The bottom boundary layer inshore of the Agulhas Current off Natal in August 1975

Abstract

Previous work off Natal showed that current flows are generally fairly strong on the narrow shelf regions inshore of the Agulhas Current. During August 1975, approximately hourly profiles of temperature, salinity and currents measured from a ship in 49 m of water over a period of six days permitted details of the bottom boundary layer (BBL) to be established. The height of the logarithmic layer was between 14 and 24 m, while Ekman veering took place over about 35 m. The BBL probably encompassed the whole water column, but processes at the sea surface also affected the conditions. Temperature and current data from a mooring in the vicinity compared favourably with the mean values obtained and indicated that conditions at the time were associated with an expected south-westward flow of the Agulhas Current. The results in the BBL, and an observed high-energy pulse, could be important in assessing mechanisms for sediment transport across the shelf.