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Antarctic Slope Undercurrent and Onshore Heat Transport Driven by Meltwater Upwelling
Si Y, Stewart A, Silvano A, Naveira Garabato A

Elevated ice shelf melt rates in West Antarctica have been attributed to transport of warm Circumpolar Deep Water (CDW) onto the continental shelf via bathymetric troughs. These inflows are supplied by an eastward, subsurface slope current that opposes the westward momentum input from local winds and tides, referred to as the Antarctic slope undercurrent. Despite its importance to basal melt, the mechanism via which the undercurrent forms, and thus what controls the shoreward heat transport, remains unclear. In this study, the dynamics of the undercurrent is investigated using a high-resolution process model with coupled ocean, sea ice, and ice shelf components. Over a wide range of parameters, the sensitivities of the undercurrent strength, onshore heat transport, and ice shelf melt rates to winds, tides, diapycnal mixing, and geometry are explored. The vorticity balance within the CDW layer reveals that the bathymetric steering of the undercurrent toward the ice shelf is related to cyclonic vorticity input associated with the diapycnal upwelling of meltwater in the ice shelf cavity. Increased basal melt thus strengthens the undercurrent and enhances onshore CDW transport, which indicates a previously unrecognized positive feedback that may accelerate future melt of ice shelves.