Oceanic gyre 776619 224708474 2008-07-10T01:44:42Z 71.142.213.42 /* Ocean gyres= */ {{refimprove|date=April 2008}} [[Image:Oceanic gyres.png|thumb|right|250px|Map of Ocean Gyres]] A '''gyre''' is any manner of swirling [[vortex]]. It is often used to describe large-scale [[wind]] or [[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]]).<ref>Heinemann, B. and the Open University (1998) ''Ocean circulation'', Oxford University Press: Page 98 </ref> ==Ocean gyres== The Earth's oceans have the following major gyres:<ref name="SIO210slides">http://www-pord.ucsd.edu/~ltalley/sio210/Wind_circulation_NAtl_SHem/lecture_natl_shem.htm</ref> * '''North Atlantic Subpolar Gyre''' * '''North Pacific Subpolar Gyre''' ** Contains the smaller Alaska Gyre * '''North Atlantic Subtropical Gyre''' ** [[Gulf Stream]], [[Labrador Current]], [[East Greenland Current]], [[North Atlantic Current]], North Atlantic Equatorial Current * '''North Pacific Subtropical Gyre''' also known as North Pacific Gyre [[Image:North Pacific Gyre.png|thumb|The currents of the North Pacific Gyre]] This gyre comprises most of the northern [[Pacific Ocean]]. It is located between the [[equator]] and 50º N [[latitude]] and occupies an area of approximately ten million [[square miles]] (34 million&nbsp;km²).<!--NOTE: This metric equivalent assumes that the miles referred to are nautical miles. Can this be confirmed? (amplified by User:Eusebeus) -->The North Pacific [[Gyre]] has a clockwise circular pattern and comprises four prevailing [[ocean currents]]: the [[North Pacific Current]] to the north, the [[California Current]] to the east, the [[North Equatorial Current]] to the south, and the [[Kuroshio Current]] to the west. <br> An accumulation of [[marine debris]] known as the "[[Great Pacific Garbage Patch]]" is collecting in the gyre.<ref>{{cite web |url=http://news.bbc.co.uk/1/hi/sci/tech/7314240.stm |title=New 'battle of Midway' over plastic |accessdate=2008-04-01 |date=26 March 2008 |publisher=BBC News }}</ref> * '''South Atlantic Subtropical Gyre''' ** Contains the smaller Brazil Current System * '''South Pacific Subtropical Gyre''' ** Contains the smaller East Australian Current System * '''Indian Ocean Subtropical Gyre''' (Southern Hemisphere) ** Contains the smaller Agulhas Current System * '''[[Antarctic Circumpolar Current]]''' * '''[[Weddell Gyre|Weddell Sea Subpolar Gyre]]''' ([[Southern Ocean]]) * '''Ross Sea Subpolar Gyre ([[Southern Ocean]])''' 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<ref>http://www.mar.dfo-mpo.gc.ca/science/ocean/BedfordBasin/Papers/Longhurst1998/Provinces/BGCP_table.htm</ref> (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 force]]. 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 Australia Current]]; 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 system]] (such as the persistent Aleution Low and the Icelandic Low). Surface currents generally move outward from the center of the system. This drives [[Ekman transport]] which creates an [[upwelling]] of nutrient-rich water from the lower depths.<ref>[http://oceanmotion.org/html/background/wind-driven-surface.htm Wind Driven Surface Currents: Gyres]</ref> 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 Wendall and Ross Seas, which circulate in a clockwise direction.<ref name="SIO210slides" /> == References == <references/> ==References== <references /> ==See also== * [[Anticyclone]] * [[Cyclone]] * [[Eddy (fluid dynamics)]] * [[Fluid dynamics]] * [[Maelstrom]] * [[Skookumchuck]] * [[Vortex]] * [[Whirlpool]] == External links == {{commonscat|Oceanic gyres}} {{wiktionary|gyre}} * [http://oceanmotion.org/html/background/wind-driven-surface.htm Wind Driven Surface Currents: Gyres] * [http://www-pord.ucsd.edu/~ltalley/sio210/Global_circulation/ SIO 210: Introduction to Physical Oceanography - Global circulation] * [http://www-pord.ucsd.edu/~ltalley/sio210/Wind_circulation_NAtl_SHem/ SIO 210: Introduction to Physical Oceanography - Wind-forced circulation notes] * [http://sam.ucsd.edu/sio210/lect_6/lecture_6.html SIO 210: Introduction to Physical Oceanography - Lecture 6] * [http://www.physicalgeography.net/fundamentals/8q.html Physical Geography - Surface and Subsurface Ocean Currents] *[http://eros.eas.gatech.edu/npgo/ North Pacific Gyre Oscillation] — Georgia Institute of Technology {{Oceanic gyres}} [[Category:Aerodynamics]] [[Category:Fluid dynamics]] [[Category:Physical oceanography]] [[Category:Ocean currents]] [[Category:Fisheries science]]