Direct observations of eddy turbulence at a ridge in the Southern Ocean

Mesoscale turbulence in the ACC is concentrated where the current interacts with prominent bottom topography. An unusual region of high levels of turbulence is found downstream of the South-West Indian Ridge. It has been inferred that this turbulence consists largely of eddies generated at a fracture zone in the ridge. A dedicated research cruise to the region has now presented data that allow us for the first time to track these eddies and to describe them in hydrographic detail. We show that these eddies are at least 1000 m deep, have a diameter of 250 km, exhibit azimuthal speeds of up to 0.74 ms(-1), have subsequent translation speeds of up to 0.09 ms(-1) and consist of water masses derived from either north or south of the SAF and APF. Eddies in general are shown to advect in a north-eastward direction and dissipate before reaching a longitude of 40 degrees E.