In the Northern Hemisphere, which direction do gyres rotate?

• A. Clockwise
• B. Counterclockwise
• C. They don't rotate
• D. Random

Answer: (A)

Coriolis effect deflects moving water to the right in the Northern Hemisphere, which makes large-scale ocean gyres rotate clockwise. Surface winds drive water westward in the tropics and eastward at higher latitudes; as the water is steered to the right, it turns north along the western boundary, then east along the northern boundary, and south along the eastern boundary, closing a clockwise loop around the basin. This same mechanism yields counterclockwise gyres in the Southern Hemisphere. So, in the Northern Hemisphere, gyres rotate clockwise.