Atmospheric and Oceanic Sciences Seminar

“Connecting Antarctic cross-slope exchange with Southern Ocean overturning” by Andrew Stewart, Environmental Science and Engineering, California Institute of Technology

Thursday, February 28, 2013
3:30 PM
Room MSB 7124

Abstract

The export of Antarctic Bottom Water (AABW) ventilates the sub-surface ocean, and drives the deepest cell of the ocean's meridional overturning circulation (MOC). Modification of this circulation may substantially influence millennial-scale climate changes via sequestration of carbon in the deep ocean. Motivated by observations of a westerly wind shift over the past few decades and at the Last Glacial Maximum, recent work has focused upon the response of the MOC in the Antarctic Circumpolar Current (ACC) to changes in the mid-latitude westerly wind forcing. Here, we focus instead on how coupling between the ACC and the circulation at the Antarctic margins, including export of AABW, modifies the response of the MOC to surface forcing. We utilize eddy-resolving simulations with an idealized Antarctic continental shelf and slope, forced by strong westerly winds at mid-latitude and weaker easterly winds close to the continent. We find that the deep cell of the MOC is four times as sensitive to modulation of the easterly winds than the upper cell is to modulation of the westerly winds. Residual-mean theory reveals that suppression of baroclinic eddies by the strong topographic vorticity gradient over the continental slope enhances the sensitivity of the deep MOC to the easterly winds. Our findings indicate the hypothesized reduction in the intensity of the deep MOC at the Last Glacial Maximum is consistent with a weaker band of polar easterly winds.