• Each of the world's oceans is home to multiple major subsurface currents.A day at the beach image by onebadtaz from Fotolia.com
  
  The phrase ocean current refers to the horizontal movement of surface seawater caused by wind circulation. Surface currents extend only a few feet, where subsurface currents pick up. Interaction of the atmosphere, energy flow from the tropics to the polar regions and the ocean causes large ocean currents that circle the world in a trip that takes about 1,000 years to complete.
  
  

Causes

• A combination of the earth's rotation, wind and water density differences produces ocean currents. Water density varies due to temperature and salinity differences. Essentially, the wind blows across the ocean and causes its surface to move. That motion passes through to each succeeding lower layer but, internal friction with water decreases the rate of motion as depth increases.
  
  

Differences

• Aside from the obvious depth differences, subsurface currents exhibit a slower flow than surface currents. The density of sea water in surface and subsurface currents also differs. Although a current generally qualifies as either surface or subsurface, one exception exists, the Gulf Stream, which exists as both. The Gulf Stream flows from just south of the tip of Florida north along the North American coast past Cape Hatteras, then turns northeast flowing past the Grand Banks and into the north Atlantic Ocean.
  
  

Major Currents

• According to the Bureau of Commercial Fisheries, the major ocean currents include the West Wind Drift, North Equatorial Counter current, South Equatorial, West Australia, East Australia, Kuroshio, Kuroshio Extension, Oyashio, Aleutian, North Pacific, California, California Extension, North Equatorial, South Equatorial, Peru, Falkland, Brazil, Benguela, Agulhas, Guinea, Canary, North Atlantic, Norway, Irminger, East Greenland, Labrador and the Florida Gulf Stream, also referred to simply as the Gulf Stream.
  
  

Paths

• Sea water begins its 1,000-year travels near the surface in the north Atlantic where evaporation cools the water and raises its salinity. Much of this evaporation occurs between northern Europe and Greenland, north of Labrador, Canada. The cooler water continues flowing along the coasts of North and South America until it reaches Antarctica. In Antarctica, the cold, dense water flows eastward meeting another cold, deep current between southernmost South America and Antarctica. After meeting, the merged current splits into two in the midst of the Indian Ocean and north Pacific Ocean--flowing northward and eastward. These currents creating upwellings as they move from the ocean floor to the water's surface. The water continues its trip sub-surface, returning to its origin in the North Atlantic. Its travels create the warm, shallow water flow that circles Antarctica.