The shelf break front to the east of the sub-Antarctic island of South Georgia

The sub-Antarctic island of South Georgia lies in polar waters to the south of the Polar Front and is influenced by the Weddell Scotia Confluence whose waters reach the island’s south east coast. In January 1996 a detailed hydrographic survey to the east of the island showed that on-shelf waters were both warmer and fresher than those off-shelf. These differences were not confined to surface waters. The inherent density differences resulted in a shelf break front, the position of which was defined as the point where the 26.96 kg m-3 isopycnal crossed 30 dbar as it rose towards the surface. The slope of the shelf break front between the on- and off-shelf waters was found to be approximately geostrophic. Although the position of the shelf break front was not linked to any particular bottom depth, its position was strongly influenced by the bottom topography in the region. Evidence is presented for upwelling in one specific region along the front. Differences between the on- and off-shelf waters are also observed in nutrient and chlorophyll a data: These data implied greater productivity on-shelf. Both physical and chemical data suggest that on- and off-shelf waters communicate at depth. This study also shows that shelf water can cross the shelf break front and remain in the vicinity of the island.

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