Britannica Sources used in this answer

Why do cold-core Gulf Stream rings rotate counterclockwise?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Map of the North Atlantic Ocean showing major ocean currents, with warm currents like the Gulf Stream and North Atlantic Drift highlighted in pink and cold currents in blue. Arrows indicate current directions and relative speeds, connecting the eastern coasts of North America, the western coasts of Europe and Africa, and the Arctic region. — Gulf Stream Major warm and cold currents of the North Atlantic Ocean.

Cold-core rings associated with the Gulf Stream rotate counterclockwise because they are cyclonic eddies formed when meanders pinch off to the south of the main current.1

In the Northern Hemisphere, the Coriolis force causes moving bodies to deflect to the right. Because cold-core rings contain a core of colder, denser water that creates a localized low-pressure region, the surrounding water is drawn inward. As this water moves toward the low-pressure center, the Coriolis force deflects the flow to the right, resulting in a counterclockwise (cyclonic) rotation.21

These rings typically form when meanders in the Gulf Stream pinch off, trapping continental slope waters within the eddy. Unlike warm-core rings, which rotate clockwise (anticyclonically) and move westward, cold-core rings move generally southwestward into the Sargasso Sea and can persist for one to two years.1