Ocean currents are like river flow in oceans. They represent a regular volume of water in a definite path and direction. The ocean current sets that connect the poles with the equator, even though it is almost imperceptible, are responsible for the dissemination of species in the world’s oceans.
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 primary forces that influence the currents are:
- heating by solar energy
- wind
- gravity
- coriolis force
Heating by solar energy causes the 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.
Characteristics of Ocean Currents
Currents are referred to by their “drift”, which is the direction in which they flow. Currents are also classified by the general areas in which they originate.
There are four major ocean currents that have an effect on global climate, due to both their large kinetic energy and the high volumes of water it transports.
These are the warm poleward current, cold equatorward current, near-equatorial counter-current and the Antarctic circumpolar current.
We refer to the speed of a current as its “drift.” Drift is measured in terms of knots. The strength of a current refers to the speed of the current.
Types of Ocean Currents
Surface currents are the horizontal movement of ocean waters and can be affected by wind and weather. Deep water currents are the vertical movement of dense water and can be affected by variations in temperature and salinity.
The ocean currents may be classified based on their depth as surface currents and deep water currents:
- Surface currents constitute about 10 per cent of all the water in the ocean, these waters are the upper 400 m of the ocean
- Deep water currents make up the other 90 per cent of the ocean water.
These waters move around the ocean basins due to variations in the density and gravity.
Ocean currents can also be classified based on temperature: as cold currents and warm currents:
Cold currents bring cold water into warm water areas. These currents are usually found on the west coast of the continents in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere;
Warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the northern hemisphere they are found on the west coasts of continents in high latitudes.
Effects of Ocean Currents
Ocean currents play an important role in the oceanic circulation. The oceanic currents are the horizontal movement of seawater under the influence of wind forces, or by density or buoyancy differences caused by temperature and salinity.
The warm waters produced within the equatorial current loop flows to places with colder water, thus playing a significant role in maintaining climatic conditions worldwide.
Their average temperatures are relatively low with a narrow diurnal and annual ranges.
Warm currents flow parallel to the east coasts of the continents in tropical and subtropical latitudes. This results in warm and rainy climates.
These areas lie in the western margins of the subtropical anti-cyclones. The mixing of warm and cold currents help to replenish the oxygen and favour the growth of planktons, the primary food for fish population. The best fishing grounds of the world exist mainly in these mixing zones.
