Cold-core rings are a type of oceanic eddy, which are characterized as unstable, time-dependent swirling, independent ‘cells’ that separate from their respective ocean current and move into water bodies with different physical, chemical, and biological characteristics, often bringing the physical, chemical, and biological characteristics of the waters of their origin into the water bodies into which they travel. Their size can range from 1 mm to over 10,000 km in diameter with depths over 5 km. Cold-core rings are the product of warm water currents wrapping around a colder water mass as it deviates away from its respective current. The direction an eddy swirls can be categorized as either cyclonic or anticyclonic, which is, in the Northern Hemisphere, counterclockwise and clockwise respectively, and in the Southern Hemisphere, clockwise and counterclockwise respectively as a result of the Coriolis Effect. Although eddies have large amounts of kinetic energy, their rotation is relatively quick to decrease in relation to the amount of viscous friction in water. They typically last for a few weeks to a year. The nature of eddies are such that the center of the eddy, the outer swirling ring, and the surrounding waters are well stratified and maintain all of their distinctive physical, chemical, and biological properties throughout the eddy’s lifetime, before losing their distinctive characteristics at the end of the life of the cold core ring.

 

Note:   The above text is excerpted from the Wikipedia article Cold core ring, which has been released under the GNU Free Documentation License.