Eddies originating at the South-West Indian Ridge

The mesoscale variability of flow in the Southern Ocean is markedly intensified along the Subtropical Convergence as well as at a small number of distinct spots, the latter seemingly related to shallower parts of the bottom topography. A very prominent example of such a spot corresponds with the location where the core of the Antarctic Circumpolar Current crosses the South-West Indian Ridge. The variability in this particular spot consists of well-developed positive as well as negative anomalies in sea surface height that may represent anticyclonic and cyclonic eddies. Based on satellite altimetry, it is shown that these flow anomalies exhibit specific trajectories beyond their generation region at the South-West Indian Ridge, one of which takes them past the Prince Edward Islands. Using extensive hydrographic observations, we describe the dimensions and T/S characteristics of some of the features identified in the altimetry that have passed these islands. In this way, we successfully verify that they are indeed eddies, thus providing evidence that the fracture zone in the South-West Indian Ridge is a source of eddies for the downstream region.