Silica Signals in the South Atlantic

Abstract

Distribution patterns of potential temperature (8) and of H4SiO4 concentrations show that the bottom water in the major part of the Angola Basin originates from the Romanche Fracture Zone. At present the bottom water of the Angola Basin is predominantly lower NADW with a 10–20% admixture of a southern component. South of about 29°S a gradually increasing percentage of the bottom water originates from the Cape Basin, entering through gaps in the Walvis Ridge. Near the deep entrances into the Guinea Basin and the southern tip of the Angola Basin, vertical gradients of temperature and salinity are large. Small changes in the relative production rates of AABW and NADW, assuming that their properties remain the same, could cause a large change in bottom water composition of the Guinea and Angola Basins.