Sedimentary Record of Pre-Satellite Retreat of Pine Island Glacier, Amundsen Sea, Antarctica

Satellite data has shown that recent ice loss from Pine Island Glacier (PIG), along with other glaciers terminating in the Amundsen Sea Embayment (ASE), contributes substantially to global mean sea-level rise. Landward dipping bathymetric troughs have been eroded deeply into the continental shelf by repeated advances of grounded ice streams during periods of past glaciation. Today, these troughs provide avenues for slightly-warmer Circumpolar Deep Water (CDW) to flow landward and melt the ice shelves and grounding lines of glaciers terminating in the ASE. Studies of sub-ice shelf sediment cores have shown that this retreat may have been triggered in the mid 1940s. However, further refinement of this forcing and PIG's response is needed. This new study provides detailed information about PIG's pre-satellite dynamics from glacimarine sediments collected at several sites proximal to the present calving margin. The sediment cores were acquired in 2020 aboard RV/IB Nathaniel B. Palmer from newly exposed seafloor due to a major ice-shelf calving event in the same year as the expedition. We use grain size and shape measurements paired with 210Pb radio-isotopic dating to reconstruct the timing of environmental changes at the core sites. Lithological changes suggest that grounding-line retreat is preserved where very poorly sorted, sub-glacial or grounding line proximal diamictons are overlain by fine-grained, well-sorted, glacimarine sediments deposited further away from grounded ice. Previous work on the sedimentary records from cores collected below the PIG Ice Shelf has provided evidence for PIG's unpinning around 1970. Results from core NBP2002 KC-26, recovered from nearly the same location as one of the sub-ice shelf cores but seven years later, show a similar facies shift to fine-grained sediments at 1970. While this match corroborates the findings of other studies, further analysis of various cores from multiple sites on the seabed previously covered by the PIG Ice Shelf and PIG's grounded ice will unveil a detailed retreat history for the glacier, reaching farther back in time. Determining the timing and pace of PIG's past retreat will help to constrain models of the dynamic response of this ice stream-ice shelf system.