Of the world’s oceans, the North Atlantic has been the saltiest. Salty water has greater density than fresh water, and that density leads to sinking, which drives some of the world’s great conveyor currents. Those currents, in turn, drive much of the earth’s climate regionally and globally.

These conveyor currents are what is known as the thermohaline circulation. Watch the video above to see an illustration of the currents or, courtesy of Climate Central, click here to view a basic diagram of what this circulation looks like in the Atlantic.

The cold, salty waters of the North Atlantic sink from their own density and weight, travel southward along the bottom of the ocean bed and eventually begin to rise as they absorb heat again near the tropics. This warming current, part of which is known as the Gulf Stream, makes all the difference in the climate of much of northern and western Europe, and eastern North America.