SEA-SURFACE HEAT-EXCHANGE AT ST HELENA BAY AND IMPLICATIONS FOR THE SOUTHERN BENGUELA UPWELLING SYSTEM

Measurements of the different components of the heat budget were taken at St Helena Bay, on the west coast of South Africa, from 14 to 21 October 1986 in order to examine heat exchange at the air-sea interface. Cold, upwelled water restricts latent heat loss by the sea surface and determines that only a small amount of sensible heat is gained by the sea. Measurements showed that these two turbulent heat fluxes are roughly equal and opposite and more or less cancel each other out. Therefore, the net radiation provided a good estimation of the total heat flux into the surface waters. During favourable conditions (in summer), the daily mean heat exchange into the sea can be as high as 315 W.m-2, and it is capable of increasing the temperature of the upper 10 m mixed layer by as much as 0,65-degrees-C per day. This has important implications for biological production in the cold upwelled water when it is sun-warmed during its movement offshore.