The surface currents of our oceans, which extend to depths of 1500 feet, are determined by wind patterns and the effect of Earth's rotation. In the Northern Hemisphere, the primary oceanic currents flow in a clockwise direction while, in the Southern Hemisphere, they move counterclockwise. Those moving from the Tropics toward the Poles are warm currents and those moving from the Poles toward the Equator are cold currents.
More that a mixing of oceanic waters, these currents have a significant impact on the climate of coastal land areas. The Gulf Stream, for example, carries warm water from the Gulf of Mexico and Caribbean toward the North Atlantic, significantly moderating the climate in Iceland and the British Isles; in like manner, the Japan Current, flowing from Southeast Asia to Alaska, warms the climate of coastal Alaska and British Columbia. Cold currents, such as the Humboldt Current along the west coast of South America, the Benguela Current along the southwest coast of Africa, the California Current along the west coast of North America and the West Australian Current have a cooling effect on these coastal areas and support rich fisheries.
At the Equator, the currents merge into a westward flow while, around the coast of Antarctic, the surface current flows to the east; from these feeder currents, the circling oceanic currents arise. In the Atlantic, the Gulf Stream and Brazil Current carry warm water away from the Equator while the Canaries and Benguela Currents return cooled water from subpolar areas to the Equator. The Indian Ocean surface currents run north along western Australia, west along the coast of India, south along the east coast of Africa and east along Antarctica. In the Pacific, the California and Humboldt Currents, arising in subpolar regions, feed the westward equatorial flow which, at the west edge of the Pacific basin, splits into the warm Japan and East Australian Currents. The climate of any given coastal area is thus a function of both its latitude and the temperature of ocean waters that bathe its shores; of course, the direction of prevailing winds and the presence or absence of nearby mountains will also affect regional weather patterns.
