Short Communication

Effects of deep-sea eddies on the northern KwaZulu-Natal shelf, South Africa

  • T Morris
  • T Lamont
  • MJ Roberts

Abstract

This paper describes the westward movement of a cyclonic eddy across the Mozambique Channel and the subsequent south-westward propagation of the eddy along the east coast of South Africa and its interaction with the shelf. A hydrographic survey on 13 September 2006 off Nine-mile Reef (NMR), Sodwana Bay, showed awell-developed Agulhas Current along the continental shelf inshore of a cyclonic eddy flanked by two anti-cyclonic eddies, further offshore. A satellite-tracked drifter and complementary altimetry data confirmed the dimensions of the eddy and tracked its movement towards the coast. Shelf-edge upwelling was measured at NMR by an underwater temperature recorder (UTR) when the cyclonic eddy first came into contact with the shelf and again when the cyclonic eddy interacted with the leading edge of the anti-cyclonic eddy moving onto the shelf. Further shelf–eddy interactions off Aliwal Shoal, south of Durban, and consequent upwelling were similarly caused by the same cyclonic eddy as it progressed south-westward along the east coast. Analysis of UTR data between 2004 and 2006 indicated that between two and five cyclonic eddies impact the shelf off NMR per year.

Keywords: Aliwal Shoal, east coast South Africa, mesoscale eddies, Nine-mile Reef, shelf interactions, upwelling

African Journal of Marine Science 2013, 35(3): 343–350

Author Biographies

T Morris
Bayworld Centre for Research and Education, PO Box 7296, Rogge Bay 8012, South Africa; Cape Peninsula University of Technology, PO Box 652, Cape Town 8000, South Africa
T Lamont
Oceans and Coasts, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa; Marine Research Institute, University of Cape Town, Private Bag X3, Rondebosch 7700, South Africa
MJ Roberts
Oceans and Coasts, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa; Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
Published
2013-10-24
Section
Articles

Journal Identifiers


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