|MadSci Network: Earth Sciences|
Ocean currents on a large scale are driven primarily by solar radiation. Ocean waters near the Equator are heated to a warm temperature by the Sun. Near the poles, ocean waters cool at the surface and sink. The dense cool water piles up on the ocean bottom and flows toward the Equator. The cool waters from the poles displace the warm water already there. This warm water is forced to flow away from the Equator toward the poles. You can see that there is a continuing cycle here, since the warm water from the Equator will cool as it approaches a polar region, while the cool water from the poles is heated at the Equator. This cycle has been described as a very large heat-driven engine. Other forces besides the Sun affect ocean currents. One major force is the Coriolis force which tends to divert water flowing away from a pole to the West and water flowing away from the Equator to the East. Another constraint on currents is the depth of the ocean. Shallow water and solid land both cause currents to change direction.
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