the Earth’s surface. Extending approximately 15,500 km (9,600 mi)
from the BERING SEA in the Arctic north to the icy margins of
Antarctica’s Ross Sea in the south, the Pacific reaches its greatest
western limit of the ocean is often placed at the Strait of Malacca. The
the rest of the world’s oceans combined), almost all of which are found
south of the equator. The Pacific covers an area of 179.7 million sq km
(69.4 million sq mi). The lowest known point on Earth, in the
MARIANAS TRENCH, lies within the Pacific.
Along the Pacific Ocean’s irregular margins lie many seas, the largest
of which are the CELEBES SEA, CORAL SEA, East China Sea, Sea
The ocean floor of the central Pacific basin is relatively uniform, with a mean depth of about 4,270 m (14,000 ft). The major
trenches, such as the Marianas Trench, the Philippine Trench, and the Tonga Trench. Most of the deep trenches lie adjacent to the
outer margins of the wide western Pacific continental shelf.
Along the eastern margin of the Pacific basin is the East Pacific Rise, which is a part of the worldwide mid-oceanic ridge. About
3,000 km (1,800 mi) across, the rise stands about 3 km (2 mi) above the adjacent ocean floor. Because a relatively small land area
sediments include montmorillonite and phillipsite. Pelagic sediments derived from seawater include pelagic red clays and the skeletal
remains of sea life. Terrigenous sediments are confined to narrow marginal bands close to land.
Water temperatures in the Pacific vary from freezing in the poleward areas to about 29 deg C (84 deg F) near the equator. Salinity
also varies latitudinally. 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 areas.
The surface circulation of Pacific waters is generally clockwise in the Northern Hemisphere and counterclockwise in the Southern
Hemisphere. The North Equatorial Current, driven westward along latitude 15 deg north by the trade winds, turns north near the
Philippines to become the warm Kuroshio, or Japan, Current. Turning eastward at about 45 deg north, the Kuroshio forks and some
waters move northward as the ALEUTIAN CURRENT, while the rest turn southward to rejoin the North Equatorial Current. The
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 deg
south latitude, and joins the main westerly circulation of the Southern Pacific, which includes the Earth-circling Antarctic Circumpolar
turns north to form the Peru, or Humboldt, Current.
Pacific. Within the area of the Pacific, five distinctively different climatic regions exist: the mid-latitude westerlies, the trades, the
monsoon region, the typhoon region, and the doldrums. Mid-latitude westerly air streams occur in both northerly and southerly
trade winds allow for relatively constant temperatures throughout the year of 21-27 deg C (70-81 deg F).
The monsoon region lies in the far western Pacific between Japan and Australia. Characteristic of this climatic region are winds that
frequency exists within the triangle from southern Japan to the central Philippines to eastern Micronesia. Although more poorly
defined than the other climatic regions, two major doldrum areas lie within the ocean, one located off the western shores of Central
America and the other within the equatorial waters of the western Pacific. Both areas are noted for their high humidity, considerable
cloudiness, light fluctuating winds, and frequent calms.
The Andesite Line is the most significant regional distinction in the Pacific. It separates the deeper, basic igneous rock of the Central
Pacific Basin from the partially submerged continental areas of acidic 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. The dissimilarity continues northeastward
Indonesia, the Philippines, Japan, New Guinea, and New Zealand–all eastward extensions of the continental blocks of Australia and
Asia–lie outside the Andesite Line.
islands that characterize the Central Pacific Basin. It is here that 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 so-called Pacific rim of fire is the world’s foremost belt of explosive volcanism.
The largest landmass in the Pacific is the continent of Australia, which is approximately equal in size to the 48 contiguous U.S.
states. About 3,200 km (2,000 mi) southeast of Australia is the large island group of New Zealand. Almost all of the smaller islands
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,
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 the 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
HISTORY AND ECONOMY
New Zealand. The ocean was sighted by Europeans early in the 16th century, first by Vasco Nunez de Balboa (1513) and then by
Ferdinand Magellan, who crossed the Pacific during his circumnavigation (1519-22). For the remainder of the 16th century Spanish
Growing imperialism during the 19th century resulted in the occupation of much of the Pacific by the Western powers. Significant
Fleet was the virtual master of the ocean.
Fourteen independent nations are located in the Pacific: Kiribati, Nauru, Papua New Guinea, Taiwan, Tuvalu, Western Samoa,
Australia, Fiji, Japan, New Zealand, the Philippines, the Solomon Islands, Tonga, and Vanuatu. Eight of these nations have achieved
relationships with the United States. Also within the Pacific are the U.S. state of Hawaii and several island territories and
The exploitation of the Pacific’s mineral wealth is hampered by the ocean’s great depths. In shallow waters off the coast of Australia,
petroleum and natural gas are extracted, and pearls are harvested along the coasts of Australia, Japan, Papua New Guinea,
waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as
shellfish. In 1986, the member nations of the South Pacific Forum declared the area a nuclear-free zone in an effort to halt nuclear
testing and prevent the dumping of nuclear waste there.
Paradise Found and Lost (1988); Terrell, J.E., Prehistory in the Pacific Islands (1986).