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Oceans on the Earth

   There are four oceans in order of their size
A. Pacific Ocean
B. Atlantic Ocean
C. Indian Ocean
D. Arctic Ocean


A.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 kilometres in area, this largest division of the World ocean – and, in turn, the hydrosphere – 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 Galapagos 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. 

    The eastern Pacific ocean was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Nunez 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". 

 

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 kilometres —significantly larger than Earth's entire landmass of some 150 million square kilometres.
* Extending approximately 15,500 kilometres 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 kilometres from Indonesia to the coast of Colombia – halfway around the world, and more than five times the diameter of the Moon. The lowest known point on Earth—the Mariana Trench—lies 10,911 meters below sea level. Its average depth is 4,280 meters. 
* Due to the effects of plate tectonics, the Pacific Ocean is currently shrinking by roughly an inch per year (2–3 cm/yr) on three sides, roughly averaging 0.2 square miles 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 icean. 
                                                 

Storm in Pacifica, California

* 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.


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 kilometres. Surface water temperatures in the Pacific can vary from −1.4 °C, the freezing point of sea water, in the pole ward areas to about 30 °C near the equator. Salinity also varies latitudinal, reaching a maximum of 37 parts per thousand in the south eastern area. The water near the equator, which can have 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 Hawaii is computed, and if the region is more than 0.5 °C above or below normal for that period, then an El Niño or La Nina 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 south western 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 climatologically 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 extra tropical 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.


B. Atlantic Ocean: The Atlantic Ocean is the world's second largest ocean, following the Pacific Ocean. With a total area of about 106,400,000 square kilometres, it covers approximately 20 percent of the Earth's surface and about 29 percent of its water surface area. The first part of its name refers to Atlas of Greek mythology, making the Atlantic the "Sea of Atlas".
The oldest known mention of "Atlantic" is in The Histories of Herodotus around 450 BC.

The term Ethiopic Ocean, derived from Ethiopia, was applied to the southern Atlantic as late as the mid-19th century. Before Europeans discovered other oceans, their term "ocean" was synonymous with the waters beyond the Strait of Gibraltar that are now known as the Atlantic. The early Greeks believed this ocean to be a gigantic river encircling the world. 
                             The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Eurasia and Africa to the east, and the Americas to the west. As one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south. The equator subdivides it into the North Atlantic Ocean and South Atlantic Ocean.

 

Geography: The Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea. To the east, the boundaries of the ocean proper are Europe: the Strait of Gibraltar (where it connects with the Mediterranean Sea–one of its marginal seas–and, in turn, the Black Sea, both of which also touch upon Asia) and Africa.
    In the southeast, the Atlantic merges into the Indian Ocean. The 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. Some authorities show it extending south to Antarctica, while others show it bounded at the 60° parallel by the Southern Ocean.
    In the southwest, the Drake Passage connects it to the Pacific Ocean. The man-made Panama Canal links the Atlantic and Pacific. Besides those mentioned, other large bodies of water adjacent to the Atlantic are the Caribbean Sea, the Gulf of Mexico, Hudson Bay, the Arctic Ocean, the Mediterranean Sea, the North Sea, the Baltic Sea, and the Celtic Sea.
    Covering approximately 22% of Earth's surface, the Atlantic is second in size to the Pacific. With its adjacent seas, it occupies an area of about 106,400,000 square kilometres; without them, it has an area of 82,400,000 square kilometres. The land that drains into the Atlantic covers four times that of either the Pacific or Indian oceans.

The volume of the Atlantic with its adjacent seas is 354,700,000 cubic kilometres (85,100,000 cu mi) and without them 323,600,000 cubic kilometres.
     The average depth of the Atlantic with its adjacent seas, is 3,339 metres (1,826 fathoms; 10,955 ft); without them it is 3,926 metres. The greatest depth, Milwaukee Deep with 8,380 metres, is in the Puerto Rico Trench. The Atlantic's width varies from 1,538 nautical miles between Brazil and Sierra Leone to over 3,450 nautical miles in the south.


Climate: Climate is influenced by the temperatures of the surface waters and water currents as well as winds. Because of the ocean's great capacity to store and release heat, maritime climates are more moderate and have less extreme seasonal variations than inland climates. Precipitation can be approximated from coastal weather data and air temperature from water temperatures.
    The oceans are the major source of the atmospheric moisture that is obtained through evaporation. Climatic zones vary with latitude; the warmest zones stretch across the Atlantic north of the equator. The coldest zones are in high latitudes, with the coldest regions corresponding to the areas covered by sea ice. Ocean currents influence climate by transporting warm and cold waters to other regions.

The winds that are cooled or warmed when blowing over these currents influence adjacent land areas.
    The Gulf Stream and its northern extension towards Europe, the North Atlantic Drift, for example, warms the atmosphere of the British Isles and north-western Europe and influences weather and climate as far south as the northern Mediterranean. The cold water currents contribute to heavy fog off the coast of eastern Canada (the Grand Banks of Newfoundland area) and Africa's north-western coast. In general, winds transport moisture and air over land areas. Hurricanes develop in the southern part of the North Atlantic Ocean.


C. Indian Ocean: The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded by Asia on the north, on the west by Africa, on the east by Australia, and on the south by the Southern Ocean (or, depending on definition, by Antarctica). Although generally assumed to be named for India, early European writers referred to the "East Indian" Ocean, the East Indies being the name given by European travellers collectively to India, South East Asia and the Indonesian archipelago.
As one component of the World Ocean, the Indian Ocean is delineated from the Atlantic Ocean by the 20° east meridian running south from Cape Agulhas, and from the Pacific Ocean by the meridian of 146°55' east. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf. The ocean is nearly 10,000 km wide at the southern tips of Africa and Australia, and its area is 73,556,000 km², including the Red Sea and the Persian Gulf. 
         The Indian Ocean's volume is estimated to be 292,131,000 km³. Small islands dot the continental rims. Island nations within the ocean are Madagascar (the world's fourth largest island), Bahrain, Comoros, Maldives,Mauritius, Seychelles and Sri Lanka. The archipelago of Indonesia and the island nation of Timor-Leste border the ocean on the east.

 

Geography: The African, Indian and Antarctic crustal plates converge in the Indian Ocean at the Rodriguez Triple Point. Their junctures are marked by branches of the mid-oceanic ridge forming an inverted Y with the stem running south from the edge of the continental shelf near Mumbai, India. The eastern, western, and southern basins thus formed are subdivided into smaller basins by ridges.
     The ocean's continental shelves are narrow, averaging 200 kilometres in width. An exception is found off Australia's western coast, where the shelf width exceeds 1,000 kilometres. The average depth of the ocean is 3,890 m. Its deepest point is Diamantine Deep in Diamantine, at 8,047 m deep; also sometimes considered is Sunda Trench, at a depth of 7,258–7,725 m. North of 50° south latitude, 86% of the main basin is covered by pelagic sediments, of which more than half is globigerina ooze. The remaining 14% is layered with terrigenous sediments. Glacial outwash dominates the extreme southern latitudes.
    The major choke points include Bab el Mandeb, Strait of Hormuz, the Lombok Strait, the Strait of Malacca and the Palk Strait.

Seas include the Gulf of Aden, Andaman Sea, Arabian Sea, Bay of Bengal, Great Australian Bight, Laccadive Sea, Gulf of Mannar, Mozambique Channel, Gulf of Oman, Persian Gulf, Red Sea and other tributary water bodies. The Indian Ocean is artificially connected to the Mediterranean Sea through the Suez Canal, which is accessible via the Red Sea.


Climate: The climate north of the equator is affected by a monsoon climate. Strong north-east winds blow from October until April; from May until October south and west winds prevail. In the Arabian Sea the violent Monsoon brings rain to the Indian subcontinent. In the southern hemisphere, the winds are generally milder, but summer storms near Mauritius can be severe. When the monsoon winds change, cyclones sometimes strike the shores of the Arabian Sea and the Bay of Bengal. The Indian Ocean is the warmest ocean in the world.


D. Arctic ocean: The Arctic ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions. The International Hydrographic Organization (IHO) recognizes it as an ocean, although some oceanographers call it the Arctic Mediterranean Sea or simply the Arctic Sea, classifying it a Mediterranean sea or an estuary of the Atlantic Ocean.
Alternatively, the Arctic Ocean can be seen as the northernmost part of the all-encompassing World Ocean.
     Almost completely surrounded by Eurasia and North America, the Arctic Ocean is partly covered by sea ice throughout the year (and almost completely in winter). The Arctic Ocean's surface temperature and salinity vary seasonally as the ice cover melts and freezes; its salinity is the lowest on average of the five major oceans, due to low evaporation, heavy fresh water inflow from rivers and streams, and limited connection and outflow to surrounding oceanic waters with higher salinities. The summer shrinking of the ice has been quoted at 50%.The US National Snow and Ice Data Centre (NSIDC) uses satellite data to provide a daily record of Arctic sea ice cover and the rate of melting compared to an average period and specific past years.

 

Geography: The Arctic Ocean occupies a roughly circular basin and covers an area of about 14,056,000 km2, almost the size of Russia. The coastline is 45,390 km long. It is surrounded by the land masses of Eurasia, North America, Greenland, and by several islands.
    It is generally taken to include Baffin Bay, Barents Sea, Beaufort Sea, Chukchi Sea, East Siberian Sea, Greenland Sea, Hudson Bay, Hudson Strait, Kara Sea, Laptev Sea, White Sea and other tributary bodies of water. It is connected to the Pacific Ocean by the Bering Strait and to the Atlantic Ocean through the Greenland Sea and Labrador Sea.


Climate: Under the influence of the Quaternary glaciations, the Arctic Ocean is contained in a polar climate characterized by persistent cold and relatively narrow annual temperature ranges. Winters are characterized by the polar night, cold and stable weather conditions, and clear skies; summers are characterized by continuous daylight (midnight sun), damp and foggy weather, and weak cyclones with rain or snow
     The temperature of the surface of the Arctic Ocean is fairly constant, near the freezing point of seawater. Because the Arctic Ocean consists of saltwater the temperature must reach −1.8 °C before freezing occur.

The density of sea water, in contrast to fresh water, increases as it nears the freezing point and thus it tends to sink. It is generally necessary that the upper 100–150 m of ocean water cools to the freezing point for sea ice to form. In the winter the relatively warm ocean water exerts a moderating influence, even when covered by ice. This is one reason why the Arctic does not experience the extreme temperatures seen on the Antarctic continent.
    There is considerable seasonal variation in how much pack ice of the Arctic ice pack covers the Arctic Ocean. Much of the Arctic ice pack is also covered in snow for about 10 months of the year. The maximum snow cover is in March or April — about 20 to 50 cm over the frozen ocean.
    The climate of the Arctic region has varied significantly in the past. As recently as 55 million years ago, during the Palaeocene, the region reached an average annual temperature of 10–20 °C. The surface waters of the northern most Arctic Ocean warmed, seasonally at least, enough to support tropical life forms requiring surface temperatures of over 22 °C.

Posted Date : 15-10-2022

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

 

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