What drives North Atlantic drift?

The Gulf Stream and the North Atlantic Drift are currents that are caused by the overall circulation of the ocean, or the thermohaline circulation. This global conveyer-like circulation has its origins in the North Atlantic Ocean, where surface waters sink during winter. Surface-water density increases as the temperatures drop, and the extra salt, left behind when sea ice forms, adds further to this density increase. Cold, dense North Atlantic Deep Water (NADW) sinks and flows along the sea floor at depths greater than 2,000 m (7,000 ft). It travels south past Greenland and out into the North Atlantic Ocean, where it feeds into a global system of deep currents. NADW has been traced in all of the world's ocean basins, and it takes roughly 1,000 years for deep water formed at the surface in the North Atlantic to return to the surface at other locations.

Thermohaline circulation drives a surface flow of warmer water from the tropics back toward the poles, and in the North Atlantic, this current system is represented by the Gulf Stream and North Atlantic Drift. This ocean-circulation pattern is sometimes called the "ocean's conveyor belt." Thermohaline circulation is very important because it redistributes heat around the globe, bringing warm water to the cold north and transporting cold water back toward the equator, contributing to the maintenance of the Earth's climate. This movement of water is often likened to a giant heat pump, warming the countries of northern Europe and keeping the North Atlantic and Arctic Oceans from freezing over completely during the winter months.

However, the ocean-circulation system is very sensitive to changes in both temperature and salinity. Recent computer models predict that the influx of fresh water into the North Atlantic from melting Arctic ice, as well as the addition of warmer river water from the effects of global warming, could result in the slowing of ocean currents and the eventual shutdown of the Gulf Stream/North Atlantic Drift, which would have profound consequences for global climate.