Ocean Conveyor Belt: the Thermohaline Circulation

The oceans of our planet are in constant motion, driven by surface winds and changes in water temperature, density, and salinity, which is the concentration of mineral salts dissolved in the water. This movement can be envisioned as a giant, slow-moving conveyor belt that moves the sun’s energy in the form of heat around the globe.

As we saw previously, the Gulf Stream wind current pushes warm ocean water up the eastern coast of the United States. As this water moves into the cooler upper latitudes, it releases heat and progressively cools. This cooling surface water is both denser and higher in salinity than the warm water. This cooler, denser water sinks thousands of feet below the ocean surface and moves along the ocean floor in a cold water current. This deep ocean water moves to the ocean’s surface, or upwells, to replace the void created in areas where surface water is pushed away from the coast by surface wind currents. As the water moves to the surface, it warms, becoming more buoyant.

This global oceanic conveyor belt is termed the thermohaline circulation, as it is driven both by differences in temperature (thermo-) and salinity (-haline). This global circulation plays a very important role in shaping the earth’s climate.

An animation of deep ocean currents.