Variability of the Benguela current off the Cape Peninsula, South Africa

Abstract

The near-surface flow off the Cape Peninsula, South Africa, was monitored weekly along a 60 km transect between August 1995 and July 1996 as part of the South African Sardine and Anchovy Recruitment Programme. Measurements from small vessels were made by means of tracking drogues by GPS (sometimes differentially corrected) and by an Acoustic Doppler Current Profiler (ADCP) when sampling from large vessels. The currents responded to the presence of Agulhas water, to wind-forcing and to barotropic shelf waves. The results suggest a marked seasonality in the position and amount of equatorward and poleward flow, which needs to be confirmed. Strong north-westward flow close inshore was measured in spring (August–October), turning into the “classic” formation of an equatorward jet, with variable barotropic flow inshore in early summer. In summer, circulation patterns became more complex, with marked southward flow. From February to April, the front was generally far offshore and often not encountered on the transect. Examples of the variability of the flow on a week-by-week basis are provided and are related to the thermal structure and to the wind record from Cape Point. The seasonality of the flow is summarized in terms of estimated mean surface transport per two-month period, and a series of northward and southward  components
for each cruise throughout the year is provided.