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How do ocean currents move heat?

Ocean currents act as a planetary conveyor belt, carrying warm surface water from the tropics toward the poles and returning cold, dense water along the seafloor1. Wind stress drives the upper limb, while differences in temperature and salinity drive the deep limb — a circulation often called the thermohaline conveyor2. Roughly a quarter of the heat that leaves the tropics travels this way, which is why a slowdown would reshape regional climate far from the equator4.