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The Pacific Ocean

The name Pacific, which means peaceful, was given to the Ocean by the Portuguese navigator Ferdinand Magellan in 1520. The Pacific Ocean is the world's largest water body covering roughly one third of the Earth's surface and containing more than half of the World Ocean’s free water. The Ocean is bounded on the east by the North and South American continents, on the north by the Bering Strait; on the west by Asia, the Malay Archipelago, and Australia, and on the south by the South Polar Ocean. In the southeast the Pacific Ocean is divided from the Atlantic Ocean by the Drake Passage along 68 degree west longitude. In the southwest, its separation from the Indian Ocean is not officially and clearly designated. The Equator divides the Pacific Ocean into the North Pacific Ocean and the South Pacific Ocean.



Using a collection of satellite-based observations, scientists and visualizers stitched together months of observations of the land surface, oceans, sea ice, and clouds into a seamless, true-color mosaic of every square kilometer (0.386 square mile) of our planet. (The Blue Marble)
The main surface currents in the Pacific ocean: 2: North equatorial current 3: South equatorial current 6: Kuroshio current 7: California current 8: Equatorial countercurrent 10: Alaska current 11 Peru current 14: Oyashio current

The oldest ocean basin


The Pacific is the oldest of the existing ocean basins. Its oldest rocks were dated at 200 million years. The major features of the basin were shaped by the phenomena associated with plate tectonics and volcanism (see story below: ‘Ring of Fire’). The ocean floor of the central Pacific basin is rather uniform, major irregularities in the area are the extremely steep-sided, flat-topped submarine peaks known as seamounts. The western part of the floor consists of mountain arcs that rise above sea level as island groups. Deep trenches lie adjacent to the outer margins of the wide western Pacific Ocean continental shelf. The ocean floor in the eastern Pacific is dominated by the East Pacific Rise, which is a part of the worldwide mid-oceanic ridge system. Most sedimentary deposits of the Pacific Ocean are of local origin like skeletal remains of sea life. Terrigenous sediments are confined to narrow marginal bands close to land.



The ocean currents


The surface circulation of Pacific Ocean waters is generally clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.


The North Equatorial Current, driven westward along latitude 15 degree north by the trade winds, turns north near the Philippines to become the warm Kuroshio, or Japan, Current. Turning eastward at about 45 degree north, the Kuroshio forks and some waters move northward as the Aleutian Current, while the rest turns southward to rejoin the North Equatorial Current. The Aleutian Current branches as it approaches North America and forms the base of a counterclockwise circulation in the Bering Sea. Its southern arm becomes the slow, south-flowing California Current.


The South Equatorial Current, flowing west along the equator, swings southward east of New Guinea, turns east at about 50 degree south latitude, and joins the main westerly circulation of the Southern Pacific, which includes the Earth-circling Antarctic Circumpolar Current. As it approaches the Chilean coast, the South Equatorial Current divides; one branch flows around Cape Horn and the other turns north to form the Peru, or Humboldt, Current.



The climate


The Pacific Monsoon region lies in the far-western Pacific between Japan and Australia. Characteristic of this climatic region are dry winds that blow from the continental interior to the ocean in winter, and moist wind causing heavy rainfall in the opposite direction in summer. Consequently, a marked regional seasonality of cloudiness and rainfall occurs. The steady trade winds move along the Equator from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. Both hurricanes and typhoons originate in the trade wind belt in late summer and early fall. Typhoons often cause extensive damage in the west and southwest Pacific while Hurricanes affect Mexico and Central America. The greatest typhoon frequency exists within the triangle from southern Japan to the central Philippines to eastern Micronesia.



El Niño

Cold water upwelling near the coast of Peru (purple) joins the South Equatorial Current, which flows westward across the Pacific Ocean. This MODIS sea surface temperature image from January 1–8, 2001 shows the ocean in normal conditions, but during an El Niño the waters off Peru are much warmer. Cold waters are black and dark green. (Photo: Jesse Allen, MODIS OCEAN Team)

The cyclical El Niño phenomenon is the most remarkable meteorological and oceanographic feature of the Pacific Ocean (see also: Indian Ocean). Under non-El Niño conditions the trade winds south of the Equator blow towards the west across the tropical Pacific. These winds pile up warm surface water in the western Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador. The sea surface temperature is about 8 degrees Celsius higher in the west; cool temperatures off South America predominate due to an upwelling of cold water from deeper layers. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries.


Rainfall is found in rising air over the warmest water in the western Pacific, and the eastern Pacific is relatively dry. During El Niño conditions, the trade winds relax in the central and western Pacific and the warm water piled up in the western Pacific spreads towards the eastern Pacific. This reduces the upwelling of cool water along the South American coastline and, thus, cut off the supply of nutrient rich water for marine life. The result is a rise in sea surface temperature and a drastic decline in primary productivity, the latter of which affects the entire food chain, including commercial fisheries in this region. The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific. Among these consequences are increased rainfall across the southern area of the US and in Peru, and drought in the West Pacific sometimes associated with devastating bush fires e.g. in Australia.





Important human migrations occurred in the Pacific in former times. Polynesians sailed from Tahiti towards Hawaii and New Zealand. In the early 16th century, Europeans explored the Pacific Ocean. Vasco Nunez de Balboa (1513) was one of the first and then followed by Ferdinand Magellan, who crossed the Pacific during his circumnavigation from 1519 to 22. In the 16th century Spanish ships sailed from Spain to the Philippines, New Guinea, and the Solomon Islands. During the 17th century, the Dutch, sailing around southern Africa, dominated discovery and trade in the Pacific Ocean.


Until the Panama Canal was finished in 1914, the Strait of Magellan was the only safe way to move between the Atlantic and Pacific Oceans. Photo: Jacques Descloitres, MODIS Rapid Response Team)

In 1642, Abel Janszoon Tasman discovered Tasmania and New Zealand. The 18th century marked a burst of exploration by the Russians in Alaska and on the Aleutian Islands, the French in Polynesia, and the British in the three voyages of James Cook: to the South Pacific and Australia, Hawaii, and the North American Pacific Northwest. Growing imperialism during the 19th century resulted in the occupation of much of the Pacific Ocean by the Western powers. Significant contributions to oceanographic knowledge were made by the voyages of the H.M.S. Beagle in the 1830s, with Charles Darwin aboard. During the 1870s, the H.M.S. Challenger; the U.S.S. Tuscarora and the German Gazelle investigated the Pacific Ocean. Although the United States took the Philippines in 1898, Japan controlled the western Pacific by 1914. By the end of World War II the U.S. Pacific Fleet was the virtual master of the ocean.


Transportation and Fisheries

The Pacific Ocean provides low-cost sea transportation between East and West. Main trading routes connect harbors like Bangkok (Thailand), Hong Kong (China), Los Angeles (US), Pusan (South Korea), Sydney (Australia), Vladivostok (Russia), Wellington (NZ), and Yokohama (Japan).


Fish is the greatest resource of the Pacific Ocean. In 1996, over 60% of the world's fish catch came from the Pacific Ocean. The shoreline waters of the continents and the more temperate island regions yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish. A large population of anchovies occurs along the South American coast that is of great importance as a World food resource. An extended guano industry was established from droppings of the seabirds that feed upon the anchovies.


The continental shelves off the coasts of California, Alaska, China, and the Indonesian area are known to contain large reserves of petroleum. Patches of the ocean floor are covered with ”manganese nodules,” potato-sized concretions of iron and manganese oxides that sometimes also contain copper, cobalt, and nickel. Moreover, different minerals, sand and gravel for the construction industry are exploited offshore.


Endangered marine species in the Pacific Ocean include the dugong, sea lion, sea otter, seals, turtles, and whales. Oil pollution occurs mainly in the Philippine Sea and the South China Sea.



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