Ocean gyre
A gyre is a large system of ocean currents moving in a circle. Gyres are caused by the Coriolis effect. Because the Earth is rotating, ocean currents in the northern hemisphere tend to move in a clockwise direction and currents in the southern hemisphere move in an anti-clockwise direction.[1]
The Coriolis force acts most strongly on the wind, and the wind then creates a torque that tends to spin the ocean currents.[2]
The Earth rotates from the west towards the east, and the Coriolis effect becomes more intense toward the poles. Because of this, gyres form strong currents on the western side of oceans, so they are pushed against the eastern coast of continents.[1][2] The vorticity (the strength of the torque force) is balanced out by frictional surface currents, which normally act against the spin of the water. However, in the middle of the ocean, the effects of friction are very weak.[2][3]
The term gyre can be used to mean any type of vortex in the air or the sea, but it is most used in oceanography for the major ocean current systems.
Major gyres
These are the five largest gyres:[4]
Other gyres
Tropical gyres
Tropical gyres tend to be mostly east-west with minor north-south extent.
Subtropical gyres
The centre of a subtropical gyre is a high pressure area, which the ocean moves around. The high pressure in the centre is due to the westerly winds on the northern side of the gyre and easterly winds on the southern side of the gyre. These cause frictional surface currents towards the latitude at the centre of the gyre.
Subpolar gyres
Subpolar gyres form at high latitudes (around 60°). The ocean moves around a low pressure area. Surface currents generally move outward from the centre of the system.
Ocean GyreOther Gyres Media
The velocity profile within the boundary layer calculated using Munk's boundary layer solution for both the case of a western boundary (top) and eastern boundary (bottom) in a northern hemisphere subtropical gyre. Note that positive vorticity is input into the flow near the boundary only in the case of the western boundary current, meaning this is the only valid solution to gyre return flow.
The distribution of the North Atlantic Subpolar Gyre shown above the North Atlantic Gyre to the South.
Central Arctic Ocean Currents: Transpolar Drift and Polar Gyre
An animation of a year in organism density on Earth. The South Pacific Gyre is visibly low (purple) in organism density.
The distribution of nitrate throughout the global ocean.
This plot shows the relationship to nitrogen and phosphorus availability throughout different areas of the global ocean. Nitrogen is most often more limiting than phosphorus for photosynthesis.
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Related pages
References
- ↑ 1.0 1.1 "Gyres and the Coriolis effect". Blue Planet: Infobursts. British Broadcasting Corporation. Archived from the original on 4 July 2013. Retrieved 6 October 2013.
- ↑ 2.0 2.1 2.2 Geoffrey K. Vallis (10 October 2011). Climate and the Oceans. pp. 83–85. ISBN 978-1400840625.
- ↑ B. Heinemann; Open University (1998). Ocean circulation. Oxford University Press. p. 98.
- ↑ Lynne Talley, Physical Oceanography Research Division. "The five most notable gyres". University of California, San Diego. Archived from the original (PowerPoint Presentation) on 4 March 2016. Retrieved 6 October 2013.