Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south and is bounded by Asia and Australia in the west and the Americas in the east.

At 165.25 million square kilometers (63.8 million square miles) in area, this largest division of the World Ocean â€" and, in turn, the hydrosphere â€" covers about 46% of the Earth's water surface and about one-third of its total surface area, making it larger than all of the Earth's land area combined. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific. The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 metres (35,797 ft).

The eastern Pacific Ocean was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur. The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favourable winds on reaching the ocean. He therefore called it Mar Pacifico in Portuguese, meaning "peaceful sea".

History

Early migrations

Important human migrations occurred in the Pacific in prehistoric times. About 3000 BC, the Austronesian peoples on the island of Taiwan mastered the art of long-distance canoe travel and spread themselves and their languages south to the Philippines, Indonesia, and maritime Southeast Asia; west towards Madagascar; southeast towards New Guinea and Melanesia (intermarrying with native Papuans); and east to the islands of Micronesia, Oceania and Polynesia.

Long-distance trade developed all along the coast from Mozambique to Japan. Trade, and therefore knowledge, extended to the Indonesian islands but apparently not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of this trade was controlled by Arabs or Muslims. In 219 BC Xu Fu sailed out into the Pacific searching for the elixir of immortality. From 1404 to 1433 Zheng He led expeditions into the Indian Ocean.

European exploration

The first contact of European navigators with the western edge of the Pacific Ocean was made by the Portuguese expeditions of António de Abreu and Francisco Serrão to the Maluku Islands in 1512, and with Jorge Álvares's expedition to southern China in 1513, both ordered by Afonso de Albuquerque.

The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and reached a new ocean. He named it Mar del Sur (literally, "Sea of the South" or "South Sea") because the ocean was to the south of the coast of the isthmus where he first observed the Pacific.

Later, Portuguese explorer Ferdinand Magellan sailed the Pacific on a Spanish expedition of world circumnavigation from 1519 to 1522. Magellan called the ocean Pacífico (or "Pacific" [meaning, "peaceful"]) because, after sailing through the stormy seas off Cape Horn, he was surprised at how calm the waters became. Although Magellan himself died in the Philippines in 1521, Spanish navigator Juan Sebastián Elcano led the expedition back to Spain across the Indian Ocean and round the Cape of Good Hope, completing the first world circumnavigation in 1522. Sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands and Papua New Guinea. In 1542â€"43 the Portuguese also reached Japan.

In 1564, five Spanish ships consisting of 379 explorers crossed the ocean from Mexico led by Miguel López de Legazpi and sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Mexico and Peru across the Pacific Ocean to the Philippines, via Guam, and establishing the Spanish East Indies. The Manila galleons operated for two and a half centuries linking Manila and Acapulco, in one of the longest trade routes in history. Spanish expeditions also discovered Tuvalu, the Marquesas, the Solomon Islands, and New Guinea in the South Pacific.

Later, in the quest for Terra Australis (i.e., "the [great] Southern Land"), Spanish explorers in the 17th century discovered the Pitcairn and Vanuatu archipelagos, and sailed the Torres Strait between Australia and New Guinea, named after navigator Luís Vaz de Torres. Dutch explorers, sailing around southern Africa, also engaged in discovery and trade; Abel Janszoon Tasman discovered Tasmania and New Zealand in 1642. The 18th century marked the beginning of major exploration by the Russians in Alaska and the Aleutian Islands. Spain also sent expeditions to the Pacific Northwest reaching Vancouver Island in southern Canada, and Alaska. The French explored and settled Polynesia, and the British made three voyages with James Cook to the South Pacific and Australia, Hawaii, and the North American Pacific Northwest. In 1768, Pierre-Antoine Véron, a young astronomer accompanying Louis Antoine de Bougainville on his voyage of exploration, established the width of the Pacific with precision for the first time in history. One of the earliest voyages of scientific exploration was organized by Spain in the Malaspina Expedition of 1789â€"1794. It sailed vast areas of the Pacific, from Cape Horn to Alaska, Guam and the Philippines, New Zealand, Australia, and the South Pacific.

In the 16th and 17th century Spain considered the Pacific Ocean a Mare clausum â€" a sea closed to other naval powers. As the only known entrance from the Atlantic the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western end of the Pacific Ocean the Dutch threatened the Spanish Philippines.

New Imperialism

Growing imperialism during the 19th century resulted in the occupation of much of Oceania by other European powers, and later, Japan and the United States. Significant contributions to oceanographic knowledge were made by the voyages of HMS Beagle in the 1830s, with Charles Darwin aboard; HMS Challenger during the 1870s; the USS Tuscarora (1873â€"76); and the German Gazelle (1874â€"76).

In Oceania, France got a leading position as imperial power after making Tahiti and New Caledonia protectorates in 1842 and 1853 respectively. After navy visits to Easter Island in 1875 and 1887, Chilean navy officer Policarpo Toro managed to negotiate an incorporation of the island into Chile with native Rapanui in 1888. By occupying Easter Island, Chile joined the imperial nations. By 1900 nearly all Pacific islands were in control of Britain, France, United States, Germany, Japan, and Chile.

Although the United States gained control of Guam and the Philippines from Spain in 1898, Japan controlled most of the western Pacific by 1914 and occupied many other islands during World War II. However, by the end of that war, Japan was defeated and the U.S. Pacific Fleet was the virtual master of the ocean. Since the end of World War II, many former colonies in the Pacific have become independent states.

Geography

The Pacific separates Asia and Australia from the Americas. It may be further subdivided by the equator into northern (North Pacific) and southern (South Pacific) portions. It extends from the Antarctic region in the South to the Arctic in the north. The Pacific Ocean encompasses approximately one-third of the Earth's surface, having an area of 165.2 million square kilometers (63.8 million square miles) â€"significantly larger than Earth's entire landmass of some 150 million square kilometers (58 million square miles).

Extending approximately 15,500 kilometers (9,600 mi) from the Bering Sea in the Arctic to the northern extent of the circumpolar Southern Ocean at 60°S (older definitions extend it to Antarctica's Ross Sea), the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800 kilometers (12,300 mi) from Indonesia to the coast of Colombia â€" halfway around the world, and more than five times the diameter of the Moon. The lowest known point on Earthâ€"the Mariana Trenchâ€"lies 10,911 meters (35,797 ft or 5,966 fathoms) below sea level. Its average depth is 4,280 meters (14,040 ft or 2,333 fathoms), putting the total water volume at 710,000,000 cubic kilometers.

Due to the effects of plate tectonics, the Pacific Ocean is currently shrinking by roughly an inch per year (2â€"3 cm/yr) on three sides, roughly averaging 0.2 square miles (0.52 km²) a year. By contrast, the Atlantic Ocean is increasing in size.

Along the Pacific Ocean's irregular western margins lie many seas, the largest of which are the Celebes Sea, Coral Sea, East China Sea, Philippine Sea, Sea of Japan, South China Sea, Sulu Sea, Tasman Sea, and Yellow Sea. The Strait of Malacca joins the Pacific and the Indian Oceans on the west, and Drake Passage and the Strait of Magellan link the Pacific with the Atlantic Ocean on the east. To the north, the Bering Strait connects the Pacific with the Arctic Ocean.

As the Pacific straddles the 180th meridian, the West Pacific (or western Pacific, near Asia) is in the Eastern Hemisphere, while the East Pacific (or eastern Pacific, near the Americas) is in the Western Hemisphere.

For most of Magellan's voyage from the Strait of Magellan to the Philippines, the explorer indeed found the ocean peaceful. However, the Pacific is not always peaceful. Many tropical storms batter the islands of the Pacific. The lands around the Pacific Rim are full of volcanoes and often affected by earthquakes. Tsunamis, caused by underwater earthquakes, have devastated many islands and in some cases destroyed entire towns.

The Martin Waldseemüller map of 1507 was the first to show the Americas separating two distinct oceans. Later, the Diogo Ribeiro map of 1529 was the first to show the Pacific at about its proper size.

Bordering countries and territories

Sovereign nations

¹ The status of Taiwan is disputed. For more information, see political status of Taiwan.

Territories

Landmasses and islands

The islands entirely within the Pacific Ocean can be divided into three main groups known as Micronesia, Melanesia and Polynesia. Micronesia, which lies north of the equator and west of the International Date Line, includes the Mariana Islands in the northwest, the Caroline Islands in the center, the Marshall Islands to the west and the islands of Kiribati in the southwest.

Melanesia, to the southwest, includes New Guinea, the world's second largest island after Greenland and by far the largest of the Pacific islands. The other main Melanesian groups from north to south are the Bismarck Archipelago, the Solomon Islands, Santa Cruz, Vanuatu, Fiji and New Caledonia.

The largest area, Polynesia, stretching from Hawaii in the north to New Zealand in the south, also encompasses Tuvalu, Tokelau, Samoa, Tonga and the Kermadec Islands to the west, the Cook Islands, Society Islands and Austral Islands in the center, and the Marquesas Islands, Tuamotu, Mangareva Islands and Easter Island to the east.

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. Some of these islands are structurally associated with nearby continents. High islands are of volcanic origin, and many contain active volcanoes. Among these are Bougainville, Hawaii, and the Solomon Islands.

The coral reefs of the South Pacific 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 with chains of reef patches. 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.

Water characteristics

The volume of the Pacific Ocean, representing about 50.1 percent of the world's oceanic water, has been estimated at some 714 million cubic kilometers. Surface water temperatures in the Pacific can vary from âˆ'1.4 °C (29.5 °F), the freezing point of sea water, in the poleward areas to about 30 °C (86 °F) near the equator. Salinity also varies latitudinally, reaching a maximum of 37 parts per thousand in the southeastern area. The water near the equator, which can have a salinity as low as 34 parts per thousand, is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year. The lowest counts of less than 32 parts per thousand are found in the far north as less evaporation of seawater takes place in these frigid areas. The motion of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific gyre) and counter-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current.

Turning eastward at about 45°N, the Kuroshio forks and some water moves northward as the Aleutian Current, while the rest turns southward to rejoin the North Equatorial Current. The Aleutian Current branches as it approaches North America and forms the base of a counter-clockwise circulation in the Bering Sea. Its southern arm becomes the chilled 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°S, and joins the main westerly circulation of the South 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

The climate patterns of the Northern and Southern Hemispheres generally mirror each other. The trade winds in the southern and eastern Pacific are remarkably steady while conditions in the North Pacific are far more varied with, for example, cold winter temperatures on the east coast of Russia contrasting with the milder weather off British Columbia during the winter months due to the preferred flow of ocean currents.

In the tropical and subtropical Pacific, the El Niño Southern Oscillation (ENSO) affects weather conditions. To determine the phase of ENSO, the most recent three-month sea surface temperature average for the area approximately 3,000 kilometres (1,900 mi) to the southeast of Hawai'i is computed, and if the region is more than 0.5 °C (0.9 °F) above or below normal for that period, then an El Niño or La Niña is considered in progress.

In the tropical western Pacific, the monsoon and the related wet season during the summer months contrast with dry winds in the winter which blow over the ocean from the Asian landmass. Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are active. Cyclones are liable to form south of Mexico, striking the western Mexican coast and occasionally the southwestern United States between June and October, with those forming in the western Pacific moving into southeast and east Asia from May to December.

In the arctic, icing from October to May can present a hazard for shipping while persistent fog occurs from June to December. A climatological low in the Gulf of Alaska keeps the southern coast wet and mild during the winter months. The Westerlies and associated jet stream within the Mid-Latitudes can be particularly strong, especially in the Southern Hemisphere, due to the temperature difference between the tropics and Antarctica, which records the coldest temperature readings on the planet. In the Southern hemisphere, because of the stormy and cloudy conditions associated with extratropical cyclones riding the jet stream, it is usual to refer to the Westerlies as the Roaring Forties, Furious Fifties and Shrieking Sixties according to the varying degrees of latitude.

Geology

The ocean was mapped by Abraham Ortelius; he called it Maris Pacifici because of Ferdinand Magellan, who sailed the Pacific during his circumnavigation from 1519 to 1522 and said that it was much more calm than the Atlantic.

The andesite line is the most significant regional distinction in the Pacific. A petrologic boundary, it separates the deeper, mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic 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's North Island.

The dissimilarity continues northeastward along the western edge of the Andes Cordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand 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 Pacific basin. Here 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 Pacific Ring of Fire is the world's foremost belt of explosive volcanism. The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones.

The Pacific Ocean is the only ocean which is almost totally bounded by subduction zones. Only the Antarctic and Australian coasts have no nearby subduction zones.

Geological history

The Pacific Ocean developed from Panthalassa following the breakup of Pangaea. There is no firm date for when the changeover occurred, as the replacement of the sea bed is a continuous process, though reconstruction maps often change the name from Panthalassic to Pacific around the time the Atlantic Ocean began to open. The Panthalassic Ocean first opened 750 million years ago at the breakup of Rodinia, but the oldest Pacific Ocean floor is only around 180 Ma old.

Seamount chains

The Pacific Ocean contains several long seamount chains, formed by hotspot volcanism. These include the Hawaiianâ€"Emperor seamount chain and the Louisville seamount chain.

Economy

The exploitation of the Pacific's mineral wealth is hampered by the ocean's great depths. In shallow waters of the continental shelves 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 in some cases.

Fishing

Fish are an important economic asset in the Pacific. The shallower shoreline waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish. Overfishing has become a serious problem in some areas. For example, catches in the rich fishing grounds of the Okhotsk Sea off the Russian coast have been reduced by at least half since the 1990s as a result of overfishing.

Environmental issues

The quantity of small plastic fragments floating in the north-east Pacific Ocean has increased a hundredfold over the past 40 years (2012).

Marine pollution is a generic term for the harmful entry into the ocean of chemicals or particles. The main culprits are those using the rivers for disposing of their waste. The rivers then empty into the ocean, often also bringing chemicals used as fertilizers in agriculture. The excess of oxygen-depleting chemicals in the water leads to hypoxia and the creation of a dead zone.

Marine debris, also known as marine litter, is human-created waste that has ended up floating in a lake, sea, ocean, or waterway. Oceanic debris tends to accumulate at the center of gyres and coastlines, frequently washing aground where it is known as beach litter.

In addition, the Pacific Ocean has served as the crash site of satellites, including Mars 96, Fobos-Grunt, and Upper Atmosphere Research Satellite.

Major ports and harbors

See also

References

Further reading

External links

• EPIC Pacific Ocean Data Collection Viewable on-line collection of observational data
• NOAA In-situ Ocean Data Viewer plot and download ocean observations
• NOAA PMEL Argo profiling floats Realtime Pacific Ocean data
• NOAA TAO El Niño data Realtime Pacific Ocean El Niño buoy data
• NOAA Ocean Surface Current Analyses â€" Realtime (OSCAR) Near-realtime Pacific Ocean Surface Currents derived from satellite altimeter and scatterometer data