An ocean (from Greek , Okeanos (Oceanus)) is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (an area of some 361 million square kilometers) 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 over 3,000 meters (9,800 ft) deep. Average oceanic salinity is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ppt.
OverviewThough generally recognized as several 'separate' oceans, these waters comprise one global, interconnected body of salt water often referred to as the World Ocean or global ocean. This concept of a global ocean as 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) the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean (which is sometimes subsumed as the southern portions of the Pacific, Atlantic, and Indian Oceans), and the Arctic Ocean (which is sometimes considered a sea of the Atlantic). The Pacific and Atlantic may be further subdivided by the equator into northerly and southerly portions. Smaller regions of the oceans are called seas, gulfs, bays and other names. There are also some smaller bodies of saltwater that are on land and not interconnected with the World Ocean, such as the Aral Sea, and the Great Salt Lake – though they may be referred to as 'seas', they are actually salt lakes.
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 where there are no continents. From this perspective, there are three oceans today: the World Ocean and the Caspian and Black Seas, the latter two having been formed by the collision of Cimmeria with Laurasia. The Mediterranean Sea is very nearly a discrete 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 African continent has closed the strait off entirely. The Black Sea is connected to the Mediterranean through the Bosporus, but this is in effect 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.
Physical propertiesThe area of the World Ocean is 361 million square kilometers (139 million sq mi), its volume is approximately 1.3 billion cubic kilometers (310 million cu mi), and its average depth is 3,790 meters (12,430 ft). 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 × 1021 kilograms, which is about 0.023% of the Earth's total mass. Less than 2% is freshwater; the rest is saltwater, mostly in the ocean.
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' nuclei of red photons from the incoming light, the only known example of color in nature resulting from vibrational, rather than electronic, dynamics.
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 Marianas Trench located in the Pacific Ocean near the Northern Mariana Islands. It has a maximum depth of 10,923 meters (35,838 ft) . 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". In 1960, the Trieste successfully reached the bottom of the trench, manned by a crew of two men.
Much of the bottom of the world's oceans are unexplored and unmapped. A global image of many underwater features larger than 10 kilometers (6 mi) was created in 1995 based on gravitational distortions of the nearby sea surface.
The oceans are essential to transportation: most 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. They are also an important source of valuable food items for the fishing industry. Some of these are shrimp, fish, crabs and lobster.
Continental drift has reconfigured the Earth's oceans, joining and splitting ancient oceans to form the current oceans. 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.
- 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.
- See also Extraterrestrial liquid water
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 it had some 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 trace of them seems to have vanished in later resurfacing.
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 Cassini-Huygens space mission initially discovered only what appeared to be dry lakebeds and empty river channels, suggesting that Titan had lost what surface liquids it might have had. A more recent fly-by of Titan made by Cassini has produced radar images that strongly suggest hydrocarbon lakes near the polar regions where it is colder. Titan is also thought likely to have a subterranean water ocean under the mix of ice and hydrocarbons that forms its outer crust.
Beyond the solar system, Gliese 581 c is at the right distance from its sun for liquid water to exist on the planet's surface. Since it does not transit its sun, there is no way to know if there is any water there. HD 209458b may have water vapour in its atmosphere - this is currently being disputed. Gliese 436 b is believed to have 'hot ice'. Neither of these planets are cool enough for liquid water: but if water molecules exist there, they are likely to be found also on planets at a suitable temperature.
MythologyThe original concept of "ocean" goes back to notions of Mesopotamian and Indo-European mythology, imagining the world to be encircled by a great river. Okeanos, "Ωκεανός" in Greek, reflects the ancient Greek observation that a strong current flowed off Gibraltar and their subsequent assumption that it was a great river. (Compare also Samudra from Hindu mythology and Jörmungandr from Norse mythology). The world was imagined to be enclosed by a celestial ocean above the heavens, and an ocean of the underworld below (compare Rasā, Varuna).
- Arctic Ocean
- Atlantic Ocean
- Indian Ocean
- International Maritime Organization
- Law of the Sea
- Marginal sea
- Marine biology
- Marine debris
- Mediterranean sea
- Ocean acidification
- Pacific Ocean
- Pelagic zone
- Sea level and sea level rise
- Sea salt
- Sea state
- Seven Seas
- Southern Ocean
- World Ocean Day
- Ocean Explorer - An educational and reference resource from NOAA
- Oceanography Image of the Day - from the Woods Hole Oceanographic Institution
- Ocean Motion - Educational reference and data resource from NASA
- NOS Data Explorer - A portal to obtain NOAA National Ocean Service data
- Science taps into ocean secrets
- Why is the ocean salty?
- Intergovernmental Oceanographic Commission
- Oceana - Protecting the World's Oceans
- CORE - Consortium for Oceanographic Research and Education
- NOPP - National Oceanographic Partnership Program
- NOSB - National Ocean Sciences Bowl
- CoML - Census of Marine Life
- World Ocean Observatory
- Greenpeace Defending our Oceans
- The Last Days of the Ocean, a Mother Jones special report on the state of the ocean
- Ocean Voyager, a five-part journey to save the seas, created by Mother Jones magazine
- The Ocean Conservancy - Advocates for Wild, Healthy Oceans
- NOAA DChart - Plot and download ocean data from your browser or Google Earth
- UN Atlas of the Oceans
- American Fisheries Society
- Cousteau Society
- Marine Environmental Research Institute
- NOAA National Fisheries
- NOAA National Ocean Service
- Ocean Alliance
- Ocean Futures Society
- National Office for Integrated and Sustained Ocean Observations
- One Fish
- Blue Ocean Institute
- Changing Currents: Charting a Course of Action for the Future of Oceans
- Shuttle Views the Earth: Oceans from Space
oceans in Arabic: محيط (جغرافيا)
oceans in Aragonese: Ozián
oceans in Official Aramaic (700-300 BCE): ܐܘܩܝܢܘܣ
oceans in Azerbaijani: Okean
oceans in Bengali: মহাসমুদ্র
oceans in Min Nan: Hái-iûⁿ
oceans in Belarusian: Акіян
oceans in Belarusian (Tarashkevitsa): Акіян
oceans in Central Bicolano: Kadagatan
oceans in Bosnian: Okean
oceans in Breton: Meurvor
oceans in Bulgarian: Световен океан
oceans in Catalan: Oceà
oceans in Chuvash: Океан
oceans in Czech: Oceán
oceans in Welsh: Cefnfor
oceans in Danish: Verdenshave
oceans in German: Ozean
oceans in Estonian: Ookean
oceans in Modern Greek (1453-): Ωκεανός
oceans in Spanish: Océano
oceans in Esperanto: Oceano
oceans in Basque: Ozeano
oceans in Persian: اقیانوس
oceans in French: Océan
oceans in Western Frisian: Oseaan
oceans in Friulian: Ocean
oceans in Galician: Océano
oceans in Classical Chinese: 洋
oceans in Korean: 대양
oceans in Armenian: Օվկիանոս
oceans in Hindi: महासागर
oceans in Croatian: Ocean
oceans in Ido: Oceano
oceans in Igbo: Oke osimiri
oceans in Indonesian: Samudra
oceans in Icelandic: Sjór
oceans in Italian: Oceano
oceans in Hebrew: אוקיינוס
oceans in Javanese: Samodra
oceans in Georgian: ოკეანე
oceans in Swahili (macrolanguage): Bahari
oceans in Haitian: Oseyan
oceans in Lao: ມະຫາສະໝຸດ
oceans in Latin: Oceanus
oceans in Latvian: Okeāns
oceans in Lithuanian: Vandenynas
oceans in Lojban: braxamsi
oceans in Hungarian: Óceán
oceans in Macedonian: Океан
oceans in Malagasy: Ranomasina
oceans in Malayalam: സമുദ്രം
oceans in Marathi: महासागर
oceans in Malay (macrolanguage): Lautan
oceans in Mongolian: Далай
oceans in Dutch: Oceaan
oceans in Japanese: 大洋
oceans in Norwegian: Hav#Verdenshavene
oceans in Norwegian Nynorsk: Verdshav
oceans in Uzbek: Okean
oceans in Low German: Ozean
oceans in Polish: Ocean
oceans in Portuguese: Oceano
oceans in Romanian: Ocean
oceans in Quechua: Mama qucha
oceans in Russian: Океан
oceans in Albanian: Oqeani
oceans in Sicilian: Ocèanu
oceans in Simple English: Ocean
oceans in Slovenian: Ocean
oceans in Serbian: Океан
oceans in Serbo-Croatian: Ocean
oceans in Sundanese: Jaladri
oceans in Swedish: Hav#V.C3.A4rldshav
oceans in Finnish: Meri
oceans in Tagalog: Karagatan
oceans in Telugu: మహాసముద్రము
oceans in Thai: มหาสมุทร
oceans in Vietnamese: Đại dương
oceans in Tajik: Уқёнус
oceans in Turkish: Okyanus
oceans in Ukrainian: Океан
oceans in Venetian: Oceano
oceans in Walloon: Oceyan
oceans in Wolof: Mbàmbulaan
oceans in Yiddish: אקעאן
oceans in Yoruba: Òkun
oceans in Contenese: 海洋
oceans in Chinese: 海洋