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Antarctic sea ice is a critical component of the climate system affecting a range of physical and biogeochemical feedbacks and supporting unique ecosystems. During the last glacial stage, Antarctic sea ice was more extensive than today, but uncertainties in geological (marine sediments), glaciological (ice core), and climate model reconstructions of past sea-ice extent continue to limit our understanding of its role in the Earth system. Here, we present a novel archive of past sea-ice environments from regurgitated stomach oils of snow petrels (Pagodroma nivea) preserved at nesting sites in Dronning Maud Land, Antarctica. We show that by combining information from fatty acid distributions and their stable carbon isotope ratios with measurements of bulk carbon and nitrogen stable isotopes and trace metal data, it is possible to reconstruct changing snow petrel diet within Marine Isotope Stage 2 (ca. 24.3–30.3 cal kyr BP). We show that, as today, a mixed diet of krill and fish characterizes much of the record. However, between 27.4 and 28.7 cal kyr BP signals of krill almost disappear. By linking dietary signals in the stomach-oil deposits to modern feeding habits and foraging ranges, we infer the use by snow petrels of open-water habitats (“polynyas”) in the sea ice during our interval of study. The periods when consumption of krill was reduced are interpreted to correspond to the opening of polynyas over the continental shelf, which became the preferred foraging habitat. Our results show that extensive, thick, and multiyear sea ice was not always present close to the continent during the last glacial stage and highlight the potential of stomach-oil deposits as a palaeoenvironmental archive of Southern Ocean conditions.

Ice sheet behavior is strongly influenced by the bed topography. However, the effect of the progressive temporal evolution of Antarctica’s subglacial landscape on the sensitivity of the Antarctic Ice Sheet (AIS) to climatic and oceanic change has yet to be fully quantified. Here we investigate the evolving sensitivity of the AIS using a series of data‐constrained reconstructions of Antarctic paleotopography since glacial inception at the Eocene–Oligocene transition. We use a numerical ice sheet model to subject the AIS to schematic climate and ocean warming experiments, and find that bed topographic evolution causes a doubling in ice volume loss and equivalent global sea level rise. Glacial erosion is primarily responsible for enhanced ice sheet retreat via the development of increasingly low‐lying and reverse sloping beds over time, particularly within near‐coastal subglacial basins. We conclude that AIS sensitivity to climate and ocean forcing has been substantially amplified by long‐term landscape evolution.

The Antarctic continent and its surrounding Southern Ocean are a key component of our planet’s climate system. Since the Eocene/Oligocene Boundary (34 Ma) the Antarctic region has undergone tremendous topographical change on the continent and in the oceanic realm. The massive erosion on the continent by the Antarctic ice sheets and the resulting glacial deposition within the Southern Ocean have shaped our modern maps of the Southern hemisphere. Detailed, high-resolution reconstructions of the palaeotopography and palaeobathymetry shed light on crucial periods in the development of the Antarctic ice sheets as well as the Southern Ocean. This includes e.g. the establishment of the modern circum-polar current system, the pathways of modern and ancient glacial systems as well as the role of the continental shelves in ice sheet stability. Most recent reconstructions of the paleotopography (Paxman et al. 2019) and paleobathymetry (Hochmuth et al. 2020) used all available geophysical as well as geological and borehole data to produce high-resolution maps (0.1 deg) of key time slices of the Southern Ocean evolution. The combined palaeobathymetry and palaeotopography allows seamless land-to-ocean studies including analysis of ice sheet behaviour and erosion and associated depositional cycles. The five time slices presented span from the onset of continental glaciation in Antarctica (34 Ma) to the warmer climates of the Miocene and early Pliocene to the manifestation of modern glacial condition at the Pliocene/Pleistocene Boundary.

Subglacial water plays an important role in ice sheet dynamics and stability. Subglacial lakes are often located at the onset of ice streams and have been hypothesised to enhance ice flow downstream by lubricating the ice–bed interface. The most recent subglacial-lake inventory of Antarctica mapped nearly 400 lakes, of which ∼ 14 % are found in West Antarctica. Despite the potential importance of subglacial water for ice dynamics, there is a lack of detailed subglacial-water characterisation in West Antarctica. Using radio-echo sounding data, we analyse the ice–bed interface to detect subglacial lakes. We report 33 previously uncharted subglacial lakes and present a systematic analysis of their physical properties. This represents a ∼ 40 % increase in subglacial lakes in West Antarctica. Additionally, a new digital elevation model of basal topography of the Ellsworth Subglacial Highlands was built and used to create a hydropotential model to simulate the subglacial hydrological network. This allows us to characterise basal hydrology, determine subglacial water catchments and assess their connectivity. We show that the simulated subglacial hydrological catchments of the Rutford Ice Stream, Pine Island Glacier and Thwaites Glacier do not correspond to their ice surface catchments.

The East Antarctic Ice Sheet (EAIS) is underlain by a series of low‐lying subglacial sedimentary basins. The extent, geology and basal topography of these sedimentary basins are important boundary conditions governing the dynamics of the overlying ice sheet. This is particularly pertinent for basins close to the grounding line wherein the EAIS is grounded below sea level, and therefore potentially vulnerable to rapid retreat. Here, we analyze newly acquired airborne geophysical data over the Pensacola‐Pole Basin (PPB), a previously unexplored sector of the EAIS. Using a combination of gravity, magnetic and ice‐penetrating radar data, we present the first detailed subglacial sedimentary basin model for the PPB. Radar data reveal that the PPB is defined by a topographic depression situated ~500 m below sea level. Gravity and magnetic depth‐to‐source modeling indicate that the southern part of the basin is underlain by a sedimentary succession 2–3 km thick. This is interpreted as an equivalent of the Beacon Supergroup and associated Ferrar dolerites that are exposed along the margin of East Antarctica. However, we find that similar rocks appear to be largely absent from the northern part of the basin, close to the present‐day grounding line. In addition, the eastern margin of the basin is characterized by a major geological boundary and a system of overdeepened subglacial troughs. We suggest that these characteristics of the basin may reflect the behavior of past ice sheets and/or exert an influence on the present‐day dynamics of the overlying EAIS.

East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) likely retreated during past warmer climates. However, the extent of retreat remains poorly constrained, making quantifying past and predicted future contributions to global sea level rise from these marine basins challenging. Geomorphological analysis and flexural modeling within the Wilkes Subglacial Basin is used to reconstruct the ice margin during warm intervals of the Oligocene–Miocene. Flat‐lying bedrock plateaus are indicative of an ice sheet margin positioned >400–500 km inland of the modern grounding zone for extended periods of the Oligocene–Miocene, equivalent to a 2 meter rise in global sea level. Our findings imply that if major EAIS retreat occurs in the future, isostatic rebound will enable the plateau surfaces to act as seeding points for extensive ice rises, thus limiting extensive ice margin retreat of the scale seen during the early EAIS.

Using a one-dimensional numerical model of ice-stream flow with robust grounding-line dynamics, we explore controls on paleo-ice-stream retreat in Marguerite Bay, Antarctica, during the last deglaciation. Landforms on the continental shelf constrain the numerical model and suggest retreat was rapid but punctuated by a series of slowdowns. We investigate the sensitivity of ice-stream retreat to changes in subglacial and lateral topography, and to forcing processes including sea-level rise, enhanced melting beneath an ice shelf, atmospheric warming, and ice-shelf debuttressing. Our experiments consistently reproduce punctuated retreat on a bed that deepens inland, with retreat-rate slowdowns controlled by narrowings in the topography. Sensitivity experiments indicate that the magnitudes of change required for individual forcing mechanisms to initiate retreat are unrealistically high but that thresholds are reduced when processes act in combination. The ice stream is, however, most sensitive to ocean warming and associated ice-shelf melting and retreat was most likely in response to external forcing that endured throughout the period of retreat rather than to a single triggering ‘event’. Timescales of retreat are further controlled by the delivery of ice from upstream of the grounding line. Due to the influence of topography, modeled retreat patterns are insensitive to the temporal pattern of forcing evolution. We therefore suggest that despite regionally similar forcing mechanisms, landscape controls significant contrasts in retreat behavior between adjacent but topographically distinct catchments. Patterns of ice-stream retreat in the past, present and future should therefore be expected to vary significantly.

Marine-based ice streams whose beds deepen inland are thought to be inherently unstable. This instability is of particular concern because significant portions of the marinebased West Antarctic and Greenland ice sheets are losing mass and their retreat could contribute significantly to future sea-level rise. However, the present understanding of icestream stability is limited by observational records that are too short to resolve multi-decadal to millennial-scale behaviour or to validate numerical models. Here we present a dynamic numerical simulation of Antarctic ice-stream retreat since the Last Glacial Maximum (LGM), constrained by geophysical data, whose behaviour is consistent with the geomorphological record. We find that retreat of Marguerite Bay Ice Stream following the LGM was highly nonlinear and was interrupted by stabilizations on a reverse-sloping bed, where theory predicts rapid unstable retreat. We demonstrate that these transient stabilizations were caused by enhanced lateral drag as the ice stream narrowed. We conclude that, as well as bed topography, ice-stream width and long-term retreat history are crucial for understanding decadal- to centennial-scale ice-stream behaviour and marine ice-sheet vulnerability.