Surface-ocean currents result largely from prevailing winds, which in turn are generated from solar energy. Other factors that contribute to ocean currents include the Coriolis effect, the position of landmasses, and the varying density of water. Gyres are large, circular ocean current systems that often encompass an entire ocean basin. Deep-ocean currents often travel in different directions and at different speeds than do surface currents. The present circulation of shallow and deep currents, known informally as the ocean conveyor belt, affects regional and possibly global climate.