<!--ImageDescript-->This illustration shows the circulation of the ocean's  surface water. Names of the major ocean currents are noted. Warm currents are  noted in the color red and cold currents are noted in the color blue. <!--/ImageDescript-->Click on image for full size (260K  JPEG) <!--ImageFrom-->Windows Original <!--/ImageFrom-->

There are two main  sections of ocean water: the  surface layer and the the deep  waters. The surface layer is the layer at the top of the ocean that is well  mixed by waves, tides, and weather events like rain or a hurricane. The surface  layer sits on top of the deep water because the surface layer is less dense. The  depth of the surface layer varies depending on location and season, but the  depth is typically a couple hundred meters. There is a boundary layer between  the surface layer and the deep waters that is called the the pycnocline (meaning rapid change  of density). The pycnocline is caused by rapid changes of temperature and salinity. 

 

Surface water movement takes place in the form of currents. Currents move  ocean water horizontally at the ocean's surface. Surface currents are driven  mainly by the wind. Other  forces such as the  Coriolis effect and the location of land masses do affect surface current  patterns. In fact, huge circular patterns called current gyres can be seen when  looking at the world's ocean currents. From the equator to middle latitudes, the  circular motion is clockwise in the Northern Hemisphere and counterclockwise in  the Southern hemisphere. Near the poles of the Earth, there is a tendency for the  gyres to flow in the opposite direction. This circulation of water helps spread  energy from the Sun. The Sun warms water  at the equator and then water and heat are transported to higher latitudes.  

 

Major ocean currents of the world include (please see illustration for a more  complete listing):  

 
• North & South Equatorial Current  
• Equatorial Counter Current  
• North Atlantic Drift  
• Gulf Stream  
• Kuroshio Current (off of Japan)  
• Antarctic Circumpolar Current  
• East Australian current

Ocean  Currents

 
 
• largely generated by wind- gyres  
• account for about 40% of global heat transport  
• water moves at 20-45 degree angle to wind dir due to coriolis  force  
• move slower than winds - several km/day - km/hr  
 

 

Major Ocean Currents:  

1- gulf stream - check out the current position of the gulf  stream:   

3- laborador current  

7- north equatorial current  

8- north equatorial. counter current  

9- south equatorial current  

10- south equatorial counter current  

11- equatorial counter current  

12- kuroshio current  

14- Alaska current  

16- California current

A current is defined as a large mass of continuously moving oceanic water  (Greene, 1998). Surface ocean currents are mainly wind-driven and occur in all  of the world's oceans. Examples of large surface currents that move across vast  expanses of ocean are the Gulf Stream, the North Atlantic Current, the  California Current, the Atlantic South Equatorial Current, and the Westwind  Drift. Associated with surface currents are counter-surface and underlying  currents. Surface ocean currents are deflected to the right in the Northern  Hemisphere and to the left in the Southern Hemisphere due to the Coriolis  effect. The Coriolis effect holds that because the Earth is spinning, surface  waters move in a clockwise direction in the Northern Hemisphere and in a  counterclockwise direction in the Southern Hemisphere. The currents eventually  come into contact with the continents which deflect them, creating giant oceanic  current circles known as gyres.

Vertical and ocean-bottom currents are mainly driven by density differences  caused by changes in temperature and salinity. Originating in polar regions,  cold, salty waters sink to the ocean bottom and move toward the opposite poles  where they again surface. Vertical upwelling currents can also be caused by  winds "blowing off" a coastline. The displaced waters are then replaced by  underlying bottom waters. Currents are important to marine life as they help to  move food and nutrients, making them available for photosynthesis, metabolic  requirements and/or consumption.

Ocean Currents

Ocean currents flow in complex patterns affected by wind, the water's  salinity and heat content, bottom topography, and the earth's rotation. These  ocean currents and the resulting global circulation patterns are of interest to  scientists studying Earth systems and global change issues.