These can be classified into two types on the basis of temperature :-
- Warm Current
- Cold Current
These can be also divided into 3 types on the basis of velocity, direction and dimension : -
1. Drift - flow under influence of wind.
2. Current - Flow in definite direction with much greater speed than drift.
3. Stream - Flow at much more speed than the previous two and flow like river (on Earth).
Ex - Gulf Streams.
Also Read: Penck's Model of Cycle of Erosion
Origin of Oceanic Currents
1. Factors related to rotation of the Earth
As the Earth rotates anticlock-wise, the Coriolis acting in opposite direction on Ocean water which results into deflection of oceanic Current Rightward in Northern Hemisphere while Leftward in Southern hemisphere.
2. Factors related to Ocean
I. Temperature Difference
The Area of high temperature makes water more lighter than the region of low temperature, where cold water being denser sinks which leads to flow of water from the Area of high temperature to the Area of low temperature on the surface but below the surface, the flow of current is opposite due to high density of water in low temperature it sinks and moves towards the area of high temperature to fill the gap created due to surface current.
II. Salinity Difference
High salinity regions of the sea are experience high density of water which led to sinking down creating a gap which attracts water from low salinity region but only on the surface. Below the surface the process is reverse.
III. Density Difference
The process is same as discussed in temperature and salinity difference but the cause of density in this case is neither the temperature nor the salinity.[post_ads]
3. Factors related to Atmosphere
I. Air Pressure and Winds
Low pressure area has more volume of water than high pressure area. Hence current moves from region of low pressure to high pressure region.
Winds like N-E Trade winds, westerly etc. blow current along with themselves.
II. Evaporation and Rainfall
The region of high rainfall coupled with low evaporation lead to high-volume of water than the region of low rainfall coupled with high evaporation lead to movement of water from region of high volume equatorial region toward low volume Tropics.
4. Factors Modifying Oceanic Currents
I. Shape, direction and size of coastline in the way of current
When coastline obstructs the flow of oceanic water it lead to deflection and moves along the coasts parallelly and sometimes bifurcates.
Example - Gulf stream flowing from Equator towards North wards obstructed by Brazilian coasts and bifurcated into two parts one going towards North ward and the other part going towards Indian Ocean in southward direction.
II. Bottom relief of Ocean
Sometimes Ocean currents are obstructed by ridges which deflects it towards Right in Northern Hemisphere and Left in Southern Hemisphere.
III. Seasonal Winds
Seasonal winds like Monsoon, which changes it's direction from S-W to N-E from summer to winter respectively and consequently changes the direction of Ocean Currents and let it flow with itself.
Effects of Oceanic Currents
1. Changes the coastal Climates
Ocean currents causes both positive and negative impact on the coastal climate. Warm current flowing from warmer region towards the colder parts of the ocean make it warm and vice-versa.
Example - Gulf stream moving in Atlantic Ocean from equator raises the temperature of coasts of Great Britain, Sweden, Norway, Netherlands, Denmark etc.
Warm Current brought moisture from warm region and rains in the coastal region.
Cold current flowing from poles lower down temperature of the affected areas and sometimes causes snowfall to the coasts of Labrador, Kurile, Falkland etc.
2. On Fishing
Ocean Currents redistributes Oxygen, Plankton, salts and other minerals which is helpful for growth and survival of fishes.
3. On Navigation
Currents sometimes beneficial as it help in the ships to move much faster when the ship is moving in the the direction of current.
But in the region fo convergence of warm and cold currents fog occurs, which posses great challenge to navigation. sometimes cold currents bring large icebergs which can damage ships.
4. For corals
Current is essential fro the growth of coral reefs as it bring oxygen as wells as maintain correct salt/mineral balance required for it's growth.