World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0018842359
Reproduction Date:

Title: Ocean  
Author: World Heritage Encyclopedia
Language: English
Subject: Physical oceanography, Nature, Indian Ocean, Pacific Ocean, Sea
Publisher: World Heritage Encyclopedia




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 (~3.6×108 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 kilometers (310 million cu mi)[7] with an average depth of 3,682 meters (12,080 ft).[8]



Earth's global ocean

Global divisions

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

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.[12][13] This concept of a continuous body of water with relatively free interchange among its parts is of fundamental importance to oceanography.[14]


Rank Ocean Notes
1 Pacific The peaceful sea west of the Magellan Strait,[16] officially separated into the North and South Pacific (divided by the Equator[17] and containing the waters between the southernmost points of Tasmania and Terra del Fuego (and including the waters of the Magellan Strait) but limited by the borders of the Tasman, Coral, Solomon, and Bismark Seas, the East Indian Archipelago, the Philippine, Japan, Okhotsk, and Bering Seas, the Gulf of Alaska, the coastal waters of southeast Alaska and British Columbia, and the Gulf of California.[18]
2 Atlantic The sea beyond the Atlas Mountains,[19][20] officially separated into the North and South Atlantic (divided by the Equator) and containing the waters between the southernmost points of Tierra del Fuego and Africa but limited by the borders of the Rio de la Plata, the Caribbean Sea, the Gulf of Mexico, the Bay of Fundy, the Gulf of St. Lawrence, the Davis Strait, the Greenland, Norwegian, North, Scottish, and Irish Seas, the Bristol and English Channels, the Bay of Biscay, the Mediterranean Sea, and the Gulf of Guinea,[18] although now often considered to end north of the Antarctic Convergence.
3 Indian The sea south of India, officially containing the waters between the southernmost points of Africa and Tasmania, bounded on the north by the Arabian and Laccadive Seas, the Bay of Bengal, the East Indian Archipelago, and the Great Australian Bight and on the south by Antarctica,[18] although now often considered to end north of the Antarctic Convergence.
4 Southern
Still officially considered an extension of the Pacific, Atlantic and Indian Oceans by the IHO,[11][18] it is distinguished by the convergence which encircles Antarctica.
5 Arctic The sea around the North Pole, officially containing the waters north of the Greenland Sea, then a line east along 80°N to the Barentsz, Kara, Laptev, East Siberian, Chuckchi, and Beaufort Seas.[18] Sometimes itself considered a sea of the Atlantic.

These adjacent regions—whether seas, gulfs, bays, bights, or straits—are very often included as part of the nearest ocean.

Physical properties

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 kilometers (139 million square miles),[21] and its volume is approximately 1.3 billion cubic kilometers (310 million cu mi).[7] This can be thought of as a cube of water with an edge length of 1,111 kilometers (690 mi). Its average depth is 3,790 meters (12,430 ft), and its maximum depth is 10,923 meters (6.787 mi).[21] Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep.[13] The vast expanses of deep ocean (anything below 200 meters (660 ft)) cover about 66% of the Earth's surface.[22] This does not include seas not connected to the World Ocean, such as the Caspian Sea.

The bluish chlorophyll.[23]

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.[24] It is most likely caused by bioluminescence.[25][26][27]

Zones with depth

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






The ocean can be divided into three density zones: the surface zone, the pycnocline, and the deep zone. The surface zone, also called the mixed layer, refers to the uppermost density zone of the ocean. Temperature and salinity are relatively constant with depth in this zone due to currents and wave action. The surface zone contains ocean water that is in contact with the atmosphere and within the photic zone. The surface zone has the ocean's least dense water and represents approximately 2% of the total volume of ocean water. The surface zone usually ranges between depths of 500 feet to 3,300 feet below ocean surface, but this can vary a great deal. In some cases, the surface zone can be entirely non-existent. The surface zone is typically thicker in the tropics than in regions of higher latitude. The transition to colder, denser water is more abrupt in the tropics than in regions of higher latitudes. The pycnocline refers to a zone wherein density substantially increases with depth due primarily to decreases in temperature. The pycnocline effectively separates the lower-density surface zone above from the higher-density deep zone below. The pycnocline represents approximately 18% of the total volume of ocean water. The deep zone refers to the lowermost density zone of the ocean. The deep zone usually begins at depths below 3,300 feet in mid-latitudes. The deep zone undergoes negligible changes in water density with depth. The deep zone represents approximately 80% of the total volume of ocean water. The deep zone contains relatively colder and stable water.

If a zone undergoes dramatic changes in temperature with depth, it contains a thermocline. The tropical thermocline is typically deeper than the thermocline at higher latitudes. Polar waters, which receive relatively little solar energy, are not stratified by temperature and generally lack a thermocline since surface water at polar latitudes are nearly as cold as water at greater depths. Below the thermocline, water is very cold, ranging from −1 °C to 3 °C. Since this deep and cold layer contains the bulk of ocean water, the average temperature of the world ocean is 3.9 °C If a zone undergoes dramatic changes in salinity with depth, it contains a halocline. If a zone undergoes a strong, vertical chemistry gradient with depth, it contains a chemocline.



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 kilometers (6.2 mi) was created in 1995 based on gravitational distortions of the nearby sea surface.










Lifeforms native to the ocean include:



Characteristics of Oceanic Gases[31][32][33]
Gas Concentration of Seawater, by Mass (in parts per million), for whole Ocean % Dissolved Gas, by Volume, in Seawater at Ocean Surface
Carbon dioxide (CO2) 64 to 107 15%
Nitrogen (N2) 10 to 18 48%
Oxygen (O2) 0 to 13 36%
Solubility of Oceanic Gases (in terms of mL/L) with Temperature at salinity of 33‰ and atmospheric pressure[34]
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

Generalized Characteristics of Ocean Surface by Latitude[35][36][37][38][39][40][41]
Characteristic Oceanic Waters in Polar regions Oceanic Waters in Temperate regions Oceanic Waters in Tropical regions
Sea Surface Temperature in Winter −2 °C 5 to 20 °C 20 to 25 °C
Average Salinity 28‰ to 32‰ 35‰ 35‰ to 37‰
Annual Variation of Air Temperature ≤ 40ªC 10 °C < 5 °C
Annual Variation of Water Temperature < 5ªC 10 °C < 5 °C

Mixing Time

Residence Time=The amount of the element in the ocean ÷ The rate at which that element is added to (or removed from) the ocean

The mean oceanic mixing time (residence time) is thought to be approximately 1,600 years. If a given element in the ocean stays in the ocean, on average, longer than the oceanic mixing time, then that element is assumed to be homogeneously spread throughout the ocean. As a result, since the major salts have a residence time that is longer than 1,600 years, the ratio of major salts is thought to be unchanging across the ocean. This constant ratio is often referred to as Forchhammer's principle or the principle of constant proportions.

Mean Oceanic Residence Times for specific Constituents[42][43]
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




Salinity (in ‰)=1.80655 x Chlorinity (in ‰)

The average chlorinity is about 19.2‰, and, thus, the average salinity is around 34.7‰ [44]

Absorption of light

Absorption of Light in Different Wavelengths by Ocean[44]
Color: Wavelength (nm) Depth wherein 99 percent of wavelength is absorbed (in meters) Percent absorbed in 1 meter of water
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




Extraterrestrial oceans

Artist's conception of subsurface ocean of Enceladus confirmed April 3, 2014.[45][46]

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


The gas giants, Jupiter and Saturn, are thought to lack surfaces and instead have a stratum of liquid hydrogen, however their planetary geology is not well understood. The possibility of Uranus and Neptune possessing hot, highly compressed, supercritical water under their thick atmospheres has been hypothesised. Although their composition is still not fully understood, a 2006 study by Wiktorowicz et al. ruled out the possibility of such a water "ocean" existing on Neptune,[47] though some studies have suggested that exotic oceans of liquid diamond are possible.[48]


Natural satellites

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[49][50] and Triton.[51][52] A magma ocean is thought to be present on Io. Geysers have been found on Saturn's moon Enceladus, possibly originating from about 10 kilometers (6.2 mi) deep ocean beneath an ice shell.[45] Other icy moons may also have internal oceans, or may once have had internal oceans that have now frozen.[53]


Dwarf planets and trans-Neptunian objects

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.[54][55]

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,[56] Eris, Sedna, and Orcus have oceans beneath solid icy crusts at the core-boundary approximately 100 to 180 km thick.[53]




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,[57] 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.[58] 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".[59] Extrasolar moons orbiting planets, particularly gas giants within their parent star's habitable zone may theoretically possess surface oceans.


Non-water surface liquids

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.[61] 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.[62] The gaseous outer layers of Jupiter and Saturn transition smoothly into oceans of supercritical hydrogen.[63][64] 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.[65][66][67][68][69] Earth is often called the ocean planet because it is 70% covered in water.[70][71] 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.[72] It is also possible that terrestrial planets had magma oceans at some point during their formation as a result of giant impacts.[73] Where there are suitable temperatures and pressures, volatile chemicals that 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.[74] Hot Neptunes close to their star could lose their atmospheres via hydrodynamic escape, leaving behind their cores with various liquids on the surface.[75]

See also


  1. ^ "Ὠκεανός".  
  6. ^ a b c "NOAA – National Oceanic and Atmospheric Administration – Ocean". Retrieved 8-11-2012. 
  10. ^ "Titan Likely To Have Huge Underground Ocean | Mind Blowing Science". Retrieved 8-11-2012. 
  11. ^ a b c "Ocean-bearing Planets: Looking For Extraterrestrial Life In All The Right Places". Retrieved 8-11-2012. 
  12. ^ "Ocean". Retrieved 8-11-2012. 
  14. ^ Spilhaus, Athelstan F. (July 1942). "Maps of the whole world ocean". 32 (3).  
  15. ^ "Pacific Ocean – University of Delaware". Retrieved 8-11-2012. 
  16. ^ Oxford English Dictionary, 3rd ed. "Pacific, adj.2 and n.2" Oxford University Press (Oxford), 2005.
  17. ^ Apart from the Galapagos and Gilbert Islands, whose surroundings waters are formally included in the South Pacific, even where they lie north of the Equator.
  18. ^ a b c d e "Limits of Oceans and Seas, 3rd edition" (PDF). International Hydrographic Organization. 1953. Retrieved 7 February 2010. 
  19. ^ Oxford English Dictionary, 1st ed. "Atlantic, adj. and n." Oxford University Press (Oxford), 1885.
  20. ^ Herodotus. Ἱστορίαι [The Histories], I.202. c. 420 BC. (Ancient Greek)
  21. ^ a b The World's Oceans and Seas. Encarta. 
  23. ^ Coble, Paula G. (2007). "Marine Optical Biogeochemistry:  The Chemistry of Ocean Color". Chemical Reviews 107: 402–418.  
  26. ^ "Sea's eerie glow seen from space".  
  28. ^ Seager, R. (2006). "The Source of Europe's Mild Climate". American Scientist 94 (4): 334.  
  31. ^ "Dissolved Gases other than Carbon Dioxide in Seawater" (PPT). Retrieved 2014-05-05. 
  32. ^ "Dissolved Oxygen and Carbon Dioxide" (PDF). 
  33. ^ Anthoni, Floor. "Composition of seawater". Retrieved 2014-05-05. 
  35. ^ "5.6 Synthesis – AR4 WGI Chapter 5: Observations: Oceanic Climate Change and Sea Level". Retrieved 2014-05-05. 
  38. ^ "Ocean Stratification". Retrieved 2014-05-05. 
  41. ^ "Chapter 6 – Temperature, Salinity, and Density – Geographical Distribution of Surface Temperature and Salinity". Introduction to Physical Oceanography :. 2009-03-23. Retrieved 2014-05-05. 
  44. ^ a b c Chester, Jickells, Roy, Tim (2012). Marine Geochemistry. Blackwell Publishing.  
  60. ^ Elkins-Tanton (2010). "Formation of Early Water Oceans on Rocky Planets". Astrophysics and Space Science 332 (2): 359–364.  
  63. ^ Guillot, T. (1999). "A comparison of the interiors of Jupiter and Saturn". Planetary and Space Science 47 (10–11): 1183–200.  
  65. ^ Coustenis, A.; Lunine, J.; Lebreton, J.; Matson, D.; Erd, C.; Reh, K.; Beauchamp, P.; Lorenz, R.; Waite, H.; Sotin, C.; Tssm Jsdt, T. (2008). "American Geophysical Union, Fall Meeting 2008, abstract #P21A-1346". American Geophysical Union 21: 1346.  
  66. ^ Nimmo, F.; Bills, B. G. (2010). "Shell thickness variations and the long-wavelength topography of Titan". Icarus 208 (2): 896–904.  
  67. ^ 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.  
  70. ^ "The ocean planet". 2011-10-03. Retrieved 2011-10-14. 
  71. ^ "Irrigating Crops with Seawater". Scientific American. August 1998. 
  72. ^ Schaefer, Laura; Fegley, Bruce, Jr. (2009). "Chemistry of Silicate Atmospheres of Evaporating Super-Earths". The Astrophysical Journal Letters 703 (2): L113–L117.  
  74. ^ Tables 3 and 4 in Bains, William (2004). "Many Chemistries Could Be Used to Build Living Systems" (PDF). Astrobiology 4 (2). 
  75. ^ Leitner, J.J.; Lammer, H.; Odert, P.; Leitzinger, M.; Firneis, M.G.; Hanslmeier, A. (2009). "Atmospheric Loss of Sub-Neptune's and Implications for Liquid Phases of Different Solvents on Their Surfaces" (PDF). European Planetary Science Congress. EPSC Abstracts 4. EPSC2009-542. 

Further reading


External links

  • Oceans at DMOZ
  • Smithsonian Ocean Portal
  • NOAA – National Oceanic and Atmospheric Administration – Ocean
  • Ocean :: Science Daily
  • Ocean-bearing Planets: Looking For Extraterrestrial Life In All The Right Places
  • Titan Likely To Have Huge Underground Ocean | Mind Blowing Science
  • Origins of the oceans and continents". UN Atlas of the Oceans.
