Antarctic sea ice reconstructions: pros and cons of highly branched isoprenoids as sea ice proxies

The reconstruction of past Antarctic sea ice coverage through the application of diatom assemblages is often hampered in near coastal environments due to silica dissolution effects. The more recently established approach of using highly branched isoprenoid biomarkers to identify past sea ice conditions seems a valid method to overcome this limitation and that may also provide insight into ice-shelf dynamics. Here, we evaluate the so-called PIPSO25 index applied to modern surface sediments from the Amundsen Sea, the Drake Passage and Bransfield Strait, and the Weddell Sea. The comparison of biomarker-based sea ice estimates with satellite-derived sea ice concentrations supports the potential of the proxy approach. In a next step, we generated biomarker records using two sediment cores from the western and eastern Weddell Sea to track sea ice variability over late Pleistocene glacial-interglacial cycles. Consideration of additional data such as XRF and multi-sensor core logging records as well as micropaleontological investigations enables a comprehensive assessment of the environmental changes in the Weddell Sea in response to large-scale climate transitions. While magnetic susceptibility and density data obtained for both cores display similar patterns, we note distinct differences between the biomarker records highlighting local feedback mechanisms affecting sea ice cover.