Ocean gyre

The five major ocean gyres

A gyre in oceanography is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity along with horizontal and vertical friction, 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.

Major gyres

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

Indian Ocean Gyre (generally flowing counter-clockwise)
North Atlantic Gyre
North Pacific Gyre
South Atlantic Gyre
South Pacific Gyre

Other gyres

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. These cause frictional surface currents towards the latitude at the center of the gyre.

This build-up of water in the center creates flow towards the equator in the upper 1,000 to 2,000 m (3,300 to 6,600 ft) of the ocean, through rather complex dynamics. This flow is returned towards the pole in an intensified western boundary current. The boundary current of the North Atlantic Gyre is the Gulf Stream, of the North Pacific Gyre the Kuroshio Current, of the South Atlantic Gyre the Brazil Current, of the South Pacific Gyre the East Australian Current, and of the Indian Ocean Gyre 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]

Climate change

Recently stronger winds, especially the subtropical trade winds in the Pacific ocean have provided a mechanism for vertical heat distribution. The effect are changes in the ocean currents, increasing the subtropical overturning, which are also related to the El Niño and La Niña phenomenon. Depending on natural variability, during La Niña years around 30% more heat from the upper ocean layer is transported into the deeper ocean.^[5] Several studies in recent years, found a multidecadal increase in OHC of the deep and upper ocean regions and attribute the heat uptake to anthropogenic warming.^[6]

The influence of the Coriolis effect on westward intensification

Because the Coriolis effect is strongest near the poles, water flowing eastward at high latitudes turns sooner and is "short circuiting" the gyre. At the equator the Coriolis effect is nonexistent and the water flows westward until it encounters a blocking continent. Westward boundary currents are therefore faster and deeper than eastern boundary currents, and the geostrophic hill is offset to the west.

Pollution

Ocean gyres are known to collect pollutants.

References

↑ Heinemann, B. and the Open University (1998) Ocean circulation, Oxford University Press: Page 98
1 2 The five most notable gyres PowerPoint Presentation
↑ Indian Monsoon Gyres
↑ Wind Driven Surface Currents: Gyres
↑ Balmaseda, Trenberth & Källén (2013). [ Essay "Distinctive climate signals in reanalysis of global ocean heat content"] Check |url= value (help). Bibcode:2013GeoRL..40.1754B. doi:10.1002/grl.50382.
↑ Abraham; et al. (2013). "A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change". Bibcode:2013RvGeo..51..450A. doi:10.1002/rog.20022.

External links

Look up Gyre in Wiktionary, the free dictionary.

Ocean currents and gyres

Currents

Arctic Ocean	East Greenland North Icelandic Norwegian Transpolar Drift Stream
Atlantic Ocean	Angola Antilles Azores Baffin Island Benguela Brazil Canary Cape Horn Caribbean East Greenland East Iceland Falkland Florida Guinea Gulf Stream Irminger Labrador Lomonosov Loop North Atlantic North Brazil North Equatorial Norwegian Portugal Slope Jet South Atlantic South Equatorial West Greenland West Spitsbergen
Indian Ocean	Agulhas Agulhas Return East Madagascar Equatorial Counter Indian Monsoon Indonesian Throughflow Leeuwin Madagascar Mozambique North Madagascar Somali South Australian South Equatorial West Australian
Pacific Ocean	Alaska Aleutian California Cromwell Davidson East Australian East Korea Warm Equatorial Counter Humboldt Indonesian Throughflow Kamchatka Kuroshio Mindanao North Equatorial North Korea Cold North Pacific Oyashio South Equatorial Tasman Front
Southern Ocean	Antarctic Circumpolar Tasman Outflow

Gyres

Major gyres	Indian Ocean Gyre North Atlantic Gyre South Atlantic Gyre North Pacific Gyre South Pacific Gyre
Other gyres	Beaufort Gyre Ross Gyre Weddell Gyre

Physical oceanography
Waves	Airy wave theory Ballantine scale Benjamin–Feir instability Boussinesq approximation Breaking wave Clapotis Cnoidal wave Cross sea Dispersion Edge wave Equatorial waves Fetch Gravity wave Green's law Infragravity wave Internal wave Iribarren number Kelvin wave Kinematic wave Longshore drift Luke's variational principle Mild-slope equation Radiation stress Rogue wave Rossby wave Rossby-gravity waves Sea state Seiche Significant wave height Soliton Stokes boundary layer Stokes drift Stokes wave Swell Trochoidal wave Tsunami megatsunami Undertow Ursell number Wave action Wave base Wave height Wave power Wave radar Wave setup Wave shoaling Wave turbulence Wave–current interaction Waves and shallow water one-dimensional Saint-Venant equations shallow water equations Wind wave model
Circulation	Atmospheric circulation Baroclinity Boundary current Coriolis force Coriolis–Stokes force Craik–Leibovich vortex force Downwelling Eddy Ekman layer Ekman spiral Ekman transport El Niño–Southern Oscillation General circulation model Geostrophic current Global Ocean Data Analysis Project Gulf Stream Halothermal circulation Humboldt Current Hydrothermal circulation Langmuir circulation Longshore drift Loop Current Modular Ocean Model Ocean dynamics Ocean gyre Princeton Ocean Model Rip current Subsurface currents Sverdrup balance Thermohaline circulation shutdown Upwelling Whirlpool World Ocean Circulation Experiment
Tides	Amphidromic point Earth tide Head of tide Internal tide Lunitidal interval Perigean spring tide Rip tide Rule of twelfths Slack water Tidal bore Tidal force Tidal power Tidal race Tidal range Tidal resonance Tide gauge Tideline
Landforms	Abyssal fan Abyssal plain Atoll Bathymetric chart Coastal geography Cold seep Continental margin Continental rise Continental shelf Contourite Guyot Hydrography Oceanic basin Oceanic plateau Oceanic trench Passive margin Seabed Seamount Submarine canyon Submarine volcano
Plate tectonics	Convergent boundary Divergent boundary Fracture zone Hydrothermal vent Marine geology Mid-ocean ridge Mohorovičić discontinuity Vine–Matthews–Morley hypothesis Oceanic crust Outer trench swell Ridge push Seafloor spreading Slab pull Slab suction Slab window Subduction Transform fault Volcanic arc
Ocean zones	Benthic Deep ocean water Deep sea Littoral Mesopelagic Oceanic Pelagic Photic Surf Swash
Sea level	Deep-ocean Assessment and Reporting of Tsunamis Future sea level Global Sea Level Observing System North West Shelf Operational Oceanographic System Sea-level curve Sea level rise World Geodetic System
Acoustics	Deep scattering layer Hydroacoustics Ocean acoustic tomography Sofar bomb SOFAR channel Underwater acoustics
Satellites	Jason-1 Jason-2 (Ocean Surface Topography Mission) Jason-3
Related	Argo Benthic lander Color of water DSV Alvin Marginal sea Marine energy Marine pollution Mooring National Oceanographic Data Center Ocean Ocean exploration Ocean observations Ocean reanalysis Ocean surface topography Ocean thermal energy conversion Oceanography Pelagic sediment Sea surface microlayer Sea surface temperature Seawater Science On a Sphere Thermocline Underwater glider Water column World Ocean Atlas
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