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THE CIRCULATION OF THE ATLANTIC OCEAN

Let us now study more closely the circulation of ocean currents in the Atlantic Ocean. We shall begin with the North and South Equatorial Current at the equator. The steady Trade Winds constantly drift two streams of water from east to west. At the ‘shoulder’ of north-east Brazil, the protruding land mass splits the South Equatorial Current into the Cayenne Current which flows along the Guiana Coast, and the Brazilian Current which flows southwards along the east coast of Brazil.

In the North Atlantic Ocean, the Cayenne Current is joined and reinforced by the North Equatorial Current and heads north-westwards as a large mass of equatorial water into the Caribbean Sea. Part of the current enters the Gulf of Mexico and emerges from the Florida Strait between Florida and Cuba as the Florida Current. The rest of the equatorial water flows northwards east of the Antilles to join the Gulf Stream off the south-eastern U.S.A. The Gulf Stream Drift is one of the strongest ocean currents, 56 to 160 km (35 to 100 miles) wide, 610 m (2000 feet) deep and with a velocity of 5 km (3 miles) an hour. The current hugs the coast of America as far as Cape Hatteras (latitude 35°N), where it is deflected eastwards under the combined influence of the Westerlies and the rotation of the earth. It reaches Europe as the North Atlantic Drift. This current, flowing at 16 km (10 miles) per day, carries the warm equatorial water for over a thousand kilometres to the coasts of Europe. From the North Atlantic, it fans out in three directions, eastwards to Britain, northwards to the Arctic and southwards along the Iberian coast, as the cool Canaries Current. Oceanographic researches show that almost two-thirds of the water brought by the Gulf Stream to the Arctic regions is returned annually to the tropical latitudes by dense, cold polar water that creeps southwards in the ocean depths.

The Canaries Current flowing southwards eventually merges with the North Equatorial Current, completing the clockwise circuit in the North Atlantic Ocean.

Within this ring of currents, an area in the middle of the Atlantic has no perceptible current. A large amount of floating seaweed gathers and the area is called the Sargasso Sea.

Apart from the clockwise circulation of the currents, there are also currents that enter the North Atlantic from the Arctic regions. These cold waters are blown south by the out-flowing polar winds. The Irminger Current drifts south-westwards between West Iceland and Greenland and cools the North Atlantic Drift at the point of convergence. The cold Labrador Current drifts south-eastwards between West Greenland and Baffin Island to meet the warm Gulf Stream off Newfoundland, as far south as 50°N where the icebergs that were carried south by the Labrador Current melt.

The South Atlantic Ocean follows the same pattern of circulation as the North Atlantic Ocean. The major differences are that the circuit is anti-clockwise and the collection of seaweed in the still waters of the mid-South Atlantic is not so distinctive.

 

Where the South Equatorial Current is split at Cape Sao Roque, one branch turns south as the warm Brazilian Current. Its deep blue waters are easily distinguishable from the yellow, muddy waters carried hundreds of kilometres out to sea by the Amazon further north. At about 40°S the influence of the prevailing Westerlies and the rotation of the earth propel the current eastwards to merge with the cold West Wind Drift as the South Atlantic Current.

On reaching the west coast of Africa the current is diverted northwards as the cold Benguela Current (the counter-part of the Canaries Current). It brings the cold polar waters of the West Wind Drift into tropical latitudes. Driven by the regular South-East Trade Winds, the Benguela Current surges equatorwards in a north-westerly direction to join the South Equatorial Current.

This completes the circulation of the currents in the South Atlantic. Between the North and South Equatorial Currents is the east-flowing Equatorial Counter Current.

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