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The ocean currents.

An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, 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 great distances, 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, due to the effect of the California Current.

Contents

Function

Major ocean surface currents, (Source: NOAA).
Device to record ocean currents.

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 m (1,300 ft) 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 (Sv), where 1Sv is equivalent to a volume flow rate of 1,000,000 m3 (35,000,000 cu ft) per second.

Importance

A 1943 map of the world's ocean currents.

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. An 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.

See also

References

External links

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Simple English

File:Ocean surface
A map of all the large ocean currents of the world.

[[File:|All the world's currents on a continuos ocean map|thumb|350px|right]] An ocean current is a continuous movement of ocean water from one place to another. Ocean currents are created by wind, water temperature, salt content, and the gravity of the moon. The current's direction and speed depend on the shoreline and the ocean floor. They can flow for thousands of miles and are found in all the major oceans of the world. One major example of an ocean current is the Gulf Stream in the Atlantic Ocean. Ocean currents can be found on the water surface and deeper down.

Contents

Major ocean currents of the world

Arctic Ocean

  • East Greenland Current
  • Norwegian Current
  • Beaufort Gyre (water or ice flow)
  • Transpolar Drift (water or ice flow)

Atlantic Ocean[1]

  • 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

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

Notes


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