Two large warm water eddies are swirling to the north of the Gulf Stream current in this satellite image recorded with the AVHRR sensor (Advanced Very High Resolution Radiometer) aboard a NOAA satellite on June 11, 1997. Blue colors indicate cooler water, while yellow and orange colors indicate warmer water.
Click on image for full size
Courtesy of the Ocean Remote Sensing Group, Johns Hopkins University Applied Physics Laboratory

The Swirling Water of Ocean Eddies

Sometimes water spins away from a surface ocean current, creating an eddy.

The swirling water of an eddy can be more than 100 km (60 miles) in diameter. The center of some eddies is cool while the center of others is warm. Marine life is sparse in warm water eddies, where the water does not have many nutrients. Cold water eddies are usually full of nutrients and marine life.

Eddies form when a bend in a surface ocean current lengthens and eventually makes a loop, which separates from the main current. The Coriolis effect causes cold water eddies to rotate counterclockwise and warm water eddies to rotate clockwise in the Northern Hemisphere while in the Southern Hemisphere cold water eddies rotate clockwise and warm water eddies rotate counterclockwise. There is evidence that the topography of the ocean floor can help eddies to form too. Once an eddy forms, the swirling waters last for at least a few months.

The satellite image at the left of sea surface temperatures (SST) shows two large circular features above the Gulf Stream current in the Atlantic near the northeast coast of the United States. These are eddies. In this image, surface water is colored depending on its temperature. Cooler water is shown with blue and purple and orange and yellow show warmer water. The orange color of these eddies means that they are warm water eddies. This area of the ocean – the Gulf Stream - tends to have some of the largest and most well defined eddies in the world.

Last modified January 8, 2010 by Randy Russell.

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