Oceanic circulation

The world’s oceans also play an important role in redistributing energy around the globe.

Energy is moved from areas of surplus to those of deficit, with warm currents transporting warm water polewards and cold currents taking colder water to lower latitudes.

Ocean currents are movements of surface water.

Because they cover 67 per cent of the Earth's surface, the oceans receive 67 per cent of the Sun's energy that reaches Earth. It holds onto this heat for longer than the land does and the ocean currents move this heat around, from the tropics to higher latitudes.

In total, ocean currents transfer about 25 per cent of the global heat budget.

The map below shows the pattern of currents across the world.

Map of the world showing all the oceans warm and cold currents.

You can see that:

  • The currents set up circular loops or gyres. Gyres are spiral oceanic surface currents and are found in both the Northern and Southern Hemispheres.
  • The pattern of current flow is clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere.
  • In the Atlantic and Pacific oceans, the currents make a similar pattern.

Ocean currents flowing away from the equator are called warm currents. The water in these currents is not necessarily warm, but it's warm compared to what you would expect for that latitude. The Gulf Stream is a good example of a warm current.

If a current flows towards the equator it is a cold current, for example the Canaries current.

The video below examines if the movement of sea water can affect the climate.

These patterns can be explained by a number of factors:

  • The prevailing winds on the surface create friction with the surface water, setting up the ocean currents.
  • The huge size of the Atlantic and Pacific oceans allows these patterns to form.
  • The trade winds drive the pattern between 0º and 30º north and south and the westerlies create the pattern between 30º and 60º north and south.
  • Ocean currents don't flow due north or due south because of the Coriolis force caused by the Earth's rotation. This deflects the currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
  • Uneven heating produces density differences in the oceans.
  • Cold dense polar water sinks, then spreads towards the equator where it pushes up the less dense warmer water which moves off towards the polar areas.
  • The flow is further complicated by the world’s land masses, which impedes the flow of most currents.

The video below explains the redistribution of energy.

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