Eddies are swirls of water currents spun off from a main current or forced by the wind. Ocean eddies may persist from a week to as long as a year, have diameters of tens to hundreds of kilometers, and extend to great depths in the oceans. These currents play an important role in ocean circulation by transporting heat, salt and nutrients through the waters.
In the atmosphere, "weather" consists of the random fluctuation of air flow. The world's oceans have their own weather, consisting of the random fluctuation of ocean currents. Eddies may be thought of as a type of oceanic weather. They play a critical role in ocean circulation, the earth's climate, and biogeochemical systems.
Eddies also play a role in human pursuits. Some large fish like to feed near the edges of cold eddies. As eddies come and go, so do schools of fish. TOPEX/Poseidon locates eddies and the average sea-surface height changes they cause.
