Ocean Circulation (DP IB Environmental Systems & Societies (ESS)): Revision Note

Ocean Circulation

What Causes Ocean Circulation?

• Ocean circulation systems are driven by differences in temperature and salinity

• The resulting difference in water density drives the ocean conveyor belt, which distributes heat around the world and thus affects climate

Ocean Conveyor Belt

• Ocean currents redistribute heat energy around the globe

• The currents (warm or cold) act a bit like 'rivers' of water in the sea

• Cold currents move towards the equator and warm currents towards the poles

• Each ocean has its own pattern of currents

  • E.g. the warm Atlantic Ocean waters of the low latitudes are moved to high latitudes via the North Atlantic Drift

• All ocean currents are triggered by the prevailing surface winds created by global atmospheric circulation

• Ocean circulation is also maintained through convection currents driven by cold water freezing into ice at the poles

  • The polar cold waters contain denser, saltier sea water, which sinks to the ocean floor

  • Water then flows in above it at the surface, which forms a current

  • The deep ocean currents then flow towards Antarctica along the western Atlantic basin, before splitting off into the Indian and Pacific Oceans where the water begins to warm up

  • The warming makes the water less dense so it loops back up to the ocean surface in the South and North Atlantic Ocean

  • The warmed surface waters continue to flow around the globe and eventually return to the North Atlantic, where the cycle begins again

• This movement of water is known as the thermohaline circulation and drives the ocean conveyor belt

The ocean conveyor belt transports heat and energy around the world, affecting climate