We provide a summary of new insights into the contemporary dynamics of Thwaites and Pine Island Glacier, West Antarctica, obtained through series of recent modelling studies.  By conducting ice-flow modelling studies with three independent models (ISSM, StreamIce, Úa), all initialized to current day conditions, we show that all models provide very similar future estimates of future mass loss for a given forcing scenario. Importantly, while description of basal processes does impact our results to some degree, we nevertheless find that estimates of mass loss over time scale of 50 to 100 years, are insensitive to the choice of basal sliding law. This can be understood to be related to the compensating impact of the initialisation process that in each case produces correct initial state for the ice sheet (i.e. surface velocities and current rates of mass loss) irrespectively of the sliding law used. Furthermore, we find that inversion produces (e.g. estimates of basal slipperiness and englacial ice rate factors) can be exchanged between models, showing that these products are to large degree model independent. A common feature found in all our ice-flow studies, and coupled ice+ocean studies, is the existence of multiple tipping points within the Thwaites and Pine Island system. In all our ice-flow simulations, the grounding line of Thwaites always becomes unstable once it has retreated by about 75km upstream from its current position. We also conclude that the grounding line of Pine Island Glacier has recently undergone a phase of irreversible retreat, and that the glacier has at least 3 further tipping points that can be crossed in the near future (centennial time scale). Additionally, the western ice shelf of Thwaites has been dramatically weakening over the past decade and we used our three independent models to assess the effect of a potential complete collapse of Thwaites’ floating extension. First, we find that this ice shelf provides limited buttressing, and disintegrations of the ice shelf, in its current configuration, will not significantly impact upstream grounded. Second, it has been suggested that Thwaites would be subject to the Marine Ice Cliff Instability (MICI) if its ice shelf collapses, as it would expose a tall ice cliff. Using recently proposed cliff-height dependent calving laws, we find no indication that such calving laws give rise to an irreversible or unstable calving-front retreat.  Thus, those calving laws do not lead to a marine ice cliff instability despite prescribing calving rates as strongly increasing functions of cliff height.

How to cite: Gudmundsson, G. H., Morlighem, M., Goldberg, D., Barnes, J., De Rydt, J., and Rosier, S.: New insights into the current dynamics of Thwaites and Pine Island Glaciers, West Antarctica., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8454, https://doi.org/10.5194/egusphere-egu24-8454, 2024.

In the Antarctic field seasons 2022/23 and 2023/24 the GHOST team (Geophysical Habitat of Subglacial Thwaites: https://thwaitesglacier.org/projects/ghost) as part of the International Thwaites Glacier Collaboration (ITGC), collected several hundred kilometers of multi-fold seismic reflection profile of Thwaites Glacier. The data cover the center flow line (first season) and across flow profiles (second season), starting 60 km upstream from the grounding line. The seismic profiling set-up consisted of a seismic vibrator source and 60 geophones on a 1.5 km long cable, all towed by a tracked vehicle. The combination of surface seismic source and towed geophone array allows for rapid and high quality data acquisition. The seismic signal penetrates approximately 200 meters into the bed with deeper structures imaged in places. The along-flow profile revealed a repeating of bedforms alternating between relatively flat and smooth regions a few km long, and regions of more pronounced topography of 10s to 100s of meter high bumps. In addition we imaged what we interpret as sediment filled basins.  Comparison with high-resolution ground-based swath radar allows the identification of geomorphological bedforms, such as megascale glacial lineations, sediment-filled basins and troughs, which can then be directly identified in the seismograms. We present a first preliminary evaluation of the subglacial characteristics and discuss the potential relevance of the subglacial boundary condition for ice flow dynamics.

How to cite: Eisen, O., Zeising, O., Hofstede, C., Laubach, H., Koch, F., Anandakrishnan, S., and Brisbourne, A. and the GHOST team: Properties of the bed of Thwaites Glacier, West Antarctica, estimated from vibroseismic surveys (2022-23 and 2023-24), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-267, https://doi.org/10.5194/egusphere-egu24-267, 2024.

A pair of automated multi-sensor stations with satellite data downlinking were installed near the center of the Thwaites Eastern Ice Shelf (TEIS) in January, 2020 and continued operating (at least partially) until November, 2022. The stations, situated 4 km apart (initially near 75.05°S, 105.5°W) recorded and transmitted weather and snow accumulation data, position, images, firn and ice temperature, and ocean conditions through a suite of instruments managed with software and uplinked commands to conserve power and/or maximize observations of events. The stations, called Automated Meteorology-Ice-Geophysics Observing Systems, mark III (AMIGOS-III) are installed on a tower and adjacent ice borehole to measure air, ice, and ocean parameters. Weather and accumulation data from the stations spanning 22 months show a mean annual air temperature for TEIS of -14.6°C, with observed extremes of +1.7°C (08 Feb 2020) to -51.0°C (17 Aug 2021). Mean air pressure was 973.7 mbar (at ~25 m elevation). Winds are highly directional and dominated by dry katabatic flow from the southeast (from 115° to 130°); however, higher snowfall is correlated with winds from more easterly and northeasterly directions. Average annual snowfall in the observation period was 0.72 to 0.90 m water equivalent. Ice flow speed was observed to accelerate throughout the observation period, ranging from ~1.7 m/d in January 2020 to more than 2.2 m/d in late 2021. The rate of acceleration increased markedly after July 2020, coinciding with satellite observations of a more disrupted northern and western shear margin for TEIS. Maximum tidal amplitude is ~1.6 meters. Comparison with the CATS2008 tide model, after correction for IBE, showed a mean difference of ±17 cm. Ocean data was acquired from the two sub-shelf cavity moorings, each of which included paired SeaBird microCAT and Nortek Aquadopp sensors at mid-cavity depths (~520 m and ~317 m) and near-seabed depths (~746 m and ~785 m), in the modified Circumpolar Deep Water (mCDW) layer. These were augmented by a fiber optic thermal profiler system that measured both ice and ocean temperatures for 19 months. The fiber optic thermal data show a minimum temperature of -19.0°C in the interior, and lower temperature gradient suggesting truncation of the ice shelf base due to basal melting. Time-series of the profile data show very little basal melting of the ice at the two sites, but a thickening of the mCDW layer over the observation period. Overall, the AMIGOS-III data have supported six published studies to date, on ice shelf dynamics, ocean flow and layer properties, basal conditions, atmospheric river events, and weather. The units demonstrate the benefit of long-duration multi-sensor observing platforms in ice shelf or ice tongue areas.

How to cite: Scambos, T., Truffer, M., Collao-Barrios, G., Dotto, T., Kratt, C., Tyler, S., and Pettit, E.: Climate, Ice, and Ocean Characteristics of the Thwaites Eastern Ice Shelf from two In-Situ Multi-Sensor Automated Stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13668, https://doi.org/10.5194/egusphere-egu24-13668, 2024.

The retreat of the Antarctic Ice Sheet is conventionally attributed to ocean melting of fringing ice shelves, potentially enhanced by internal instability due to the proximity of its grounding lines to retrograde bed slopes. Ocean melting is enhanced by increased intrusion of modified Circumpolar Deep Water (mCDW) within ice shelf cavities. Several processes can enhance the ability of mCDW to melt ice shelves. Upwelling from the release of subglacial melt water at the grounding line is arguably one of the least well constrained and understood and is currently not accounted for in projections of ice sheet loss.

The Thwaites glacier in the Amundsen Sea sector of the west Antarctic ice sheet has been the focus of recent investigations given its current rapid retreat, potential instability, and its impact on rates of future sea level change. In 2013, a network of subglacial lakes under the Thwaites glacier drained, the combined outflow reached a peak discharge in excess of 500 m³ s^-1 and likely reached the grounding line. During this period, several other processes took place at the grounding line and under the fringing floating ice. This event offers a natural experiment to examine the impact of subglacial outflow on ocean melting of ice shelves.

In this presentation we revisit the various events affecting the Thwaites system during this period and generate several new observations of lake discharge, rates of ice shelf basal melting, and grounding line thinning and retreat. We focus the discussion on the potential feedback between lake discharge, variation in ocean melting, and grounding line retreat, and on the contribution of subglacial discharge to the recent retreat of the Thwaites glacier.

How to cite: Gourmelen, N., Jakob, L., Holland, P., Goldberg, D., and Dutrieux, P.: Ice-ocean-subglacial hydrology interactions, and recent evolution of the Thwaites glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10321, https://doi.org/10.5194/egusphere-egu24-10321, 2024.

A number of studies have defined a boundary in the Amundsen Sea embayment between an inner continental shelf, which contains areas where crystalline bedrock is at or near the seabed, and the shelf further offshore, which is underlain by sedimentary strata that increase in overall thickness oceanward. Other studies have shown that much of the inner shelf in Pine Island Bay is covered by a drape of sandy mud averaging about 1 m in thickness, interpreted as having been deposited from meltwater plumes during the mid-late Holocene. Much thicker sediments have been shown to be present in isolated deep basins based on acoustic sub-bottom profiles and sparse seismic reflection profiles, including an estimated maximum thickness of >400 m in one basin close to the front of Pine Island Glacier.  Thus, the widespread impression exists that, apart from the thin Holocene drape, sedimentary cover in Pine Island Bay is restricted to isolated basins.

Here we examine the distribution and thickness of sediments in Pine Island Bay using a network of high-resolution seismic reflection profiles collected in 2020 on RV Nathaniel B Palmer cruise NBP20-02. We show that more extensive thick sediments are present near the front of Pine Island Glacier than have been reported previously. In some places sediment units exhibit characteristics that suggest their deposition was influenced by bottom currents. We also show that sedimentary deposits are present over the tops and on the flanks of some bathymetric highs that must have been former ice shelf pinning points. Finally, we consider what the extent, thickness and character of the sedimentary units identified tell us about glacial/glacimarine processes and ice sheet history in the area, and what could be learned by further study and sampling.

How to cite: Larter, R., Hogan, K., Graham, A., Nitsche, F., Wellner, J., Hillenbrand, C.-D., Totten, R., Smith, J., Miller, L., Anderson, J., Mawbey, E., Clark, R., Hopkins, R., Lehrmann, A., Lepp, A., Marschalek, J., Munevar Garcia, S., and Taylor, L.: How much, how deposited, how old – what can we learn from sediments in Pine Island Bay?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19707, https://doi.org/10.5194/egusphere-egu24-19707, 2024.

Predicting future change to the Antarctic Ice Sheets requires high quality data to constrain numerical ice sheet models. A major uncertainty stems from a lack of knowledge regarding the late Holocene trajectory of the West Antarctic Ice Sheet (WAIS). There are two hypotheses regarding the late Holocene behaviour of the WAIS. A) Steady retreat throughout the Holocene with stabilisation at or near the present-day position (ice relaxation hypothesis) or, B) retreat to a smaller-than-present configuration with subsequent readvance to the present-day position (the retreat-readvance hypothesis). The two hypotheses represent profoundly different ice sheet trajectories. These hypotheses have been discussed with particular reference to the Amundsen, Ross and Weddell Sea sectors of the WAIS.

Initial studies proposing the retreat-readvance model suggested that GIA related uplift caused re-grounding of ice rises in the Weddell Sea, increasing ice shelf buttressing and leading to grounding line re-advance. In the southern Weddell Sea major ice streams are currently at threshold positions on reverse bed slopes where they are vulnerable to Marine Ice Sheet/Cliff Instabilities. As this region drains ~22% of Antarctica the lack of geological constraint on the current ice sheet trajectory contributes significant uncertainty to future predictions. Any groundling line retreat beyond present day limits would be accompanied by up-stream ice sheet thinning thus retreat to a smaller-than-present configuration would be accompanied by thinning of the ice sheet surface below the present-day level. Consequently, determining whether sub-glacial rock samples from the Weddell Sea sector have been exposed in the recent past can robustly test for a smaller-than-present ice sheet configuration.

We present an update on two field seasons where, using a modified Winkie Drill, we recovered sub-glacial rock samples from the Ellsworth Mountains and Pensacola Mountains. These mountain ranges bracket the proposed zone of retreat and can thus provide limiting data points on the extent and duration of any retreat. The subglacial cores are to be analysed using in situ ¹⁴C and luminescence to test for any past exposure to cosmic rays and sunlight respectively. We will present a summary of the field season outcomes and preliminary analytical data along with initial interpretations.

How to cite: Small, D., Smedley, R., Dunai, T., Lees, T., Trabucatti, S., and Boeckmann, G.: New geological constraints on Holocene retreat-readvance of the West Antarctic Ice Sheet in the Weddell Sea Embayment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12136, https://doi.org/10.5194/egusphere-egu24-12136, 2024.

Paleoceanographic records spanning the Oligocene (33.9–23.03 Ma) provide insights into Antarctic ice-sheet (AIS) dynamics in a world warmer-than-today, allowing to improve future projections linked to current global warming. While the long-term evolution of Oligocene glaciations is relatively well-known, current knowledge about the short-term (i.e., orbital to suborbital scale) AIS dynamics is still limited. Here, we investigate short-term dynamics of the AIS during the late Oligocene (spanning ~26–25 Ma), using a high-resolution multi-proxy record from Ocean Drilling Program Site 689 (Maud Rise, Southern Ocean). Variations in ice volume were quantified using the stable oxygen isotope composition of seawater (δ¹⁸O_SW) inferred from benthic foraminiferal δ¹⁸O and Mg/Ca-based bottom-water temperatures. Changes in sediment provenance and weathering inputs were characterised using detrital neodymium isotopic compositions (εNd) of the sediments. The δ¹⁸O_SW record reflects a highly dynamic AIS during the late Oligocene, with glacial conditions characterised by an AIS volume larger than the modern one (up to +14%) and interglacial conditions characterised by a much smaller AIS volume (up to -29%) than today. Detrital εNd varies from -12 to -9, with less radiogenic εNd signatures generally matching higher δ¹⁸O_SW values (i.e., glacials) and vice-versa. This co-variation between an ice-volume proxy and a tracer of sediment provenance characterises crustal sequences exposure to weathering as the ice-sheet retreated. The detrital εNd record thus supports recent interpretations of a highly dynamic AIS during the late Oligocene, which is mirrored by large changes in the provenance of weathering products induced by the waning and waxing of the AIS.

How to cite: Creac'h, L., Brzelinski, S., Friedrich, O., Frank, M., Gutjahr, M., and Lippold, J.: Short-term Antarctic ice-sheet dynamics during the late Oligocene: Multi-proxy records from ODP Site 689, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2465, https://doi.org/10.5194/egusphere-egu24-2465, 2024.

While most of West Antarctic ice shelves are thinning due to ongoing oceanic warming, East Antarctic ice shelves, except a few ones, are apparently more stable. One sector in particular, the Wilkes Subglacial Basin, is not showing any or very little sign of weakness to ongoing climate change. This sector of Antarctica is drained by the Cook ice shelf, the Ninnis ice shelf and the Mertz ice tongue. Those ice shelves have experienced some observed calving events in the past decades, but actual ice flow does not indicate that this sector is retreating and contributing to global mean sea level rise. But can we really measure the sensitivity of a sector only accounting for two decades of observations? Geological archives and morphological evidence of the George V Land continental margin in front of those glaciers suggest, on the contrary, that the ice sheet over the WSB has been one of the most active of East Antarctic sectors through its glaciological history. A multi-year sea ice cover, reducing only under exceptional atmospheric conditions, does not allow the systematic exploration of the area.  Rare geophysical, glaciological, oceanographical, geological and geographical hampers a proper assessment of the instability potential of this area. International cooperation not only is needed to reach and operate in such difficult sector of Antarctica, both at land and on sea, but is also needed to perform multi-disciplinary measurements.

How to cite: Colleoni, F., De Santis, L., Barruol, G., and Dutrieux, P.: The critical importance of Wilkes Land Subglacial Basin stability (East Antarctica), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4151, https://doi.org/10.5194/egusphere-egu24-4151, 2024.

The glaciers terminating in the Cook Ice Shelf and the Ninnis Glacier drain most of the Antarctic marine ice sheet covering the Wilkes Subglacial Basin (WSB), whose ice volume is equivalent to 3-4 m of global sea level rise. Long-term climate projections and multiproxies studies of ice records suggest that ice sheet retreat in this area, thought to be colder and more stable, may be triggered by warm ocean water intrusion.
During the 2022 campaign of the Italian Programma Nazionale delle Ricerche in Antartide (PNRA) with the icebreaker L. Bassi, the project COLLAPSE (Cook glacier-Ocean system, sea LeveL and Antarctic Past Stability) mapped two systems of canyons and hills located at the mouth of suspected glacial valleys off Cook and Ninnis glaciers. The combination of geomorphological, seismic, oceanographic, and sedimentary data (see abstract from Torricella et al.) allowed identification of a variety of processes active on the seafloor today and in the late Quaternary. The geophysical data show evidence of slope instability offshore of the presumed major glacial troughs. Sediment drifts controlled by bottom currents grow on channel-levees and slope terraces. This information will help, albeit indirectly, to reconstruct the dynamics of different glaciers in relation to paleoclimatic changes and ocean circulation, and to estimate their respective contributions to global sea-level rise.
In addition to the co-authors listed in this summary who are involved in the analysis of the geophysical and oceanographic data, the project PNRA COLLAPSE includes a large group of scientists for the analysis of the sediment cores, from the Universities of Trieste, Siena and Milan-Bicocca, CNR-ISP e ISMAR, INGV (I), Univ. Bordeaux, Grenoble and LOCEAN, Paris (F), CSIC (E), Colgate Univ. (USA), Australian National University and Univ. of Tasmania (AUS), Russian FSBI VNIIOkeangeologia, (RU), Alfred Wegener Institute (D), GNS (NZ).

How to cite: De Santis, L., Accaino, F., Accettella, D., Bensi, M., Colleoni, F., Cova, A., Donda, F., Facchin, L., Kovacevic, V., Martellucci, R., Mauri, E., Ursella, L., and Zgur, F.: Cook glacier-Ocean Antarctic Past Stability (COLLAPSE) project preliminary results from geophysical and oceanographic data analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3663, https://doi.org/10.5194/egusphere-egu24-3663, 2024.

Understanding ocean-ice sheet interactions in the geological past is critical for evaluating the ice sheet sensitivity to ocean forcing in future climate warming. Geological evidence suggests major oceanographic changes across the Southern Ocean during the Middle Miocene Climate Transition (MMCT) (~15-12 Million years ago (Ma)). However, the response of the East Antarctic Ice Sheet to these changes remains poorly constrained. Here we explore ocean-ice interactions during the MMCT by presenting data from two marine sedimentary cores along a latitudinal transect offshore Prydz Bay (East Antarctica). Ocean Drilling Program (ODP) Site 1165 is located on the continental rise off Prydz Bay (64◦27.27^o S, 67◦13.08^o E, 3537.5 water depth) and ODP Site 744 is located on the Southern Kerguelen Plateau (61^o 34.66´S, 80^o 35.43´E, 2307 m water depth). Neodymium and strontium isotopic compositions of fine-grained (< 63μm) detrital sediments from ODP Site 1165 were generated to constrain potential changes in sediment provenance, revealing potential changes in ice sheet dynamics (expansion/retreat). Neodymium isotope ratios (ε_Nd) from fossil fish teeth from ODP Site 744 were used to trace regional water masses and Southern Ocean circulation changes for the same period. Additionally, marine productivity records generated from both ODP sites were used to track changes on the position of the Southern Ocean frontal system. We report an equatorward migration of the Southern Ocean frontal system around 13 Ma, associated with global climate cooling, sea ice expansion and CO₂ decline during the MMCT. Despite this major ocean-climate reorganization, our data suggest the presence of a rather stable and large ice sheet in the Prydz Bay throughout the MMCT, implying that the ice sheet was less sensitive to ocean forcing during the MMCT.

How to cite: Evangelinos, D., van de Flierdt, T., Paredes, E., D. Pena, L., and Cacho, I.: East Antarctic Ice Sheet response to ocean forcing during the Middle Miocene Climate Transition: Insights from Prydz Bay, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18013, https://doi.org/10.5194/egusphere-egu24-18013, 2024.

Recent studies have indicated that the migration of grounding line is extremely sensitive to basal melt in the grounding zone. Different representations of melting at the grounding line introduce significant uncertainties in predictions of ice mass loss and global sea level rise. However, there remains an absence of targeted, systematic studies grounded in real-domain, and robustly representing melt in partially floating cells of ice sheet models remains a pressing technical challenge. This study delves into four distinct melt schemes at the grounding line within the Wilkes Subglacial Basin (WSB) model, focusing on their impact on ice loss predictions. Specifically, we analyse the No Melt Parameterization (NMP), Full Melt Parameterization (FMP), and two variants of the Sub-Element Melt parameterization (SEM1, SEM3) as applied to partially floating elements at the grounding line. We found that both the SEM and NMP schemes outperform FMP in terms of convergence with finer mesh resolution, with each exhibiting varying advantages over the other.  Notably, the discrepancies in results attributed to various melt schemes are significantly amplified when high melt rates are applied near the grounding line. Our results consistently suggest that the FMP should be avoided under all circumstances due to its poor convergence and substantial overestimation of ice mass loss. We recommend that future ice sheet models carefully evaluate the choice between NMP and SEM in their specific model contexts.

How to cite: Wang, Y., Zhao, C., Gladstone, R., Zwinger, T., Galton-Fenzi, B., and Christoffersen, P.: Parameterization Solutions for Basal Melting at the Grounding Line in Ice Flow Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4251, https://doi.org/10.5194/egusphere-egu24-4251, 2024.

As part of the PNRA_BOOST project (Bridging Onshore-Offshore STructures at the Pacific Coast of North Victoria Land, Antarctica: an integrated approach), new offshore geophysical data (multichannel high-resolution seismic lines, bathymetric and magnetic data) were acquired on board of OGS R/V Laura Bassi (Feb 2023, XXXVIII Italian Antarctic Expedition), along the Pacific side of North Victoria Land, an underexplored key area at the boundary between East and West Antarctica. A preliminary analysis of the seismic and bathymetric data allows the identification and interpretation of morphological and tectonic features representing key hints for the study of the influence of lithosphere dynamics on ice-sheet evolution.

In the study area, the northern sector of the shelf has an outer concave shape of its break and slope and is incised by several gullies; on the contrary the southern sector shows a stepped geometry with a WNW-ESE straight linear trend abruptly turning to a NW-SE trend. The continental shelf consists of a thin, horizontally layered succession lying on a crystalline basement dissected by two U-shaped glacial troughs several kilometers wide. The slope consists of seaward-prograding sedimentary strata that are truncated on the shelf by a regional unconformity (RSU 1). In the upper part of the slope of the NW sector, three distinct seaward prograding wedges were recognized, whereas they were not identified in the southern sector.

NW-trending basement highs, bounded by faults, are visible both on the shelf and on the continental rise (towards the abyssal plain). Growth strata associated with these faults allow a tentative dating of activation to Oligocene times. The unconformity at the top of the growth strata may be related to the U3 surface (36 Ma) of Sauermilch et al. (2019). In addition, a ca. 20 km-long ridge of basement, covered by drift deposits, revealed at a depth of about 2500 m, is bounded by faults with indications of recent tectonic activity. The observed faults could have reactivated inherited zones of weakness that bound rift blocks formed during the breakup between Australia and Antarctica. In particular, the U3 surface is associated with the beginning of the phase of fast seafloor-spreading between Australia and Antarctica.

In the SW part of the study area, two broad “linear” volcanic zones occur along a roughly NNW-SSE direction; i.e. the orientation of the main tectonic lineaments inland. These zones consist of individual volcanic edifices and small volcanic ridges composed of coalescing bodies. Several volcanoes are clearly active and fluid-related features are visible cutting through the surrounding sedimentary successions. This volcanism correlates well with airborne magnetic observations and may represent the NNW continuation of the Mid-Miocene to Quaternary Hallett Volcanic Province forming the Adare Peninsula, or may be related to the post-spreading Pliocene-Recent volcanism of the Adare Basin.

Sauermilch et al., 2019. JGR: Solid Earth, 124, 7699–7724 (doi.org/10.1029/2018JB016683).

How to cite: Crispini, L., Civile, D., Ferrante, G. M., Locatelli, M., Morelli, D., Volpi, V., Accettella, D., Accaino, F., Busetti, M., Läufer, A., Armadillo, E., Colizza, E., Salvini, F., and Ruppel, A.: Lithosphere-cryosphere interactions at the Pacific coast of North Victoria Land: new evidence of past to recent geodynamic processes from offshore geophysical data (PNRA_BOOST Project), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10149, https://doi.org/10.5194/egusphere-egu24-10149, 2024.

Detecting and understanding potential changes in annual mean temperature and accumulation rate at the East Antarctic Plateau is crucial to assess the sensitivity and future response of the Antarctic ice sheet to global warming. Due the very low accumulation rate and its spatial variability the interpretation of climate proxies from shallow firn cores with centennial to decadal time resolution is challenging. A major limitation is the available time resolution obtained by available dating approaches and a reliable assessment of its uncertainty.
In this study a 204 m long firn core, B56, drilled in 2016 on the East Antarctic Plateau, is analysed. The major goal of this study is dating of the firn core by combining different dating methods on the basis of available density data, dielectric properties, and ion chromatography (non-sea-salt sulphate) data. In order to utilize density, the Herron-Langway Model is used for determining the depth-age relation. In this model temperature and snow accumulation are assumed to be constant and the relationship between the snow density and the depth below the snow surface does not change over time. Depending on the used accumulation rate, the resulting age at 200 m depth varies between 6200 to 7200 years. Secondly, the dielectric profile and non-sea-salt sulphate's (nssSO4-2) concentration data are used for constructing another depth-age model, thereby matching prominent data peaks to known volcanic eruptions that have been recorded in the past. Here, the resulting age at 200 m depth is determined to about 4400 years, which compares well to published age models of firn cores from the East Antarctic Plateau. In comparison we find all age models to be consistent within the upper 40 of meters (approximately 1000years), but the Herron-Langway model to overestimate the age at greater depths. We propose that our findings indicate changes in accumulatıon rate in the past leading to the offset in the Herron-Langway model (using a constant accumulation rate).
However, by combining the dating methods we are able to not only provide a reasonable dating over the full firn core, but also to improve the time resolution of the derived age model. This will improve the interpretation of the climate proxies of this firn core and serve as a role model for other shallow firn cores from the East Antarctic Plateau.

How to cite: Sagol, F. K., Schwamborn, G., Freitag, J., Kipfstuhl, S., Wilhelms, F., and Hörhold, M.: Dating and interpreting a firn core from the East Antarctic Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15484, https://doi.org/10.5194/egusphere-egu24-15484, 2024.

East Antarctic Ice Sheet (EAIS) has an overall balanced or slightly positive mass balance. However, Wilkes Land and Totten Glacier (TG) in EAIS have been losing ice mass significantly since 1989. There is a lack of knowledge of long-term mass balance in the region which hinders the estimation of its contribution to global sea level rise. We reconstruct ice flow velocity fields of 1963–1989 in TG from the first-generation satellite images of ARGON and Landsat-1&4, and build a five decade-long record of ice dynamics. Based on these velocity maps, we show that this acceleration trend in TG has occurred since the 1960s. Combined with recently published velocity maps, we find a persistent long-term ice discharge rate of 68 ± 1 Gt/y and an acceleration of 0.17 ± 0.02 Gt/y2 from 1963 to 2018, making TG the greatest contributor to global sea level rise in EA. We attribute the long-term acceleration near grounding line from 1963 to 2018 to basal melting likely induced by warm modified Circumpolar Deep Water. The speed up in shelf front during 1973–1989 was caused by a large calving front retreat. As the current trend continues, intensified monitoring in the TG region is recommended in the next decades.

How to cite: Li, R., Cheng, Y., Chang, T., Gwyther, D. E., Forbes, M., An, L., Xia, M., Yuan, X., Qiao, G., Tong, X., and Ye, W.: 60 Years of satellite record reveals high level velocity and mass discharge in Totten Glacier, East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4890, https://doi.org/10.5194/egusphere-egu24-4890, 2024.

Totten Glacier is the largest contributor to the global sea level rise from the East Antarctic Ice Sheet and has been losing mass since the earliest satellite observations in the 1970s. However, unlike other outlet glaciers that are losing mass in Antarctica (e.g. Pine Island and Thwaites), there has been no obvious long-term speed-up and subsequent increase in ice discharge over the satellite observational record, despite large interannual variability in ice flow. This indicates that the imbalance at Totten Glacier must have initiated prior to our earliest satellite observations.

Utilizing the complete record of satellite imagery, we track the pattern of surface undulations that form near the Totten grounding line and are preserved for decades as they are subsequently transported downstream. In our earliest satellite image from 1973, we observe surface undulations estimated to have formed near the grounding line in the 1920s. We suggest that changes in the size and formation of these surface undulations are caused by changes in the melt rate and ice thickness near the grounding line that alters the degree of contact between the ice shelf and a nearby pinning point. By monitoring the size of these surface undulations, we provide a qualitative record of ice thickness change near the grounding line from the 1920s to the present day. We reveal a clear shift in pattern in the mid-20th century, where, despite pronounced and consistent surface undulation formation between the 1920s and 1950s, no detectable surface undulations were formed between the late 1950s and 1980s.

Elsewhere on the glacier, we demonstrate the long-term opening of a previously identified channel connecting the eastern ice shelf to the open ocean and observe grounding line changes since the 1970s.

How to cite: Miles, B. and Bingham, R.: Change in melt pattern at Totten Ice Shelf in the 1950s, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16595, https://doi.org/10.5194/egusphere-egu24-16595, 2024.

Existing marine sedimentological constraints on the timing of deglaciation in the Weddell Sector are sparse, owing to the combination of inaccessibility due to thick sea ice, and chronological difficulties typical of Antarctic shelf sediments. Here, we present new results from near the calving line in the Hughes Trough, located in the central-southern Weddell Sea. Ramped pyrolysis 14C dating was used to determine a robust chronology from the 5.0 m long sediment core, PS111_53. The core preserves a full glaciomarine sequence from subglacial, sub-ice shelf, and open marine / polynya environments. The sedimentological transition interpreted to be formed at the grounding zone during ice shelf retreat was dated to 18.2 – 19.0 ka, indicating that grounded ice retreat was underway by this time. Further, the sedimentation rate was drastically reduced at ~6 ka, indicating that the oceanographic and glaciological regimes of the continental shelf may have changed at this time.

The proposed timing of glacial mass loss is well placed in the context of recent studies from the continental ice sheet and off-shelf marine sediments, which have suggested that a significant ice mass loss event from the Weddell Sector of the Antarctic Ice Sheet (AIS) may have occurred early in the deglaciation. A synchronous timing of deglaciation between the Weddell Sector of the AIS and Laurentide Ice Sheets during MWP-1A0 points towards bi-polar tele-connections.

How to cite: Bollen, M., Müller, J., Gutjahr, M., and Jaccard, S.: Sedimentological evidence for an early deglaciation in the Weddell Sector at ~19 ka, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19800, https://doi.org/10.5194/egusphere-egu24-19800, 2024.

Our understanding of Antarctic Ice Sheet evolution has largely relied on geological evidence from a combination of onshore and offshore archives. In particular, terrestrial cosmogenic nuclides (e.g., ¹⁰Be, ²⁶Al, ³⁶Cl, ¹⁴C) have now been extensively employed to assess the timing and drivers of past ice sheet change. Yet, such chronologies are incomplete, can be compromised by complex burial-exposure histories, and are not ideally suited to reconstructing the long-term (hundreds of thousands to millions of years) evolution of the ice sheet.

To address this gap in understanding long-term Antarctic Ice Sheet evolution, we investigate the application of a cross-disciplinary approach that incorporates a combination of geological and biological evidence. Recent work has implied that certain biota, such as Antarctic springtails (Arthropoda: Collembola), survived consecutive glacial periods in ice-free refugia by shifting up and down nunataks or on moraines above the ice (see: Stevens and Mackintosh, 2023; https://doi.org/10.1098/rsbl.2022.0590). Due to these prolonged periods of isolation, springtails have now developed high levels of species endemism across Antarctica. These species are often short-range endemics, and now combined with extensive molecular data are the only terrestrial invertebrate group with unequivocal Antarctic provenance across successive glacial maxima on the continent. As a result, incorporating these growing records of Antarctic springtail distribution into chronological studies may yield a more complete understanding of ice sheet evolution through time. Here, we demonstrate the use of this combined approach across the whole of Dronning Maud Land, East Antarctica. 

How to cite: Cooper, E.-L., Stevens, M. I., and Mackintosh, A. N.: A cross-disciplinary approach to understanding Antarctic Ice Sheet histories: combining cosmogenic nuclides with records of Antarctic springtails in Dronning Maud Land, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21830, https://doi.org/10.5194/egusphere-egu24-21830, 2024.

The Cook Ice Shelf and Ninnis Glacier drain a large part of the Wilkes Land Basin, which contains the equivalent of about 4 metres of sea level. The glaciers in this region are thought to have retreated during the warm climatic phases of the Pleistocene, but the extent of the retreat and the identification of the driving forces are still controversial. The aim of this study is to contribute to the understanding of regional depositional processes and environmental conditions that shed light on the dynamics of the ice sheet and the factors that determine its stability and instability (ocean and atmospheric temperature and precipitation), and ultimately to refine the projected evolution of these glaciers. We here present the preliminary results of a multidisciplinary study (textural analyses, geochemical, chemical and petrographic analyses, paleomagnetic and micropaleontological determinations) carried out on six sediment cores collected on the continental slope off the Cook Ice Shelf and Ninnis Glacier in the framework of the Programma Nazionale di Ricerca in Antartide - PNRA project COLLAPSE ("Cook glacier-Ocean system, sea LeveL and Antarctic Past Stability'). We are currently documenting sedimentological processes and oceanographic conditions in this region during the Late Pleistocene. We identified three main units: the first unit consists of laminated silt with low microfossil content and is interpreted as influenced by bottom current; the second unit is a massive silt with ice debris, and very low microfossil content and is interpreted as indicating a period with intense ice calving with iceberg production; the third unit is a bioturbated mud with high microfossil content.   The microfossil content, especially the diatoms, suggest that this unit is deposited during a period of open water.

How to cite: Torricella, F., Andò, S., Battaglia, F., Caburlotto, A., Colizza, E., Crosta, X., De Santis, L., Etorneau, J., Gallerani, A., Gentz, T., Leventer, A., Macrì, P., Melis, R., Perotti, M., Salvi, G., Tesi, T., and Zurli, L.: Pleistocene evolution of Ninnis and Cook glaciers (East Antarctica) from a micropaleontological and sedimentological study: Preliminary result, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22344, https://doi.org/10.5194/egusphere-egu24-22344, 2024.

A giant submarine landslide in front of the Wilkes subglacial basin along the Cook continental margin—one of the least explored areas on Earth—has been documented for the first time. This area is critical to understanding the stability of one among the most vulnerable sectors of the Antarctic Ice sheet to climate and ocean warming. It is named as Cook mega-slide complex (CMSC), which occurred in the early Pliocene according to the seismic interpretation correlated to the IODP Exp 318 sites. The giant submarine landslide is well imaged on the seismic profiles and exhibits various kinematic indicators with the basal glide planes and original headwall scarps. It affected the area of c. 22, 686.5 km², approximately 3399 km³ of sediments evacuated from the continental margin. With a scale similar to Storegga Slide on the Norway margin, the size of the CMSC is mostly likely the largest submarine landslide ever discovered around the Antarctic margin. We propose that glacial isostatic adjustment and glacial outburst floods caused by the East Antarctic Ice Sheet (EAIS) retreat lead to the formation of the large slides and create the condition for slope instability and erosion. The development and collapse of peripheral bulge has been firstly observed from Antarctic margin, associated with the glaciation and subsequent deglaciation of the EAIS, led to a distinct spatial variation in sea level changes and further affected the deposition on the slope. Our results yield intriguing insights into the relationship of stratigraphic evolution, submarine landslides, and past EAIS instabilities throughout the warm periods of the late Miocene-Pliocene, and thereby provide important constraints for ice sheet modeling and sea level prediction.

How to cite: Huang, X., De Santis, L., Leitchenkov, G., and Escutia, C.: Submarine landslides unravel the dynamics of the past East Antarctic Ice Sheet , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7756, https://doi.org/10.5194/egusphere-egu24-7756, 2024.