Seasonality in the oxygen minimum layers at the extremities of the Benguela system

Seasonal variations in the occurrence and movement of water depleted in dissolved oxygen are described and examined for both northern Namibia/Angola and the Agulhas Bank. In the former, the variations can be explained as being related to changes in the offshore wind field, which affects upwelling and hence primary production, although the relationship is not a direct one. On the Agulhas Bank, it is more likely that the low oxygen water is stabilized by shelf-edge upwelling, which causes a "ridge" of dense cold water to advect onto the Bank. This allows a semi-stagnant pool to develop to the west, where local decomposition can occur over a period of months below the stable intense thermocline.