The effect of bathymetry on the deep flow in Drake Passage

Abstract

Abstract The results from year-long deep current-meter records at 20 sites in Drake Passage show a complex mean circulation in the region. The orientation of the deep mean flow at each location has been compared both to the geostrophic contour distribution, as it has been reconstructed to show the features at two smoothing scales, and to the direction of the major axis of the first EOF for the low-frequency motions. The directions of the mean and low-frequency flows coincide on the average, although there are several individual large differences between them. Both are interpreted in terms of possible relationships with the ƒ/H contours. The low-frequency flow directions at 2700 m conform preferentially to the large scale bathymetry while the mean flow directions at this depth follow the smaller scale isobaths. The mean deep flow is consistent with the bottom velocities being directed along geostrophic contours, including those that encircle the many small-scale features in the passage. Enhanced flow, accompanied by stronger-than-average baroclinicity, occurs in and downstream of gaps through the main ridge. The gaps and the confluence of the deep flow on the Antarctic continental slope appear to control the average locations of fronts as observed in Drake Passage.