Ocean currents are general movements or drifts of the surface water of the ocean in a fairly defined direction. They are a continuous general movement of masses of surface ocean waters horizontally and in a fairly defined direction.
They tend to be persistent. Most ocean currents drift very slowly and that is why they are commonly referred to as drifts. Ocean currents may be either warm or cold i.e. there are warm ocean currents and cold ocean currents.
The following are Causes of ocean currents
- The prevailing winds; winds influence oceanic circulation, this is because as winds blow friction is generated between the wind and water surface causing the water to move in the general direction of the wind. Some winds such as trade winds which almost continuously blow in the same direction cause surface waters over which they blow to move in the direction to which they blow e.g. across the Atlantic ocean westerlies produce the North Atlantic drift and Kuro Siwo currents (in the Pacific).
- Rotation of the earth; the earth’s rotation influences the direction of movement of ocean currents. It causes the currents to be deflected to the right in the direction to which they flow in the northern hemisphere and in the southern hemisphere the currents tend to be deflected towards the left.It is generally because of the Coriolis force that the ocean currents are deflected.
- Differences in temperature; ocean currents may be caused by differences in temperature. Such currents are generally referred to as convection currents.Heating by the sun in the low altitudes makes the waters less dense and the waters therefore drift pole wards. In the equatorial belt, temperatures are high and therefore waters are warm and tend to be less dense, unlike the polar region or high latitude region waters. As a result, the warm waters of the equatorial region drift towards the higher latitudes.
- Salinity of the waters; salinity may increase the density of the waters. Saline waters (these of high PH/basic waters) tend to be denser than waters of low salinity. It is generally noted that waters of high salinity tend to flow to areas of low salinity e.g. the surface water current from the Mediterranean Sea which enters the Atlantic Ocean is due to difference in salinity. The high rate of evaporation and limited rainfall may result into high salinity. This means that the Mediterranean Sea is made up of waters of high salinity and therefore flows into relatively less saline waters of the Atlantic Ocean while the under current flows in the opposite direction.
- Coastal configuration; the alignment the coast and the existence of sub marine ridges is partly responsible for the direction of flow of ocean currents. The shape of the land helps in the direction of moving currents e.g. the North equatorial current tends to be deflected north wards because of the shape of the horn of Africa.
Ocean currents may be characterized by under currents. These are return or compensating currents that normally flow within the equatorial latitudes. They flow in the opposite direction from which the opposite currents are flowing. They are normally known as counter currents that replace the surface waters that may have moved to another region.