Ocean current

An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences.[1] Depth contours, shoreline configurations, and interactions with other currents influence a current's direction and strength. Ocean currents are primarily horizontal water movements.

Ocean surface currents
Distinctive white lines trace the flow of surface currents around the world.
Visualization showing global ocean currents from January 1, 2010, to December 31, 2012, at sea level, then at 2,000 m (6,600 ft) below sea level
Animation of circulation around ice shelves of Antarctica

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 for its high latitude than other areas at the same latitude. Another example is Lima, Peru, whose cooler subtropical climate contrasts with that of its surrounding tropical latitudes because of the Humboldt Current. Ocean currents are patterns of water movement that influence climate zones and weather patterns around the world. They are 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.[2][3]

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,[4] and the Coriolis effect plays a major role in their development.[5] 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.[6] 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

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.[7][8] 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)[9] upwell in the North Pacific.[10] 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  Northward cold water Atlantic Ocean current
  • 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  Current of the Atlantic Ocean
  • North Brazil Current  North Atlantic ocean current
  • North Equatorial Current  Current in the Pacific and Atlantic Oceans
  • 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
  • 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  Oceanic flow feature near Madagascar
  • 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 Western Australia
  • Madagascar Current  Ocean current in the West Indian Ocean
  • Mozambique Current  Warm ocean current in the Indian Ocean
  • 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
  • Southwest Madagascar Coastal Current  Warm poleward ocean current flowing in the south-west of Madagascar
  • West Australian Current  Cool oceanic current

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
  • Equatorial Counter Current  Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans
  • Humboldt Current  Current of the Pacific Ocean
  • Indonesian Throughflow  Ocean current
  • Kamchatka Current  Pacific Ocean current
  • 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  Current in the Pacific and Atlantic Oceans
  • 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
  • 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[2][3]

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  Part of large-scale ocean circulation
  • Tidal current
  • Volta do mar  Archaic navigational technique

References

  1. NOAA, NOAA. "What is a current?". Ocean Service Noaa. National Ocean Service. Retrieved 13 December 2020.
  2. "Massive Southern Ocean current discovered". ScienceDaily. Apr 27, 2010.
  3. Yasushi Fukamachi, Stephen Rintoul; et al. (Apr 2010). "Strong export of Antarctic Bottom Water east of the Kerguelen plateau". Nature Geoscience. 3 (5): 327–331. Bibcode:2010NatGe...3..327F. doi:10.1038/NGEO842. hdl:2115/44116.
  4. "Current". www.nationalgeographic.org. National Geographic. 2 September 2011. Retrieved 7 January 2021.
  5. "Ocean Currents of the World: Causes". 29 August 2020. Retrieved 2020-11-20.
  6. National Ocean Service (March 25, 2008). "Surface Ocean Currents". noaa.gov. National Oceanic and Atmospheric Administration. Archived from the original on July 6, 2017. Retrieved 2017-06-13.
  7. Rahmstorf, S (2003). "The concept of the thermohaline circulation" (PDF). Nature. 421 (6924): 699. Bibcode:2003Natur.421..699R. doi:10.1038/421699a. PMID 12610602. S2CID 4414604.
  8. Lappo, SS (1984). "On reason of the northward heat advection across the Equator in the South Pacific and Atlantic ocean". Study of Ocean and Atmosphere Interaction Processes. Moscow Department of Gidrometeoizdat (in Mandarin): 125–9.
  9. The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity; What is the global ocean conveyor belt?
  10. Primeau, F (2005). "Characterizing transport between the surface mixed layer and the ocean interior with a forward and adjoint global ocean transport model" (PDF). Journal of Physical Oceanography. 35 (4): 545–64. Bibcode:2005JPO....35..545P. doi:10.1175/JPO2699.1. S2CID 130736022.

Further reading

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