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Abstract

Elevated ice shelf melt rates in the Amundsen Sea have been attributed to transport of warm Circumpolar Deep Water 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. Previous studies have linked variations in the melt rates of the Amundsen Sea ice shelves to wind fluctuations. Yet the mechanism via which the undercurrent forms, and thus what controls the mean shoreward heat transport, remains unclear. In this study we investigate the dynamics of the undercurrent using a high-resolution ocean-sea ice process model coupled to a static ice shelf. We explore the sensitivities of the undercurrent strength, shoreward heat transport, and ice shelf melt rates to winds, tides, diapycnal mixing, and geometry. We find that the undercurrent forms with realistic strength provided that there is a trough allowing access to the continental shelf and ice shelf cavity, and that there is a cross-slope buoyancy gradient. The vorticity balance within the CDW layer reveals that the bathymetric steering of the undercurrent toward the ice shelf is related to diapycnal upwelling that occurs as CDW melts the ice. These findings imply that the mean flow of the Antarctic slope undercurrent is primarily established by buoyancy forcing on the continental shelf, and motivate a focus on processes that influence cross-shelf/slope buoyancy gradients to better understand future changes in shoreward heat transport.