Abstract:

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.

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