Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon the water, such as the wind, Coriolis force, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun. Depth contours, shoreline configurations and interaction with other currents influence a current's direction and strength.
Ocean currents can flow for thousands of kilometers, and together they create the great flow of the global conveyor belt which plays a dominant part in determining the climate of many of the Earth’s regions. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any other region at the same latitude. Another example is the Hawaiian Islands, where the climate is cooler (sub-tropical) than the tropical latitudes in which they are located, because of the effect of the California Current.
Background
Surface ocean currents are generally wind driven and develop their typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in the southern hemisphere because of the imposed wind stresses. In wind driven currents, the Ekman spiral effect results in the currents flowing at an angle to the driving winds. The areas of surface ocean currents move somewhat with the seasons; this is most notable in equatorial currents.
Ocean basins generally have a non-symmetric surface current, in that the eastern equatorward-flowing branch is broad and diffuse whereas the western poleward-flowing branch is very narrow. These western boundary currents (of which the gulf stream is an example) are a consequence of basic fluid dynamics.
Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation, also known as the ocean's conveyor belt, refers to the deep ocean density-driven ocean basin currents. These currents, which flow under the surface of the ocean and are thus hidden from immediate detection, are called submarine rivers. These are currently being researched by a fleet of underwater robots called Argo. Upwelling and downwelling areas in the oceans are areas where significant vertical movement of ocean water is observed.
Surface currents make up about 10% of all the water in the ocean. Surface currents are generally restricted to the upper 400 meters of the ocean. The movement of deep water in the ocean basins is by density driven forces and gravity. The density difference is a function of different temperatures and salinity. Deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.
Ocean currents are measured in Sverdrup with the symbol Sv, where 1 Sv is equivalent to a volume flow rate of 106 cubic meters per second.
Significance to people and sea life
Knowledge of surface ocean currents is essential in reducing costs of shipping, since they reduce fuel costs. In the sail-ship era knowledge was even more essential. A good example of this is the Agulhas current, which long prevented Portuguese sailors from reaching India. Even today, the round-the-world sailing competitors employ surface currents to their benefit.
Ocean currents are also very important in the dispersal of many life forms. A example is the life-cycle of the eel.
Ocean currents are important in the study of marine debris, and vice versa.
These currents also affect temperatures throughout the world. For example, the current that brings warm water up the north Atlantic to northwest Europe stops ice from forming by the shores, which would block ships from entering and exiting ports.
Important currents
Atlantic Ocean
Agulhas Current
Angola Current
Antilles Current
Azores Current
Baffin Island Current
Benguela current
Brazil Current
Canary Current
Cape Horn Current
Caribbean Current
East Greenland Current
East Iceland Current
Falkland Current
Florida Current
Guiana Current
Guinea Current
Gulf Stream
Irminger Current
Labrador Current
Lomonosov current (a deep current)
Loop Current
North Atlantic Current
North Atlantic Drift
North Brazil Current
North Equatorial Current
North Equatorial Counter Current
Norwegian Current
Portugal Current
Slope/Shelf Edge Current
Slope Jet Current
South Atlantic Current
South Equatorial Current
Spitsbergen Current
Subtropical Counter Current
West Greenland Current
West Wind Drift
Pacific Ocean
Alaska Current
Aleutian Current
California Current
Cromwell current (a deep current)
East Australian Current
Equatorial Counter Current
Humboldt Current (or Peru Current)
Kamchatka Current
Kuroshio Current (or Japan Current, Kuro Siwo)
Mindanao Current
North Equatorial Current
North Pacific Current (or North Pacific Drift)
Oyashio Current (or Oya Siwo)
South Equatorial Current
West Wind Drift
Arctic Ocean
East Greenland Current
Norwegian Current
Beaufort Gyre (water or ice flow)
Transpolar Drift (water or ice flow)
Indian Ocean
Agulhas Current
East Madagascar Current
Equatorial Counter Current
Indonesian Through-flow
Leeuwin Current
Madagascar Current
Mozambique Current
Somali Current
South Australian Counter Current
South Equatorial Current
Southwest and Northeast Monsoon Drift
(or Indian Monsoon Current)
West Australian Current
West Wind Drift
Southern Ocean
Antarctic Circumpolar Current
Weddell Gyre
Tasman Outflow
Translation
The phrase "Ocean current" occurs as such in the following languages: English, Simple English.
Translation(s) in other languages: Bengali: মহাসাগরীয় স্রোত, Min Nan: Iûⁿ-lâu, Bosnian: Morska struja, Breton: Kasenn, Bulgarian: Океанско течение, Catalan: Corrent oceànic, Czech: Mořský proud, Danish: Havstrøm, German: Meeresströmung, Estonian: Hoovus, Spanish: Corriente marina, Esperanto: Marfluo, Basque: Itsaslaster, Persian: جریان اقیانوسی, French: Courant marin, Galician: Corrente oceánica, Korean: 해류, Hindi: महासागरीय धारा, Croatian: Morska struja, Indonesian: Arus air laut, Italian: Corrente oceanica, Hebrew: זרם ימי, Kazakh: Мұхит және теңіз ағыстары, Swahili: Mkondo wa bahari, Latvian: Okeāna straume, Hungarian: Tengeráramlatok, Marathi: समुद्री प्रवाह, Dutch: Zeestroom, Japanese: 海流, Norwegian (Bokmål): Havstrøm, Norwegian (Nynorsk): Havstraum, Khmer: ខ្សែទឹកមហាសមុទ្រ, Polish: Prąd morski, Portuguese: Corrente oceânica, Romanian: Curent marin, Russian: Морские течения, Albanian: Rrymat detare, Slovak: Morský prúd, Slovenian: Oceanski tok, Serbian: Морска струја, Finnish: Merivirta, Swedish: Havsström, Ukrainian: Морська течія, Vietnamese: Hải lưu, Chinese: 洋流.
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