Shelf/Deep-Ocean Exchanges in the South Georgia Region

The northeastern corner of the Scotia Sea hosts some of the largest chlorophyll-a blooms of the Southern Ocean. They peak to the northwest of the South Georgia Island and extend eastward for hundred of kilometers. Although the Southern Ocean has many islands of similar size South Georgia is arguably the most important—it not only sustains one of the Southern Ocean’s largest and most diverse ecosystems but also is its single most important region for carbon sequestration. The exceptionality of South Georgia’s blooms has been extensively recognized in the literature but the physical processes that contribute to their fertilization remain unknown. We characterize the exchanges of mass between the Southern Ocean and the South Georgia shelf using the results of a sub-mesoscale resolving, dually nested, numerical model. Our results show that eddies and meanders of the Southern Antarctic Circumpolar Current Front (SACCF) drives the entrainment of deep ocean waters onto the South Georgia shelf. These waters are driven into the shelf’s interior and upwelled along the northern coast of the island whereupon they are detrained onto the Georgia Basin. The model results indicate that the geographic configuration of the Georgia Basin basin shields the fertilized waters from the dispersive effects of strong currents and eddies thus facilitating the formation of the exceptional chlorophyll-a blooms reported in satellite imagery.