| Summary: | Glacial retreat of the West Antarctic Ice Sheet is a major driver of global sea-level rise. Accelerating ice retreat has created an urgency to understand the forcing mechanisms driving retreat and the expected timelines of continued acceleration, tipping points, and potential collapse. To determine what is driving the retreat, collection of in situ datasets from individual glacial systems is needed to complement satellite-based observations. The marine sediment record provides opportunities to understand spatial and temporal trends of glacial and oceanographic change. This work focuses on ice-proximal records collected in the eastern Amundsen Sea, where Thwaites and Pine Island glaciers are located, and the western Antarctic Peninsula. Previously unexplored coastline along Thwaites Glacier was surveyed in 2019 and 2020. Sedimentological data, physical properties, clay mineral provenance, and computed tomography scans reveal evidence for past depositional environments, which were dated using radioisotopes, 210Pb and 14C. The sediment record from the past century indicates Thwaites Glacier and neighboring Pine Island Glacier experienced synchronous retreat as early as the mid-20th century, suggesting an external driver of glacial change rather than internal ice dynamics. In the second investigation, sediment cores and associated geophysical surveys were analyzed to address local and regional sediment transport patterns. Sediment facies interpretations and mass accumulation rates indicate multiple styles of deposition at some core sites. Notably, regional sediment accumulation has decreased over the 20th century, suggesting that the grounding zone is becoming more distal. However, the magnitude of the decrease is greater than expected for the observed change in grounding-zone position. Therefore, other changes affecting sediment delivery are suggested. The final study investigates sediment transport across the polar Bellingshausen Sea (74°S) to the subpolar tip of the Antarctic Peninsula (63°S). Short cores were ...
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