Description: The West Antarctic Ice Sheet (WAIS) plays a key role in the global climate system and its collapse could contribute up to 4.3 m of sea-level rise. Mass loss of this marine-based ice sheet is largely caused by ocean-driven melting of ice shelves. This is confimed by modern observational data which show significant glacier thinning and retreat of grounding lines, particularly in the Amundsen Sea area. We here apply an integrated approach to determine provenance of marine sediments, which enables us to trace erosion of different bedrock lithologies, ultimately tied to the location of the eroding ice through time. We present provenance analysis on detrital Holocene seafloor sediments from the Amundsen Sea Embayment as well as from two marine cores PS58/254 (69°19´S, 108°27´W) and PC493 (71°09´S, 119°57´W), located on the continental rise of the Amundsen Sea and covering glacial-interglacial cycles of the past 800 kyrs. We use strontium (Sr) and neodymium (Nd) isotopic compositions of fine terrigenous grains (〈63μm), and 40Ar/39Ar ages on ice-rafted (〉150μm) hornblende and biotite grains. Our Holocene mapping results reveal drainage pathways with distinct signatures in the eastern and western Amundsen Sea Embayment. The western embayment records a homogenous provenance signature, pointing to a local source area in the hinterland, while the eastern embayment shows a range of compositions indicating erosion of the eastern coastal margin and a distinct, but unexposed source lithology under Pine Island Glacier and/or its drainage basin. Systematic isotope variations are detected between glacial and interglacial stages in both downcore records. Core PS58/254 exhibits a radiogenic fingerprint throughout the Late Pleistocene and systematic glacial-interglacial fluctuations in the order of three εNd units. They correlate with physical properties of the sediments (i.e. magnetic susceptibility) and trend towards lower values during interglacials, notably during Marine Isotope Stage (MIS) 5 and MIS 7. Core PC493 exhibits similar radiogenic Nd isotope composition, but a slightly reduced magnitude of glacial-interglacial changes. Detailed analysis of our results will offer a framework for interpreting sediment records from the area, including those from a recent MeBo expedition (PS104) and upcoming IODP expedition 379.

Description: The Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) is experiencing rapid mass loss and there is a pressing need to place the contemporary ice-sheet changes into a longer term context. The continental rise in this region is characterised by large sediment mounds that are shaped by westward flowing bottom currents and that resemble contouritic drifts existing offshore from the Antarctic Peninsula. Similar to the Antarctic Peninsula drifts, marine sediment cores from the poorly studied sediment mounds in the Amundsen Sea have the potential to provide reliable records of dynamical ice-sheet behaviour in West Antarctica and palaeoceanographic changes in the Southern Ocean during the Late Quaternary that can be reconstructed from their terrestrial, biogenic and authigenic components. Here we use multi-proxy data from three sediment cores recovered from two of the Amundsen Sea mounds to present the first high-resolution study of environmental changes on this part of the West Antarctic continental margin over the glacial-interglacial cycles of the Late Quaternary. Age constraints for the records are derived from biostratigraphy, AMS 14C dates and lithostratigraphy. We focus on the investigation of processes for drift formation, thereby using grain size and sortable silt data to reconstruct changes in bottom current speed and to identify episodes of current winnowing. Data on geochemical and mineralogical sediment composition and physical properties are used to infer both changes in terrigenous sediment supply in response to the advance and retreat of the WAIS across the Amundsen Sea shelf and changes in biological productivity that are mainly controlled by the duration of annual sea-ice coverage. We compare our data sets from the Amundsen Sea mounds to those from the well-studied Antarctic Peninsula drifts, thereby highlighting similarities and discrepancies in depositional processes and climatically-driven environmental changes.