Ocean
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Ocean (Okeanos, a Greek god of sea and water;
Greek ωκεανός) covers almost three quarters (71%) of the surface of the
Earth. This global, interconnected body of
salt water is divided by the continents and
- Atlantic Ocean
- Indian Ocean
- Pacific Ocean
- Southern Ocean — in some regions and cultures, including North America and most of Continental Europe, the Southern Ocean is generally not considered an ocean in its own right, and is divided among the Atlantic, Indian and Pacific oceans.
The area of the global ocean is 361 million square kilometres, its volume is 1370 million cubic kilometres, and its average depth 3790 metres. This does not include seas not connected to the oceans, such as the
Caspian Sea.
The total mass of the hydrosphere is about 1.4 × 10
21 kg, ca. 0.023 % of the Earth's total mass.
The boundaries between the oceans are set by the
International Hydrographic Organization; e.g., the Southern Ocean extends from the coast of
Antarctica to 60 degrees south latitude. Smaller regions of the oceans are known as
seas,
gulfs,
straits, etc.
See
sea water for a detailed discussion of ocean water composition, most notably its
salinity.
Exploration
Study of Earth's oceans is called
oceanography. Travel on the surface of the ocean through the use of boats 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. It has a maximum depth of
10,924 m (35,838 ft). It was fully surveyed in 1951 by the British navy vessel, "Challenger II" which gave its name to the deepest part of the trench, the "
Challenger Deep".
Climate
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).
Ocean currents greatly affect Earth's climate by transferring warm or cold air and precipitation to coastal regions, where they may be carried inland by winds. For example, even though western
Europe lies at about the latitude of the northeastern
United States or southeastern
Canada, it has a more temperate climate than would be expected because of the
Gulf Stream, an ocean current that transfers warm, tropical air to western Europe.
Ecology
The oceans are home to many forms of
life, such as:
Economy
The oceans are essential to transportation: a huge portion of the world's goods are moved by
ship between the world's seaports. Important
ship canals include the
Saint Lawrence Seaway,
Panama Canal, and
Suez Canal.
Earth is the only planet known with liquid water on its surface, and is certainly the only such in our own
solar system. However, liquid water is thought to be present under the surface of several
natural satellites, particularly the
Galilean moons of
Europa, and, with less certainty, its fellows
Callisto and
Ganymede. Other icy moons may have once had internal oceans that have now frozen, such as
Triton. 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 at this time.
There is currently much debate over whether
Mars once had an ocean of water in its northern hemisphere, and over what happened to it if it did; recent findings by the
Mars Exploration Rover mission indicate that it had some long-term standing water in at least one location, but its extent is not known.
Liquid hydrocarbons are thought to be present on the surface of Titan, though it may be more accurate to describe them as "lakes" rather than an "ocean". The distribution of these liquid regions will hopefully be better known after the full analysis of data from the
Huygens probe of the
Cassini-Huygens space mission, which dropped onto Titan's surface in January 2005. Titan is also thought likely to have a subterranean water ocean under the mix of ice and hydrocarbons that forms its outer crust.
External links
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Category:Forms of water
Category:Oceanography