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The five major ocean gyres

A gyre in oceanography is any large system of rotating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis Effect; planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque).[1] The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, but it is most commonly used in oceanography, to refer to the major ocean systems.

Contents

Major gyres

The following are the five most notable gyres:[2]

Other gyres

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Tropical gyres

All of the world's larger gyres

Tropical gyres are less unified and tend to be mostly east-west with minor north-south extent.

  • Atlantic Equatorial Current System (two counter-rotating circulations)
  • Pacific Equatorial Current System
  • Indian Monsoon Gyres (two counter-rotating circulations in northern Indian Ocean)[3]

Subtropical gyres

The center of a subtropical gyre is a high pressure zone. Circulation around the high pressure is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere, due to the Coriolis effect. The high pressure in the center is due to the westerly winds on the northern side of the gyre and easterly trade winds on the southern side of the gyre. These cause frictional surface currents towards the latitude at the center of the gyre. The build-up of water in the center of the gyre creates equatorward flow in the upper 1,000 to 2,000 m (3,300 to 6,600 ft) of the ocean, through rather complex dynamics. This equatorward flow is returned poleward in an intensified western boundary current.

The intensified western boundary current of the North Atlantic Gyre is the Gulf Stream, in the North Pacific it's the Kuroshio Current, in the South Atlantic it's the Brazil Current, in the South Pacific it's the East Australian Current, and in the Indian Ocean it's the Agulhas Current.

Subpolar gyres

Subpolar gyres form at high latitudes (around 60°). Circulation of surface wind and ocean water is counterclockwise in the Northern Hemisphere, around a low-pressure area, such as the persistent Aleutian Low and the Icelandic Low. Surface currents generally move outward from the center of the system. This drives the Ekman transport, which creates an upwelling of nutrient-rich water from the lower depths.[4]

Subpolar circulation in the southern hemisphere is dominated by the Antarctic Circumpolar Current, due to the lack of large landmasses breaking up the Southern Ocean. There are minor gyres in the Weddell Sea and the Ross Sea, the Weddell Gyre and Ross Gyre, which circulate in a clockwise direction.[2]

See also

References

  1. ^ Heinemann, B. and the Open University (1998) Ocean circulation, Oxford University Press: Page 98
  2. ^ a b The five most notable gyres PowerPoint Presentation
  3. ^ Indian Monsoon Gyres
  4. ^ Wind Driven Surface Currents: Gyres

External links


A gyre is any manner of particularly large-scale wind, swirling vortex and ocean currents. Gyres are caused by the Coriolis effect; planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque).[1]

Contents

Ocean gyres

The Earth's oceans have the following major gyres:[2]

Tropical circulations

Tropical circulations are less unified and tend to be mostly east-west with minor north-south extent.

  • Atlantic Equatorial Current System (two counter-rotating circulations)
  • Pacific Equatorial/Tropical Current System
  • Indian Monsoon Gyres[4] (Northern Indian Ocean, two counter-rotating circulations)

Subtropical gyres

The center of a subtropical gyre is a high pressure zone. Circulation around the high pressure is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere, due to the Coriolis effect. The high pressure in the center is due to the westerly winds on the northern side of the gyre and easterly trade winds on the southern side of the gyre. These cause frictional surface currents towards the latitude at the center of the gyre. The buildup of water in the center of the gyre creates equatorward flow in the upper 1000 to 2000 meters of the ocean, through rather complex dynamics. This equatorward flow is returned poleward in an intensified western boundary current (Western intensification).

The intensified western boundary current of the North Atlantic's subtropical gyre is the Gulf Stream; in the North Pacific, it is the Kuroshio; in the South Atlantic, it is the Brazil Current; in the South Pacific, it is the East Australian Current; and in the Indian Ocean, it is the Agulhas Current.

Subpolar gyres

Subpolar gyres form at high latitudes (around 60 degrees). Circulation of surface wind and ocean water is counterclockwise in the Northern Hemisphere, around a low-pressure area, such as the persistent Aleution Low and the Icelandic Low. Surface currents generally move outward from the center of the system. This drives the Ekman transport, which creates an upwelling of nutrient-rich water from the lower depths.[5]

Subpolar circulation in the southern hemisphere is dominated by the Antarctic circumpolar current, due to the lack of large landmasses breaking up the Southern Ocean. There are minor gyres in the Weddell and Ross Seas, which circulate in a clockwise direction.[2]

See also

References

  1. Heinemann, B. and the Open University (1998) Ocean circulation, Oxford University Press: Page 98
  2. 2.0 2.1 PowerPoint Presentation
  3. "New 'battle of Midway' over plastic". BBC News. 26 March 2008. http://news.bbc.co.uk/1/hi/sci/tech/7314240.stm. Retrieved on 2008-04-01. 
  4. http://www.mar.dfo-mpo.gc.ca/science/ocean/BedfordBasin/Papers/Longhurst1998/Provinces/BGCP_table.htm
  5. Wind Driven Surface Currents: Gyres

External links

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