Highly branched isoprenoids reveal onset of deglaciation followed by dynamic sea-ice conditions in the western Amundsen Sea, Antarctica

The Amundsen Sea drainage sector of the West Antarctic Ice Sheet (WAIS) is widely regarded as a candidate for triggering potential WAIS collapse. The grounded ice sheet drains into the Amundsen Sea Embayment and is thereby buttressed by its fringing ice shelves, which have thinned at an alarming rate. Satellite-based observations additionally reveal a considerable long-term decrease in sea-ice cover in the Amundsen Sea over the last two decades although the long-term significance of this trend is unclear due to the short instrumental record since the 1970s. In this context, investigations of past sea-ice conditions are crucial for improving our understanding of the influence that sea-ice variability has on the adjacent marine environment as well as any role it plays in modulating ice shelf and ice sheet dynamics. In this study, we apply novel organic geochemical biomarker techniques to a marine sediment core from the western Amundsen Sea shelf in order to provide a valuable long-term perspective on sea-ice conditions and the retreat of the Getz Ice Shelf during the last deglaciation. We analysed a specific biomarker lipid called IPSO25 alongside a phytoplankton biomarker and sedimentological parameters and additionally applied diatom transfer functions for reconstructing palaeo sea-ice coverage. This multi-proxy data set reveals a dynamic behaviour of the Getz Ice Shelf and sea-ice cover during the deglaciation following the last ice age, with potential linkages to inter-hemispheric seesaw climate patterns. We further apply and evaluate the recently proposed PIPSO25 approach for semi-quantitative sea-ice reconstructions and discuss potential limitations.

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