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This image shows the five major ocean gyres. It shows that gyres rotate in a clockwise direction in the Northern hemisphere and a counter-clockwise direction in the Southern hemisphere. The black square shows the approximate location of the Great Pacific Garbage Patch and the red circle shows the position of the Beaufort gyre in the Arctic Ocean.
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Windows Original (Original map is from Wikipedia Commons)

Ocean Gyres

A gyre is another name for a swirling vortex. Ocean gyres are large swirling bodies of water that are often on the scale of a whole ocean basin or 1000’s of kilometers across (hundreds to thousands of miles across). They are larger than the whirpools of water in the ocean called eddies. Eddies are on the scale of 100 km (60 miles) across and dissipate over a few months. Ocean gyres dominate the central regions of open ocean and represent the long-term average pattern of ocean surface currents. Ocean gyres in the Northern hemisphere rotate clockwise and gyres in the Southern hemisphere rotate counter-clockwise due to the Coriolis effect.

The major gyres of the ocean include: North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Ocean gyres. A simplistic representation of those can be seen on the graphic on this page. Of course, many other smaller gyres exist in the ocean too.

One such smaller gyre is the Beaufort gyre found in the Arctic Ocean. The Beaufort gyre is a huge vortex of water being driven by strong winds that force currents in a clockwise direction. This gyre is full of relatively fresh water as Siberian and Canadian rivers drain into the Beaufort gyre. Scientists have been keeping a close eye on the Beaufort gyre because of the relatively fresh water it holds. When winds slack off and the gyre weakens, fresh water leaks out of the gyre and into the North Atlantic Ocean. The addition of fresh water from the Beaufort gyre along with fresh water from melting sea ice could be contributing to the disruption of the global ocean current system known as the ocean conveyor. This slowing or halting of the ocean conveyor system will have impacts on ocean-atmosphere interactions which drive much of the climate in the North Atlantic and surrounding areas.

Scientists are concerned about material leaking out of the Beaufort gyre, and they are equally concerned about other gyres that have captured and are "holding onto" material. One of the largest ocean gyres, the North Pacific gyre, is home to an area called the Great Pacific Garbage Patch. This area contains a relatively high concentration of marine litter. It is estimated to cover an area roughly twice the size of Texas and contains approximately 3 million tons of plastic litter, though much of this plastic is broken up into pieces too small to see with the naked eye. Although the precise origin of the litter is not known, scientists believe that the Garbage Patch was created gradually as the Northern Pacific Gyre captured foreign material and that material was transported to the center of the gyre by centripetal forces and wind-driven surface currents, creating an area with concentrated litter.

Surface ocean currents, ocean gyres, deep ocean circulation and the atmosphere are all parts of the complex Earth system. Understanding ocean-atmosphere interactions is a key part of understanding global climate change as well as how different things like water, energy, nutrients or pollutants move through (or get trapped within!) different parts of the Earth system.

Last modified January 26, 2011 by Jennifer Bergman.

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The Summer 2010 issue of The Earth Scientist, available in our online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.

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