Influence of Freshwater Fluxes and Topography on the Distribution of Water Masses on the Antarctic Continental Shelf

At the Antarctic coast, ice shelves flow from the ice sheet and are vulnerable to future changes in sub-surface ocean temperatures at the southern margins. A better understanding of how projected changes in freshwater fluxes drive the onshore transport of warm deep waters across the shelf break toward the ice shelves is needed. This study uses idealized ocean simulations to explore how changes in freshwater flux influence the temperature structure on Antarctica's shelf seas across Southern Ocean circulation regimes (throughflow or gyre—determined by basin geometry). We use idealized freshwater perturbations applied as a surface salt flux to disentangle the effects of spatially varying reduced sea ice from spatially uniform increases in precipitation. Overall, we find that reductions in sea ice and increases in precipitation both lead to warmer waters on the shelf across all flow regimes. A cross-slope density gradient threshold is identified which leads to warmer shelf temperatures. We also find that the large-scale circulation regime (throughflow or gyre) influences how susceptible the existing shelf temperatures are to changes in freshwater flux but this effect is less important than with wind changes. Whilst the overall tendency is for the shelf to warm under a uniform decrease in the salt flux, simulations with a throughflow on the shelf warm more strongly than simulations with a gyre on the shelf, this is due to a stronger meridional density gradient in the throughflow case. On the large-scale, imprints of the circulation regime manifest in temperature and salinity changes, driving the spatial pattern of change.