. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 250 ANNALS OF THE SOUTH AFRICAN MUSEUM PHYSIOGRAPHIC AND OCEANOGRAPHIC SETTINGS The continental margin off south-western Africa forms the eastern edge of the Cape Basin, which is further bounded in a clockwise direction by the Agulhas Ridge, the mid-Atlantic Ridge, and the Walvis Ridge. Abyssal connec- tions to adjacent deep ocean basins (>4,5 km) are probably limited to two small sills: via the central Walvis Ridge to the Angola Basin, and adjacent to the southern tip of Africa to the Agulhas and
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 250 ANNALS OF THE SOUTH AFRICAN MUSEUM PHYSIOGRAPHIC AND OCEANOGRAPHIC SETTINGS The continental margin off south-western Africa forms the eastern edge of the Cape Basin, which is further bounded in a clockwise direction by the Agulhas Ridge, the mid-Atlantic Ridge, and the Walvis Ridge. Abyssal connec- tions to adjacent deep ocean basins (>4,5 km) are probably limited to two small sills: via the central Walvis Ridge to the Angola Basin, and adjacent to the southern tip of Africa to the Agulhas and Mozambique basins. Our samples come from the continental slope and rise off south-western Africa, which has been a sediment-starved margin since mid-Tertiary times (Dingle et al. 1987). The principle physiographic features of this region are slumps. These produce minor sea-floor irregularities north of 34°S, and major relief, with numerous small canyons, south of 34°S. Only in the southern region is the continental shelf narrow and shallow enough to have allowed the advance of the coastline (and river discharge) to within 30 km of the shelf break during glacial sea-level lows. Consequently, the potential for allochthonous shelf contaminants on the slope is relatively low over most of the study area, although at 28°S (just south of Liide- ritz) the head structures of a large slump lie in a re-entrant of the shelf edge. The regional physical oceanography along the outer continental margin of south-western Africa has been summarized by Shannon (1985—see pp. 122-125 mixed laye Antarctic Intermediate Water. 600 Fig. 2. Schematic water column structure off south-western Africa superimposed on a bathy- metric profile across the continental margin south of Liideritz (28°S). Depths for the various water masses are taken from Shannon (1985). Circled symbols indicate direction of water flow: + is towards reader, - is away from reader. Depth range of the ostracod faunas studied is i
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