Ocean Currents - Factors and Impact on Climate

The movements of water in oceans can be categorized into currents, waves, and tides. Among these, ocean currents are the large masses of surface water that circulate in regular patterns around the oceans.

Ocean Current

Depending upon their temperature, ocean currents can be classified into warm currents and cold currents.

Warm currents flow from equatorial regions towards the polar regions and hence have a higher surface temperature. [from lower latitudes to higher latitudes]. These currents flow in the clockwise direction in the northern hemisphere and in the anti-clockwise direction in the southern hemisphere.

Cold currents flow from polar regions towards the equator and have a lower surface temperature [ from higher latitudes to lower latitudes]. They flow in the anti-clockwise direction in the northern hemisphere and in the clockwise direction in the southern hemisphere.

 

Factors responsible for Ocean Currents

The following are the factors responsible for ocean currents:
  • The Planetary winds,
  • Temperatures,
  • Salinity,
  • The earth s rotation,
  • Obstruction from land

The Planetary winds

The general distribution of winds in the lower atmosphere is called as Planetary winds. The Earth's atmosphere is divided into permanent pressure belts - The Equatorial low-pressure belt, The Sub-tropical high-pressure belt, Sub-polar low-pressure belt and Polar high-pressure belts. The planetary winds are permanent winds that blow from one pressure belt to the other. Accordingly, they have been divided into - Tradewinds, Westerlies and Polar Easterlies.

The Planetary winds are probably the dominant influence on the flow of ocean currents. The strongest evidence of prevailing winds on the flow of ocean currents can be witnessed in the North Indian Ocean where there is a change in the direction of ocean currents with a change in direction of the monsoon winds. The oceanic circulation pattern roughly corresponds to the earth s atmospheric circulation pattern.

Temperature

Thedifferential heating of the Sun at the equator and the poles causes a difference in the temperature of ocean water. At the equator, since the temperature is higher the ocean water gets heated up and expands. This makes the warm water lighter and hence rises while at the poles, cold water is denser and sinks. 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.

Hence, the difference in heating and surface temperatures play a key role in movements of ocean water.

Salinity

The density of water also depends on its salinity and the salinity of water varies from place to place. Waters of low salinity flow on the surface of waters of high salinity while waters of high salinity flow at the bottom.

The earth's rotation and Coriolis force

The earth's rotation deflects moving objects to the right and ocean currents are no exception. Under the action of Coriolis force, the movement of ocean currents in the northern hemisphere is in the clockwise and in the southern hemisphere it is in the anti-clockwise direction. Hence it can be said that ocean currents obey Ferrel's law.

Obstruction due to land

A land mass obstructs the direction of flow of ocean current and divides the ocean current which in turns flow in a different direction. Example: The south equatorial current in the Atlantic Ocean is obstructed by South American continent and the South equatorial current divides to create the Brazilian current which flows in the south Atlantic Ocean.

Currents in the Pacific Ocean

  • North Equatorial Current (Warm)
  • South Equatorial Current (Warm)
  • Counter Equatorial Current (Warm)
  • Kuroshio System (Warm)
  • Oyashio Current (Cold)
  • California Current (Cold)
  • Peruvian or Humboldt Current (Cold)
  • East Australia Current (Warm)
  • North Pacific Drift (Warm)

Currents in the Atlantic Ocean

  • North Equatorial Current (warm)
  • South Equatorial Current (warm)
  • Equatorial Counter Current
  • Gulf Stream (warm)
  • Florida Current (Warm)
  • Canaries Current (Cold)
  • Labrador Current (Cold)
  • Brazilian Current (Warm)
  • Falkland Current (Cold)
  • South Atlantic Drift (Cold)
  • Benguela Current (Cold)

Currents in the Indian Ocean

  • The North East Monsoon Drift
  • The South West Monsoon Drift
  • North Equatorial Current (Warm)
  • South Equatorial Current (Warm)
  • Somali Current (Cold)
  • Mozambique Current (Warm)
  • Madagascar Current (Warm)
  • Agulhas Current (Warm)
  • West Australian Current (Cold)

Apart from these, the Antarctic Circumpolar Current circles the Earth across the Pacific, the Atlantic and the Indian Oceans almost without any interruption.

Impact of Ocean Currents

Local Climate

  • Warm and Cold currents affect the local climate of a region.
  • For example, the Gulf Stream which is driven to the western coast of Europe as the North Atlantic Drift keeps the coasts of North Sea warm which is unusual for such high latitudes.
  • Similarly, the warm waters of the Kuroshio current in the North Pacific ocean are carried as the North Pacific Drift keeping the ports of the Alaskan coast ice-free in winter.

Rains and Desert Formation

  • Warm ocean currents bring rains to the coastal regions and also the interiors while cold currents do not.
  • Warm currents flow along the east coast of continents in tropical and sub-tropical latitudes resulting in warm and rainy climates while cold currents flow along the west coast of continents.
  • Cold currents are one of the reasons why deserts are located the western margins of continents in the sub-tropical belts.
  • For example, Californian current which is a cold current brings a dry and desert type of climate to the region.
Fishing grounds
  • The mixing of warm and cold currents help to replenish the oxygen and favour the growth of planktons which is the regions are rich in microscopic marine plants and animals.
  • These are crucial for the survival of marine ecosystems.
  • Hence these regions form excellent fishing grounds as phytoplankton is the primary source of food for the fish.
  • For example, the Great Banks near Newfoundland is formed by the mixing of cold Labrador current with the warm Gulf Stream.

Navigation

  • The atmospheric circulation of the winds and the oceanic circulation of the currents are almost coincidental and together they aid in the navigation of the ships.
  • Ocean currents flow for great distances and together with the winds create a conveyor belt kind of system for navigation of the ships.

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