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Where is the Pacific Ocean located?
The Pacific Ocean is a body of salt water extending from the Antarctic region in the south to the Arctic in the north and lying between the continents of Asia and Australia on the west and North America and South America on the east.
How far from north to south does the Pacific Ocean extend?
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).
What is the temperature of the deep zone of the Pacific Ocean?
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).
What is the salinity of the Pacific Ocean?
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.
What is the deepest region of the Pacific Ocean?
TheMariana Trench, also called the Marianas Trench, is a deep-sea trench in the floor of the western North Pacific Ocean, and 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.
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Pacific Ocean, body ofsalt water extending from the 60°S parallel in the south to theArctic in the north and lying between the continents ofAsia andAustralia on the west andNorth America andSouth America on the east.
Of the three major oceans, the Pacific is by far the largest, occupying about one-third of the surface of the globe. Its area, excluding the South China Sea,encompasses about 62.5 million square miles (161.76 million square km). It has double the area and more than double the water volume of theAtlantic Ocean—the next largest division of the hydrosphere—and its area more than exceeds that of the whole land surface of the globe. The Pacific Ocean stretches from theBering Strait to 60° S latitude through more than 120° of latitude, nearly 9,000 miles (about 14,500 km). Its greatest latitudinal extent measures some 12,000 miles (about 19,000 km) along latitude 5° N, between the coasts ofColombia in South America and theMalay Peninsula in Asia. The mean depth of the Pacific (excludingadjacent seas) is 14,040feet (4,280 metres), and its greatest known depth is 36,201 feet (11,034 metres)—in theMariana Trench—also the greatest depth found in any ocean.
In the Northern Hemisphere the Pacific Ocean meets theArctic Ocean in the Bering Sea. In the Southern Hemisphere the Pacific and Atlantic mix in the relatively narrowDrake Passage betweenTierra del Fuego in South America andGraham Land inAntarctica, and the Pacific Ocean and theSouthern Ocean meet at the 60° S parallel. The separation between the Pacific andIndian oceans is less distinct, but generally it is considered to lie along the line of islands extending eastward fromSumatra, throughJava toTimor, thence across theTimor Sea to Cape Londonderry in Australia. To the south of Australia the boundary extends across theBass Strait and thence fromTasmania to 60° S.
Because of the pattern of major mountain systems of the globe, a relatively small proportion (one-seventh) of the total continentaldrainage 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 ofChina andSoutheast Asia are of the greatest importance; thebasins of those rivers support more than one-fourth of the world’s population.
The eastern boundary of the Pacific is associated with theAmerican cordilleran system, which stretches fromAlaska in the north to Tierra del Fuego in the south. Except for its extreme northern and southern sections, which are characterized byfjords and their numerous off-lying islands, and except for the deeply indentedGulf of California, the coastal boundary is relatively regular and thecontinental shelf narrow. The western, or Asiatic, coastal boundary, in contrast, is irregular. Although the mountain systems there lie roughly parallel to the coast, as they do on the eastern Pacific coastlands, the western Pacific is noted for its many marginal seas. From north to south they include the Bering Sea, theSea of Okhotsk, theSea of Japan (East Sea), theYellow Sea, theEast China Sea, and theSouth China Sea. Their eastern boundaries are formed by southward-jutting peninsulas orisland arcs or both. It is of oceanographic significance that the great rivers of eastern Asia—including theAmur, theHuang He (Yellow River), theYangtze, theXi andPearl (Zhu), and theMekong—enter the Pacific indirectly by way of themarginal seas.
This article treats the physical and human geography of the Pacific Ocean. For discussion of the physical and chemical oceanography andmarine geology of the Pacific,seeocean.
Physiography
Relief
The Pacific basin may conveniently be divided into three major physiographic regions: the eastern, western, and central Pacific regions.
Eastern region
The eastern Pacific region, which extends southward from Alaska to Tierra del Fuego, is relatively narrow and 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 and South America. The continental shelf, which runs parallel to it, is narrow, while theadjacentcontinental slope is very steep. Significantoceanic trenches in this region are theMiddle America Trench in the North Pacific and thePeru-Chile Trench in the South Pacific.
Western region
The seaward boundary of the western Pacific region is marked by a broken line of oceanic trenches, extending from theAleutian Trench in the north through theKuril andJapan trenches and southward to theTonga andKermadec trenches, terminating close to the northeast ofNorth Island,New Zealand. Its structure is more complex than that of the eastern region. Characteristically associated with the ocean trenches of the western region are festoons of either peninsulas or islands or both. The islands, which include those ofJapan as well as numerous smaller islands, represent the upper parts of mountain systems that rise abruptly from the deep ocean floor. The islandclusters of the western Pacific form the boundaries of the several wide and deep continental seas of the region.
Central region
The central Pacific region lies between the boundaries of the eastern and western regions. The largest and the most geologically stable of the structural provinces of theEarth’s crust, it is characterized by expansive areas oflow relief, lying at a general depth of about 15,000 feet (4,600 metres) below the surface.
Principalridges andbasins
To the east of longitude 150° W, the relief of the ocean floor is considerably less pronounced than it is to the west. In the eastern Pacific theCocos Ridge extends southwestward from the Central American isthmus to theGalapagos Islands. To the south of the Galapagos lies the PeruBasin, which is separated by the extensive Sala y Gómez Ridge from theSoutheast Pacific Basin, which in turn is separated from the Southwest Pacific Basin by theEast Pacific Rise and indeterminate Pacific-Antarctic Ridge, which runs from the Sala y Gómez Ridge to Antarctica in the vicinity of 150° W.
Extending southward from theTasman Basin (between New Zealand and eastern Australia) is theMacquarie Ridge, which forms a major boundary between the deep waters of the Pacific and Indian oceans. TheHawaiian Ridge extends westward fromHawaii to the 180° meridian.
The submerged parts of the series of ridges that are capped by the islandarchipelagoes of the western Pacific are continuous and 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 theKuril,Bonin, andMariana island groups, and the archipelagoes ofYap andPalau; those extending eastward fromNew Guinea, including theBismarck Archipelago and theSolomon andSanta Cruz island chains; and, finally, the ridges extending southward, from which rise theSamoa,Tonga,Kermadec, andChatham island groups, as well asMacquarie Island.
Bottom deposits
Apart from the narrow coastal zone of the eastern region and the broad continental seas of the western region, the Pacific is floored withpelagic (oceanic) material derived from the remains of marine plants and animals that once inhabited the waters lying above. Red or brownradiolarianooze is found along the zone of the Pacific NorthEquatorial Current, east of longitude 170° W, and on the floors of some deep Indonesian basins. A belt ofdiatom ooze occurs between latitudes 45° and 60° S and across the North Pacific, between Japan and Alaska.Calcareous globigerina ooze occurs in the shallower parts of the South Pacific, the dissolving power of the seawater at great depths being sufficient to dissolve calcareous material to 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 and diatom ooze, is found at greater depths, but even these siliceous remains aredissolved at very great depths, where the characteristic deposit isred clay. Red clay, which covers no less than half of the Pacific floor, is believed to be formed of colloidal (extremely finely divided) clays derived essentially from the land.
On theabyssal plains, where sediments accumulate slowly, chemical and biological processes lead to the formation of metal-bearing coatings around objects such as the ear bones of fishes. Thenodules so formed contain manganese, iron, nickel, copper, cobalt, and traces of other metals such as platinum. They cover large areas of the ocean floor in the Pacific. Similar processes form coatings, called manganese crusts, on the rock surfaces ofseamounts.
Among the many different forms of land-derived muds (formed by the erosive action of rivers, tides, and currents) that floor the continental shelves and slopes of the Pacific, the yellow mud of theYellow Sea is of particular interest. The mud isconveyed to the seabed by the Huang He, which drains a vast area of northern China blanketed withloess, a fine-grained soil.
Islands
The islands of the western region—including theAleutians, the Kurils, theRyukyus,Taiwan, theMalay Archipelago (including New Guinea), and New Zealand—are continental in character. Geologically, they consist partly ofsedimentary 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 and the numerous truly oceanic, or “low,” islands of the Pacific is theAndesite Line, a region of intense volcanic and seismic activity. In the northern and western Pacific the Andesite Line follows close to seaward thetrend of the island arcs from the Aleutians southward to the Yap and Palau arcs, thence eastward through the Bismarck, Solomon, and Santa Cruz archipelagoes, and thence southward through theSamoa, Tonga, and Chatham groups and Macquarie Island to Antarctica. Islands to the west of the line are rich inandesite, a type of intrusive igneous rock; islands to the east (oceanic side) of it are essentially ofbasalt, anextrusive igneous rock.
The numerous oceanic islands of the Pacific are unevenly distributed. They lie, in the main, between the Tropics of Cancer and Capricorn and occur in great numbers in the western Pacific. The northernmost chain of oceanic islands is associated with theHawaiian Ridge. The Hawaiianarchipelago consists of about 2,000 islands, although the term Hawaiian Islands is usually applied to the small group that lies at the eastern end of the archipelago.
The numerous small islands ofMicronesia lie mainly north of theEquator and to the west of the 180° meridian. Nearly all are coralline; the principal groups are the Marianas, theMarshalls, theCarolines,Kiribati (Gilbert Islands), andTuvalu (Ellice Islands).
To the south of Micronesia liesMelanesia, which consists mostly of smallcoral 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, andFiji.
Theimmense area ofPolynesia includes the Hawaiian Islands, thePhoenix Islands, Samoa, Tonga, theCook Islands, theSociety Islands,Tuamotu, and theMarquesas.
Geology
Evidence drawn from various geophysical fields—seismology,volcanology, gravimetry, and paleomagnetism (remanent magnetism)—points to the general validity of the theory ofplate tectonics. All the major physical features in the Pacific are understood to originate in plate tectonics. The western Pacific arcs of volcanic islands and deep trenches are convergent zones where two plates are colliding, one being subducted (forced under the other). The East Pacific Rise is an activespreading 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 majorSan Andreas Fault system. In the southeastern Pacific, however, theNazca Plate and the South American Plate are colliding to form theAndes 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 majorfracture zones, which extend east and west and which, in some instances, are identifiable over distances of thousands of miles.
Of great geologic interest are theseamounts (submerged volcanoes),guyots (flat-topped seamounts), andoceanic islands of the Pacific. The numerous tropical islands of the Pacific are mainly coralline. The principal types ofcoral reefs—fringing,barrier, andatoll—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 theslowsubsidence theory advanced by the English naturalistCharles Darwin during the 19th century and partially by the theory of plate tectonics.
Climate
The wind and pressure systems of the Pacific conform closely to theplanetary system—the patterns of air pressure and the consequent wind patterns that develop in the atmosphere of the Earth as a result of its rotation (Coriolis force) and theinclination of its axis (ecliptic) toward the Sun. They are, in essence, a three-celled latitudinal arrangement of theatmospheric circulation, with the systems in the Northern and Southern hemispheres mirroring each other on opposite sides of the Equator. The vast extent of open water in the Pacific influences wind and pressure patterns over it, and climatic conditions in the southern and eastern Pacific—where the steadiness of thetrade winds and 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 and western regions in the same latitude. The rigour of the winters off the east coast ofRussia, for instance, contrasts sharply with the relative mildness of winters in the region ofBritish Columbia.