Pacific Ocean





The Pacific Ocean, the world's largest body of water, encompasses a third of
the Earth's surface, having an area of 179.7 million km2 (69.4 million sq mi).
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 east-west width at about 5 deg N latitude, where it
stretches approximately 19,800 km (12,300 mi) from Indonesia to the coast of
Colombia. The western limit of the ocean is often placed at the Strait of
Malacca. The lowest known point on the earth surface — the Marianas
Trench — lies within the Pacific.

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. See: List of islands in the Pacific Ocean.

Along the Pacific Ocean's irregular margins lie many seas, the largest of
which are the Celebes Sea, Coral Sea, East China Sea, Sea of Japan, Sulu
Sea, Tasman Sea and Yellow Sea. The Straits of Malacca joins the Pacific and
the Indian oceans on the west, and the Straits of Magellan links the Pacific
with the Atlantic Ocean on the east.

The Portuguese explorer Ferdinand Magellan named this ocean Pacific, which
mean peaceful. For most of his voyage from the Strait of Magellan to the
Philippines, Magellan indeed found the ocean peaceful. However, the Pacific
is not always peaceful. Many typhoons and hurricanes batter the islands of
the Pacific and the lands around the Pacific rim are full of volcanoes and
often rocked by earthquakes. Tsunamis, due to underwater earthquakes have
devastated many islands and wiped out whole towns.

Ocean bottom

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 irregularities in the
area are the extremely steep-sided, flat-topped submarine peaks known as
seamounts. The western part of the floor consists of mountain arcs that rise
above the sea as island groups, such as the Solomon Islands and New Zealand,
and deep 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 drains into the Pacific, and
because of the ocean's immense size, most sediments are authigenic or
pelagic in origin. Authigenic 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 characteristics

Water temperatures in the Pacific vary from freezing in the poleward areas
to about 29 degrees Celsius (84 degrees Fahrenheit) 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
Current, 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 Aleutian
Current branches as it approaches North America and forms the base of a
counterclockwise circulation in the Bering Sea. 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 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.

Climate

Only the interiors of the large land masses of Australia, New Guinea, and
New Zealand escape the pervasive climatic influence of the 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 latitudes, bringing marked seasonal differences
in temperature. Closer to the equator, where most of the islands lie,
steadily blowing trade winds allow for relatively constant temperatures
throughout the year of 21-27 degrees Celsius (70-81 degrees Fahrenheit).

The monsoon region lies in the far western Pacific between Japan and
Australia. Characteristic of this climatic region are winds that blow from
the continental interior to the ocean in winter and in the opposite
direction in summer. Consequently, a marked seasonality of cloudiness and
rainfall occurs. Typhoons often cause extensive damage in the west and
southwest Pacific. The greatest typhoon 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.

Geology

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 along the western edge of the Albatross 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 Australia and Asia--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 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.

Landmasses

The largest landmass in the Pacific Ocean 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 of the Pacific lie between 30 deg
north and 30 deg south latitude, extending from Southeast Asia to Easter
Island; the rest of the Pacific Basin is almost devoid of land. The great
triangle of Polynesia connecting Hawaii, Easter Island, and New Zealand
encompasses the island arcs and clusters of the Cook, Marquesas, Samoa,
Society, Tokelau, Tonga, and Tuamotu 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 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 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 Polynesians from Tahiti to Hawaii and 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 influence was paramount, with ships sailing from Spain to
the Philippines, New Guinea, and the Solomons. During the 17th century the
Dutch, sailing around southern Africa, dominated discovery and trade; Abel
Janszoon Tasman discovered (1642) Tasmania and New Zealand. 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 the Pacific by the Western powers. Significant contributions to
oceanographic knowledge were made by the voyages of the H.M.S. Beagle in the
1830s, with Charles Darwin aboard; the H.M.S. Challenger during the 1870s;
the U.S.S. Tuscarora (1873-76); and the German Gazelle (1874-76). Although
the United States took the Philippines in 1898, Japan controlled the western
Pacific by 1914, and occupied many other islands during World War II. By the
end of that war the U.S. Pacific Fleet was the virtual master of the ocean.

Seventeen independent nations are located in the Pacific: Australia, Fiji,
Japan, Kiribati, Marshall Islands, Micronesia, Nauru, New Zealand, Palau,
Papua New Guinea, the Philippines, Samoa, Solomon Islands, Republic of China
(Taiwan), Tonga, Tuvalu, and Vanuatu. Eleven of these nations have achieved
full independence since 1960. The Northern Mariana Islands are
self-governing with external affairs handled by the United States, and Cook
Islands and Niue are in similar relationships with New Zealand. Also within
the Pacific are the U.S. state of Hawaii and several island territories and
possessions of Australia, Chile, France, Japan, New Zealand, the United
Kingdom, and the United States.

The exploitation of the Pacific's mineral wealth is hampered by the ocean's
great depths. In shallow waters 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. 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. 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.