Future changes in Antarctic coastal polynyas and bottom water formation simulated by a high-resolution coupled model

Antarctic coastal polynyas produce Dense Shelf Water, a precursor to Antarctic Bottom Waters that supply the global abyssal circulation. Future projections of Dense Shelf Water formation are hindered by unresolved small-scale atmosphere-sea ice-ocean interactions in polynyas. Here, we investigate the future evolution of Antarctic coastal polynyas using a high-resolution ocean-ice-atmosphere model. We find that wintertime sea ice production rates remain active even under elevated atmospheric CO2 concentrations. Antarctic winter sea ice production rates are sensitive to atmospheric CO2 concentrations: doubling CO2 (734 ppm) decreases sea ice production by only 6–8%, versus 10–30% under CO2 quadrupling (1468 ppm). While considerable uncertainty remains in future ice-shelf basal melting, which is not accounted for in this study, doubling or quadrupling CO2 substantially freshens Dense Shelf Water due to increased precipitation. Consequently, doubling CO2 weakens Dense Shelf Water formation by ~ 75%, while CO2 quadrupling shuts down Dense Shelf Water formation. Under scenarios of doubling or quadrupling of atmospheric carbon dioxide levels, Antarctic Dense Shelf Water freshens significantly, which in turn inhibits the formation of abyssal water, according to simulations with a high-resolution ocean-ice-atmosphere model.