Marine surface currents

What can debris tell us about surface currents?

The ocean surface is in motion. One way to realize that is when you dump something into the ocean. Where does it end up? The tsunami that hit Japan in March 2011 washed a lot of stuff into the ocean. The image above is a model created in April 2012. The orange and red colors show where the floating debris might be. Scientists create models of where the debris will go. But no one knows for sure where it will go or when it will get there.

Surface currents

Like air in the atmosphere, seawater moves in currents. A current is a flow of water moving through the ocean. The main cause of surface currents is winds, but not normal winds. Prevailing winds cause surface currents. These winds blow in the same direction all the time, so they can cause the water to keep moving in that same direction.

Surface currents are created by three things:

• global wind patterns
• the rotation of the Earth
• the shape of ocean basins

Surface currents are extremely important because they distribute heat around the planet. They also have a tremendous influence on the world’s climate.

Global wind patterns

The Earth’s winds are either global or local. Global winds blow in the same direction all the time. They are created when solar energy is stronger over the equator than in the polar regions. In “Global Wind Belts” global wind patterns are described in detail.

Prevailing winds push water in surface currents. Water moves in the directions set by the:

• trade winds: from east to west between the equator and 30°N and 30°S.
• westerly winds: from west to east in the mid-latitudes.
• east polar winds: from east to west between 50° and 60° north and south of the Equator and the North and South Poles.

Earth’s rotation

The rotation of the Earth (i.e. the Coriolis effect) causes ocean currents to rotate. More information on this phenomenon can be found in “Coriolis Effect.

The Shape of Ocean Basins

A surface current moves through the ocean. Eventually, the current makes landfall ( next image ). As it does so, it turns to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The direction it takes is due to the Coriolis effect.