Ocean Current

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.