Geography and climate


Where the two oceans really meet

18 December 2007

South Africa's Cape coast attracts thousands of local and international tourists each year to witness the Indian and Atlantic oceans splashing together - or so they believe.

Cape Point, an hour's drive from Cape Town, cashes in on the visitors who flock to witness this supposed natural phenomenon. An estimated 800 000 people a year visit its spectacular cliffs, lighthouses and "Two Oceans" curio shops.

However, the residents of Cape Agulhas - over 100km east of Cape Point - insist that visitors wanting to see the confluence of the two oceans will have to travel a little further south ...

Cape Agulhas residents want what they see as their rightful piece of the tourism pie - the town attracts about 250 000 tourists a year - arguing that visitors are tricked into believing the seas meet at Cape Point, and that the shops there trade under false pretences.

According to CapeInfo.com's Cape Agulhas web page, somebody did draw a line to demarcate where the Indian and Atlantic Oceans meet: the International Hydrographic Organisation (IHO), which describes the western boundary of the Indian Ocean as follows:

    From the coast of the Antarctic continent northwards, along the meridian of 20 E to Cape Agulhas (34 50S 20 00E), the southern extremity of the Republic of South Africa, in Africa (the common limit with the South Atlantic Ocean).

According to CapeInfo.com, this finding is accepted and applied by both the Hydrographic Office of the South African Navy and the Department of Oceanography at the University of Cape Town.

A common misunderstanding fuelling the controversy, argues the web site, is "the erroneous assumption that oceans and currents are synonymous".

The Indian Ocean, on the east, is warmed by the Mozambique or Agulhas Current which flows down from the tropics, while the Atlantic, on the west coast, is cooled by the icy Benguela Current which comes up from the Antarctic.

These two different oceans, the prevailing wind and the topography of South Africa combine to create lush forests and subtropical savanna on the east coast, gradually changing to desert or semi-desert on the west coast.

Says CapeInfo.com: "The Agulhas Current brings warm water from the subtropics down the east coast of South Africa. From the region of East London, because of the widening of the continental shelf, the current flows further offshore and the coastal waters become cooler. On the west coast, the water is chilled by the north-drifting, cold Benguela Current. When the wind blows the surface waters offshore, deep water, which is rich in nutrients, swells up to replace it.

"The changes in temperature along the coast bring about changes in marine life. One example, which is there for all to see, is the prolific kelp (Ecklonia maxima) forests which prefer the colder, nutrient-rich waters of the west coast."

These kelp forests, the web site argues, grow all the way along the west coast, past Cape Point in an easterly direction - only as far as Cape Agulhas.

"This fact supports the argument that the dividing line between the warm and cold waters is more often at Cape Agulhas than anywhere else ... However, because of the effect of the south-easterly and north-westerly winds, the warm current can on occasion drift even as far as Cape Point."

What about the warmer temperature of the waters in False Bay, just to the East of Cape Point? This, Cape Agulhas argues, is merely due to False Bay's being shallow and sheltered and hence not affected by the currents to the same extent as the waters of the open sea.

Who is right, asks The Economist in a January 2002 article sub-titled "South Africa's oceanic squabble", noting that oceans are divided by man, not nature, and quoting University of Cape Town oceanographer Howard Waldron: "Oceans exchange water all the time, and there is never a neat dividing line."

SAinfo reporter

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 Spectacular Cape Point  cape agulhas, lighthouse, cape point, capeCape Agulhas boasts Africa's second-oldest working lighthouse, built in 1848 (Photo: Pride of Africa Lodge)

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