Bottom pressure changes around Antarctica and wind-driven meridional flows

Abstract

Spatially-averaged bottom pressure anomalies near Antarctica (south of 60°S) calculated from GRACE data are well correlated with those produced by the ECCO project using least-squares optimization methods to fit an ocean model to most available data. Both GRACE and ECCO results indicate mass exchange primarily between the Southern Ocean and the Pacific and the importance of zonal wind stress to this exchange. The ECCO flow fields show that the near-surface meridional Ekman transport, directly driven by the zonal wind stress, is nearly balanced by return flows below the shallowest topography at 60°S (∼1300 m at this Drake Passage latitude), with the return transport being slightly lagged in time relative to the Ekman transport. Such time lags, which may result from geostrophic adjustment at depth, cause the small associated net transport across 60°S to be ∼90° out of phase with the wind. This in turn can explain why zonal wind stress and bottom pressure anomalies around Antarctica tend to be anticorrelated in both GRACE and ECCO results. Copyright 2009 by the American Geophysical Union.