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Earth Ocean


Earth Ocean ::-- Arctic Ocean||Indian Ocean|| Pacific Ocean||Southern Ocean||Atlantic Ocean||


An ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (~3.6×108 km2) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.
More than half of this area is about 4,267 metres (13,999 ft) deep. Average oceanic salinity is around 35 parts per thousand (‰) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ‰. Scientists estimate that 230,000 marine species are currently known, but the total could be up to 10 times that number.



Ocean Overview

Though generally described as several 'separate' oceans, these waters comprise one global, interconnected body of salt water sometimes referred to as the World Ocean or global ocean. This concept of a continuous body of water with relatively free interchange among its parts is of fundamental importance to oceanography.
The major oceanic divisions are defined in part by the continents, various archipelagos, and other criteria. These divisions are (in descending order of size):

  • Pacific Ocean, which separates Asia and Australia from the Americas
  • Atlantic Ocean, which separates the Americas from Europe and Africa
  • Indian Ocean, which washes upon southern Asia and separates Africa and Australia
  • Southern Ocean, sometimes considered an extension of the Pacific, Atlantic and Indian Oceans, which encircles Antarctica.
  • Arctic Ocean, sometimes considered a sea of the Atlantic, which covers much of the Arctic and washes upon northern North America and Eurasia.

The Pacific and Atlantic may be further subdivided by the equator into northern and southern portions. Smaller regions of the oceans are called seas, gulfs, bays, straits and other names.
Geologically, an ocean is an area of oceanic crust covered by water. Oceanic crust is the thin layer of solidified volcanic basalt that covers the Earth's mantle. Continental crust is thicker but less dense. From this perspective, the earth has three oceans: the World Ocean, the Caspian Sea, and Black Sea. The latter two were formed by the collision of Cimmeria with Laurasia. The Mediterranean Sea is at times a discrete ocean, because tectonic plate movement has repeatedly broken its connection to the World Ocean through the Strait of Gibraltar. The Black Sea is connected to the Mediterranean through the Bosporus, but the Bosporus is a natural canal cut through continental rock some 7,000 years ago, rather than a piece of oceanic sea floor like the Strait of Gibraltar.
Despite their names, smaller landlocked bodies of saltwater that are not connected with the World Ocean, such as the Aral Sea, are actually salt lakes.



Physical properties

The area of the World Ocean is 361 million square kilometres (139 million square miles) Its volume is approximately 1.3 billion cubic kilometres (310 million cu mi). This can be thought of as a cube of water with an edge length of 1,111 kilometres (690 mi). Its average depth is 3,790 metres (12,430 ft), and its maximum depth is 10,923 metres (6.787 mi) Nearly half of the world's marine waters are over 3,000 metres (9,800 ft) deep. The vast expanses of deep ocean (anything below 200 metres (660 ft)) cover about 66% of the Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea.
The total mass of the hydrosphere is about 1,400,000,000,000,000,000 metric tons (1.5×1018 short tons) or 1.4×1021 kg, which is about 0.023 percent of the Earth's total mass. Less than 3 percent is freshwater; the rest is saltwater, mostly in the ocean.


world ocean map

Ocean Water Color

A common misconception is that the oceans are blue primarily because the sky is blue. In fact, water has a very slight blue color that can only be seen in large volumes. While the sky's reflection does contribute to the blue appearance of the surface, it is not the primary cause. The primary cause is the absorption by the water molecules of red photons from the incoming light, the only known example of color in nature resulting from vibrational, rather than electronic, dynamics.

Ocean Exploration

Ocean travel by boat dates back to prehistoric times, but only in modern times has extensive underwater travel become possible.
The deepest point in the ocean is the Mariana Trench, located in the Pacific Ocean near the Northern Mariana Islands. Its maximum depth has been estimated to be 10,971 metres (35,994 ft) (plus or minus 11 meters; see the Mariana Trench article for discussion of the various estimates of the maximum depth.) The British naval vessel, Challenger II surveyed the trench in 1951 and named the deepest part of the trench, the "Challenger Deep". In 1960, the Trieste successfully reached the bottom of the trench, manned by a crew of two men.
Much of the ocean bottom remains unexplored and unmapped. A global image of many underwater features larger than 10 kilometres (6.2 mi) was created in 1995 based on gravitational distortions of the nearby sea surface.

Climate effects

Ocean currents greatly affect the Earth's climate by transferring heat from the tropics to the polar regions, and transferring warm or cold air and precipitation to coastal regions, where winds may carry them inland. Surface heat and freshwater fluxes create global density gradients that drive the thermohaline circulation part of large-scale ocean circulation. It plays an important role in supplying heat to the polar regions, and thus in sea ice regulation. Changes in the thermohaline circulation are thought to have significant impacts on the Earth's radiation budget. Insofar as the thermohaline circulation governs the rate at which deep waters reach the surface, it may also significantly influence atmospheric carbon dioxide concentrations.
For a discussion of the possibilities of changes to the thermohaline circulation under global warming, see shutdown of thermohaline circulation.
It is often stated that the thermohaline circulation is the primary reason that the climate of Western Europe is so temperate. An alternate hypothesis claims that this is largely incorrect, and that Europe is warm mostly because it lies downwind of an ocean basin, and because atmospheric waves bring warm air north from the subtropics.
The Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans.One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where the system forms).

Ancient oceans

Continental drift continually reconfigures the oceans, joining and splitting bodies of water. Ancient oceans include:

  • Bridge River Ocean, the ocean between the ancient Insular Islands and North America.
  • Iapetus Ocean, the southern hemisphere ocean between Baltica and Avalonia.
  • Panthalassa, the vast world ocean that surrounded the Pangaea supercontinent.
  • Rheic Ocean
  • Slide Mountain Ocean, the ocean between the ancient Intermontane Islands and North America.
  • Tethys Ocean, the ocean between the ancient continents of Gondwana and Laurasia.
  • Khanty Ocean, the ocean between Baltica and Siberia.
  • Mirovia, the ocean that surrounded the Rodinia supercontinent.
  • Paleo-Tethys Ocean, the ocean between Gondwana and the Hunic terranes.
  • Poseidon Ocean
  • Proto-Tethys Ocean
  • Pan-African Ocean, the ocean that surrounded the Pannotia supercontinent.
  • Superocean, the ocean that surrounds a global supercontinent.
  • Ural Ocean, the ocean between Siberia and Baltica.

Extraterrestrial oceans

Earth is the only known planet with liquid water on its surface and is certainly the only one in our own solar system. However, a layer of liquid water thick enough to decouple the crust from the mantle is thought to be present under the surfaces of the moons Titan, Europa and, with less certainty, Callisto and Ganymede. A similar magma ocean is thought to be present on Io. Geysers have been found on Saturn's moon Enceladus, though these may not involve bodies of liquid water. Other icy moons and trans-neptunian objects may also have internal oceans, or have once had internal oceans that have now frozen. The planets Uranus and Neptune may also possess large oceans of liquid water under their thick atmospheres, though their internal structure is not well understood.
There is currently much debate over whether Mars once had an ocean in its northern hemisphere, and over what happened to it; recent findings by the Mars Exploration Rover mission indicate Mars had long-term standing water in at least one location, but its extent is not known.
Astronomers believe that Venus had liquid water and perhaps oceans in its very early history. If they existed, all later vanished via resurfacing.

 

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