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Waves on an ocean coast.

An ocean (from Ancient Greek Ὠκεανός (Okeanos); the World Ocean of classical antiquity[1]) is a body of saline water that composes much of a planet's hydrosphere.[2] On Earth, an ocean is one of the major conventional divisions of the World Ocean, which occupies two-thirds of planet's surface. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans.[3][4] The word sea is often used interchangeably with "ocean" in American English but, strictly speaking, a sea is a body of saline water (generally a division of the World Ocean) that land partly or fully encloses.[5]

Earth is the only planet that is known to have an ocean (or any large amounts of open liquid water). Saline water covers approximately 72% of the planet's surface (~3.6x108 km2) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of the Earth's surface.[6] The ocean contains 97% of the Earth's water, and oceanographers have stated that only 5% of the World Ocean has been explored.[6] The total volume is approximately 1.3 billion cubic kilometres (310 million cu mi)[7] with an average depth of 3,682 metres (12,080 ft).[8]



Earth's global ocean[edit]


Rotating series of maps showing alternate divisions of the oceans
Various ways to divide the World Ocean



Rank Ocean Notes
1 Pacific Ocean Separates Asia and Oceania from the Americas[15]
2 Atlantic Ocean Separates the Americas from Eurasia and Africa
3 Indian Ocean Washes upon southern Asia and separates Africa and Australia[15][16][17]
4 Southern Ocean Sometimes considered an extension of the Pacific, Atlantic and Indian Oceans,[11][18] which encircles Antarctica

The Pacific and Atlantic may be further subdivided by the equator into northern and southern portions. A smaller region of the ocean can be called other names, such as sea, gulf, bay, and strait.

Physical properties[edit]

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. The area of the World Ocean is 361 million square kilometres (139 million square miles),[19] and its volume is approximately 1.3 billion cubic kilometres (310 million cu mi).[7] 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).[19] Nearly half of the world's marine waters are over 3,000 metres (9,800 ft) deep.[13] The vast expanses of deep ocean (anything below 200 metres (660 ft)) cover about 66% of the Earth's surface.[20] This does not include seas not connected to the World Ocean, such as the Caspian Sea.


Sailors and other mariners have reported that the ocean often emits a visible glow, or luminescence, which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow.[22] It is most likely caused by bioluminescence.[23][24][25]

Zones and depths[edit]

Drawing showing divisions according to depth and distance from shore
The major oceanic divisions

Oceanographers divide the ocean into different zones by physical and biological conditions. The pelagic zone includes all open ocean and comprises further regions of depth and light abundance. The photic zone falls two-hundred meters below the oceanic surface and is where photosynthesis can occur and is, therefore, the most biodiverse. Plants require photosynthesis: deeper life relies on material sinking from above (see marine snow) or another energy source. Hydrothermal vents are the primary source in what is known as the aphotic zone (depths exceeding 200 m). The pelagic part of the photic zone is known as the epipelagic.

The pelagic part of the aphotic zone comprises regions that descend in vertical order according to temperature. The mesopelagic is the uppermost region. Its lowermost boundary is at a thermocline of 12 °C (54 °F), which, in the tropics generally lies at 700–1,000 metres (2,300–3,300 ft). Next is the bathypelagic lying between 10 and 4 °C (50 and 39 °F), typically between 700–1,000 metres (2,300–3,300 ft) and 2,000–4,000 metres (6,600–13,100 ft) Lying along the top of the abyssal plain is the abyssopelagic, whose lower boundary lies at about 6,000 metres (20,000 ft). The last zone includes the deep oceanic trench, and is known as the hadalpelagic. This lies between 6,000–11,000 metres (20,000–36,000 ft) and is the deepest oceanic zone.

The benthic zones are aphotic and correspond to the three deepest zones of the deep-sea. The bathyal zone covers the continental slope down to about 4,000 metres (13,000 ft). The abyssal zone covers the abyssal plains between 4,000 and 6,000 m. Lastly, the hadal zone corresponds to the hadalpelagic zone, which is found in oceanic trenches. The pelagic zone comprises two subregions: the neritic zone and the oceanic zone. The neritic encompasses the water mass directly above the continental shelves whereas the oceanic zone includes all the completely open water. Whereas the littoral zone covers the region between low and high tide and represents the transitional area between marine and terrestrial conditions. It is also known as the intertidal zone because it is the area where tide level affects the conditions of the region.





False color photo
Map of large underwater features (1995, NOAA)



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.[citation needed]










Lifeforms native to the ocean include:


Characteristics of Oceanic Gases [29][30][31]
Carbon dioxide (CO2) 64 to 107 15%
Nitrogen (N2) 10 to 18 48%
Oxygen (O2) 0 to 13 36%
Temperature O2 CO2 N2
0°C 8.14 8,700 14.47
10°C 6.42 8,030 11.59
20°C 5.26 7,350 9.65
30°C 4.41 6,600 8.26

Ocean Surface[edit]

Generalized Characteristics of Ocean Surface by Latitude [33][34][35][36] [37] [37][38][39]
Sea Surface Temperature in Winter -2°C 5 to 20°C 20 to 25°C

Mixing Time[edit]



Mean Oceanic Residence Times for specific Constituents [40][41]
Constituent Residence Time (in years)
Iron (Fe) 200
Aluminum (Al) 600
Manganese (Mn) 1,300
Water (H2O) 4,100
Silicon (Si) 20,000
Carbonate (CO32-) 110,000
Calcium (Ca2+) 1,000,000
Sulfate (SO42-) 11,000,000
Potassium (K+) 12,000,000
Magnesium (Mg2+) 13,000,000
Sodium (Na+) 68,000,000
Chloride (Cl-) 100,000,000





The average chlorinity is about 19.2‰, and, thus, the average salinity is around 34.7‰ [42]

Absorption of light[edit]

Absorption of Light in Different Wavelengths by Ocean [42]
Ultraviolet (UV): 310 31 14.0
Violet (V): 400 107 4.2
Blue (B): 475 254 1.8
Green (G): 525 113 4.0
Yellow (Y): 575 51 8.7
Orange (O): 600 25 16.7
Red (R): 725 4 71.0
Infrared (IR): 800 3 82.0

Economic value[edit]



The motions which first present themselves to our notice are partial and alternate rising and falling of the surface is known as undulations or waves.

Extraterrestrial oceans[edit]

See also Extraterrestrial liquid water
Artists conception of subsurface ocean of Enceladus confirmed April 3, 2014.[43][44]

While Earth is the only known planet with large stable bodies of liquid water on its surface and the only one in our Solar System, other celestial bodies are believed to possess large oceans.




Natural satellites[edit]

A global layer of liquid water thick enough to decouple the crust from the mantle is believed to be present on Titan, Europa and, with less certainty, Callisto, Ganymede[47] and Triton.[48][49] A magma ocean is thought to be present on Io. Geysers have been found on Saturn's moon Enceladus, possibly originating from about 10 kilometres (6.2 mi) deep ocean beneath an ice shell.[43] Other icy moons may also have internal oceans, or have once had internal oceans that have now frozen.[47]

Large bodies of liquid hydrocarbons are thought to be present on the surface of Titan, though they are not large enough to be described as oceans and are sometimes referred to as lakes or seas. 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. Cassini's more recent fly-by of Titan offers radar images that strongly suggest hydrocarbon lakes exist near the colder polar regions. Titan is thought to have a subterranean water ocean under the ice and hydrocarbon mix that forms its outer crust.

Dwarf planets and trans-Neptunian objects[edit]

Diagram showing a possible internal structure of Ceres

Ceres appears to be differentiated into a rocky core and icy mantle and may harbour a liquid-water ocean under its surface.[50][51]

Not enough is known of the larger Trans-Neptunian objects to determine whether they are differentiated bodies capable of possessing oceans, although models of radioactive decay suggest that Pluto,[52] Eris, Sedna, and Orcus have oceans beneath solid icy crusts at the core-boundary approximately 100 to 180 km thick.[47]




Theoretical models have been used to predict with high probability that GJ 1214 b, detected by transit, is composed of exotic form of ice VII, making up 75% of its mass,[53] making it an ocean planet.

Other possible candidates are merely speculated based on their mass and position in the habitable zone include planet though little is actually known of their composition. Some scientists speculate Kepler-22b may be an "ocean-like" planet.[54] Models have been proposed for Gliese 581 d that could include surface oceans. Gliese 436 b is speculated to have an ocean of "hot ice".[55] Extrasolar moons orbiting planets, particularly gas giants within their parent star's habitable zone may theoretically possess surface oceans.


Non-water surface liquids[edit]

Oceans, seas, lakes, etc., can be composed of liquids other than water: e.g. the hydrocarbon lakes on Titan. The possibility of seas of nitrogen on Triton was also considered but ruled out.[57] Underneath the thick atmospheres of Uranus and Neptune it is expected that these planets are composed of oceans of hot high-density fluid mixtures of water, ammonia and other volatiles.[58] The gaseous outer layers of Jupiter and Saturn transition smoothly into oceans of liquid hydrogen.[59][60] There is evidence that the icy surfaces of the moons Ganymede, Callisto, Europa, Titan and Enceladus are shells floating on oceans of very dense liquid water or water–ammonia.[61][62][63][64][65] Earth is often called the ocean planet because it is 70% covered in water.[66][67] The atmosphere of Venus is 96.5% carbon dioxide and at the surface the pressure makes the CO2 a supercritical fluid. Extrasolar terrestrial planets that are extremely close to their parent star will be tidally locked and so one half of the planet will be a magma ocean.[68] It is also possible that terrestrial planets had magma oceans at some point during their formation as a result of giant impacts.[69] Where there are suitable temperatures and pressures, volatile chemicals which might exist as liquids in abundant quantities on planets include ammonia, argon, carbon disulfide, ethane, hydrazine, hydrogen, hydrogen cyanide, hydrogen sulfide, methane, neon, nitrogen, nitric oxide, phosphine, silane, sulfuric acid, and water.[70] Hot Neptunes close to their star could lose their atmospheres via hydrodynamic escape, leaving behind their cores with various liquids on the surface.[71]

See also[edit]


  6. ^ a b c "NOAA – National Oceanic and Atmospheric Administration – Ocean". Noaa.gov. Retrieved 8-11-2012. 
  10. ^ "Titan Likely To Have Huge Underground Ocean | Mind Blowing Science". Mindblowingscience.com. Retrieved 8-11-2012. 
  11. ^ a b c "Ocean-bearing Planets: Looking For Extraterrestrial Life In All The Right Places". Sciencedaily.com. Retrieved 8-11-2012. 
  12. ^ "Ocean". Sciencedaily.com. Retrieved 8-11-2012. 
  13. ^ a b "Distribution of land and water on the planet". UN Atlas of the Oceans
  14. ^ Spilhaus, Athelstan F. (July 1942). Maps of the whole world ocean. 32 (3). American Geographical Society. pp. 431–5. 
  15. ^ a b c "Pacific Ocean – University of Delaware". Ceoe.udel.edu. Retrieved 8-11-2012. 
  16. ^ "Indian Ocean – Wikipedia, the Free Encyclopedia". Wikipedia.org. Retrieved 8-11-2012. 
  17. ^ "Indian Ocean – Britannica Online Encyclopedia". Britannica.com. Retrieved 8-11-2012. 
  19. ^ a b The World's Oceans and Seas. Encarta. 
  21. ^ Paula G. Coble "Marine Optical Biogeochemistry:  The Chemistry of Ocean Color" Chemical Reviews, 2007, volume 107, pp 402–418. doi: 10.1021/cr050350
  27. ^ Rhines and Hakkinen (2003). "Is the Oceanic Heat Transport in the North Atlantic Irrelevant to the Climate in Europe?". ASOF Newsletter. 
  28. ^ Biology: Concepts & Connections. Chapter 34: The Biosphere: An Introduction to Earth's Diverse Environment. (sec 34.7)
  29. ^ http://www.soest.hawaii.edu/oceanography/courses/OCN623/Spring2012/Non_CO2_gases.pdf
  30. ^ http://butane.chem.uiuc.edu/pshapley/GenChem1/L23/web-L23.pdf
  31. ^ Composition of seawater
  32. ^ http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-742-marine-chemistry-fall-2006/lecture-notes/lec_11_gas_exch.pdf
  33. ^ 5.6 Synthesis - AR4 WGI Chapter 5: Observations: Oceanic Climate Change and Sea Level
  34. ^ Annual mean
  35. ^ Roger Graham Barry, Richard J. Chorley (2003). "Atmosphere, Weather, and Climate". [Routledge]. p. 68. 
  36. ^ Ocean Stratification
  37. ^ a b Rui Xin Huang (2010). "Ocean Circulation: Wind-Driven and Thermohaline Processes". [Cambridge University Press]. 
  38. ^ http://www.cgd.ucar.edu/cas/cdeser/Docs/deser.sstvariability.annrevmarsci10.pdf
  39. ^ Introduction to Physical Oceanography : Chapter 6 - Temperature, Salinity, and Density - Geographical Distribution of Surface Temperature and Salinity
  40. ^ http://www.gly.uga.edu/railsback/3030/3030Tres.pdf
  49. ^ Javier Ruiz (December 2003). "Heat flow and depth to a possible internal ocean on Triton". Icarus 166 (2): 436–439. Bibcode:2003Icar..166..436R. doi:10.1016/j.icarus.2003.09.009. 
  57. ^ Page 485, Encyclopedia of the solar system By Lucy-Ann Adams McFadden, Paul Robert Weissman, Torrence V. Johnson
  58. ^ Atreya, S.; Egeler, P.; Baines, K. (2006). "Water-ammonia ionic ocean on Uranus and Neptune?". Geophysical Research Abstracts 8: 05179. Bibcode:2005AGUFM.P11A0088A. 
  61. ^ Coustenis, A.; Lunine, J.; Lebreton, J.; Matson, D.; Erd, C.; Reh, K.; Beauchamp, P.; Lorenz, R. et al. (2008). The Titan Saturn System Mission. "American Geophysical Union, Fall Meeting 2008, abstract #P21A-1346". American Geophysical Union 21: 1346. Bibcode:2008AGUFM.P21A1346C. "the Titan system, rich in organics, containing a vast subsurface ocean of liquid water" 
  62. ^ Nimmo, F; Bills, B. G. (2010). "Shell thickness variations and the long-wavelength topography of Titan". Icarus 208 (2): 896–904. Bibcode:2010Icar..208..896N. doi:10.1016/j.icarus.2010.02.020. "observations can be explained if Titan has a floating, isostatically-compensated ice shell" 
  63. ^ Goldreich, Peter M.; Mitchell, Jonathan L. (2010). "Elastic ice shells of synchronous moons: Implications for cracks on Europa and non-synchronous rotation of Titan". Icarus 209 (2): 631–638. arXiv:0910.0032. Bibcode:2010Icar..209..631G. doi:10.1016/j.icarus.2010.04.013. "A number of synchronous moons are thought to harbor water oceans beneath their outer ice shells. A subsurface ocean frictionally decouples the shell from the interior" 
  66. ^ USA (2011-10-03). "The ocean planet". Ncbi.nlm.nih.gov. Retrieved 2011-10-14. 
  67. ^ Irrigating Crops with Seawater; August 1998; Scientific American
  69. ^ Fluid Dynamics of a Terrestrial Magma Ocean, V. S. Solomatov, 2000
  70. ^ Tables 3 and 4 in Many Chemistries Could Be Used to Build Living Systems, WILLIAM BAINS, ASTROBIOLOGY, Volume 4, Number 2, 2004
  71. ^ Atmospheric Loss of Sub-Neptune’s and Implications for Liquid Phases of Different Solvents on Their Surfaces, J.J. Leitner (1), H. Lammer (2), P. Odert (3), M. Leitzinger (3), M.G. Firneis (1) and A. Hanslmeier (3), EPSC Abstracts, Vol. 4, EPSC2009-542, 2009, European Planetary Science Congress

Further reading[edit]


External links[edit]