The ocean waters at the equator are warm because they receive more of the sun rays than the waters at the at the poles. Therefore, the water in these regions is less dense than those at the poles. The oceans currents, moving towards the poles from the equator, move on the surface waters while those from the poles move on the ocean floor.
As the warm currents move to the poles and cool, they become more saline because they become more concentrated with salts –saturation point lowers with temperatures. At the poles, most of the salts in ejected from the waters as brine as the water sinks to the ocean floor due to density.
This movement of water currents in such circular motion forms the Thermohaline Circulation. Heat on the planet is distributed in this way.
