On the deep water circulation of the eastern South Atlantic Ocean

The main flow patterns and transports of North Atlantic Deep Water (NADW) in the eastern South Atlantic and round southern Africa were inferred from two quasi-meridional WOCE hydrographic lines at 9°W and 5°E nominal longitudes, and from segments of other sections in the Atlantic-to-Indian Oceans transition region. An export of 11±4 Sv of NADW from the Atlantic was estimated near southern Africa inshore of the Subtropical Front. Most of this flow can be traced back across the Cape Basin to passages south of 28°S in Walvis Ridge, and farther upstream to an entry in the eastern basin at 20–25°S. Other transfers of NADW from the western boundary current to the eastern boundary were confirmed near the equator and at 22°S near the Namib Col of Walvis Ridge, yet a cyclonic recirculation of the former in the Angola Basin, and the weakness of the latter (4±2 Sv), make their direct contributions to the export of NADW minor ones. As another consequence, the estimated transport of the deep southward boundary current against the western continental slope of Africa shows important latitudinal variations (12±9 Sv at 7°30′S, 3±5 Sv at 22°30′S, 11±4 Sv at 35°S), with even a suggestion of its reversal in the northern Cape Basin. To the southwest of Cape Town, the deep boundary current is influenced by the temporal variability of the Agulhas retroflection region, and most of it separates from the slope to enter the Indian Ocean in the deep return flow of the Agulhas Current. Only a 2–3 Sv remnant against the continental slope was estimated at 30°E to the east of the Agulhas Plateau.