The general pattern of water circulation, particularly in the northern hemisphere's Atlantic Ocean, is fairly well understood. As cold water sinks to… - Isaac Asimov

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The general pattern of water circulation, particularly in the northern hemisphere's Atlantic Ocean, is fairly well understood. As cold water sinks to the bottom of the sea around the Arctic Ocean, it travels slowly southward along the sea-bottom toward the Equator. Once it reaches the equatorial tropics it is warmed and accordingly rises to the surface, after which it slowly moves northward, in the form of the ocean surface currents mariners have long learned to map, making a complete circuit as the water returns toward the Pole.