2.3.1. Causes of Ocean Currents

Ocean currents are influenced by two types of forces namely:

♤ Primary forces that initiate the movement of water.

♤ Secondary forces that influence the currents to flow. The forces that influence the currents are:

1. Heating by solar energy causes water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.

There is much difference in the temperature of ocean waters at the equator and at the poles. As warm water is lighter and rises, and cold water is denser and sinks, warm equatorial waters move slowly along the surface polewards, while the heavier cold waters of the polar regions creep slowly along the bottom of the sea equatorwards.

2. Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course. Most of the ocean currents of the world follow the direction of the prevailing winds.

3. Coriolis force causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres. These produce large circular currents in all the ocean basins.

4. Salinity of ocean water varies from place to place. Waters of high salinity are denser than waters of low salinity. Hence on the surface, waters of low salinity flow towards waters of high salinity while at the bottom, waters of high salinity flow towards waters of low salinity.

5. The configuration of the coastline serves as an obstruction for the natural flow of ocean currents and succeeds in changing its direction. This is quite conspicuous in the equatorial region where the landmasses deflect the current towards the north and the south.