A simplified model of global ocean circulation shows warm (red), salty water moving up from warmer latitudes toward the colder North Atlantic Ocean. The ocean gives up heat to the atmosphere (large arrows), which warms the region. Colder (blue) saltier waters are denser, and so they sink into the abyss. This propels the global ocean circulation system, which is often called the Great Ocean Conveyor. (Animation by Jack Cook, WHOI Graphic Services)