[HBI:2]/[HBI:3] and sortable silt distribution in the Amundsen Sea (36th Antarctic expedition of China)

This study explores the interplay between sea-ice dynamics and bottom-current strength in the Amundsen Sea (72°S–76°S, 150°W–110°W) by analyzing highly branched isoprenoid (HBI) lipids and grain-size parameters from ten surface sediment samples. These results yield new insights for paleoenvironmental reconstructions in a region critical to the retreat of the West Antarctic Ice Sheet. The sedimentary record preserves the mean condition of summer sea ice concentrations and bottom-water hydrodynamics within the Holocene. Our data indicate that the ratio of diene- to triene-unsaturated HBIs ([HBI:2]/[HBI:3]) tracks summer sea ice concentration, while mean sortable silt () reflects the upwelling intensity of Circumpolar Deep Water (CDW). We find a negative correlation between [HBI:2]/[HBI:3] and , suggesting that enhanced CDW upwelling and sea ice melt may form positive feedback. Specifically, the upwelling of CDW accelerates summer sea ice melt, and the resultant freshwater release, in turn, further enhances this upwelling. Although this observation does not align with numerical models predicting that sea ice melt suppresses CDW upwelling, it underscores the value of integrating HBI biomarkers with grain-size proxies to unravel ice-ocean interactions in the Amundsen Sea. To fully resolve the mechanisms underlying these processes, however, future work must draw upon sediment core records that capture a more comprehensive history of ice-ocean environmental change.