Ocean currents (image: Edesignua).Ocean currents are large scale movements of surface sea water. Surface ocean currents follow a circular pattern. These movements of water play an important role in shaping the earth’s climate. The movement of the water is driven mostly by the winds.

What Causes the Ocean Currents?

The ocean currents get their energy from the tradewinds. In the Northern Hemisphere, the winds blow from the northeast to the southwest. This results in the clockwise movement of the currents in a gyre. Most of this movement occurs in the top 100 meters of the ocean.

In the Southern Hemisphere, the winds blow from the southeast to the northwest. This results in the counter-clockwise movement of the ocean currents.

Are There Other Kinds of Currents?

In addition to surface ocean currents, there are two other types of currents.

Tidal Currents: Smaller scale and more local currents may also be caused by the tides. During the high tide, the water moves inland and floods the shore. During the low tides, the water recedes from the shore and ebbs. This type of current is called a tidal current.

Thermohaline Currents: In addition to wind driven currents, there are deep sea currents as well. These deep water currents may flow thousands of meters below the ocean’s surface. In the earth’s polar regions, sea water is frozen. As the water turns into ice, the seawater becomes more salty and more dense.

The cold and salty water is very dense and begins to sink. This begins the movement of water from the surface at the polar regions in the North Atlantic to the ocean depths. The deep ocean currents then begin a journey to the South polar regions. There, the currents are recharged with more cold salty water.

The currents then travel into the Indian and Pacific Oceans. There the waters begin to warm and rise up and become part of the ocean currents at the sea’s surface. The warmed waters eventually move back to the North Atlantic and start the cycle again.

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Surface Ocean Currents, NOAA.