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PACIFIC OCEAN

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Originally appearing in Volume V20, Page 436 of the 1911 Encyclopedia Britannica.
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PACIFIC OCEAN , the largest See also:

division of the See also:hydrosphere, lying between See also:Asia and See also:Australia and See also:North and See also:South See also:America. It is nearly landlocked to the N., communicating with the See also:Arctic Ocean only by See also:Bering Strait, which is 36 m. wide and of small See also:depth. The See also:southern boundary is generally regarded as the parallel of 4o° S., but sometimes the See also:part of the See also:great Southern Ocean (400 to 661° S.) between the meridians passing through South Cape in See also:Tasmania and Cape See also:Horn is included. The north to south distance from Bering Strait to the See also:Antarctic circle is 9300 m., and the Pacific attains its greatest breadth, 10,000 m., at the See also:equator. The coasts of the Pacific are of varied See also:contour. The See also:American coasts are for the most part mountainous and unbroken, the See also:chief indentation being the Gulf of See also:California; but the See also:general type is departed from in the extreme north and south, the southern See also:coast of South America consisting of bays and fjords with scattered islands, while the coast of See also:Alaska is similarly broken in the south and becomes See also:low and swampy towards the north. The coast of Australia is high and unbroken; there are no inlets of considerable See also:size, although the small openings include some of the finest harbours in the See also:world, as Moreton See also:Bay and See also:Port See also:Jackson. The See also:Asiatic coasts are for the most part low and irregular, and a number of seas are more or less completely enclosed and cut off from communication with the open ocean. Bering See also:Sea is bounded by the Alaskan See also:Peninsula and the See also:chain of the Aleutian Islands; the sea of See also:Okhotsk is enclosed by the peninsula of See also:Kamchatka and the Kurile Islands; the Sea of See also:Japan is shut off by See also:Sakhalin See also:Island, the See also:Japanese Islands and the peninsula of See also:Korea; the Yellow Sea is an opening between the coast of See also:China and Korea; the China Sea lies between the Asiatic See also:continent and the island of See also:Formosa, the Philippine See also:group, Palawan and See also:Borneo. Amongst the islands of the See also:Malay See also:Archipelago are a number of endosed areas—the Sulu,. See also:Celebes, See also:Java, See also:Banda and Arafura seas. The Arafura Sea extends eastwards to Torres Strait, and beyond the strait is the See also:Coral Sea, bounded by New See also:Guinea, the islands of See also:Melanesia and north-eastern Australia.

The See also:

area and See also:volume of the Pacific Ocean and its seas, with the mean depths calculated therefrom, are given in the See also:article OCEAN. Extent. The Pacific Ocean has one and three-See also:quarter times the area of the See also:Atlantic—the next largest division of the hydrosphere—and has more than See also:double its volume of See also:water. Its area is greater than the whole See also:land See also:surface of the globe, and the volume of its See also:waters is six times that of all the land above sea-level. The See also:total land area draining to the Pacific is estimated by See also:Murray at 7,500,000 sq. m., or little more than one-See also:fourth of the area draining to the Atlantic. The American See also:rivers draining to the Pacific, except the See also:Yukon, See also:Columbia and See also:Colorado, are unimportant. The chief Asiatic rivers are the See also:Amur, the Hwang-ho and the Yangtsze-kiang: none of which enters the open Pacific directly. Hence the proportion of purely oceanic area to the total area is greater in the Pacific than in the Atlantic, the See also:supply of detritus being smaller, and See also:terrigenous deposits are not See also:borne so far from land. The See also:bed of the Pacific is not naturally divided into See also:physical regions, but for descriptive purposes the parts of the area lying See also:Relief oP See also:east and See also:west of 150 W. are conveniently dealt with Bed. separately. The eastern region is characterized by great uniformity of depth; the 2000-See also:fathom See also:line keeps See also:close to the American coast except off the See also:Isthmus of See also:Panama, whence an See also:ill-defined See also:ridge of less than 2000 fathoms runs south-westwards, and again off the coast of South America in about 4o° S., where a similar See also:bank runs west and unites with the former. The bank then continues south to the Antarctic Ocean, in about 12o° W. Practically the whole of the north-east Pacific is therefore more than 2000 fathoms deep, and the south-east has two roughly triangular spaces, including the greater part of the area, between 2000 and 3000 fathoms.

Notwithstanding this great See also:

average depth, the " deeps " or areas over 3000 fathoms are small in number and extent. Five small deeps are recognized along a line close to the coast of South 'America and parallel to it, in the depression enclosed by the two See also:banks mentioned—they extend from about 12° to 30° S.—and are named, from north to south, Milne-See also:Edwards deep, Krummel deep, See also:Bartholomew deep, See also:Richards deep and See also:Haeckel deep. In the north-east the deeps are again few and small, but they are quite irregularly distributed, and not near the land. East of 15o° W. the Pacific has few islands; the oceanic islands are volcanic, and coral formations are of course scanty. The most important group is the Galapagos Islands. The western Pacific is in See also:complete contrast to thb part just described. Depths of less than 2000 fathoms occur continuously on a bank extending from south-eastern Asia, on which stands the Malay Archipelago. This bank continues southwards to the Antarctic Ocean, expanding into a See also:plateau on which Australia stands, and a See also:branch runs eastwards and then southwards from the north-east of Australia through New See also:Zealand. The most considerable areas over 3000 fathoms are the See also:Aldrich deep, an irregular triangle nearly as large as Australia, situated to the east of New Zealand, in which a See also:sounding of 5155 fathoms was obtained by H.M.S. " See also:Penguin," near the See also:Tonga Islands: and the See also:Tuscarora deep, a See also:long, narrow trough See also:running immediately to the east of Kamchatka, the Kurile Islands and Japan. A long See also:strip within the Tuscarora deep forms the largest continuous area with a depth greater than 4000 fathoms. All the See also:rest of the western Pacific is a region of quite irregular contour.

The average depth varies from 1500 to 2500 fathoms, and from this level innumerable volcanic ridges and peaks rise almost or quite to the surface, their summits for the most part occupied by atolls and reefs of coral formation, while interspersed with these are depressions, mostly of small area, among which the deepest soundings recorded have been obtained. The See also:

United States See also:telegraph See also:ship " See also:Nero," while See also:surveying for a See also:cable between See also:Hawaii and the Philippines, sounded in 1900 the greatest depth yet known between Midway Islands and See also:Guam ((12 43 N., 145 49' E.) in 5269 fathoms, or almost exactly 6 m. The following table, showing the area of the See also:floor of the Pacific (to 4o° S.) and the volume of water at different levels, is due to See also:Sir J. Murray: : Fathoms. Areas. Volume. (sq. m.) (cub. m.) 0-100 3,379,700 6,128,500 See also:loo-500 1,753,450 23,348,350 500-1000 1,707,650 28,323,700 1000-2000 6,902,550 52,628,500 2000-3000 39,621,550 32,545,400 3000-4000 2,164,150 1.357,900 over 4000 94,850 70,600 55,623,900 144,402,950 So far as our knowledge goes, the See also:present contours of the open Pacific Ocean are almost as they. were in Palaeozoic times, and in the intervening ages changes of level and See also:form have been slight. There is no See also:reason to suppose that any considerable part of the vast area now covered by the waters of the Pacific has ever been exposed as dry land. Hence the Pacific See also:basin may be regarded as a See also:stable and homogeneous See also:geographical unit, clearly marked off See also:round nearly all its margin by steep See also:sharp slopes, extending in places through the whole known range of See also:elevation above sea-level and of depression below it—from the Cordilleras of South America to the island chains of See also:Siberia and Australia. (See OCEAN.) The deeper parts of the bed of the Pacific are covered by deposits of red See also:clay, which occupies an area estimated at no less than 105,672,000 sq. kilometres, or three-fifths of the Deposits. whole. Over a large part of the central Pacific, far removed from any possible land-influences or deposits of See also:ooze, the red-clay region is characterized by the occurrence of See also:manganese, which gives the clay a See also:chocolate See also:colour, and manganese nodules are found in vast See also:numbers, along with sharks' See also:teeth and the See also:ear-bones and other bones of whales. Radiolarian ooze is found in the central Pacific in a region between 15° N. to 10° S. and 140° E. to 15o° W., occurring in seven distinct localities, and covering an area of about 3,007,000 sq. kilometres.

The " Challenger " discovered an area of radiolarian ooze between 7°-12° N. and 147°-152° W., and another in 2°-I0° S., 152°-153° W. Between these two areas, almost on the equator, a strip of See also:

globigerina ooze was found, corresponding to the See also:zone of globigerina in the See also:equatorial region of the Atlantic. Globigerina ooze covers considerable areas in the intermediate depths of the west and south Pacific—west of New Zealand, and along the parallel of 4o° S., between 8o°-98° W. and 15o°-118° W.—but this See also:deposit is not known in the north-eastern part of the basin. The total area covered by it is estimated at 38,332,000 sq. kilometres—about two-thirds of that in the Atlantic. Pteropod ooze occurs only in the neighbourhood of See also:Fiji and other islands of the western Pacific, passing up into See also:fine coral sands and mud. Diatom ooze has been found in detached areas between the Philippine and See also:Mariana islands, and near the Aleutian and Galapagos See also:groups, forming an exception to the general See also:rule of its occurrence only in high latitudes. All the enclosed seas are occupied by characteristic terrigenous deposits. Partly on See also:account of its great extent, and partly because there is no wide opening to the Arctic regions, the normal See also:wind circulation is on the whole less modified in the North Pacific than in Meteorothe Atlantic, except in the west, where the south-west logy. See also:monsoon of southern Asia controls the prevailing winds, its See also:influence extending eastwards to 145° E., near the Ladrones, and southwards to the equator. In the South Pacific the north-west monsoon of Australia affects a See also:belt running east of New Guinea to the See also:Solomon Islands. In the east the north-east See also:trade-belt extends between 5° and 25° N.; the south-east trade crosses the equator, and its mean southern limit is 25° S. The trade-winds are generally weaker and less persistent in the Pacific than in the Atlantic, and the intervening belt of equatorial calms is broader.

Except in the east of the Pacific, the south-east trade is only fully See also:

developed during the southern See also:winter; at other seasons the See also:regular trade-belt is cut across from north-west to south-east by a See also:band twenty to See also:thirty degrees wide, in which the trades alternate with winds from north-east and north, and with calms, the calms prevailing chiefly at the boundary of the monsoon region (5° N.-15° S., 16o°-185 E.). This area, in which the south-east trade is interrupted, includes the Fiji, Navigator and Society groups, and the Paumotus. In the See also:Marquesas group the trade-wind is See also:constant. Within the southern monsoon region there is a See also:gradual transition to the north-west monsoon of New Guinea in low latitudes, and in higher latitudes to the north-east wind of the See also:Queensland coast. The great warming and abundant rainfall of the island regions of the western Pacific, and the low temperature of the surface water in the east, cause a displacement of the southern tropical maximum of pressure to the east; hence we have a permanent " South Pacific See also:anticyclone " close to the coast of South America. The characteristic feature of the south-western Pacific is therefore the relatively low pressure and the existence of a true monsoon region in the See also:middle of the trade-wind belt. It is to be noted that the See also:climate of the islands of the Pacific becomes more and more healthy the farther they are from the monsoon region. The island regions of the Pacific are every-where characterized by See also:uniform high See also:air-temperatures; the mean See also:annual range varies from 1° to 9° F., with extremes of 24° to 27°, and the diurnal range from 9° to 16°. In the monsoon region relative humidity is high, viz. 8o to 90%. The rainfall is abundant; in the western island groups there is no well-marked See also:rainy See also:season, but over the whole region the greater part of the rainfall takes See also:place during the southern summer, even as far north as Hawaii. In the trade-wind region we find the characteristic heavy rainfall on the See also:weather sides of the islands, and a shorter rainy season at the season of highest See also:sun on the See also:lee See also:side.

See also:

Buchan describes the island-studded portion of the western Pacific as the most extensive region of the globe characterized by an unusually heavy rainfall. Beyond the tropical high-pressure belt, the winds of the North Pacific are under the See also:control of an area of low pressure, which, however, attains neither the size nor the intensity of the See also:Iceland " depression in the north Atlantic. The result is that north-See also:westerly winds, which in winter are exceedingly dry and See also:cold, See also:blow over the western or Asiatic area; westerly winds prevail in the centre, and south-westerly and southerly winds off the American coast. In the southern hemisphere there is a transition to the low-pressure belt encircling the Southern Ocean, in which westerly and north-westerly winds continue all the See also:year round. The See also:distribution of temperature in the waters of the Pacific Ocean has been fully investigated, so far as is possible with the existing Temperature. observations, by G. Schott. At the surface an extensive area of maximum temperature (over 20 C.) occurs over to° on each side of the equator to the west of the ocean. On the eastern side temperature falls to 22° on the equator and is slightly higher to N. and S. In the North Pacific, beyond See also:lat. 40°, the surface is generally warmer on the E. than on the W., but this See also:condition is, on the whole, reversed in corresponding southern latitudes. In the intermediate levels, down to depths not exceeding moo metres, a remarkable distribution appears. A narrow strip of cold water runs along the equator, widest to the east and narrowing westward, and separates two areas of maximum which have their greatest intensity in the western part of the ocean, and have their central portions in higher latitudes as depth increases, apparently tending constantly to a position in about See also:latitude 30° to 35° N. and S.

A comparison of this distribution with that of atmospheric pressure is of great See also:

interest. High temperature in the depth may be taken to mean descending water, just as high atmospheric pressure means descending air, and hence it would seem that the slow See also:vertical See also:movement of water in the Pacific reproduces to some extent the phenomena of the " See also:doldrums " and " See also:horse latitudes," with this difference, that the centres of maximum intensity See also:lie off the east of the land instead of the west as in the See also:case of the continents. The isothermal lines, in fact, suggest that in the vast area of the Pacific something corresponding to the " planetary circulation "' is established, further investigation of which may be of extreme value in relation to current inquiries concerning the upper air. In the greater depths temperature is extraordinarily uniform, 80 % of the existing observations falling within the limits of 1•6° C. and i•9° C. In the enclosed seas of the western Pacific, temperature usually falls till a depth corresponding to that of the See also:summit of the barriers which isolate them from the open ocean is reached, and below that point temperature is uniform to the bottom. In the Sulu Sea, for example, a temperature of io•3° C. is reached at 400 fathoms, and this remains constant to the bottom in 2500 fathoms. The surface waters of the North Pacific are relatively fresh, the salinity being on the whole much See also:lower than in the other great salinity. oceans. The saltest waters are found along a belt extend- See also:ing westwards from the American coast on the Tropic of See also:Cancer to 16o° E., then turning southwards to the equator. North of this salinity diminishes steadily, especially to the north-west, the Sea of Okhotsk showing the lowest salinity observed in any part of the globe. South and east of the See also:axis mentioned salinity becomes less to just north of the equator, where it increases again, and the saltest waters of the whole Pacific are found, as we should expect, in the south-east trade-wind region, the maximum occurring in about 18° S. and 120° W. South of the Tropic of Capricorn the isohalines run nearly east and west, salinity diminishing quickly to the Southern Ocean. The bottom waters have almost uniformly a salinity of 34.8 per mille, corresponding closely with the bottom waters of the South Atlantic, but fresher than those of the North Atlantic.

The surface currents of the Pacific have not been studied in the same detail as those of the Atlantic, and their seasonal See also:

variations Ciradatlon. are little known except in the monsoon regions. Speak- ing generally, however, it may be said that they are for the most part under the See also:direct control of the prevailing winds. The North Equatorial Current is due to the See also:action of the north-east trades. It splits into two parts east of the Philippines, one division flowing northwards as the Kuro Siwo or See also:Black Stream, the analogue of the Gulf Stream, to feed a See also:drift circulation which follows the winds of the North Pacific, and finally forms the See also:Cali- fornian Current flowing southwards along the American coast. Part of this rejoins the North Equatorial Current, and part probably forms the variable Mexican Current, which follows the coasts of See also:Mexico and California close to the land. • The Equatorial See also:Counter- Current flowing eastwards is largely assisted during the latter See also:half of the year by the south-west monsoon, and from See also:July to See also:October the south-west winds prevailing east of 150° E. further strengthen the current, but later in the year the easterly winds weaken or even destroy it. The South Equatorial Current is produced by the south- east trades, and is more vigorous than its See also:northern counterpart. On reaching the western Pacific part of this current passes south- wards, east of New Zealand, and again east of Australia, as the East Australian Current, part northwards to join the Equatorial Counter- Current, and during the north-east monsoon part makes its way through the China Sea towards the See also:Indian Ocean. During the south-west monsoon this last branch is reversed, and the surface waters of the China Sea probably unite with the Kuro Biwo. Between the Kuro Siwo and the Asiatic coast a band of cold water, with a slight movement to the southward, known as the Oya Siwo, forms the analogue of the " Cold See also:Wall " of the Atlantic. In the higher latitudes of the South Pacific the surface movement forms part of the west wind-drift of the Roaring Forties. On the west coast of South America the cold waters of the See also:Humboldt or Peruvian Current corresponding to the Benguela Current of the South Atlantic, make their way northwards, ultimately joining the South Equatorial Current.

The surface circulation of the Pacific is, on the whole, less active than that of the Atlantic. The centres of the rotational movement are marked by " Sargasso Seas " in the north and south basins, but they are of small extent compared with the Sargasso Sea of the North Atlantic. From the known peculiarities of the distribution of temperature, it is' probable that definite circulation of water is in the Pacific confined to levels very near the surface, except in the region of the Kuro Siwo, and possibly also in parts of the Peruvian Current. The only movement in the depths is the slow creep of See also:

ice-cold water northwards along the bottom from the Southern Ocean; but this is more marked, and apparently penetrates farther north, than in the Atlantic. See Reports of expeditions of the U.S.S. " See also:Albatross " and " See also:Thetis," 1888—1892; A.

End of Article: PACIFIC OCEAN

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