Abstract: Currents generated by wind and the interaction of the rotation of the earth and the gravitational pull of the sun and moon give rise to horizontal surface movement of sea water. Two basic mechanisms that drive the vertical mixing of ocean waters are reviewed in this article, the action of marine organisms and the regional differences in temperature and salinity. The latter mechanism is called thermohaline circulation. Upwelling of cold water of polar origin helps to prevent further warming of the surface of the tropical ocean areas.