The ocean never stands still. Beneath the surface currents that the wind pushes along, a slower, larger motion carries water around the entire planet. Scientists call it the global ocean conveyor belt: a constantly moving system of deep-ocean circulation powered by two things — temperature and salt.
The great ocean conveyor moves water around the globe. Credit: NOAA.
Heavy water sinks
The conveyor runs on density. Cold, salty water is dense and sinks toward the bottom of the ocean; warm water is less dense and stays near the surface. Currents driven by these differences are called thermohaline currents — thermo for temperature, haline for salinity. Together with the wind-driven currents at the surface, they keep the whole ocean in motion.
Where the belt starts
The conveyor gets its start in the Norwegian Sea. There, warm water carried north by the Gulf Stream gives up its heat to the atmosphere of the cold northern latitudes. Losing that heat makes the water cooler and denser, and it sinks to the bottom of the ocean.
A loop around the planet
As more warm water arrives from the south, the cooled water that has sunk moves south along the bottom to make room for it. This cold bottom water flows past the equator and all the way down to Antarctica. Eventually it rises back to the surface, through mixing and upwelling driven by the wind — and the loop that encircles the globe continues.
Sources
Based on "What is the global ocean conveyor belt?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from oceanservice.noaa.gov
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