Physical Properties of Water
Like the heated air in a hot-air balloon, heated water expands. Solar heat absorbed at the equator causes water to expand. Such heated water raises the normal level of the sea surface, and such changed ocean topography can be measured. The heat in the water is carried to higher latitudes by ocean currents where it is released into the atmosphere. Water chilled by colder temperatures at high latitudes contracts (thus gets more dense), sinks, (lowers the local topography) and returns to the equator via the global ocean water circulation conveyor belt to complete the cycle.
The Global Conveyor Belt