About Ocean Currents

How Ocean Currents are formed

Major Ocean Currents of the World

Ocean surface currents are caused by:

• Sun's energy

The oceans and atmosphere receive more energy from the Sun at low latitudes (closer to the equator) and receive less energy near the poles

The Sun heats the oceans and atmosphere producing winds.  When the winds blow over the oceans, they experience friction due to the ocean surface roughness.  This frictional interaction results in transfer of energy to the sea surface and produces waves and currents.

• Earth's rotation

The Earth’s rotation gives rise to a ‘virtual force’ known as the Coriolis effect.  The Coriolis effect is an apparent deflection of objects moving on earth from a straight path due to the rotating frame of reference on earth.  In the northern hemisphere this forces moving air and water to move in a clockwise spiral.  In the southern hemisphere, the motion will spiral counterclockwise.

•     Flow over and around topographical obstacles

Flow of ocean waters over undersea mountains and valleys also produces currents.

Deep ocean currents (also known as Thermohaline Circulation) are caused by:

• Variations in the density of sea water due to differences in temperature and salinity.

Surface water is heated by the sun, and warm water is less dense than cold water.  Similarly, fresh water is less dense than salty water. At northern latitudes, surface water is cooled by extremely cold air.  This cool water can becomes denser than the underlying water causing it to sink.  The sinking and transport of large masses of cool water gives rise to the thermohaline circulation, which is driven by density gradients due to variations in temperature and salinity.

• The earth’s rotation also influences deep ocean currents

In general, wind-driven currents dominate the upper ocean, and thermohaline circulation  drives the movement of the deep ocean.