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 (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.