Examining micropaleontology to gain insights into long -term oceanographic, glacial, and climatic processes in the Western Amundsen Sea, Antarctica

The West Antarctic Ice Sheet (WAIS) is undergoing rapid glacial retreat, posing a significant threat to global climate, sea level, and elemental cycles. The sector of WAIS that has exhibited the highest rates of change are the outlet glaciers draining into the Amundsen Sea Embayment (ASE). These glaciers release high volumes of glacial meltwater, disrupting the formation of dense shelf water and enabling warm Circumpolar Deep Water (CDW) to freely access the underside of ice shelves and generate basal melt. The precise timing and frequency of these events are unknown, largely due to the remote location of the ASE, heavy ice coverage, and limited satellite observations over this region. However, with concerns that a large-scale collapse of this portion of the WAIS is possible on human timescales, it is crucial we understand the specific atmosphere-ocean-ice dynamics that drive elevated melt in this region. To obtain the most complete spatiotemporal observations of this change while also avoiding the logistical challenges of working directly at the modern ice margin, we focus on the geologic record from the portions of the continental shelf that have already deglaciated. This study of ten archived sediment cores is the first-ever high-resolution diatom analysis to be conducted on the deglaciated continental shelf offshore of the eastern Getz ice shelves and the Dotson Ice Shelf, which currently see some of the most rapid volume changes of the WAIS. Diatoms are well diversified, and their composition and distribution are closely connected to ecological conditions, rendering them excellent proxies for environmental changes over time. Our analysis revealed four major paleoenvironmental units. One unit was dominated by sea-ice diatoms, one exhibited evidence of high primary production, one was characterized by a relatively high abundance of F. kerguelensis, which is commonly associated with warm CDW, and the final unit displayed elevated levels of reworked species. The distribution and relative timing of these units, as well as the overall unexpectedly low abundance of Chaetoceros and F. kerguelensis, were interpreted within the context of existing records of environmental conditions and deglacial retreat in the Amundsen Sea, shedding light on the intricate interplay between oceanic processes and glacial change over time. Most notably, diatom assemblages suggest strong similarities in water mass structure during both the present and the time of initial deglaciation following the Last Glacial Maximum; namely, these two intervals show that water column mixing, sea ice formation, and brine export are reduced due to the interference of fresh meltwater. This study also revealed discrepancies between different coring methods, highlighting the need for improved core handling in the field.