gyre

A spiral oceanic surface current driven primarily by the global wind system and constrained by the continents surrounding the three ocean basins (Atlantic, Pacific, and Indian). Each ocean basin has a large gyre in the subtropical region, centered around 30° north and south latitude. Smaller gyres occur at 50° north latitude in the North Atlantic and Pacific Oceans. The direction of a gyre's rotation is determined by the prevailing winds in the region, with the large subtropical gyres rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.