Spatial variations in biological productivity and preservation in seafloor surface sediments from the Amundsen Sea Embayment, West Antarctica - including a first look at recently deglaciated seafloor

The Amundsen Sea Embayment (ASE) is an under-explored sector of the West Antarctic continental shelf, where sea-ice cover is typically dense. During recent decades, the West Antarctic Ice Sheet sector draining into the ASE experienced ice-shelf front retreat and sea-ice decrease, increasing accessibility to the ice-sheet margin. The Amundsen Sea Polynya (ASP) and Pine Island Polynya (PIP) of the ASE are among the most biologically productive polynyas in Antarctica. Between 2006 and 2022, multiple international expeditions collected marine sediment cores from the ASE, with recent expeditions by the Thwaites Glacier Offshore Research (THOR) team recovering samples near the ice margins of major glaciers and ice shelves. Here, we investigate biological productivity in the water column that has been recorded in surface sediments using relative diatom abundance, organic carbon and nitrogen contents, stable carbon isotopes of the bulk sediments, and biogenic barium contents by comparing barium to aluminum ratios (Ba/Al). Diatoms are abundant offshore Thwaites Glacier and sparse in recently deglaciated areas. Surprisingly, the ASP is characterized by intermediate levels of productivity, with Cranton Bay and the Pine Island Trough showing higher levels of productivity. We explore these findings in the context of modern environmental conditions and propose explanations for the observed regional differences in the sedimentary record. As glaciated regions continue to rapidly change, it is imperative to establish baselines for factors that shape the global carbon cycle, including productivity in and near polynyas, so that we can better understand these systems and predict their response to future change.