Frontal Zones, Chlorophyll and Primary Production Patterns in the Surface Waters of the Southern Ocean South of Cape Town

Abstract

The enhancing effects of certain frontal regions in the world ocean to biological activity is becoming recognised to an increasing degree. A number of underlying mechanisms for such enhancing effects are being hypothesised. In the Southern Ocean a series of coherent fronts are formed due to a variety of physical factors, making it an ideal area to study the proposed hypotheses. Fronts in the Southern Ocean sector south of Africa are particularly good candidates for such investigations since they exhibit some of the most extreme horizontal gradients in physico-chemical variables. It has, furthermore, been noted that the primary production of the Southern Ocean as a whole is considerably lower than would be suggested by the usual controlling factors. This process is not well understood. Results of recent research cruises in the area between Africa and Antarctica show that many fronts in this area exhibit relatively high chlorophyll concentrations at the sea surface, increases in potential primary production as well as increases in photosynthetic efficiency. These fronts, because of their unique and special characteristics, may thus offer superior areas for studying not only the interaction between physico-chemical factors and open ocean biological activity in general, but also Southern Ocean primary productivity in particular.