Introduction to The Pacific Ocean
Pacific Ocean, the world's largest body of water. It lies between North and South America on the east, Asia and Australia on the west, and Antarctica on the south. The Pacific, including adjoining seas, has an area of about 64,186,300 square miles (166,241,700 km 2). It makes up almost 33 per cent of the earth's total surface and 46 per cent of its water surface, and is larger than all land areas combined. The ocean is commonly divided at the Equator into the North and the South Pacific.
Maximum dimensions are almost 11,000 miles (17,700 km) east-west (along the Equator) and 9,500 miles (15,200 km) north-south (near the International Date Line). Average depth is about 14,000 feet (4,270 m). Bordering the Pacific are numerous seas. They lie mainly in the west and include the Tasman, Arafura, Coral, South China, Philippine, East China, Japan, Okhotsk, and Bering seas.
The Ocean Floor
The Pacific's floor is covered principally by oozes (soft deposits consisting chiefly of the remains of minute organisms). There are also extensive areas of sand, mud, and lava, and deposits of manganese ore and ores of other useful metals. Like the land areas of the world, the floor of the Pacific varies from smooth to rough and extremely irregular. Many of its formations, such as mountains and volcanoes, were built underwater in much the same manner as those on land. Others consist of sediments that accumulated during millions of years. Because exploration is still in the early stages, only the general configuration of the ocean's floor is known.
Bordering the Pacific along the continents is a shallow, gently sloping edge, known as the continental shelf. It varies from narrow along the Americas to wide off the Asian and Australian coasts. In some places, deep valleys, called submarine canyons, cut the shelf. Beyond it, the floor descends rapidly to great depths.
Underwater mountains, called ridges and rises, jut from the floor. Consisting of slowly evolving mountains and volcanoes, they occur where the earth's crust is weakest. One of the largest is the East Pacific Rise, sometimes called the Easter Island Cordillera. It runs parallel to the South American coast, turns southeastward toward Antarctica, continues past Australia into the Indian Ocean, and eventually joins the Mid-Atlantic Ridge to form a world-encircling range. There is no well-defined mid-ocean ridge in the Pacific such as the one that runs the length of the Atlantic.
Some of the underwater ranges are isolated; others branch into complex systems that run for thousands of miles. They are often marked by exposed volcanic summits, which dot the water as islands and island chains. The Hawaiian Islands, a volcanic chain, rise more than 29,000 feet (8,840 m) above the ocean floor. Throughout much of the Pacific, there are submerged, isolated peaks called seamounts and flat-topped peaks known as guyots. Summits that are almost awash are often the foundations of coral atolls.
Slicing the floor of the Pacific are canyon-like trenches, or deeps. They lie mainly in the western Pacific and adjacent to island chains. In the Mariana Trench off Guam, oceanographers have measured a depth of 35,810 feet (10,915 m), the greatest ocean depth in the world. Depths of more than 32,000 feet (10,000 m) are found also in the Kuril, Philippine, Kermadec, and Tonga trenches.
Currents and Tides
The surface currents move at speeds of roughly two to four miles per hour (3 to 6 km/h). Their motions are affected by such factors as the prevailing surface winds, the density of the water, gravity, the rotation of the earth on its axis, and the shape of the ocean basin.
General circulation of the currents is clockwise in the North Pacific, counterclockwise in the South Pacific. It is somewhat like the rotations of two giant disks turning in opposite directions. As a result, warm equatorial water is constantly being carried poleward along the Asian and Australian coasts, while cold water is flowing toward the equator along the coasts of North and South America. Thus, the currents have distinct climatic effects on nearby lands. In some areas, such as the coast of Chile and Peru, they are cooling effects; in others, such as southern Japan, they are tempering and warming. In regions where warm and cold currents meet, notably northern Japan to southern Alaska, dense fogs frequently occur.
The chief currents of the North Pacific, beginning at the equator, are the North Equatorial Current, Kuroshio (Japan Current), North Pacific Current, or Drift, and California Current. Entering this circulation from the Arctic is the cold Oyashio (Okhotsk, or Kamchatka, Current). The Alaska Current starts off the coast of Oregon and flows northward along the coast of North America as far as Kodiak Island, bringing warmth to the coastal areas in winter. In the South Pacific are the South Equatorial Current, East Australian Current, West Wind Drift, and Peru (Humboldt) Current. Separating the two systems in the vicinity of the equator is the Equatorial Countercurrent, which flows eastward from Indonesia and the Philippines to the South American coast. map titled Major Surface Currents.)
There are also deep, underwater currents, but little is known of them. They tend to form separate layers flowing in different directions, each layer being denser than the layer above. For example, Antarctic water is known to subside suddenly beneath warmer water at a line called the Antarctic Convergence. From here it flows northward far below the surface of the ocean.
In general, the Pacific has low tides. In certain inlets, however, the water rises to significant heights. The tidal bore of Cook Inlet in Alaska ranks second only to that of the Atlantic's Bay of Fundy. Significant bores also occur in other Alaskan inlets and in southern Chile, Siberia, and Korea's west coast.
Ocean Life
Marine creatures exist in the depths of the Pacific far beyond the penetrating rays of light. Little is known of them, however, and few are ever seen. Most of the marine life occurs in the surface waters, especially on or near the continental shelf. The species are almost infinite in number. They range in size from huge blue whales to microscopic plankton (the tiny plants and animals that make up the basic food in the sea).
Particularly important are the cold, coastal waters of Asia and North and South America. In these commercial fisheries, the water teems with minerals, plankton, and fish, including tuna, salmon, sardines, herring, anchovies, and mackerel. In some shallow sections, shellfish such as crabs and clams are the chief catch. Specialized catches include sharks and whales for oil.
Although of great variety, fish in the tropical parts of the Pacific are only moderately abundant and are of little commercial use. They do, however, provide a principal food for many island people. Some species, because of their rarity or brilliant colors, are taken for aquarium use. Pearl oysters and sponges are found in some of the warmer waters; corals are widespread.
Islands
There are more than 20,000 islands in the Pacific. Most of them lie in the Central and South Pacific, a region called Oceania. Oceania's divisions are Melanesia on the southwest, including New Guinea; Micronesia on the northwest; and Polynesia on the east, including Hawaii and New Zealand. Other islands lie near Australia and near western North and South America; and off eastern Asia are the Japanese, Philippine, and Indonesian groups.
Islands of the South Pacific have been called South Sea Islands ; those of the extreme southwestern Pacific, East Indies.
The total population of all the islands in 1990 was more than 390,000,000; of this number, some 364,000,000 persons were concentrated on the islands of Japan, the Philippines, and Indonesia. Most of the other islands are thinly populated or uninhabited.
The world's second- and third-largest islands—New Guinea and Borneo—are in the Pacific, but most islands in this ocean are small, many less than one square mile (2.6 km 2) each.
Coastal Lands
Flanking the Pacific Ocean and its adjacent seas are more than 25 nations. The climate ranges from arctic to tropical, and landforms include mountains, plains, tundras, and deserts. Some areas are densely populated, others virtually uninhabited.
Fringing most of the Pacific is the Circum-Pacific Mobile Belt (the so-called Ring of Fire), a belt of active, dormant, and extinct volcanoes. Volcanic eruptions and earthquakes often occur, destroying life and property. Such disturbances when underwater cause tidal waves called tsunamis. These are particularly destructive when they break on heavily populated coasts.
History
Vasco Núñez de Balboa, a Spaniard who crossed the Isthmus of Panama in 1513 and viewed what he called the South Sea, is credited with the Pacific's discovery. However, the people of Micronesia, Melanesia, and Polynesia had long before settled the islands and traveled extensively. Even Marco Polo and other medieval European travelers in Asia probably reached the Pacific centuries before Balboa.
In 1520 Ferdinand Magellan became the first European to cross the ocean. He named it “Pacific” for its calm waters. During the following three centuries, such men as Francis Drake, Abel Tasman, Vitus Bering, James Cook, and George Vancouver added to the world's knowledge of the ocean. Cook's work was particularly significant, for between 1768 and 1779 he charted most of the South Pacific lands. Following the explorers were whalers, traders, missionaries, and colonists. Contact with European diseases was disastrous on some islands, all but destroying the native populations.
The 19th century brought investigations by naturalists Alfred Russel Wallace and Charles Darwin. In the early 1870's the voyage of the British ship Challenger became the first of many scientific expeditions probing the Pacific's waters. One of particular importance was conducted as part of the International Geophysical Year (1957–58).
American interests in the Pacific date back to the 1800's, as evidenced by its whaling activity there and the opening of Japan to commerce by Commodore Matthew C. Perry. Late in the century, the Philippine Islands and Guam were acquired, at the conclusion of the Spanish-American War. Hawaii was annexed in 1900. The United States fought numerous sea and island battles in the Pacific during World War II.
In 1946 the Philippines achieved independence, and during the 1970's and 1980's a number of island groups in Melanesia and Polynesia became independent. In 1994 Palau achieved independence.