The Agulhas Return Current

Abstract

The Agulhas Return Current constitutes the intense flow along the Subtropical Convergence south of Africa. It forms the connecting link between the generically similar South Atlantic Current and the South Indian Ocean Current, thus contributing to the water exchange between these two basins. This general along-front flow is, however, substantially modified south of Africa by contributions from the Agulhas Current. We have carried out a first study of the hydrography and dynamics of the Agulhas Return Current along its full length using a collection of available modern hydrographic data. It is shown that on average the current lies at a latitude of 39°30′S south of Africa, increasing slowly downstream to a latitude of 44°30′S at 60°E, except where it crosses a number of meridional ridges where northward shifts of up to 2°30′ are occasionally observed. Geostrophic speeds relative to 1500 m demonstrate a gradual eastward decrease in the velocity of the current from an average of 75 cm/s at the Agulhas retroflection to 13 cm/s at 76°E. Volume transports are similarly reduced from 54×10 6 m 3/s in the retroflection region to 15×10 6 m 3/s at 76°E. Temperature/salinity properties show water mass characteristics of the Agulhas Current to extend to at least 61°E. Based on these results, we suggest that the Agulhas Return Current is zonally continuous and terminates between 66°E and 70°E. We therefore propose that the name South Indian Ocean Current be retained for the flow east of here only.