This article is the continuation of the previous article “The World Ocean”, which has mentioned on 8th January 2021in the Global New Light of Myanmar. The article pointed out five principal oceanic areas of the World Ocean, such as the Atlantic Ocean, Arctic Ocean, Indian Ocean, Pacific Ocean and the Southern Ocean. In the previous article, of all the oceans, I have introduced a concise account of the Indian Ocean, our neighbour. This is the second article about the Pacific Ocean.
The Pacific Ocean, a body of saltwater extending from the Antarctic region in the south to the Arctic in the north and lying between the continents of Asia and Australia on the west and North and South American on the east. Of the three oceans that extend northward from the Antarctic continent, the Pacific is by far the largest, occupying about a third of the surface of the globe. Its area, excluding adjacent seas, encompasses about 63.8 million square miles (165.25 million square km). It has double the area and more than double the water volume of the Atlantic Ocean.
The Pacific basin may conveniently be divided into three major physiographic regions: the eastern, western, and central Pacific regions.
The eastern Pacific region, which extends southward from Alaska to Tierra del Fuego, is relatively narrow and is associated with the American cordilleran system of almost unbroken mountain chains, the coastal ranges of which rise steeply from the western shores of North and South America. The continental shelf, which runs parallel to it, is narrow, while the adjacent continental slope is very steep. Significant oceanic trenches in this region are the Middle American Trench in the North Pacific and the Peru-Chile Trench in the South Pacific.
The seaward boundary of the western Pacific region is marked by a broken line of oceanic trenches, extending from the Aleutian Trench in the north through the Kuril and Japan trenches and southward to the Tonga and Kermadec trenches, terminating close to the northeast of North Island, New Zealand.
The central Pacific region lies between the boundaries of the eastern and western regions. The largest and the most geologically stable of the structural provinces of the Earth’s crust, it is characterized by expansive areas of low relief, lying at a general depth of about 15,000 feet (4,600 metres) below the surface.
The islands of the western region-including the Aleutians, the Kurils, the Ryukyus, Taiwan, the Malay Archipelago (including New Guinea), and New Zealand- are continental in character. Geologically, they consist partly of sedimentary rocks, and their structures are similar to those of the coastal mountain ranges of the adjacent continent.
The numerous oceanic islands of the Pacific are unevenly distributed. They lie, in the main, between the Tropics of Cancer and Capricorn and occur in great numbers in the western Pacific. The northernmost chain of oceanic islands is associated with the Hawaiian Ridge. The Hawaiian archipelago consists of about 2,000 islands, although the term the Hawaiian Islands is usually applied to the small group that lies at the eastern end of the archipelago.
The numerous small islands of Micronesia lie mainly north of the Equator and to the west of the 180° meridian. Nearly all are coralline; the principal groups are the Marianas, the Marshalls, the Carolines, Kiribati (Gilbert Islands), and Tuvalu (Ellice Islands).
To the south of Micronesia lies Melanesia, which consists mostly of small coral islands. The region’s physiography is dominated by a group of large continental islands, however, including New Guinea. The principal Melanesian island groups are the Bismarck Archipelago, the Solomons, Vanuatu (New Hebrides), New Caledonia, and Fiji.
The immense area of Polynesia includes the Hawaiian Islands, the Phoenix Islands, Samoa, Tonga, the Cook Islands, the Society Islands, Tuamotu, and the Marquesas.
The Pacific Ocean was born 750 million years ago at the breakup of Rodinia, although it is generally called the Panthalassa until the breakup of Pangea, about 200 million years ago. The oldest Pacific Ocean floor is only around 180 million years old, with older crust subducted by now (Wikipedia).
All the major physical features in the Pacific are understood to originate in plate tectonics. The western Pacific arcs of volcanic islands and deep trenches are convergent zones where two plates are colliding, one being subducted. The East Pacific Rise is an active spreading centre where new crust is being created. The north-eastern Pacific margin is the strike-slip zone where the American Plate and the Pacific Plate are gliding laterally past each other via the major San Andreas Fault system. In the south-eastern Pacific, however, the Nazca Plate and the South American Plate are colliding to form the Andes Mountains along western South America and, a short distance offshore, the Peru-Chile Trench.
Of great geologic interest are the seamounts (submerged volcanoes), guyots (flat-topped seamounts), and oceanic islands of the Pacific. The numerous tropical islands of the Pacific are mainly coralline. The principal types of coral reefs-fringing, barrier, and atoll- as well as the guyots, which rise within the Pacific from the ocean floor in latitudes north and south of the tropics, are explained partially by the slow subsidence theory advanced by the English naturalist Charles Darwin during the 19th century and partially by the theory of plate tectonics.
Apart from the narrow coastal zone of the eastern region and the broad continental seas of the western region, the Pacific is floored with pelagic (oceanic) material derived from the remains of marine plants and animals that once inhabited the waters lying above. Red or brown radiolarian ooze is found along the zone of the Pacific North Equatorial Current, east of longitude 170° W, and on the floors of some deep Indonesian basins. A belt of diatom ooze occurs between latitudes 45° and 60° S and across the North Pacific, between Japan and Alaska. Calcareous globigerina ooze occurs in the shallower parts of the South Pacific, the dissolving power of the seawater at great depths being sufficient to dissolve calcareous material to such an extent that these oozes are not generally found at depths in excess of about 15,000 feet (4,600 metres). Silica-containing material, such as radiolarian and diatom ooze, is found at greater depths, but even these siliceous remains are dissolved at very great depths, where the characteristic deposit is red clay. Red clay, which covers no less than half of the Pacific floor, is believed to form colloidal (extremely finely divided) clays derived essentially from the land.
On the abyssal plains, where sediments accumulate slowly, chemical and biological processes lead to the formation of metal-bearing coatings around objects such as the ear bones of fishes. The nodules so formed contain manganese, iron, nickel, copper, cobalt, and traces of other metals such as platinum. They cover large areas of the ocean floor in the Pacific.
Metal-bearing deposits on the deep-sea floor, consisting of nodules, crusts, and accumulations of metallic sulphides from deep vents, are of potential economic interest. In the 1970s and ’80s, it was hoped that mining the nodules—which contain quantities of manganese, iron, copper, nickel, titanium, and cobalt, as well as small traces of other metals—might be a way to contribute to the wealth of newly industrializing countries. Marine sulphide ores, containing iron, copper, cobalt, zinc, and traces of other metallic elements, are deposited in large amounts by the actions of deep water hydrothermal vents, such as occur in the Pacific off the Galapagos Islands and on the Juan de Fuca and Gorda ridges in the Okinawa Trough and the Manus Basin off New Guinea.
The principal areas in the south-western Pacific for offshore oil and gas exploration are in the South China Sea—the waters off Vietnam and off Hainan Island in China and on the continental shelf northwest of the island of Palawan in the Philippines—but they also include the area off Natuna Islands and some areas off the Sumatran coast in Indonesia. In the northwestern Pacific, the main areas lie to the northwest of the island of Kyushu in Japan, in the southern portion of the Yellow Sea and the Bo Hai (Gulf of Chihli), and in regions off Sakhalin Island and the Kamchatka Peninsula. Oil and gas wells have been drilled in the Bering Sea in the north and areas off the coast of southern California in the eastern Pacific. In the southern Pacific, hydrocarbon production and exploration is taking place off northwestern and northern Australia and in the Gippsland Basin off southeast Australia.
Sources:1. Charles Henry Cotter: Pacific Ocean
2. Wikipedia, the free encyclopaedia