Causes of Ocean Currents
The causes and factors affecting the ocean currents may be divided into two classes:
Primary causes, and,
Primary factors are responsible for the origin whereas the secondary factors determine the direction of flow of ocean currents.
- Primary causes:
Planetary winds: Planetary winds are the principal cause of the origin of ocean currents. Such winds drive surface water along with them.
Difference of density and salinity: Difference of density and salinity in ocean water motivates denser waters to sink and move as undercurrents; whereas lighter waters move towards the denser water as surface currents. Such density differences are mainly the result of differences in temperature and salinity of ocean waters. As for example, in the Polar areas, the cold surface waters of high density sink, while in the tropics heating of the surface tends to make the water less dense and move away pole wards as surface current. Similarly more saline and denser water of the Mediterranean Sea moves as an undercurrent though the strait of Gibraltar whiles the less saline lighter water of the Atlantic enters the Mediterranean via Gibraltar strait.
- Secondary causes:
The rotation of the Earth: The rotation of the Earth, which affects the direction of movement, deflects polward current eastwards, equator wards currents westwards. It may be pointed out here that the wind induced surface current deflects 45° or less from the wind direction so that the deflection of ocean currents are much more than the deflection of wind caused by Earth’s rotation.
The shape of the coastline: The shape of the coastline of the ocean basins often deflects currents from their direct courses.