Understanding Ocean Currents

What are ocean currents and how are they formed? What causes water to be pushed around the planet in some directions but not others? Read more to find out!

How are ocean currents created?
There are different types of ocean currents that are formed in a variety of ways. Deep ocean currents are formed by differences in water temperature. Currents closer to the surface are usually caused by the wind, while currents near the shore are caused by tides. 

Deep sea ocean currents are caused by varying ocean temperatures, but how exactly does that work?
Ocean water at the equator is heated up by the sun and then travels back towards the poles. As ocean water travels away from the equator it cools down and eventually some of it freezes turning into sea ice. The salt in water doesn’t freeze, so where sea ice forms around the planet, the salinity of the ocean water increases as the fresh water freezes into ice. With increased salinity and colder temperature, the ocean water becomes more dense. Because it is now denser, the water sinks lower in the ocean and is replaced with new warmer water traveling away from the equator. This cycle continues creating a current called the global conveyor belt. This process can be referred to as the thermohaline circulation; ‘thermo’ meaning heat and ‘haline’ meaning salinity. 

Currents formed by winds
The formation of currents by winds is more straightforward than that of deep ocean currents. Winds that blow across the surface of the ocean move mass amounts of water as they blow, which in turn, cause currents to form. The trade winds, or easterlies, can be found on either side of the equator and contribute to these ocean currents by continuously blowing over the ocean from east to west. Because of the Coriolis effect which deflects moving winds or water clockwise in the northern hemisphere and counterclockwise in the southern hemisphere, these currents form gyres. The Coriolis effect takes place because of the time it takes for the circumference of the earth to make a rotation near the equator is longer than near the poles.

What are the different kinds of ocean currents?
Ocean Gyres
Ocean gyres are sustained rotating systems of currents that tend to be thousands of miles in diameter. These systems are made up of sustained currents created by wind. They can move as fast as 25 to 75 miles per day. The Coriolis effect that deflects winds and currents causes gyres to rotate.

Eddies 
Eddies are relatively small currents in comparison to gyres and currents. They break off from bigger currents and can travel many miles for up to several months before dissipating. 

What are the 5 major ocean currents?
The five major ocean currents are the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres. Some of these currents have other common names as well. For example parts of the North Atlantic gyre are also called the Gulf Stream. The Gulf Stream flows from the Gulf of Mexico up the eastern coast of the United States all the way up to Newfoundland in Canada. This gyre spans the Atlantic Ocean in the northern hemisphere from the east coast of the United States to western Europe and Africa. The North Pacific gyre spans from the west coast of north america to the east coast Asia. Both of these gyres are in the northern hemisphere so they rotate clockwise. 

The southern hemisphere has three distinct gyres all of which rotate counterclockwise. The Indian Ocean gyre extends over the Indian Ocean as the name suggests, between the east coast of Africa and the western coast of Oceania and Australia. The South Atlantic gyre is the southern equivalent of the North Atlantic gyre, but spans between the eastern coast of South America and the west coast of Africa. Lastly, the South Pacific gyre ranges from the west coast of South America to eastern Oceania.

What are the fastest, longest and strongest currents?
The fastest ocean current is the Gulf Stream. It can reach speeds up to 5.6 miles per hour. The longest and strongest wind current is the Antarctic Circumpolar Current. This current circles the earth around Antarctica and can be more than 120 miles wide.

What is the importance of ocean currents?Ocean currents are significant for ocean environments. The flow of these currents brings oxygen into the ocean for aquatic organisms. Currents can also help provide food, nutrients and transportation for sea life while also regulating the climates on the nearby coasts. In the summer the ocean absorbs heat and in the winter it releases heat meaning coastal areas often have less extreme weather than inland areas.

Saiyana Toran

Saiyana Toran is a junior at Albany High School. She grew up in Berkeley and Albany, California. She plays ultimate frisbee and the flute and she works with OYA as an intern.