Ocean Current

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Primary forces that initiate the movement of water

  • Heating by solar energy – Expand water, so near the equator the ocean water is about 8 cm higher in level than in the middle latitudes.
  • Wind – Water to Move.
  • Gravity -  Pull the water down the pile and create gradient variation.
  • Coriolis force - water to move to the right in the northern hemisphere and to the left in the southern hemisphere.
Secondary forces that influence the currents to flow
  • Large accumulations of water and the flow around them are called Gyres.
  • Differences in water density affect vertical mobility of ocean currents.
    • High salinity > Low Salinity.
    • Cold water > Warm water.
  • Denser water - sink, while relatively lighter water tends to rise.
  • Cold-water currents occur when the cold water at the poles sinks and slowly moves towards the equator.
  • Warm-water currents travel out from the equator along the surface, flowing towards the poles to replace the sinking cold water
Types of Ocean Currents
Based on Depth
  • Surface currents – 10 %, upper 400 m of the Ocean.
  • Deep water currents – 90 %
Based on Temperature
  • Cold currents bring cold water into warm water areas.
  • Warm currents bring warm water into cold water areas.
Major Ocean Currents
  • Oceanic circulation pattern roughly corresponds to the earth’s atmospheric circulation pattern.
  • Middle latitude – anticyclonic. & Higher latitude – Cyclonic.
  • Monsoon winds influence the current movements.
  • Cold waters of the Arctic and Antarctic circles move towards warmer water in tropical and equatorial regions.
  • Warm waters of the lower latitudes move poleward.
Effects of Ocean Currents
  • West coasts of the continents in tropical and subtropical latitudes (except close to the equator) are bordered by cool waters - fog, but generally the areas are arid.
  • West coasts of the continents in the middle and higher latitudes are bordered by warm waters which cause a distinct marine climate - cool summers and relatively mild winters.
  • Warm currents flow parallel to the east coasts of the continents in tropical and subtropical latitudes - warm and rainy climates.
  • Areas lie in the western margins of the subtropical anti-cyclones.
  • Mixing Zone - mixing of warm and cold currents help to replenish the oxygen and favour the growth of planktons, the primary food for fish population.

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