Transient-Tracer Information on Ventilation and Transport of South Atlantic Waters

We report distributions of the chlorofluorocarbon CFC 11, of CC1₄, and of terrigenic 3He, along three zonal sections across the South Atlantic (WOCE WHP sections A8 – A10, 11.7°S, 19°S, 30°S). The distributions fully reflect the water mass structure of the sections. They reveal a region of comparably much slower water renewal in the range of the Central and Antarctic Intermediate Waters, northeast of the Angola-Benguela Front. For all water masses further down, the distributions demonstrate that renewal is very much slower still, and that it occurs via advective cores adjacent to the respective western boundaries of the basins. The oldest waters are found to be present in a wedge centered in about 3000 m depth and extending from the African slope westward across the Midatlantic Ridge. The tracers are characterized by different input time scales, and these are well apparent in their distributions. The observed correlation between tracers indicates rather steady formation of Upper North Atlantic Deep Water over the past several decades. CC1₄ is powerful in tracing relatively older waters, but in the upper South Atlantic waters our data confirm the decomposition of CC1₄ reported previously.