Upwelling and ocean structures off Algoa Bay and the south-east coast of South Africa

Goschen W. S., E. H. Schumann, K. S. Bernard, S. E. Bailey & S. H. P Deyzel (2012). Upwelling and ocean structures off Algoa Bay and the southeast coast of South Africa. African Journal of Marine Science 34(4): 525-536.

As the Agulhas Current flows along the south-east coast of South Africa, a number of processes operate that bring
cold, deep water up onto the narrow shelf. As a consequence, upwelling along the coastline is enhanced farther
southward and downstream. This situation is investigated off Algoa Bay and along the south-east coast to Port
Alfred, where measurements demonstrate that marked temperature variability occurs at the coastline, particularly
in summer when temperature structures are more intense and easterly-component winds more common. There is
no indication that upwelling is more prevalent at Port Alfred; increasing variability farther south is evident at Woody
Cape/Cape Padrone, where the coastline veers westwards, forming the eastern boundary of Algoa Bay. Here it is
found that, after a wind change to north-easterly, cold water is upwelled along the shoreline between 19 hours and
2.5 days later. Such upwelling progresses north-eastwards with the movement of the wind and weather systems,
although colder water also moves south-westwards into Algoa Bay. Winds, currents, sea level and sea temperatures
are highly correlated, with fluctuations in sea level measuring >50 cm being associated with coastal trapped
waves (CTWs). Such barotropic wind-driven CTWs are frequently active during upwelling, although it is unclear
whether there is any interaction between the two phenomena.