||An eddy that forms when a boundary current meander pinches off and closes, trapping
a parcel of colder water in a surrounding ring of warmer water. The ring measures
up to 300 kilometers and extends to 4,000 meters depth or the ocean bottom. The colder
water in the core tends to be higher in nutrients and more productive than that in
the surrounding ring, so they become islands of biological activity as they move through
the ocean. Rings form in all oceans and can persist for months to years.