Pacific ocean

     
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The Pacific Ocean is a body of salt water extending from the Antarctic region in the south to lớn the Arctic in the north and lying between the continents of Asia and australia on the west và North America & South America on the east.


The Pacific Ocean stretches from the Bering Strait near the Arctic Circle to the shores of Antarctica through 135° of latitude, some 9,600 miles (15,500 km). The mean depth of the Pacific (excluding adjacent seas) is 14,040 feet (4,280 metres), and its greatest known depth is 36,201 feet (11,034 metres).


The deep zone of the Pacific Ocean, which contains about 80 percent of the ocean’s volume, has relatively stable temperature and salinity patterns; its average temperature is 38.3 °F (3.5 °C).


The highest surface salinities in the Pacific Ocean occur in the southeastern area, where they reach 37 parts per thousand; the lowest salinities—less than about 32 parts—occur in the extreme northern zone of the Pacific. The salinity in the equatorial belt can be as low as 34 parts per thousand.


The Mariana Trench, also called the Marianas Trench, is a deep-sea trench in the floor of the western North Pacific Ocean, và it is the deepest such trench known on Earth. It is part of the western Pacific system of oceanic trenches coinciding with subduction zones—points where two adjacent tectonic plates collide, one being forced below the other.


Pacific Ocean, body of salt water extending from the 60° S parallel in the south to the Arctic in the north and lying between the continents of Asia and australia on the west & North America & South America on the east.


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In the Northern Hemisphere the Pacific Ocean meets the Arctic Ocean in the Bering Sea. In the Southern Hemisphere the Pacific and Atlantic set in the relatively narrow Drake Passage between Tierra del Fuego in South America & Graham Land in Antarctica, & the Pacific Ocean và the Southern Ocean meet at the 60° S parallel. The separation between the Pacific and Indian oceans is less distinct, but generally it is considered to lie along the line of islands extending eastward from Sumatra, through Java to lớn Timor, thence across the Timor Sea khổng lồ Cape Londonderry in Australia. To lớn the south of nước australia the boundary extends across the Bass Strait và thence from Tasmania lớn 60° S.

Because of the pattern of major mountain systems of the globe, a relatively small proportion (one-seventh) of the total continental drainage enters the Pacific—a total drainage area of less than about three times the total area of Australia. Of the rivers that drain into the Pacific, those of china and Southeast Asia are of the greatest importance; the basins of those rivers support more than one-fourth of the world’s population.

The eastern boundary of the Pacific is associated with the American cordilleran system, which stretches from Alaska in the north to lớn Tierra del Fuego in the south. Except for its extreme northern và southern sections, which are characterized by fjords & their numerous off-lying islands, and except for the deeply indented Gulf of California, the coastal boundary is relatively regular và the continental shelf narrow. The western, or Asiatic, coastal boundary, in contrast, is irregular. Although the mountain systems there lie roughly parallel lớn the coast, as they do on the eastern Pacific coastlands, the western Pacific is noted for its many marginal seas. From north to lớn south they include the Bering Sea, the Sea of Okhotsk, the Sea of nhật bản (East Sea), the Yellow Sea, the East trung quốc Sea, and the South đài loan trung quốc Sea. Their eastern boundaries are formed by southward-jutting peninsulas or island arcs or both. It is of oceanographic significance that the great rivers of eastern Asia—including the Amur, the Huang He (Yellow River), the Yangtze, the Xi & Pearl (Zhu), & the Mekong—enter the Pacific indirectly by way of the marginal seas.

This article treats the physical và human geography of the Pacific Ocean. For discussion of the physical và chemical oceanography & marine geology of the Pacific, see ocean.

Physiography

Relief

The Pacific basin may conveniently be divided into three major physiographic regions: the eastern, western, và central Pacific regions.

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Eastern region

The eastern Pacific region, which extends southward from Alaska khổng lồ Tierra del Fuego, is relatively narrow và is associated with the American cordilleran system of almost unbroken mountain chains, the coastal ranges of which rise steeply from the western shores of North và South America. The continental shelf, which runs parallel khổng lồ it, is narrow, while the adjacent continental slope is very steep. Significant oceanic trenches in this region are the Middle America Trench in the North Pacific và the Peru-Chile Trench in the South Pacific.


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Central region

The central Pacific region lies between the boundaries of the eastern và western regions. The largest & the most geologically stable of the structural provinces of the Earth’s crust, it is characterized by expansive areas of low relief, lying at a general depth of about 15,000 feet (4,600 metres) below the surface.

Principal ridges và basins

To the east of longitude 150° W, the relief of the ocean floor is considerably less pronounced than it is to lớn the west. In the eastern Pacific the Cocos Ridge extends southwestward from the Central American isthmus to the Galapagos Islands. To the south of the Galapagos lies the Peru Basin, which is separated by the extensive Sala y Gómez Ridge from the Southeast Pacific Basin, which in turn is separated from the Southwest Pacific Basin by the East Pacific Rise & indeterminate Pacific-Antarctic Ridge, which runs from the Sala y Gómez Ridge to Antarctica in the vicinity of 150° W.


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Extending southward from the Tasman Basin (between New Zealand và eastern Australia) is the Macquarie Ridge, which forms a major boundary between the deep waters of the Pacific và Indian oceans. The Hawaiian Ridge extends westward from Hawaii lớn the 180° meridian.

The submerged parts of the series of ridges that are capped by the island archipelagoes of the western Pacific are continuous & are to be found at depths of less than about 2,000 feet (610 metres). These ridges include the Aleutian Ridge in the northwestern Pacific; the series of ridges extending southward through the Kuril, Bonin, and Mariana island groups, and the archipelagoes of Yap & Palau; those extending eastward from New Guinea, including the Bismarck Archipelago & the Solomon và Santa Cruz island chains; and, finally, the ridges extending southward, from which rise the Samoa, Tonga, Kermadec, and Chatham island groups, as well as Macquarie Island.

Bottom deposits

Apart from the narrow coastal zone of the eastern region & the broad continental seas of the western region, the Pacific is floored with pelagic (oceanic) material derived from the remains of marine plants và animals that once inhabited the waters lying above. Red or brown radiolarian ooze is found along the zone of the Pacific North Equatorial Current, east of longitude 170° W, & on the floors of some deep Indonesian basins. A belt of diatom ooze occurs between latitudes 45° và 60° S and across the North Pacific, between nhật bản and Alaska. Calcareous globigerina ooze occurs in the shallower parts of the South Pacific, the dissolving power nguồn of the seawater at great depths being sufficient khổng lồ dissolve calcareous material khổng lồ such an extent that these oozes are not generally found at depths in excess of about 15,000 feet (4,600 metres). Silica-containing material, such as radiolarian và diatom ooze, is found at greater depths, but even these siliceous remains are dissolved at very great depths, where the characteristic deposit is red clay. Red clay, which covers no less than half of the Pacific floor, is believed khổng lồ be formed of colloidal (extremely finely divided) clays derived essentially from the land.


On the abyssal plains, where sediments accumulate slowly, chemical and biological processes lead khổng lồ the formation of metal-bearing coatings around objects such as the ear bones of fishes. The nodules so formed contain manganese, iron, nickel, copper, cobalt, và traces of other metals such as platinum. They cover large areas of the ocean floor in the Pacific. Similar processes size coatings, called manganese crusts, on the rock surfaces of seamounts.

Among the many different forms of land-derived muds (formed by the erosive action of rivers, tides, và currents) that floor the continental shelves & slopes of the Pacific, the yellow mud of the Yellow Sea is of particular interest. The mud is conveyed khổng lồ the seabed by the Huang He, which drains a vast area of northern trung quốc blanketed with loess, a fine-grained soil.

Islands

The islands of the western region—including the Aleutians, the Kurils, the Ryukyus, Taiwan, the Malay Archipelago (including New Guinea), và New Zealand—are continental in character. Geologically, they consist partly of sedimentary rocks, and their structures are similar to those of the coastal mountain ranges of the adjacent continent.


A geologically important boundary between the continental, or “high,” islands và the numerous truly oceanic, or “low,” islands of the Pacific is the Andesite Line, a region of intense volcanic & seismic activity. In the northern and western Pacific the Andesite Line follows close to seaward the trend of the island arcs from the Aleutians southward to lớn the Yap và Palau arcs, thence eastward through the Bismarck, Solomon, and Santa Cruz archipelagoes, & thence southward through the Samoa, Tonga, & Chatham groups and Macquarie Island khổng lồ Antarctica. Islands khổng lồ the west of the line are rich in andesite, a type of intrusive igneous rock; islands to lớn the east (oceanic side) of it are essentially of basalt, an extrusive igneous rock.

The numerous oceanic islands of the Pacific are unevenly distributed. They lie, in the main, between the Tropics of Cancer & Capricorn và occur in great numbers in the western Pacific. The northernmost chain of oceanic islands is associated with the Hawaiian Ridge. The Hawaiian archipelago consists of about 2,000 islands, although the term Hawaiian Islands is usually applied to lớn the small group that lies at the eastern over of the archipelago.

The numerous small islands of Micronesia lie mainly north of the Equator và to the west of the 180° meridian. Nearly all are coralline; the principal groups are the Marianas, the Marshalls, the Carolines, Kiribati (Gilbert Islands), and Tuvalu (Ellice Islands).


To the south of Micronesia lies Melanesia, which consists mostly of small coral islands. The region’s physiography is dominated by a group of large continental islands, however, including New Guinea. The principal Melanesian island groups are the Bismarck Archipelago, the Solomons, Vanuatu (New Hebrides), New Caledonia, và Fiji.

The immense area of Polynesia includes the Hawaiian Islands, the Phoenix Islands, Samoa, Tonga, the Cook Islands, the Society Islands, Tuamotu, và the Marquesas.

Geology

Evidence drawn from various geophysical fields—seismology, volcanology, gravimetry, and paleomagnetism (remanent magnetism)—points khổng lồ the general validity of the theory of plate tectonics. All the major physical features in the Pacific are understood to lớn originate in plate tectonics. The western Pacific arcs of volcanic islands và deep trenches are convergent zones where two plates are colliding, one being subducted (forced under the other). The East Pacific Rise is an active spreading centre where new crust is being created. The northeastern Pacific margin is the strike-slip zone where the American Plate and the Pacific Plate are gliding laterally past each other via the major San Andreas Fault system. In the southeastern Pacific, however, the Nazca Plate và the South American Plate are colliding to size the Andes Mountains along western South America and, a short distance offshore, the Peru-Chile Trench. The floor of the northeastern Pacific is remarkable for its several major fracture zones, which extend east and west & which, in some instances, are identifiable over distances of thousands of miles.

Of great geologic interest are the seamounts (submerged volcanoes), guyots (flat-topped seamounts), & oceanic islands of the Pacific. The numerous tropical islands of the Pacific are mainly coralline. The principal types of coral reefs—fringing, barrier, and atoll—as well as the guyots, which rise within the Pacific from the ocean floor in latitudes north and south of the tropics, are explained partially by the slow subsidence theory advanced by the English naturalist Charles Darwin during the 19th century and partially by the theory of plate tectonics.

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Climate

The wind và pressure systems of the Pacific conform closely to the planetary system—the patterns of air pressure & the consequent wind patterns that develop in the atmosphere of the Earth as a result of its rotation (Coriolis force) & the inclination of its axis (ecliptic) toward the Sun. They are, in essence, a three-celled latitudinal arrangement of the atmospheric circulation, with the systems in the Northern và Southern hemispheres mirroring each other on opposite sides of the Equator. The vast extent of open water in the Pacific influences wind & pressure patterns over it, and climatic conditions in the southern & eastern Pacific—where the steadiness of the trade winds & the westerlies is remarkable—are the most uniform on the globe. In the North Pacific, however, conditions are not so uniform, particularly the considerable climatic differences between the eastern và western regions in the same latitude. The rigour of the winters off the east coast of Russia, for instance, contrasts sharply with the relative mildness of winters in the region of British Columbia.