Ocean currents

Ocean currents are movements of surface water. How the world's oceans move has a huge influence on our climate and it, in turn, is influenced by a number of factors. You need to be able to describe and explain the patterns and impacts of the earth's ocean currents.

Like atmospheric circulation, ocean currents help to redistribute energy across the earth. Because they cover 67% of the earth's surface, the oceans receive 67% of the sun's energy that reaches earth. The ocean holds on to 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% of the global heat budget.

Map showing global patterns of warm and cold ocean currents

World pattern of ocean currents

The map above shows the pattern of currents across the world. You can see that:

the currents set up circular loops or gyresgyres: spiral oceanic surface currents. 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.

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 0 and 30 degrees north and south and the westerlies create the pattern between 30 and 60 degrees 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.

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