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.

Description: Diatom assemblages preserved in 16 sediment cores recovered in the eastern Indian, Atlantic and Pacific sectors of the Southern Ocean are used for the reconstruction of the variability of summer sea surface temperature (SSST) and sea ice concentration during the Last Interglacial (LIG) or Marine Isotope Stage 5 (MIS 5). The large coverage of the core sites allows for reconstructions on latitudinal and longitudinal transects across the Southern Ocean and thus for the comparison of the environmental signal evolution in different sedimentary basins of the Southern Ocean. Such information is crucial for the understanding of climate signal propagation in the Southern Ocean and on inter-hemispheric scale. The quantitative temperature and sea ice records are derived with newly established diatom-based transfer functions at millennial to centennial resolution. Stratigraphic age assignment relies on a combination of oxygen isotope stratigraphy, biostratigraphy, core-core correlation using physical, geochemical and microfossil abundance pattern together with a tuning of sediment core signals with climate records in Antarctic ice cores. All records display a rapid transition from glacial (MIS 6) to MIS 5 conditions to reach maximum temperatures in the latest MIS 6/MIS 5 transition (Termination II) and the early LIG attributed to MIS 5.5. The amplitude of the SSST change is up to 5◦C, with generally smaller values in the Pacific sector. During this period Southern Ocean temperature may exceed modern surface temperatures by up to 3◦C and the winter sea ice edge is located south of the modern ice edge. Higher resolution cores display short-term temperature rebounds during the Termination II warming. Such cold rebounds are not discerned in the ice core records. The Southern Ocean warming could be triggered by precessional changes influencing high latitude summer insolation and potentially be accelerated by feedback mechanisms such as the reduction of surface albedo (sea ice), CO2 outgassing of the Southern Ocean and changes in meridional overturning circulation. The new set of data fills a gap in information in the global evolution of Earth climate during the Last Interglacial and will be useful for the testing of numerical modeling results of the last distinctly warmer and higher sea level than present climate period.

Description: Dust deposition in the Southern Ocean constitutes a critical modulator of past global climate variability, but how it has varied temporally and geographically is underdetermined. Here, we present data sets of glacial-interglacial dust-supply cycles from the largest Southern Ocean sector, the polar South Pacific, indicating three times higher dust deposition during glacial periods than during interglacials for the past million years. Although the most likely dust source for the South Pacific is Australia and New Zealand, the glacial-interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from Antarctica and the South Atlantic dominated by Patagonian sources. These similarities imply large-scale common climate forcings, such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia.