Ocean Currents Explained – UPSC Notes/PDF

Ocean currents are like river flow in oceans.
or
Ocean currents are bulk of water moving in a particular direction in hundred of kilometres.

Forces influencing the currents

Heating by solar energy

The solar energy causes water to expand and resultantly, near the equator the ocean water is about 8cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.

Wind

Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.

Gravity

Gravity tends to pull the water down the pile and create gradient variation.

Coriolis Force

The Coriolis force intervenes and causes the water to move to the right in the southern hemisphere. These large accumulations of water and the flow around them are called ‘Gyres’. These produce large circular current in all the ocean basin.
Know about Coriolis force in detail.

Types of Ocean Currents

Based on depth
(a) Surface Currents: they constitute about 10% of all the water in the ocean, these waters are the upper 400 metres of the ocean
(b) Deep Water Currents: they constitute the other 70% of the ocean water. These waters move around the ocean basins due to variations in the density and gravity.

Based on temperature
(a) Cold Currents: These 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 and on the east coast in the higher latitudes in the Northern Hemisphere.
(b) Warm Currents: These currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes. In the northern hemisphere, they are found on the west coast of continents in high latitudes.

Movements of Ocean Currents

Source: Internet

We will understand the movements of oceanic current separately in three oceans viz. Atlantic Ocean, Pacific Ocean and the Indian Ocean.

Atlantic Ocean

  • The Atlantic Ocean lies between American and African continent.
  • In the influence of the Trade winds, the Equatorial Currents move from east to west direction. Let us divide the equatorial currents into two parts viz. North Equatorial Current and South Equatorial Current.
  • Now we will separately deal with North Atlantic and South Atlantic Ocean.

The North Atlantic Ocean

  • The North Equatorial Current (warm current) moves in the east to the west direction in the influence of trade winds.
  • After hitting North America, it moves towards the north pole and is known is Gulf Stream (warm current).
  • A cold current, Labrador Current flowing along the east coast of Canada joins the Gulf Stream (warm current) near the north-east corner of the USA.
  • The confluence of these two currents generates fog in this region. It is one of the best fishing ground in the world.
  • Further, the Gulf Stream (warm current) bifurcates into two parts the northern part moves towards north pole known as North Atlantic Drift and the southern part moves along west Africa known as Canary current (cold current)
  • The Canary Current joins the North Equatorial Current and completes the circuit.

The South Atlantic Ocean

  • The South Equatorial Current (warm current) moves in the east to the west direction in the influence of trade winds.
  • Then it moves along the east coast of South America and known as Brazillian Current (warm current). Moving along the east coast of South America, it counters with the Falkland Current (cold current) coming from the south pole.
  • This current moves towards the east direction in the influence of West Wind Drift or Antarctic Circumpolar (cold current).
  • After some distance, it moves in the north direction and known as Benguela Current (cold current). And this Benguela current further joins the South Equatorial Current completing a circuit.

What is Equatorial Counter Current?

In the influence of the trade winds, the Equatorial Current moves from the east to the west direction. When they hit with and continental mass, they start piling up there. When a large amount of water is accumulated, it starts flowing in the opposite direction (west to east). This flowing of water in the opposite direction is known as Equatorial Counter Current.

Pacific Ocean

The Pacific Ocean lies between Autralia and South America.

North Pacific Ocean

  • The North Equatorial Current moves in the east to the west direction under the influence of trade winds.
  • After hitting the islands near the Philippines, it moves towards the north pole along the east coast of China known as Kuroshio Current (warm current).
  • A cold current, Oyashio Current moving along the coast of Russia joins the Kuroshio Current.
  • The Kuroshio Current (warm current) comes under the influence of westerlies and moves towards the west coast of N. America.
  • After hitting the west coast of N. America Kuroshio Current bifurcates into two. The northern branch is called Alaska Current (warm current) and the southern branch is called California Current (cold current) which moves along the coast of California.
  • This California Current (cold current) finally merges with North Equatorial Current and completes the circuit.

South Pacific Ocean

  • The South Equatorial Current moves in the east to the west direction under the influence of trade winds.
  • After hitting Australia, it starts moving in a southward direction and along the coast of Australia, it is known as East Australian Current (warm current).
  • Under the influence of westerlies and West Wind Drift, it starts moving towards the east and moves along the coast of Peru (South America) and known as Peru or Humboldt Current (cold current).
  • This Peru or Humboldt Current (cold current) then merges with South Equatorial Current and completes the circuit.

Indian Ocean

The Indian Ocean is confined between Africa and Australia. As there is a large amount of landmass on the northern hemisphere, therefore, oceanic currents do not exist in the northern hemisphere.

South Indian Ocean

  • The South Equatorial Current moves in the westward direction under the influence of trade winds.
  • After hitting with the African continent, it moves southward along the east coast of Africa and known as Auglhas Current (warm current).
  • With further movement of southward, the Auglhas Current (warm current) comes under the influence of West Wind Drift and moves in the eastward direction.
  • This further, after hitting Australia, moves in the northward direction and known as West Australian Current (cold current).
  • The West Australian Current (cold current) further joins the South Equatorial Current and completes the circuit.

UPSC generally asks about the cold and warm currents in prelims.

List of cold and warm currents