Ocean current

Ocean surface currents

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Distinctive white lines trace the flow of surface currents around the world.

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Visualization showing global ocean currents from Jan 01, 2010 to Dec 31, 2012 at sea level then at 2000 meters below sea level

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Animation of circulation around ice shelves of Antarctica

An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, shoreline configurations, and interactions with other currents influence a current's direction and strength. Ocean currents are primarily horizontal water movements.

An ocean current flows for great distances and together they create the global conveyor belt, which plays a dominant role in determining the climate of many of Earth’s regions. More specifically, ocean currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. 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 Lima, Peru, where the climate is cooler, being sub-tropical, than the tropical latitudes in which the area is located, due to the effect of the Humboldt Current. Ocean currents are patterns of water movement that influence climate zones and weather patterns around the world. They’re primarily driven by winds and by seawater density, although many other factors – including the shape and configuration of the ocean basin they flow through – influence them. The two basic types of currents – surface and deep-water currents – help define the character and flow of ocean waters across the planet.

Causes

The bathymetry of the Kerguelen Plateau in the Southern Ocean governs the course of the Kerguelen deep western boundary current, part of the global network of ocean currents.

Ocean dynamics define and describe the motion of water within the oceans. Ocean temperature and motion fields can be separated into three distinct layers: mixed (surface) layer, upper ocean (above the thermocline), and deep ocean. Ocean currents are measured in sverdrup (sv), where 1 sv is equivalent to a volume flow rate of 1,000,000 m³ (35,000,000 cu ft) per second.

Surface currents, which make up only 8% of all water in the ocean, are generally restricted to the upper 400 m (1,300 ft) of ocean water, and are separated from lower regions by varying temperatures and salinity which affect the density of the water, which in turn, defines each oceanic region. Because the movement of deep water in ocean basins is caused by density-driven forces and gravity, deep waters sink into deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.

Wind driven circulation

Surface oceanic currents are driven by wind currents, the large scale prevailing winds drive major persistent ocean currents, and seasonal or occasional winds drive currents of similar persistence to the winds that drive them, and the Coriolis effect plays a major role in their development. The Ekman spiral velocity distribution results in the currents flowing at an angle to the driving winds, and they develop typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in the southern hemisphere. In addition, the areas of surface ocean currents move somewhat with the seasons; this is most notable in equatorial currents.

Deep ocean basins generally have a non-symmetric surface current, in that the eastern equator-ward flowing branch is broad and diffuse whereas the pole-ward flowing western boundary current is relatively narrow.

Thermohaline circulation

Main article: Thermohaline circulation

Further information: Deep ocean water

Deep ocean currents are driven by density and temperature gradients. This thermohaline circulation is also known as the ocean's conveyor belt. These currents, sometimes called submarine rivers, flow deep below the surface of the ocean and are hidden from immediate detection. Where significant vertical movement of ocean currents is observed, this is known as upwelling and downwelling. Deep ocean currents are currently being researched using a fleet of underwater robots called Argo.

The thermohaline circulation is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is imprecisely used to refer to the meridional overturning circulation, (MOC).

Coupling data collected by NASA/JPL by several different satellite-borne sensors, researchers have been able to "break through" the ocean's surface to detect "Meddies" – super-salty warm-water eddies that originate in the Mediterranean Sea and then sink more than a half-mile underwater in the Atlantic Ocean. The Meddies are shown in red in this scientific figure.

A recording current meter

Distribution

A 1943 map of the world's ocean currents

Currents of the Arctic Ocean

• Baffin Island Current – Arctic Ocean current
• Beaufort Gyre – Wind-driven ocean current in the Arctic Ocean polar region
• East Greenland Current – Current from Fram Strait to Cape Farewell off the eastern coat of Greenland
• East Iceland Current – Cold water ocean current that forms as a branch of the East Greenland Current
• Labrador Current – Cold current in the Atlantic ocean along the coasts of Labrador, Newfoundland and Nova Scotia
• North Icelandic Jet – Deep-reaching current that flows along the continental slope of Iceland
• Norwegian Current – A current that flows northeasterly along the Atlantic coast of Norway into the Barents Sea
• Transpolar Drift Stream – An ocean current of the Arctic Ocean
• West Greenland Current – Weak cold water current that flows to the north along the west coast of Greenland
• West Spitsbergen Current – Warm, salty current that runs poleward just west of Spitsbergen

Currents of the Atlantic Ocean

• Angola Current – Temporary ocean surface current
• Antilles Current – Ocean current
• Atlantic meridional overturning circulation – System of currents in the Atlantic Ocean
• Azores Current – Ocean current in the North Atlantic Ocean
• Benguela Current – Ocean current in the South Atlantic
• Brazil Current – Warm current that flows south along the Brazilian south coast to the mouth of the Río de la Plata
• Canary Current – Wind-driven surface current that is part of the North Atlantic Gyre
• Cape Horn Current – Cold water current that flows west-to-east around Cape Horn
• Caribbean Current – Atlantic Ocean current
• East Greenland Current – Current from Fram Strait to Cape Farewell off the eastern coat of Greenland
• East Iceland Current – Cold water ocean current that forms as a branch of the East Greenland Current
• Equatorial Counter Current – Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans
• Falkland Current – Cold water current that flows northward along the Atlantic coast of Patagonia as far north as the mouth of the Río de la Plata
• Florida Current – Thermal ocean current
• Guinea Current – A slow warm water current that flows to the east along the Guinea coast of West Africa
• Gulf Stream – Warm Atlantic Ocean current
• Irminger Current – North Atlantic current setting westward off the southwest coast of Iceland
• Labrador Current – Cold current in the Atlantic ocean along the coasts of Labrador, Newfoundland and Nova Scotia
• Lomonosov Current – Deep current in the Atlantic Ocean. from the coast of Brazil to the Gulf of Guinea
• Loop Current – Ocean current between Cuba and Yucatán Peninsula
• North Atlantic Current – Powerful warm western boundary current in the north Atlantic Ocean that extends the Gulf stream northeastward
• North Brazil Current – North Atlantic ocean current
• North Equatorial Current – Pacific and Atlantic Ocean current that flows east-to-west between about 10° north and 20° north on the southern side of a clockwise subtropical gyre
• Norwegian Current – A current that flows northeasterly along the Atlantic coast of Norway into the Barents Sea
• Portugal Current – Weak ocean current that flows south along the coast of Portugal
• South Atlantic Current – Eastward ocean current, fed by the Brazil Current
• South Equatorial Current – Ocean current in the Pacific, Atlantic, and Indian Ocean that flows east-to-west between the equator and about 20 degrees south
• West Greenland Current – Weak cold water current that flows to the north along the west coast of Greenland
• West Spitsbergen Current – Warm, salty current that runs poleward just west of Spitsbergen

Currents of the Indian Ocean

• Agulhas Current – Western boundary current of the southwest Indian Ocean that flows down the east coast of Africa
• Agulhas Return Current – Ocean current in the southern Indian Ocean
• East Madagascar Current – Current that flows southward on the east side of Madagascar and subsequently feeds the Agulhas Current
• Equatorial Counter Current – Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans
• Indian Monsoon Current – Seasonally-varying ocean current regime found in the tropical regions of the northern Indian Ocean
• Indonesian Throughflow – Ocean current
• Leeuwin Current – Ocean current off the western coast of Australia
• Madagascar Current – Ocean current in the West Indian Ocean
• Mozambique Current – Warm ocean current in the Indian Ocean flowing south along the African east coast in the Mozambique Channel
• North Madagascar Current – Ocean current near Madagascar that flows into the South Equatorial Current
• Somali Current – Ocean boundary current that flows along the coast of Somalia and Oman in the Western Indian Ocean
• South Equatorial Current – Ocean current in the Pacific, Atlantic, and Indian Ocean that flows east-to-west between the equator and about 20 degrees south
• Southwest Madagascar Coastal Current – Warm poleward ocean current flowing in the south-west of Madagascar
• West Australian Current – Cool surface current that starts as the Southern Indian Ocean Current and turns north when it approaches Western Australia

Currents of the Pacific Ocean

• Alaska Current – Warm-water current flowing nortwards along the coast of British Columbia and the Alaska Panhandle
• Aleutian Current – Eastward-flowing ocean current which lies north of the North Pacific Current;
• California Current – Pacific Ocean current
• Cape Horn Current – Cold water current that flows west-to-east around Cape Horn
• Cromwell Current – Eastward-flowing subsurface current that extends along the equator in the Pacific Ocean
• Davidson Current – Countercurrent of the Pacific Ocean
• East Australian Current – Currents of the Pacific Ocean
• East Korea Warm Current – Ocean current in the Sea of Japan which branches off from the Tsushima Current at the eastern end of the Korea Strait, and flows north along the southeastern coast of the Korean peninsula
• Equatorial Counter Current – Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans
• Humboldt Current – Cold, low-salinity eastern boundary current that flows north along the western coast of South America from southern Chile to northern Peru
• Indonesian Throughflow – Ocean current
• Kamchatka Current – Cold-water current flowing south-westward from the Bering Strait, along the Siberian Pacific coast and the Kamchatka Peninsula
• Kuroshio Current – North flowing ocean current on the west side of the North Pacific Ocean
• Mindanao Current – Narrow, southward flowing ocean current along the southeastern coast of the Philippines
• Mindanao Eddy – Semi-permanent cold-ring eddy formed in the retroflection area of the Mindanao Current.
• North Equatorial Current – Pacific and Atlantic Ocean current that flows east-to-west between about 10° north and 20° north on the southern side of a clockwise subtropical gyre
• North Korea Cold Current – Cold water current in the Sea of Japan
• North Pacific Current – Slow warm water current that flows west-to-east between 30 and 50 degrees north in the Pacific Ocean
• Oyashio Current – Cold subarctic ocean current in the Pacific Ocean
• South Equatorial Current – Ocean current in the Pacific, Atlantic, and Indian Ocean that flows east-to-west between the equator and about 20 degrees south
• Subtropical Countercurrent – Narrow eastward ocean current in the central North Pacific Ocean
• Tasman Front – Pacific Ocean current
• Tasman Outflow – Deepwater current that flows from the Pacific Ocean past Tasmania into the Indian Ocean

Currents of the Southern Ocean

• Antarctic Circumpolar Current – Ocean current that flows clockwise from west to east around Antarctica
• Tasman Outflow – Deepwater current that flows from the Pacific Ocean past Tasmania into the Indian Ocean
• Kerguelen deep western boundary current

Oceanic gyres

• Beaufort Gyre – Wind-driven ocean current in the Arctic Ocean polar region
• Indian Ocean Gyre – Major oceanic gyre in the Indian Ocean
• North Atlantic Gyre – Major circular system of ocean currents
• North Pacific Gyre – Major circulating system of ocean currents
• Ross Gyre – Circulating system of ocean currents in the Ross Sea
• South Atlantic Gyre – Subtropical gyre in the south Atlantic Ocean
• South Pacific Gyre – Major circulating system of ocean currents
• Weddell Gyre – One of two gyres within the Southern Ocean

Effects on climate and ecology

Ocean currents are important in the study of marine debris, and vice versa. These currents also affect temperatures throughout the world. For example, the ocean current that brings warm water up the north Atlantic to northwest Europe also cumulatively and slowly blocks ice from forming along the seashores, which would also block ships from entering and exiting inland waterways and seaports, hence ocean currents play a decisive role in influencing the climates of regions through which they flow. Cold ocean water currents flowing from polar and sub-polar regions bring in a lot of plankton that are crucial to the continued survival of several key sea creature species in marine ecosystems. Since plankton are the food of fish, abundant fish populations often live where these currents prevail.

Ocean currents are also very important in the dispersal of many life forms. An example is the life-cycle of the European Eel.

Economic importance

Knowledge of surface ocean currents is essential in reducing costs of shipping, since traveling with them reduces fuel costs. In the wind powered sailing-ship era, knowledge of wind patterns and ocean currents was even more essential. A good example of this is the Agulhas Current (down along eastern Africa), which long prevented sailors from reaching India. In recent times, around-the-world sailing competitors make good use of surface currents to build and maintain speed. Ocean currents can also be used for marine power generation, with areas of Japan, Florida and Hawaii being considered for test projects.

See also

• Currentology – Science that studies the internal movements of water masses
• Deep ocean water – Cold, salty water deep below the surface of Earth's oceans
• Fish migration – Movement of fishes from one part of a water body to another on a regular basis
• Geostrophic current – Oceanic flow in which the pressure gradient force is balanced by the Coriolis effect
• Latitude of the Gulf Stream and the Gulf Stream north wall index
• List of ocean circulation models – Models used in physical oceanography.
• Marine habitats § Ocean currents
• Marine current power – Extraction of power from ocean currents
• Ocean gyre – Any large system of circulating ocean currents
• Physical oceanography – Study of physical conditions and physical processes within the ocean
• Subsurface ocean current – Oceanic currents that flow beneath surface currents
• Thermohaline circulation – A part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes
• Tidal current
• Volta do mar – Archaic navigational technique

Further reading

• Hansen, B.; Østerhus, S; Quadfasel, D; Turrell, W (2004). "Already the day after tomorrow?". Science. 305 (5686): 953–954. doi:10.1126/science.1100085. PMID 15310882. S2CID 12968045.
• Kerr, Richard A. (2004). "A slowing cog in the North Atlantic ocean's climate machine". Science. 304 (5669): 371–372. doi:10.1126/science.304.5669.371a. PMID 15087513. S2CID 42150417.
• Munday, Phillip L.; Jones, Geoffrey P.; Pratchett, Morgan S.; Williams, Ashley J. (2008). "Climate change and the future for coral reef fishes". Fish and Fisheries. 9 (3): 261–285. doi:10.1111/j.1467-2979.2008.00281.x.
• Rahmstorf, S. (2003). "Thermohaline circulation: The current climate". Nature. 421 (6924): 699. Bibcode:2003Natur.421..699R. doi:10.1038/421699a. PMID 12610602. S2CID 4414604.
• Roemmich, D. (2007). "Physical oceanography: Super spin in the southern seas". Nature. 449 (7158): 34–35. Bibcode:2007Natur.449...34R. doi:10.1038/449034a. PMID 17805284. S2CID 2951110.

External links

• Current global map of sea surface currents