What are Ocean Currents?
- Ocean currents are continuous movements of water in the ocean that follow set paths, kind of rivers in the ocean. Ocean currents are the horizontal flow of a mass of waters in a fairly defined direction over great distances.
- They are like a stream of water (like rivers) flowing through the main body of the ocean in a regular pattern. Ocean currents (Avg speed 3.2 km to 10 kmph) with higher speed are called streams and currents with lower speed are called drifts.
- There are two types of Ocean Currents-
based on depth–
Surface currents (surface circulation– which make up about 10% of all the water in the ocean) and deep water currents (thermohaline circulation– which make up the other 90% of the ocean).
Based on temperature–
Cold currents (Labrador Current) and warm currents (Kuroshio current)
- The general movement of the currents in the northern hemisphere is clockwise and in the southern hemisphere, anti-clockwise.
- This is due to the Coriolis force which is a deflective force and follows Ferrel’s law.
- A notable exception to this trend is seen in the northern part of the Indian Ocean where the current movement changes its direction in response to the seasonal change in the direction of monsoon winds.
Factors that impact the ocean current formations are:
The primary forces-
- heating by solar energy;
- Coriolis force.
The secondary forces-
- Temperature difference;
- Salinity difference
- Influence of insolation
- The planetary winds are permanent winds (Trade winds, Westerlies and Polar Easterlies) that blow from one pressure belt to the other.
- The oceanic circulation pattern roughly corresponds to the earth’s atmospheric circulation pattern. E.g.: There is a change in the direction of ocean currents with a change in direction of the monsoon winds in the Indian Ocean.
- Most of the currents of the world tend to follow the direction of planetary winds. For example, within the tropics, the trade winds blow from the east, and hence, north equatorial and south equatorial currents flow east to west.
- The differential heating of the Sun at the equator and the poles causes a difference in the temperature of ocean water.
- Heating by solar energy causes the water to expand. That is why, near the equator, the ocean water is higher in level than in the middle latitudes.
- This causes a very slight gradient and water tends to flow down the slope.
- Warm water from the equator slowly moves along the surface towards the poles, while the cold water from the poles slowly creeps along the bottom of the sea towards the equator.
- Waters of low salinity have lower density enabling them to flow on the surface of waters of high salinity while waters of high salinity flow at the bottom.
- g. the current between the Mediterranean Sea with higher salinity and the Atlantic Ocean with lower salinity.
- According to Ferrel’s law– Coriolis forces deflect winds and freely moving objects to the right in the northern hemisphere and to the left in the southern hemisphere.
- Therefore, the movement of ocean currents in the northern hemisphere is clockwise, and in the southern hemisphere, it is in the anti-clockwise direction.
- A landmass obstructs the direction of the flow of ocean current and divides the ocean current to flow in a different direction.
- The circulation of the ocean currents depends on the following factors:
Differences in Density:
- Differences in water density affect the vertical mobility of ocean currents. The less-dense water of the equator rises and moves towards the poles (warm current) while the cold and dense waters of the poles sink and move towards the equator.
Coastlines and Bottom Reliefs-
- This also affects the direction of currents. Eg. The Equatorial current after being obstructed by the Brazilian coast bifurcates into two branches.
- Gravity tends to pull the water down to pile and create gradient variation.
- The Coriolis force intervenes and 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 These produce large circular currents in all the ocean basins. One such circular current is the Sargasso Sea.
***To be noted***:
- The warm currents move towards the cold seas and cool currents towards the warm seas.
- In the lower latitudes, the warm currents flow on the eastern shores and cold on the western shores [food for imagination].
- The situation is reversed in the higher latitudes. The warm currents move along the western shores and the cold currents along the eastern shores.
Effects of Ocean Currents-
- Cold ocean currents have a direct effect on desert formation in west coast regions of the tropical and subtropical continents.
- There is fog and mist in the areas that are arid due to the desiccating effect (loss of moisture).
(Click on the question to view model answer for this question)
- Warm ocean currents bring rain to coastal areas and even interiors. Example: Summer Rainfall in British Type climate.
- 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.
- They are responsible for moderate temperatures at coasts. [North Atlantic Drift brings warmness to England. The canary cold current brings a cooling effect to Spain, Portugal etc.]
Fishing Ground Formation
- Mixing of cold and warm ocean currents bears the richest fishing grounds in the world.
- The mixing of warm and cold currents helps to replenish the oxygen and favor the growth of plankton, the primary food for the fish population. The best fishing grounds of the world exist mainly in these mixing zones.
- Example: Grand Banks around Newfoundland, Canada, and North-Eastern Coast of Japan.
- Warm and rainy climates in tropical and subtropical latitudes [Florida, Natal etc.],
- Cold and dry climates on the western margins in the sub-tropics due to desiccating effect,
- Foggy weather and drizzle in the mixing zones,
- Moderate clime along with the western coasts in the sub-tropics.
- Currents are referred to by their “drift”. Ships usually follow routes that are aided by ocean currents and winds. Example: If a ship wants to travel from Mexico to the Philippines, it can use the route along the North Equatorial Drift which flows from east to west.
- When it wants to travel from the Philippines to Mexico, it can follow the route along with the doldrums when there is counter equatorial current flowing from west to east.
Distribution of Ocean Currents-
Name of Current
Nature of Current
North Equatorial Current
Hot or Warm
North Pacific Current
Counter Equatorial Current
El Nino Current
South Equatorial Current
East Australian Current
Humboldt or Peruvian Current
Kuril or Oya shio Current
Eastern Greenland Current
Warm and Stable
Warm and Stable
South-West Monsoon Current
Warm and unstable
North-East Monsoon Current
Cold and unstable
Cold and unstable
Western Australian Current
Cold and Stable