Simulation of a coastal jet retention process using a barotropic model

In the southern Benguela, sardine and anchovy spawn on the Western Agulhas Bank. Eggs and larvae are transported to the West coast nursery ground by a! coastal current. Once the larvae reach the West coast, retention within the favorable coastal domain is key to larvae survival and recruitment. The Cape Columbine-St Helena Bay area is the main nursery ground along the West Coast. In this area, the interaction between upwelling and topography results in the formation of an upwelling plume. The plume, and the associated circulation patterns, is thought to be the mechanism providing retention within the coastal domain. The dynamics of the plume are studied using a set of:numerical experiments. It is shown that an equatorward wind forcing produces a cyclonic eddy in the lee of Cape Columbine. A balance between advection and bottom friction regulates the evolution of this eddy. The eddy contributes to create a dynamic boundary between the coastal and the offshore domains. Retention induced by the eddy is quantified using a tracer. The magnitude of retention is positively related to the wind for weak to moderate wind intensities. For strong wind intensity, retention reaches a maximum or slightly decreases. This is in agreement with previous results relating recruitment success with wind speed. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.