Pacific Ocean

Pacific Ocean

Pacific Ocean, largest and deepest ocean, c.70,000,000 sq mi (181,300,000 sq km), occupying about one third of the earth's surface; named by the explorer Ferdinand Magellan; the southern part is also known as the South Sea.

Physical Geography

Extent and Seas

The Pacific Ocean extends from the arctic to antarctic regions between North and South America on the east and Asia and Australia on the west. The international date line passes through it. It is connected with the Arctic Ocean by the Bering Strait; with the Atlantic Ocean by the Drake Passage, Straits of Magellan, and the Panama Canal; and with the Indian Ocean by passages in the Malay Archipelago and between Australia and Antarctica. Its maximum length is c.9,000 mi (14,500 km), and its greatest width c.11,000 mi (17,700 km), between the Isthmus of Panama and the Malay Peninsula. The principal arms of the Pacific Ocean are (in the north) the Bering Sea; (in the east) the Gulf of California; (in the south) Ross Sea; and (in the west) the Sea of Okhotsk, the Sea of Japan, and the Yellow, East China, South China, Philippine, Coral, and Tasman seas. Few large rivers drain into the Pacific Ocean; the largest are the Columbia of North America and the Huang He and Chang (Yangtze) of China.

Coastline and Islands

Along the E Pacific shore, generally, the coast rises abruptly from a deep seafloor to mountain heights on land, and there is a narrow continental shelf. The Asian coast is generally low and indented and is fringed with islands rising from a wide continental shelf. A series of volcanoes, the Circum-Pacific Ring of Fire, rims the Pacific basin.

The approximately 20,000 islands in the Pacific Ocean are concentrated in the south and west. Most of the larger islands are structurally part of the continent and rise from the continental shelf; these include the Japanese island arc, the Malay Archipelago, and the islands of NW North America and SW South America. Scattered around the Pacific and rising from the ocean floor are high volcanic islands (such as the Hawaiian Islands) and low coral islands (such as those of Oceania).

Ocean Floor

The floor of the Pacific Ocean, which has an average depth of c.14,000 ft (4,300 m), is largely a deep-sea plain. The greatest known depth (35,798.6 ft/10,911.5 m) is in the Challenger Deep in the Marianas trench c.250 mi (400 km) SW of Guam. Rising from the plain are swells (many of which are volcanic), seamounts, and guyots; the extensive Albatross Plateau covers most of the SE and E central Pacific basin.

Currents

Huge whirls, formed by the major ocean currents, are found roughly north and south of the equator; the Equatorial Counter Current separates them. The northern whirl is formed by the North Equatorial Current, Japan Current, North Pacific Drift, and California Current; the southern whirl is formed by the South Equatorial Current, East Australian Current, West Wind Drift, and Peruvian (or Humboldt) Current. There are many branch and feeder currents that help to constantly circulate ocean water of differing temperatures and salinities.

Commerce and Shipping

The principal commercial fishing areas in the Pacific are found in the shallower waters of the continental shelf; salmon, halibut, herring, sardines, and tuna are the chief catch. Most of the transpacific sea-lanes pass through the Hawaiian Islands; the chief Pacific ports are San Francisco, Los Angeles, Seattle, Tokyo-Yokohama, Guangzhou, Hong Kong, Shanghai, Manila, and Sydney. Since the 1950s many of the South Pacific islands have become tourist centers.

Exploration and Settlement

The Pacific islands of the south and west were populated by Asian migrants who crossed long distances of open sea in primitive boats. European travelers including Marco Polo had reported an ocean off Asia, and in the late 15th cent. trading ships had sailed around Africa to the western rim of the Pacific, but recognition of the Pacific as distinct from the Atlantic Ocean dates from Balboa's sighting of its eastern shore (1513). Magellan's crossing of the Philippines (1520-21) initiated a series of explorations, including those of Drake, Tasman, Dampier, Cook, Bering, and Vancouver, which by the end of the 18th cent. had disclosed the coastline and the major islands. In the 16th cent. supremacy in the Pacific area was shared by Spain and Portugal. The English and the Dutch established footholds in the 17th cent., France and Russia in the 18th, and Germany, Japan, and the United States in the 19th. Sealers and whalers sailed the Pacific from the late 18th cent., and Yankee clippers entered Pacific trade in the early 19th cent.

Bibliography

See G. Soule, The Greatest Depths (1970); E. S. Dodge, Beyond the Capes (1971); J. Gilbert, Charting the Vast Pacific (1971); V. S. Gorshkov, ed., Pacific Ocean (1976).

Body of salt water extending from the Antarctic region in the south to the Arctic circle in the north and lying between the continents of Asia and Australia on the west and North and South America on the east. It occupies about one-third of the surface of the earth and is by far the largest of the world's oceans. Its area, excluding adjacent seas, is approximately 63,800,000 sq mi (165,250,000 sq km), twice that of the Atlantic Ocean and more than the whole land area of the globe. Its mean depth is 14,040 ft (4,280 m). The western Pacific is noted for its many peripheral seas.

Learn more about Pacific Ocean with a free trial on Britannica.com.

The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and Australia in the west and the Americas in the east. At 169.2 million square kilometers (105.1 million square miles) in area, this largest division of the World Ocean – and, in turn, the hydrosphere – covers about 46% of the Earth's water surface and about 32% of its total surface area, making it larger than all of the Earth's land area combined. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean. The Mariana Trench in the western North Pacific is the deepest point in the Pacific and in the world, reaching a depth of 10,911 metres (35,798 ft).

Overview

The ocean encompasses almost a third of the Earth's surface, having an area of 179.7 million square kilometres (69.4 million sq mi and 161 million cubic mi) —significantly larger than Earth's entire landmass, with room for another Africa to spare . Extending approximately 15,500 kilometres (9,600  mi) from the Bering Sea in the Arctic to the icy margins of Antarctica's Ross Sea in the south (although the Antarctic regions of the Pacific are sometimes described as part of the circumpolar Southern Ocean), the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800 kilometres (12,300 mi) from Indonesia to the coast of Colombia and Peru - halfway across the world, and more than five times the diameter of the Moon. The western limit of the ocean is often placed at the Strait of Malacca. The lowest point on earth—the Mariana Trench—lies 10,911 metres (35,797 ft) below sea level. Its average depth is 4,280 metres (14,000 ft).

The Pacific contains about 25,000 islands (more than the total number in the rest of the world's oceans combined), the majority of which are found south of the equator. Including partially submerged islands, the figure is substantially higher.

The Pacific Ocean is currently shrinking from plate tectonics, while the Atlantic Ocean is increasing in size, by roughly 2-3 cm/yr on 3 sides, roughly averaging 0.5 sq km a year, though global warming is counteracting this process and may even reverse the shrinkage for a while.

Along the Pacific Ocean's irregular western margins lie many seas, the largest of which are the Celebes Sea, Coral Sea, East China Sea, Philippine Sea, Sea of Japan, South China Sea, Sulu Sea, Tasman Sea, and Yellow Sea. The Strait of Malacca joins the Pacific and the Indian Oceans on the west, and Drake Passage and the Strait of Magellan link the Pacific with the Atlantic Ocean on the east. To the north, the Bering Strait connects the Pacific with the Arctic Ocean.

As the Pacific straddles the ± 180° meridian, the West Pacific (or western Pacific, near Asia) is in the Eastern Hemisphere, while the East Pacific (or eastern Pacific, near the Americas) is in the Western Hemisphere.

For most of Magellan's voyage from the Strait of Magellan to the Philippines, the explorer indeed found the ocean peaceful. However, the Pacific is not always peaceful. Many tropical cyclones (typhoons, the equivalent of Atlantic hurricanes), batter the islands of the Pacific. The lands around the Pacific rim are full of volcanoes and often affected by earthquakes. Tsunamis, caused by underwater earthquakes, have devastated many islands and destroyed entire towns.

Water characteristics

Water temperatures in the Pacific vary from freezing in the poleward areas to about near the equator. Salinity also varies latitudinally. The water near the equator is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year. Poleward of the temperate latitudes salinity is also low, because little evaporation of seawater takes place in these frigid areas.

The surface circulation of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific Gyre) and counter-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current.

Turning eastward at about 45°N, the Kuroshio forks and some waters move northward as the Aleutian Current, while the rest turn southward to rejoin the North Equatorial Current. The Aleutian Current branches as it approaches North America and forms the base of a counter-clockwise circulation in the Bering Sea. Its southern arm becomes the chilled 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°S, 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.

Geology

The andesite line is the most significant regional distinction in the Pacific. It separates the deeper, mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins. The andesite line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island. The dissimilarity continues northeastward along the western edge of the Andes Cordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand—all eastward extensions of the continental blocks of Asia, Australia and Zealandia—lie outside the Andesite Line.

Within the closed loop of the andesite line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Pacific basin. Here basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the Andesite Line, volcanism is of the explosive type, and the Pacific Ring of Fire is the world's foremost belt of explosive volcanism. The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones.

The Pacific Ocean is the only ocean which is almost totally bounded by subduction zones. Only the Antarctic and Australian coasts have no nearby subduction zones.

Landmasses

The largest landmass entirely within the Pacific Ocean is the island of New Guinea— the second largest island in the world. Almost all of the smaller islands of the Pacific lie between 30°N and 30°S, extending from Southeast Asia to Easter Island; the rest of the Pacific Basin is almost entirely submerged. During the Last glacial period, New Guinea was part of Australia so the largest landmass would have been Borneo-Palawan.

The great triangle of Polynesia, connecting Hawaii, Easter Island, and New Zealand, encompasses the island arcs and clusters of the Cook Islands, Marquesas, Samoa, Society, Tokelau, Tonga, Tuamotu, Tuvalu and the Wallis and Futuna islands.

North of the equator and west of the International Date Line are the numerous small islands of Micronesia, including the Caroline Islands, the Marshall Islands and the Mariana Islands.

In the southwestern corner of the Pacific lie the islands of Melanesia, dominated by New Guinea. Other important island groups of Melanesia include the Bismarck Archipelago, Fiji, New Caledonia, the Solomon Islands and Vanuatu.

Islands in the Pacific Ocean are of four basic types: continental islands, high islands, coral reefs, and uplifted coral platforms. Continental islands lie outside the Andesite Line and include New Guinea, the islands of New Zealand, and the Philippines. These islands are structurally associated with nearby continents. High islands are of volcanic origin, and many contain active volcanoes. Among these are Bougainville, Hawaii, and the Solomon Islands.

The third and fourth types of islands are both the result of coralline island building. Coral reefs are low-lying structures that have built up on basaltic lava flows under the ocean's surface. One of the most dramatic is the Great Barrier Reef off northeastern Australia. A second island type formed of coral is the uplifted coral platform, which is usually slightly larger than the low coral islands. Examples include Banaba (formerly Ocean Island) and Makatea in the Tuamotu group of French Polynesia.

History and economy

Important human migrations occurred in the Pacific in prehistoric times, most notably those of the Polynesians from the Asian edge of the ocean to Tahiti and then to Hawaii, New Zealand, and Easter Island.

The ocean was first sighted by Europeans early in the 16th century, first by the Spanish explorer Vasco Núñez de Balboa who crossed the Isthmus of Panama in 1513, and then by Ferdinand Magellan, who sailed the Pacific during his circumnavigation from 1519 to 1522. In 1564, conquistadors crossed the ocean from Mexico led by Miguel López de Legazpi who sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing 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; Abel Janszoon Tasman discovered Tasmania and New Zealand in 1642. The 18th century marked a burst of exploration by the Russians in Alaska and 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 Oceania by European powers, and later, the United States and Japan. Significant contributions to oceanographic knowledge were made by the voyages of HMS Beagle in the 1830s, with Charles Darwin aboard; HMS Challenger during the 1870s; the USS Tuscarora (1873-76); and the German Gazelle (1874-76). Although the United States gained control of the Philippines from Spain in 1898, Japan controlled most of the western Pacific by 1914 and occupied many other islands during World War II. However, by the end of that war, Japan was defeated and the U.S. Pacific Fleet was the virtual master of the ocean. Since the end of World War II, many former colonies in the Pacific have become independent states.

The exploitation of the Pacific's mineral wealth is hampered by the ocean's great depths. In shallow waters of the continental shelves off the coasts of Australia and New Zealand, petroleum and natural gas are extracted, and pearls are harvested along the coasts of Australia, Japan, Papua New Guinea, Nicaragua, Panama, and the Philippines, although in sharply declining volume in some cases. The Pacific's greatest asset is its fish. The shoreline waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish.

Environmental Issues

Marine pollution is a generic term for the harmful entry into the ocean of chemicals or particles. The biggest culprit are rivers that empty into the Ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. The excess of oxygen depleting chemicals in the water leads to hypoxia and the creation of a dead zone (ecology).

Marine debris, also known as marine litter, is a term used to describe human-created waste that has found itself floating in a lake, sea, ocean or waterway. Oceanic debris tends to accumulate at the centre of gyres and coastlines, frequently washing aground where it is known as beach litter.

Major ports and harbours

See also

References

Further reading

Based on public domain text from US Naval Oceanographer

  • Barkley, Richard A. (1968). Oceanographic Atlas of the Pacific Ocean. Honolulu: University of Hawaii Press.
  • (1985). Blue Horizons: Paradise Isles of the Pacific. Washington, D.C.: National Geographic Society. ISBN 0-87044-544-8.
  • Cameron, Ian (1987). Lost Paradise: The Exploration of the Pacific. Topsfield, Mass.: Salem House. ISBN 0-88162-275-3.
  • Couper, A. D. (ed.) (1989). Development and Social Change in the Pacific Islands. London: Routledge. ISBN 0-415-00917-0.
  • Gilbert, John (1971). Charting the Vast Pacific. London: Aldus. ISBN 0-490-00226-9.
  • Lower, J. Arthur (1978). Ocean of Destiny: A Concise History of the North Pacific, 1500-1978. Vancouver: University of British Columbia Press. ISBN 0-7748-0101-8.
  • Napier, W.; Gilbert, J., and Holland, J. (1973). Pacific Voyages. Garden City, N.Y.: Doubleday. ISBN 0-385-04335-X.
  • Oliver, Douglas L. (1989). The Pacific Islands. 3rd ed., Honolulu: University of Hawaii Press. ISBN 0-8248-1233-6.
  • Ridgell, Reilly (1988). Pacific Nations and Territories: The Islands of Micronesia, Melanesia, and Polynesia. 2nd ed., Honolulu: Bess Press. ISBN 0-935848-50-9.
  • Soule, Gardner The Greatest Depths: Probing the Seas to
  • Spate, O. H. K. (1988). Paradise Found and Lost. Minneapolis: University of Minnesota Press. ISBN 0-8166-1715-5.
  • Terrell, John (1986). Prehistory in the Pacific Islands: A Study of Variation in Language, Customs, and Human Biology. Cambridge: Cambridge University Press. ISBN 0-521-30604-3.

External links

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