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ID #4951

Water Temperature, Marine Diversity and the Coriolis Effect, East Coast, South Africa.

The warm Mozambique current, one of the largest streams of water on the planet, flows down the east coast of Africa. Water temperatures are higher and, as a result, tropical fish and corals are found further south than would otherwise be the case. For this reason, Sodwana Bay boasts the southernmost coral reefs in the world.

As it moves further south, the current moves away from the coast, encountering the icy Benguella current that flows northwards up the West Coast.  Eddies of colder water migrate eastwards up the coast, counter to the direction of the Mozambique current.  This mixing is responsible for the diversity of marine life in the region. One encounters tropical species in the warm waters of Natal but far out to sea (e.g. marlin and tuna), with different species close inshore further south.  Many are endemic to the area because of the changes in temperature to which they are continuously subjected. Water temperature can change from balmy to icy within hours.  Incidentally, this is the subject of endless discussion amongst fishermen of the region. Are the fish on the bite? Has the wind shifted?

What seems to have escaped the attention of most is that one might reasonably expect the water on the coast to be warm when the southeaster is blowing (it should blow the warm water towards the coast, should it not?) and icy cold when the south-westerly prevails.  However, the opposite is true. When the southeaster blows the water is icy while when the south-westerly wind blows the water is warm. Why?  It arises because of the rotation of the earth, which results in a phenomenon called the Coriolis Effect, which causes the opposite to occur. Africa is full of surprises! Alan McIver AVWater

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Last update: 2014-03-28 08:12
Author: Alan McIver
Revision: 1.1

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