USAP-DC

The glaciers in the Amundsen Sea Embayment of West Antarctica, such as Thwaites and Pine Island Glaciers, are rapidly retreating and contributing to sea level rise. There is evidence that the current stage of retreat began in the mid-20th century before the start of the observational record, making it difficult to understand the cause of glacier change. While modeling studies suggest that anthropogenic forcing starting in the early 1900s causing a trend toward stronger westerly conditions and consequently warmer ocean conditions near glaciers, new proxy-based reconstructions of winds since the early 1900s provide robust evidence that wind trends in this region were likely easterly instead of westerly. This project will leverage ocean models to address whether a 20th century easterly wind trend could lead to warmer ocean conditions near glaciers in the Amundsen Sea, improving our understanding of projections of sea level rise due to Antarctic ice mass loss. This project will generate the first data-constrained hindcast simulation of 20th century ocean conditions in the Amundsen Sea Embayment, using proxy-based atmospheric reconstructions and a high-resolution ocean model which has been validated against past observations. The project will downscale annual mean surface temperature, sea level pressure, and surface zonal wind anomalies to produce daily resolved datasets, simulating realistic ocean states by adding sub-annual variability from reanalyses to each of the reconstructed states. These downscaled paleoclimate reconstructions will provide forcing for ensembles of ocean simulations using a regional domain of the MITgcm that includes dynamic sea ice and thermodynamic ice shelf representation. Four sets of simulations are targeted, first to verify the efficacy of using downscaled proxy-reconstructed atmospheric fields as model forcing, then to investigate the causes of the anomalous westerly wind event of the 1940s, and finally to explore the impact of 20th century atmospheric trends on ocean conditions. This project will provide key new insight into the varied pathways that link rising greenhouse gas concentrations to glacier retreat in West Antarctica. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Person	Role
Thompson, LuAnne	Investigator and contact
steig@uw.edu, Eric J Steig	Co-Investigator
karmour@u.washington.edu, Kyle C Armour	Co-Investigator

Antarctic Glaciology	Award # 2333370
Antarctic Ocean and Atmospheric Sciences	Award # 2333370

USAP-2333370_1

None in the Database

Repository	Title (link)	Format(s)	Status
Zenodo	Proxy Reconstructions and Amundsen Sea Simulations with Repeated Atmospheric Forcings	netCDF	exists

1. O’Connor, G.K., Nakayama, Y., Steig, E.J. et al. Enhanced West Antarctic ice loss triggered by polynya response to meridional winds. Nat. Geosci. 18, 840–847 (2025). https://doi.org/10.1038/s41561-025-01757-6 (doi:10.1038)