Impacts of wind stress on the Antarctic Circumpolar Current fronts and associated subduction

Recent studies suggest that the overturning circulation in the Antarctic Circumpolar Current (ACC) region shows a weak sensitivity to overlying wind stress changes, due to balancing of changes in the eddy-induced and Eulerian mean transports. We use an eddy-permitting coupled climate model with 1/4-degree horizontal resolution to investigate changes in the large-scale circulation and regional dynamics of the ACC region in response to a large poleward shift and intensification of the westerlies. As in previous studies, we find a small increase in the net ACC transport (less than 10%), and a poleward shift in the mean position of the ACC flow. However, the ACC is restructured, with the Subantarctic Front and Polar Front branches shifting poleward by differing magnitudes, resulting in 4 Sv less ACC flow in the Subantarctic Zone and 16 Sv less flow in the Polar Front Zone. The wind stress anomaly drives a stronger northward Ekman transport and deepens the winter mixed layer, causing a 9 Sv increase in the net subduction of Subantarctic Mode Water north of the SAF zone, and stronger upwelling into the mixed layer within the SAF and PF zones where Antarctic Intermediate Water forms. The subduction and upwelling changes vary considerably across the Southern Ocean. Our results suggest that changes in the wind stress impact the Southern Ocean large-scale circulation, including the flow of the ACC in its primary jets, which presumably will affect the distribution of heat and nutrients via water mass formation and subduction in this complex region.