Pacific Ocean

The driving forces for ocean currents are the Earth's rotation, wind friction at the surface of the water, and variations in seawater density due to differences in temperature and salinity. The interaction between wind and current has a major effect on climate and is studied for long-range weather prediction and for sea travel.

The surface currents of the North Pacific consist of two gyres, or circular systems. In the extreme north the anticlockwise Subarctic Gyre encompasses the westward-flowing Alaska Current and the eastward-flowing Subarctic Current. The main body of the North Pacific, however, is dominated by the huge North Central Gyre, which circulates clockwise. It encompasses the North Pacific Current, flowing east; the California Current, flowing south-east; and the Kuroshio, or Japan, Current, flowing north up the coast of Japan. The California Current is cold, broad, and slow-moving; the Kuroshio is warm, narrow, and rapid, similar to the Gulf Stream. Close to the equator at 5° north latitude, the eastward-flowing Equatorial Countercurrent separates the North and South Pacific systems but sends most of its waters into the North Equatorial Current. The South Pacific is dominated by the anticlockwise-moving South Central Gyre, which encompasses the South Equatorial Current flowing east and south, the South Pacific Current flowing west, and the Mentor Current flowing north, parallel to South America. Located in the extreme south is the Antarctic Circumpolar Current (West Wind Drift), which encircles the globe, merging the waters of the Pacific, Atlantic, and Indian oceans. It is the most important source of deep-sea circulation. From it flows the broad, cold Peru, or Humboldt, Current, which travels north along the coast of South America and sends its waters into the South Equatorial Current.

The atmospheric and oceanic phenomenon of El Niño in the Pacific creates unusually warm ocean conditions, causing climatic disturbances of varying severity. The warm southward current, often accompanied by fluctuating air pressure and wind patterns, occurs each December but is exceptionally intense every seven to ten years. El Niño of 1982 and 1983 was the most severe of the 20th century.

The outstanding wind systems of the Pacific Ocean are the twin belts of westerlies, which blow from west to east between 30° and 60° latitude, one in the northern hemisphere and one in the southern hemisphere. These winds vary in seasonal patterns. The stormy and unpredictable westerly of the North Central Pacific is being studied for its possible controlling effect on global weather patterns. Between the westerlies are the much more steady trade winds, which move from the north-east in the Northern hemisphere and from the south-east in the Southern hemisphere. Violent tropical storms, called typhoons in the western Pacific and hurricanes in the southern and eastern Pacific, originate in the trade wind belt in late summer and early autumn. At the equator are the equatorial doldrums, light winds with seasonal cyclonic activity. At the highest latitudes of the Pacific, the winds have little direct effect on climate and water currents.

Much of the plant and animal life of the Pacific Ocean is concentrated along its margins. Nutrient-rich waters from the deep Antarctic Circumpolar Current upwell to the surface in the Peru Current along the coast of Chile and Peru, and the area sustains a large population of anchovy that is of great importance as a world food resource. A large guano industry has been established from droppings of the seabirds that feed upon the anchovy. The north-western Pacific, including the Sea of Japan (East Sea) and the Sea of Okhotsk, is another major world fishery. Coral reefs rich with sea life reach their peak in the Great Barrier Reef, which extends for about 2,010 km (1,250 mi) along the north-eastern coast of Australia. Tuna is another important Pacific resource, bringing fleets of many nations in search of the schools that migrate over much of the ocean. The Pacific has also begun to be exploited for its vast mineral resources. The continental shelves off the coasts of California, Alaska, China, and the Indonesian area are known to contain large reserves of petroleum. Deep-Sea Exploration has revealed patches of the ocean floor covered with “manganese nodules”, potato-sized concretions of iron and manganese oxides that sometimes also contain copper, cobalt, and nickel. Research is under way to examine the feasibility of mining these deposits. See also Oceans and Oceanography; Earth: Composition.