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Ocean
*** Shopping-Tip: Ocean
{{otheruses}}
Image:Oceans.png right|thumb|400px|The world's oceans as seen from the [[Pacific Ocean|South Pacific]]
'''Ocean''' (from
Oceanus Okeanos, Greek for river, the ancient Greeks noticed that a strong current flowed off Gibraltar, and assumed it was a great river); covers almost three quarters (71%) of the surface of the
Earth, and nearly half of the world's marine waters are over 3000 m deep.
This global, interconnected body of
sea water salt water, called the World Ocean, is divided by the
continents and
archipelagos into the following bodies, from the largest to the smallest: the
Pacific Ocean, the
Atlantic Ocean, the
Indian Ocean, the
Southern Ocean (according to some authorities such as
International Hydrographic Organization (IHO)), and the
Arctic Ocean.
Some geographers and some governments but not the US, recognize the IHO as defining official water body names and boundaries. (The US authority is the
United States Board on Geographic Names.) The IHO officially sanctioned the Southern Ocean name only in
2000, but its definition by a line of
latitude (with IHO members widely disputing which line of latitude) has left its acceptance as a fifth ocean open to question. The
National Geographic Society and some other leading geographers and cartographers continue to use "South Pacific", "South Atlantic", and "Indian" Ocean for the waters around Antarctica. A few
oceanography Oceanographers recognize only three oceans also, treating the Arctic Ocean (or ''the Arctic Sea'') as a part of the Atlantic Ocean.
Smaller regions of the oceans are called
seas,
gulfs,
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 (geology) mantle where there are no continents. From this point of view, there are three "oceans" today: the World Ocean, and the
Black Sea Black and
Caspian Sea Caspian Seas that were formed by the collision of
Cimmerian plate Cimmeria with
Laurasia. The
Mediterranean Sea is very nearly its own "ocean", being connected to the World Ocean through the
Strait of Gibraltar, and indeed several times over the last few million years movement of the
Africa African Continent has closed the strait off entirely, making the Mediterranean a fourth "ocean". (The Black Sea is connected to the Mediterranean through the
Bosporus, but this is in effect a natural
canal cut through continental rock some 7000 years ago, rather than a piece of oceanic sea floor like the Strait of Gibraltar.)
The area of the World Ocean is 361 million km², its volume is 1340 million km³, and its average depth is 3711 m. Nearly half of the world's marine waters are over 3000 m deep.[http://www.oceansatlas.com/unatlas/about/physicalandchemicalproperties/background/seemore1.html]
This does not include seas not connected to the World Ocean, such as the
Caspian Sea.
The total mass of the
hydrosphere is about 1.4 × 10
21 kg, ca. 0.023 % of the Earth's total mass.
See
sea water for a detailed discussion of ocean water composition, most notably its
salinity.
Origins
{{main|Origin of the world's oceans}}
There are thought to have been two primary sources for the primordial water that formed Earth's oceans, with debate as to their relative importance. One is outgassing of steam from the Earth's interior, which contributed to the atmosphere and, once the young planet had sufficiently cooled, produced rain; the other is the large numbers of
comets which impacted with the Earth and added their water to it.
Exploration
{{main|Ocean exploration}}
Image:Ocean gravity map.gif right|thumb|350px|Map of large underwater features. (1995, [[NOAA)]]
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
1 E4 m 10,923 m (35,838 ft) [http://www.rain.org/ocean/ocean-studies-challenger-deep-mariana-trench.html]. It was fully surveyed in
1951 by the British naval vessel, "Challenger II" which gave its name to the deepest part of the trench, the "
Challenger Deep".
Much of the bottom of the world's oceans is unexplored and unmapped. A global image of many underwater features larger than 10 km was created in
1995 based on gravitational distortions of the nearby sea surface.
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. The
Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans.
Ecology
The oceans are home to the majority of
plant and
animal life on Earth. These lifeforms include:
*
fish
*
cetacea such as
whale whales,
dolphin dolphins and
porpoise porpoises,
*
cephalopods such as the
octopus
*
crustaceans such as
lobsters and
shrimp
*
marine worms
*
plankton
*
krill
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.
Ancient oceans
Continental drift has reconfigured the Earth's oceans, joining and splitting ancient oceans to form the current oceans. Ancient oceans include:
*
Panthalassa, the vast world ocean that surrounded the
Pangaea supercontinent.
*
Tethys Ocean, the ocean between the ancient continents of
Gondwana and
Laurasia.
*
Iapetus Ocean, the southern hemisphere ocean between
Baltica and
Avalonia.
Extraterrestrial oceans
Earth is the only known planet 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 (moon) Europa, and, with less certainty,
Callisto (moon) Callisto and
Ganymede (moon) Ganymede.
Geysers have been found on
Enceladus (moon) Enceladus. Other icy moons may have once had internal oceans that have now frozen, such as
Triton (moon) Triton. The planets
Uranus (planet) Uranus and
Neptune (planet) 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 (planet) 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 it had some long-term standing water in at least one location, but its extent is not known.
Liquid hydrocarbons were thought to be present on the surface of
Titan (moon) Titan, though it may be more accurate to describe them as "lakes" rather than an "ocean".
Cassini-Huygens space mission, which dropped the
Huygens probe onto Titan's surface in January
2005, found that Titan is currently without such lakes but that it may gain and lose them periodically. Titan is also thought likely to have a subterranean water ocean under the mix of ice and hydrocarbons that forms its outer crust.
See also
*
Oceanography
*
International Maritime Organization
*
Sea
*
Mediterranean sea
*
Marginal sea
*
Sea salt
*
Water
*
World Ocean Day
*
Marine biology
*
Pelagic zone
External links
{{wiktionary}}
-
Ocean Explorer - An educational and reference resource from NOAA
-
Science taps into ocean secrets
-
Why is the ocean salty?
-
Official IHO boundaries of Oceans and Seas
-
The Hydrogen Expedition The first circumnavigation of the globe in a hydrogen fuel cell powered boat
-
Oceana - Protecting the World's Oceans
-
Coreocean
-
NOPP - The National Oceanographic Partnership Program
-
World Ocean Observatory
-
Greenpeace Defending our Oceans
Category:Bodies of water Oceans
Category:Oceans
Category:Oceanography Oceans
Category:Sustainability Oceans
an:Ozián
bg:Световен океан
zh-min-nan:Hái-iû�
bn:মহাসম�দ�র
br:Meurvor
ca:OceÃ
cs:Oceán
da:Verdenshave
de:Ozean
et:Ookean
es:Océano
eo:Oceano
eu:Ozeano
fr:Océan
gl:Océano
ko:대양
hr:Ocean
io:Oceano
id:Samudra
it:Oceano (geografia)
he:×?×•×§×™×™× ×•×¡
la:Oceanus
lt:Vandenynas
ms:Lautan
nl:Oceaan
ja:大洋
ka:�კე�ნე
no:Hav
nn:Hav
pl:Ocean
pt:Oceano
ro:Ocean
ru:Океан
sh:Ocean
simple:Ocean
sk:Oceán
sl:Ocean
sr:Океан
sv:Världshav
tl:Karagatan
th:มหาสมุทร
uk:Океан
zh:æµ·æ´‹
*** Shopping-Tip: Ocean
