Syllabus Edition

First teaching 2015

Last exams 2025

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

Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

Updated on

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

thermohaline-circulation

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

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Alistair Marjot

Author: Alistair Marjot

Expertise: Biology & Environmental Systems and Societies Content Creator

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

Bridgette Barrett

Reviewer: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.

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