Dove Basin or there were no ice-terminating glaciers.

How to cite: OConnell, S., Fenton-Samuels, K., Hemming, S., Reilly, B., Wang, C., and Anee, S.: Evidence from IODP Site U1537 in the Dove Basin, Scotia Sea for a warmer Antarctica during the early Pleistocene (2.4-2.1 Ma) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14057, https://doi.org/10.5194/egusphere-egu25-14057, 2025.

Radiolarians are siliceous marine zooplankton found in all of the world’s oceans, inhabiting the entire water column. Their fossilised skeletons, preserved in marine sediments, provide valuable paleoceanographic information due to their distinct depth preferences. In the Southern Ocean, radiolarians preserved in ice-edge marine sediment cores offer a snapshot into  past oceanographic conditions and climatic changes linked to ocean-ice interactions.

Detailed counts of radiolarian taxa have been generated using a sediment core from the Sabrina Coast, East Antarctica. The Sabrina Coast serves as the marine exit point of the Totten Glacier, which is currently thinning due to surface and basal processes. The radiolarian record reveals instances of water mass change on the continental slope during the four most recent interglacial periods (Marine Isotope Stages 1, 5, 7, and 9).

Radiolarian assemblages in this region exhibit greater species richness and diversity than other microfossil groups, such as diatoms and silicoflagellates. Factor analysis highlights that radiolarian assemblages are more dynamic and variable than diatom assemblages during interglacial periods. Fluctuations in the abundance of key radiolarian taxa indicate the presence of intermediate water at times in each interglacial. When paired with subsurface temperature reconstructions, these findings may reveal past periods of basal melting of the Totten Glacier.

How to cite: Lawler, K.-A., Lowe, V., Cortese, G., Leventer, A., Noble, T., O'Brien, P., Opdyke, B., Post, A., and Armand, L.: Radiolarians reveal past water mass changes at the Sabrina Coast, East Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14857, https://doi.org/10.5194/egusphere-egu25-14857, 2025.

During the Late Quaternary global climate variations and interactions with the southern westerly wind belt and the adjacent surface ocean circulation caused glacier advances and retreats in New Zealand’s Southern Alps. Most studies in this region, however, focus on the last glacial period and evidence of older glacier activity is more fragmentary. The use of marine sediment cores as continuous archives for glacier fluctuations over glacial-interglacial cycles is a common method to circumvent such terrestrial archive limitations. Our study investigates the glaciation history of New Zealand’s South Island over the past 200,000 years and its interaction with paleoceanographic changes of the adjacent Southeast Tasman Sea. Solander Trough south of New Zealand represents a major conduit of terrestrial sediments from the Southern Alps. Core SO290-17-1 from Solander Trough is therefore ideally suited for a multi-proxy approach. The stratigraphy of the core is based on oxygen isotopes from benthic foraminifera and X-ray fluorescence core scanning, paleo- and rockmagnetic measurements. In addition, stable oxygen and carbon isotopes from planktic and benthic foraminifera are combined with the former methods for the paleoenvironmental reconstructions. The XRF Fe/Ca ratio indicates enhanced terrestrial inputs during MIS 2, MIS 4 and MIS 6. To investigate changes in sediment source and hence glacier dynamics on land, we use radiogenic neodymium isotopes (expressed in ɛNd) as a proxy for source-specific terrestrial input. Significant ɛNd changes in SO290-17-1 are expected in response to glacier fluctuations because of the complex geology (in nature and age) of the Fiordland and East Southland regions, on which glaciers fluctuated during the last glacial periods. Our data for MIS 4-6 will be compared to results obtained on core TAN1106-28 from the Solander Trough for MIS 1-4 (Toucanne et al., submitted).

How to cite: Krüger, H., Arz, H., Toucanne, S., Kaiser, J., Lamy, F., Lembke-Jene, L., Nowaczyk, N., and Pahnke, K.: Land-ocean interaction in southern New Zealand during the past 200 ka, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17190, https://doi.org/10.5194/egusphere-egu25-17190, 2025.

Persistent deep-water formation in the North Atlantic and Southern Ocean is believed to drive the ventilation of the global deep ocean throughout late Pleistocene interglacial periods. The persistency of interglacial deep-ocean ventilation was, however, challenged based on reconstructed deep ocean deoxygenation events at Ocean Drilling Program (ODP) Site 1094 from the Antarctic Atlantic Ocean attributed to a perturbation in Antarctic Bottom water (AABW) formation during Marine Isotope Stage (MIS) 5e and 11. While a connection to instabilities of the West Antarctic Ice Sheet related to warming of Circumpolar Deep Water was postulated, the drivers and spatial extent of these ‘AABW stagnation events’ remain incompletely known. Here, we present new bottom water oxygen (BWO) reconstructions based on authigenic U enrichments in benthic foraminiferal coatings of Uvigerina spp. from Subantarctic Atlantic sediment core MD07-3077 (44.15°S, 14.23°E; 3770 m) for MIS 11 (424-374 ka before present). A combination of these BWO estimates with Uvigerina spp. Mg/Ca-derived bottom water temperature (BWT)- and δ¹⁸O-derived bottom water salinity (BWS) reconstructions at the same study site provides insights into the impact and mechanisms driving AABW stagnation events in the Atlantic Southern Ocean. Our results reveal predominantly well-oxygenated deep-water conditions in the Subantarctic Atlantic during MIS 11, with only one transient low-BWO event at 395 ka before present. This suggests that AABW stagnation events during MIS 11 were largely confined to the Antarctic Atlantic Ocean, indicating a limited northward expansion of poorly oxygenated water. Although this hints at a driver from the south, the variability in our reconstructed BWT and BWS records during the postulated MIS11 AABW stagnation events suggest various hydrographic settings that pinpoint mechanistic differences in the drivers among the bottom water deoxygenation events. Our new data provides crucial constraints on the (in)stability of climatic conditions in the Atlantic Southern Ocean, and by inference near the Antarctic ice sheet margin, during the warmer-than-present climate interval MIS 11.

How to cite: Oelkers, L. S., Vazquez Riveiros, N., Frick, D. A., Waelbroeck, C., and Gottschalk, J.: Changes in deep water circulation dynamics in the South Atlantic Ocean during Marine Isotope Stage 11, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18269, https://doi.org/10.5194/egusphere-egu25-18269, 2025.