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 whos e waters reach the island's south east coast. In January 1996 a detailed hy drographic survey to the east of the island showed that on-shelf waters wer e 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. T he 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 b reak front was not linked to any particular bottom depth, its position was strongly influenced by the bottom topography in the region. Evidence is pre sented for upwelling in one specific region along the front. Differences be tween the on- and off-shelf waters are also observed in nutrient and chloro phyll a data: These data implied greater productivity on-shelf. Both physic al and chemical data suggest that on- and off-shelf waters communicate at d epth. This study also shows that shelf water can cross the shelf break fron t and remain in the vicinity of the island. (C) 1999 Elsevier Science Ltd. All rights reserved.