Regional MITgcm simulation output and proxy reconstructions presented in O'Connor et al., 2025. MITgcm simulations span the Amundsen Sea and adjacent regions. The model is run for five years, forced by idealized atmospheric forcings generated using one year of atmospheric data drawn from ERA Interim reanalysis, repeated for all five years. There are ten forcings, named after the year of data drawn from ERA Interim. The ten forcings are applied to three sets of initial conditions (warm, moderate, and cool), yielding 30 total experiments. Simulated output files are grouped by initial condition (main figures in O'Connor et al., 2025 primarily reflect the moderate initial condition set). The proxy reconstructions are named after the climate model simulation used to form the data assimilation prior. More details on reconstruction methods can be found in O'Connor et al., 2021 and O'Connor et al., 2025. When using these data, please cite O'Connor et al., 2025: 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