Reshaping the Antarctic Circumpolar Current Via Antarctic Bottom Water Export

Zonal momentum input into the Antarctic Circumpolar Current (ACC) by westerly winds is ultimately removed via topographic form stress induced by large bathymetric features that obstruct the path of the current. These bathymetric features also support the export of Antarctic Bottom Water (AABW) across the ACC via deep geostrophically-balanced northward flows. These deep geostrophic currents modify the topographic form stress, implying that changes in AABW export will alter the ocean bottom pressure and require a rearrangement of the ACC in order to preserve its zonal momentum balance. We use a conceptual model of the ACC momentum balance to derive a relationship between the volume export of AABW and the depth of the sea surface depression in the ACC's standing meanders. We test this prediction using an idealized eddy-resolving ACC/Antarctic shelf channel model that includes both the upper and lower cells of the Southern Ocean meridional overturning circulation, using two different topographic configurations to obstruct the flow of the ACC. We show that eliminating AABW production produces a qualitatively similar response in the ACC's surface circulation as does weakening the westerly winds, leading to a shallowing of the sea surface elevation within the standing meander and reducing the magnitude of the eddy kinetic energy generated downstream of the meander. These findings raise the possibility that ongoing changes in AABW export may be detectable via satellite altimetry on time scales as short as a few years.