Currents

Currents, Ocean, movements of the surface waters of the ocean in a constant direction under the influence mainly of the constant or trade-winds (q.v.). Thus, currents from the north-east and southeast unite in equatorial latitudes into one westerly current. This is deflected to the north and south by the intervention of continental land-masses, and the resulting currents may also be influenced by the earth's rotation and by the anti-trade winds. These causes seem, in fact, to tend to produce an easterly current in temperate latitudes. Thus, in the Atlantic a current from between the Azores and Portugal towards Cape Verd, known as the African current, unites with one from the Cape of Good Hope to the Gulf of Guinea, the South African current, to form an Equatorial current. The south-east trade-wind, being stronger than the north-east, deflects the greater part of this current north-westward from Cape St. Roque into the Caribbean Sea and the Gulf of Mexico, whence it issues as the Gulf Stream, whilst the smaller part turns southwards to the mouth of the La Plata as the Brazil current. The Gulf Stream flows through the Florida Strait at a rate of between four and five miles an hour, with a surface temperature reaching 80° F. It flows parallel to the coast of the United States, but is separated therefrom by a cold prolongation of the Labrador current from Baffin's Bay until it is lost about the latitude of the Azores. In the comparatively still water between it and the North Equatorial current is the mass of floating seaweed known as the Sargasso Sea. The Brazil current flowing eastwards from the La Plata towards the Cape of Good Hope is mainly absorbed in the northerly South African current, but in part flows eastward towards the Crozet Islands. Similarly, in the Pacific, the Pacific current from Alaska down the coast to Mexico, and the Peruvian current from Patagonia up the coast to Ecuador, cross the ocean as parallel equatorial currents mainly to the north of the equator. The northern one is mainly deflected northward and north-eastward as the Japan current or Kuro Siwo to the Aleutian Isles, whilst no defined cold current meets it from the narrow and shallow Behring Strait. The South Equatorial finds its way in part through Torres and Sunda Straits into the Indian Ocean, the remainder being deflected from Fiji towards Brisbane, whence it flows back eastward to the north of New Zealand and toward Cape Horn. In the Indian Ocean a single equatorial current flows from the Sunda Islands to the Mascarenes, whence part of it circles round past Socotra into the Arabian Sea, whilst two other parts flow down each side of Madagascar, unite, and off Cape Agulhas are abruptly deflected eastword towards St. Paul, and so on to Tasmania and the South Pacific. These currents are seldom more than 500 feet deep.

Besides these currents due mainly to wind, there seems good evidence of a slow general circulation of all the water of the ocean, clue to convection currents.