Oceanic exchanges and temperature variability in the Knysna Estuary

Abstract

This paper utilises a temperature record about 4 years long made near the tidal inlet of the Knysna Estuary on the south coast of South Africa. It is shown that such a record is very useful as a tool to investigate the hydrodynamics of the estuary, particularly in terms of ocean-estuary exchanges. Thus ocean temperatures were generally colder than estuary temperatures, and tidal fluctuations are clearly evident. In summer, upwelling in the ocean can impact markedly on the estuary, and one situation is shown where a temperature drop of over 13°C occurred in about 2 hours. A more detailed analysis using sea level and wind records shows the importance of coastal trapped waves and the variability associated with the wind. Similar temperature fluctuations also occur in other estuaries, and the impacts on the biota could be substantial.