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

Abstract

Antarctic coastal polynyas produce Dense Shelf Water, a precursor to Antarctic Bottom Waters (AABW) that supply the global abyssal circulation. Recent studies suggest that increasing atmospheric CO2 concentrations will weaken AABW export by suppressing heat loss to the atmosphere. However, future projections of DSW formation are hindered by the small spatial scales of atmosphere-sea ice-ocean interactions in polynyas. Here, using a high-resolution ocean-ice-atmosphere coupled model, this study shows that wintertime sea ice production rates are still active under elevated CO2 concentrations, although delayed freeze-up decreases autumn sea ice production. In winter, Antarctic coasts exhibit a nonlinear response CO2 concentration: doubling CO2 decreases sea ice production only by around 6–8%, versus 10–30% under CO2 quadrupling. Despite continued sea ice production in winter, doubling or quadrupling CO2 substantially freshens Dense Shelf Water, primarily due to increased precipitation, implying a shutdown of AABW formation.