Discovery Science: Earth – Oceans – Ocean Currents

Earth Science: Oceans – Ocean Currents

Ocean currents, dependent upon the winds and varying salt concentrations, drive huge masses of water over long distances.

Numerous surface and deepwater currents act as giant conveyer belts, circulating the water in the world’s oceans. The Earth’s ocean waters can complete a turnover in a few hundred years, though it can take up to 2,000 years.

Influence of the winds

Prevailing winds drive the ocean’s surface currents, circulating warm water away from the Equator and circulating cold water toward the Equator by the currents created by the circulating trade winds. Coastal desert areas are the result of cold ocean currents near the shore. Because cold ocean currents result in cold air masses directly above them, moist air does not rise, so clouds and rain do not form, creating a desert environment.

Warm ocean currents also warm the air over the nearby land. Without the warm ocean currents, many areas of the Earth would have significantly lower average temperatures. One example of this system of currents is the Gulf Stream (see in focus), which forms in the Caribbean and directs warm water across the North Atlantic toward Europe, creating a relatively mild climate.

Deep water currents

The ocean is a complex system of warm and cold currents, both on the surface and at great depths. While surface currents are driven by winds, deep currents are driven by density and temperature gradients. In the Atlantic, the Gulf Stream flows from the Caribbean across the North Atlantic toward Europe. Between Greenland and Norway, the Gulf Stream waters are cooled by the frigid winds from the North Pole, become denser, and sink deeper into the ocean until they reach the bottom.

They continue to flow along the ocean floor toward the southern end of the Atlantic. The current is then channeled through the Indian Ocean to the South Pacific, gradually warming along the way and rising to the surface off the coast of South Africa, where it is picked up by a circulating current and routed back to the Caribbean to start its journey again.


The Gulf Stream affects more than just water temperature. When the Gulf Stream flows into the open Atlantic oft the coast of North America it splits into smaller circulating streams of warm water called eddies The warm water eddies mix with the colder surrounding water to produce the lukewarm water found off the coasts of western and northern Europe.

This results in the region’s unusually mild climate, as compared to other countries at similar latitudes, such as Canada—allowing palm trees to grow in Ireland, and causing fjords of the Norwegian coast to remain free of ice all year.


OCEAN CURRENTS are measured in Sverdrup with the symbol Sv. where 1 Sv is equivalent to a volume flow rate of 10^6 cubic meters (over 264 million gallons) per second.