Description: The Western Antarctic Peninsula is an exceptionally climate-sensitive area and investigations into its environmental response to recent and past climate changes may support our understanding of the complex interactions in the ice-ocean-atmosphere system. Organic geochemical and micropaleontological analyses of a 210Pb-dated sediment core from the Bransfield Strait (located between the Antarctic Peninsula and the South Shetland Islands) reveal highly variable sea ice conditions over the past 200 years and increased phytoplankton productivity since the 1930s. Concentrations of biomarker lipids (highly branched isoprenoids (IPSO25), phytosterols) and diatom-based sea ice estimates are compared to satellite data and further environmental information derived from Antarctic Peninsula ice cores extending back in time beyond instrumental records. Fluctuations in the sedimentary abundance of the sea ice biomarker IPSO25 (Belt et al., 2016) and sea ice-associated diatom assemblages seem to be linked to changes in atmospheric (ENSO, SAM) and oceanic circulation patterns. Interestingly, both IPSO25- and diatom-based sea ice reconstructions for the spring and winter season, respectively, do not reflect the overall warming trend and sea ice decline observed in the study area over past decades (e.g., Stammerjohn et al., 2008). This observation may highlight the need for an improved understanding and more reasoned interpretations of proxy archives.

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: 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.