Tropical Atlantic Water within the Benguela Upwelling System at 27 deg S

摘要

A CTD-O2 and ADCP section across the African Altantic continental margin near 27deg S, reveals the water mass structure and associated velocity field of the shelf and upper slope of the Benguela upwelling system. Continental shelf water upwelling within the Benguela Current is drawn from the 12 C (about 200 m) level. The upwelling water is drawn from oxygen depleted, tropical South Atlantic thermocline water that is advected along the shelf floor by a southward flowing subsurface current. Lower thermocline and intermediate water from the tropical South Atlantic are also observed flowing southward over the continental slope. Tropical Atlantic water generally resides north of the Angola-Benguela Front at 16 deg S. A narrow band of upwelled water is observed well seaward of the shelf, along the western edge of a large Agulhas eddy, indicating that Agulhas eddies play a role in stirring eastern boundary upwelled water into the ocean interior. These eddies also draw into the interior tropical Atlantic water found over the upper continental slope. The net transport between the 120 and 350 isobaths as measured by the ship-mounted ADCP, is referenced to the sea floor.