The history of deep-water upwelling and heat delivery to the Amundsen Sea Embayment, West Antarctica: a palaeoceanographic perspective

Thwaites and Pine Island glaciers serve as main outlets for ice draining the West Antarctic Ice Sheet into the Amundsen Sea Embayment (ASE). Observational records show that these ice streams exhibit continuous and substantial thinning and grounding-line retreat since the 1940s, particularly accelerating from the 1990s onwards . Furthermore, modeling studies suggest that ASE glaciers are susceptible to runaway retreat. Thus, the rate and magnitude of potential mass loss from these ice streams presents a major source of uncertainty for future sea level rise predictions. Ocean-driven melting of the underside of ASE glacier ice-shelves, caused by the upwelling of warm Circumpolar Deep Water (CDW) at the shelf break and its advection across the continental shelf, is thought to be the main driver of mass loss. CDW upwelling onto the ASE shelf has varied due to natural decadal variability, longer centennial variability as well recent changes in anthropogenic forcing (Holland et al., 2022). However, regional observational records are limited to the last few decades, and the onset and evolution of the oceanic forcing, prior to the instrumental period, remains uncertain. Here, we present high-resolution foraminiferal geochemical data from marine sediment cores recovered from the ASE shelf, including material collected during the Thwaites Glacier Offshore Research (THOR) expeditions in 2019, 2020 and 2021. Preliminary Mg/Ca records of benthic foraminifera shells, a proxy for bottom-water temperature, accompanied by benthic foraminiferal 13C records, used as a water mass tracer, reveal that CDW incursions onto the ASE shelf contributed to glacier retreat on centennial to millennial timescales. Future work will aim to further constrain changes in CDW advection to the inner ASE shelf, particularly in western Pine Island Bay and at the Dotson Ice Shelf front, for the 20th century and beyond.