A simple model of the effect of the Kerguelen Plateau on the strength of the Antarctic Circumpolar Current

The strong westerly winds of the Southern Ocean drive a northwards Ekman transport which increases in magnitude from 9 Sv, at the southern latitudes of Drake passage, to a maximum of 37 Sv at 45°S. The return flow can occur as a western boundary current along the coasts of South America and the Antarctic Peninsula but at depths above 3000m such a boundary current cannot cross Drake Passage and so another mechanism must be involved. In this paper it is shown that one possible mechanism is for the flow to continue south as a western boundary current attached to the islands and other topographic barriers, which span the latitudes of the passage. A simple model of this process shows that it also generates a strong circumpolar current. The model is then applied to the Southern Ocean using the Kerguelen Plateau as the second topographic barrier. The Kerguelen Plateau occludes the Drake Passage between 1600m and 3000m depths which other model studies have shown to include the Ekman return flow. Using Hellerman and Rosenstein estimates of the wind stress, the model predicts an Antarctic Circumpolar Current with a transport of 151 Sv. This is in reasonable agreement with observations and other model studies. The model does less well south of the Kerguelen Plateau, where it predicts a second strong current. In practice such a current is not observed.