Eddies originating in the eastern South Indian Ocean are unique in that anticyclones contain elevated levels of chlorophyll-a, enhanced primary production and phytoplankton communities generally associated with nutrientreplete environments. From analysis of satellite measurements of sea surface height, chlorophyll and surface stress curl (Ekman pumping), we present evidence that the eddy-induced Ekman upwelling in these anticyclones sustains the enhanced chlorophyll anomalies observed within the eddy cores. The primary mechanism for this eddy-induced Ekman upwelling is the curl of the surface stress resulting from the difference between the surface vector winds and the rotating surface currents within the interiors of the anticyclones. The biological response to this eddy-induced Ekman upwelling is evident only during the Austral winter. This seasonal dependence appears to be attributable to wintertime deepening of the mixed layer that facilitates the injection of nutrients from the deep water into the euphotic zone. In contrast to anticyclones, the chlorophyll-a content of cyclones is anomalously low throughout the year. This is consistent with the persistent surface current-induced downwelling that occurs within cyclones.
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