Original Articles

Ocean current and temperature structures in Algoa Bay and beyond in November 1986

Published in: South African Journal of Marine Science
Volume 7, issue 1, 1988 , pages: 101–116
DOI: 10.2989/025776188784379198

Abstract

Data on ocean temperature, currents, salinity and nutrients were obtained in an area off Algoa Bay on the south-east coast of South Africa during a ship's cruise in early November 1986. Satellite imagery provided information on the position of the Agulhas Current during the cruise period, while wind data were available from weather stations on the eastern and western sides of Algoa Bay. It is surmised that wind-forcing plays a major role in water circulation in the Bay and over the inshore continental shelf remote from the influence of the open ocean. The predominantly barotropic current flow, of the order of 0,5 m·s−1, was downwind and influenced by topographic features and coastline shape. The Agulhas Current influences the ocean structures by long-term (large episodic meanders) and short-term (upwelling forced by the Current, core upwelling in frontal eddies and warm frontal plumes at the surface) fluctuations. Temperature structures showed well mixed water in Algoa Bay and a strong thermocline over the continental shelf, and were typical of a western boundary current in the Agulhas Current itself. The presence of a thermocline at 30–50 m over the shelf prevented upward mixing of nutrients. The Current exerted a dominant effect on shelf waters north of Algoa Bay.

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