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

  • WS Goschen
  • EH Schumann
  • KS Bernard
  • SE Bailey
  • SHP Deyzel

Abstract

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.

Keywords: coastal trapped waves, currents, Port Alfred, temperature

African Journal of Marine Science 2012, 34(4): 525–536

Author Biographies

WS Goschen
South African Environmental Observation Network (SAEON), SAEON Egagasini Node, Private Bag X2, Rogge Bay 8012, South Africa; Department of Geosciences, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa
EH Schumann
Department of Geosciences, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa
KS Bernard
South African Environmental Observation Network (SAEON), SAEON Elwandle Node, Private Bag 1015, Grahamstown 6140, South Africa; Current address: Virginia Institute of Marine Science, Department of Biological Sciences, Chesapeake Bay Hall, PO Box 1346, Gloucester Point, VA 23062, USA
SE Bailey
South African Environmental Observation Network (SAEON), SAEON Elwandle Node, Private Bag 1015, Grahamstown 6140, South Africa
SHP Deyzel
South African Environmental Observation Network (SAEON), SAEON Elwandle Node, Private Bag 1015, Grahamstown 6140, South Africa
Published
2013-01-10
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X