The ocean encompasses almost a third of the Earth's surface, having an area of 179.7 million square kilometres (69.4 million sq mi and 161 million cubic mi) —significantly larger than Earth's entire landmass, with room for another Africa to spare . Extending approximately 15,500 kilometres (9,600 mi) from the Bering Sea in the Arctic to the icy margins of Antarctica's Ross Sea in the south (although the Antarctic regions of the Pacific are sometimes described as part of the circumpolar Southern Ocean), the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800 kilometres (12,300 mi) from Indonesia to the coast of Colombia and Peru - halfway across the world, and more than five times the diameter of the Moon. The western limit of the ocean is often placed at the Strait of Malacca. The lowest point on earth—the Mariana Trench—lies 10,911 metres (35,797 ft) below sea level. Its average depth is 4,280 metres (14,000 ft).
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. Including partially submerged islands, the figure is substantially higher.
The Pacific Ocean is currently shrinking from plate tectonics, while the Atlantic Ocean is increasing in size, by roughly 2-3 cm/yr on 3 sides, roughly averaging 0.5 sq km a year, though global warming is counteracting this process and may even reverse the shrinkage for a while.
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 ± 180° 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 cyclones (typhoons, the equivalent of Atlantic hurricanes), 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 destroyed entire towns.
Water temperatures in the Pacific vary from freezing in the poleward areas to about near the equator. Salinity also varies latitudinally. The 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 frigid areas.
The surface circulation 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 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 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 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.
The andesite line is the most significant regional distinction in the Pacific. 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—all eastward extensions of the continental blocks of Asia, Australia and Zealandia—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.
The largest landmass entirely within the Pacific Ocean is the island of New Guinea— the second largest island in the world. Almost all of the smaller islands of the Pacific lie between 30°N and 30°S, extending from Southeast Asia to Easter Island; the rest of the Pacific Basin is almost entirely submerged. During the Last glacial period, New Guinea was part of Australia so the largest landmass would have been Borneo-Palawan.
The great triangle of Polynesia, connecting Hawaii, Easter Island, and New Zealand, encompasses the island arcs and clusters of the Cook Islands, Marquesas, Samoa, Society, Tokelau, Tonga, Tuamotu, Tuvalu and the Wallis and Futuna 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 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.
Important human migrations occurred in the Pacific in prehistoric times, most notably those of the Polynesians from the Asian edge of the ocean to Tahiti and then to Hawaii, New Zealand, and Easter Island.
The ocean was first sighted by Europeans early in the 16th century, first by the Spanish explorer Vasco Núñez de Balboa who crossed the Isthmus of Panama in 1513, and then by Ferdinand Magellan, who sailed the Pacific during his circumnavigation from 1519 to 1522. In 1564, conquistadors crossed the ocean from Mexico led by Miguel López de Legazpi who sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Spain to the Philippines, New Guinea, and the Solomon Islands.
During the 17th century, the Dutch, sailing around southern Africa, dominated discovery and trade; Abel Janszoon Tasman discovered Tasmania and New Zealand in 1642. 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 Oceania by European powers, and later, the United States and Japan. 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 (1873-76); and the German Gazelle (1874-76). Although the United States gained control of 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.
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. 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.
Marine pollution is a generic term for the harmful entry into the ocean of chemicals or particles. The biggest culprit are rivers that empty into the Ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. The excess of oxygen depleting chemicals in the water leads to hypoxia and the creation of a dead zone (ecology).
Marine debris, also known as marine litter, is a term used to describe human-created waste that has found itself floating in a lake, sea, ocean or waterway. Oceanic debris tends to accumulate at the centre of gyres and coastlines, frequently washing aground where it is known as beach litter.