VARIABILITY AND SOURCES OF THE SOUTHEASTERN ATLANTIC CIRCULATION

The 1992-1993 Benguela Sources and Transport (BEST) time series provid e a quantitative view of the Benguela Current transport and the eddy h eld crossing 30S, as well as an estimate of the relation between its b arotropic and baroclinic components. This is done by a simultaneous an alysis of the BEST data derived from inverted echo sounders, pressure sensors, current meter moorings, CTD, and ADCP stations. The analysis of the time Series indicates that the annual mean baroclinic transport of the BengueIa Current is 13 Sv with a total transport of 16 Sv. Thr ough the combination of instruments the total baroclinic plus barotrop ic transport of the upper 2600 m was obtained without making any assum ption about the level of no motion. Results from this calculation corr oborated the assumption that 1000 m as a level of no motion could be u sed as a fairly good approximation. The stationary flow of the Benguel a Current is mostly confined near the African Continent while a transi ent flow, composed by large eddies shed from the Agulhas retroflection , dominates the western portion of the Benguela Current. In the statio nary part of the Benguela Current, both barotropic and baroclinic comp onents are equally important while in the transient part, the barotrop ic is more substantial. Several rings were observed during the experim ent that migrated toward the west. An initial speed of 12 km/day dimin ished to 6 to 7 km/day at the Walvis Ridge. The water mass source of t he Benguela Current includes Indian and South Atlantic subtropical the rmocline water; relatively saline, low oxygen tropical Atlantic water; and the cooler, fresher subantarctic water. Changes in thermocline sa linity correlate with transport: in general when the northward transpo rt is increasing the thermocline salinity also increases, without a de crease in oxygen. This indicates that the Benguela Current increases i n strength by bringing in more subtropical thermocline water. As the A gulhas input is most effective in boosting the salinity of the upper t hermocline (the South Atlantic Current water being deficit in salinity relative to the Indian Ocean source) we suggest that the spatial vari ations in transport are tied to Agulhas water influx, presumably assoc iated with the eddy field.