Review of primary production and related processes on the Agulhas-Bank

Abstract

Phytoplankton biomass and productivity in different sectors of the Agulhas Bank are discussed in a broad hydrographic content centred predominantly on thermocline characteristics. The delineation of the different sectors is largely subjective, though based on some degree of physical and biological uniformity within each sub-region. The primary physical forcing mechanisms of wind-driven coastal upwelling and current-driven shelf-break upwelling stimulate phytoplankton productivity in the coastal region of the western Bank and over the eastern sector, respectively. Vertical thermal structure is adjectively maintained but modified by summer insulation and wind-induced mixing. Deep mixing associated with the deep pool south of Cape Agulhas severely retards primary production. In the winter the predominantly westerly wind conditions and reduced advection of bottom water onto the Agulhas Bank result in a deepening of thermocline over much of the region. The Agulhas Bank appears to be more productive with respect to phytoplankton than other major western-boundary current systems.