Gulf stream rings
From Glossary of Meteorology
Gulf Stream rings
Eddies formed by pinching off of meanders in the Gulf Stream.
Eddies forming to the north (coastward side) of the Gulf Stream are called warm-core rings (anticyclonic) because they encapsulate relatively warm Sargasso Sea water in the pinching off process, and those forming to the south (oceanward side) are called cold-core rings because they encapsulate relatively cold Slope Water in their centers.