Notes-Class 8-Geography-Chapter-5-Ocean Currents-Maharashtra Board

Ocean Currents

Maharashtra Board -Class 8-Geography-Chapter-5

Notes

Topics to be learn :

  • Horizontal (Surface) Ocean Current
  • Rotation of the Earth
  • Continental structure
  • Effects of Ocean Surface Currents on Human life
  • Deep Ocean Currents
  • Importance of deep ocean currents

Ocean currents :

  • Ocean currents are formed due to the differences in temperature and density of sea Water and planetary winds.
  • The ocean currents flow in clockwise direction in the northern hemisphere and in anti-clockwise direction in the southern hemisphere.
  • Alignment of the coastline also changes the direction of the ocean currents.
  • The velocity of ocean currents is around 2 km to 10 km per hour.
  • Because of the rotation of the earth, the ocean currents move in clockwise direction in the Northern Hemisphere and in anti-clockwise direction in the Southern Hemisphere.

Cold and Warm Ocean Currents :

Cold and Warm Ocean Currents :

Cold ocean currents and warm ocean currents are the two main types of ocean currents.

Cold ocean currents :

  • Ocean currents that move water away from the poles to the Equator are called cold ocean currents.
  • The cold currents decrease the temperature and precipitation in the coastal areas along with which they flow. For example, the cold ocean currents flowing along with the coastal areas of Peru, Chile, and southeastern Africa, decreases the amount of precipitation in the coastal areas along with which they flow. As its effect, arid desert areas are formed in Peru, Chile, and southwestern Africa.
  • Falkland, Labrador, Canary, Oyashio, Benguela, etc. are some of the cold ocean currents.

Warm ocean currents :

Ocean currents that move water away from the Equator to the poles are called warm ocean currents.

  • Warm ocean currents are formed in the equatorial region and they flow towards the poles.
  • The warm currents increase the temperature and precipitation in the coastal areas along with which they flow. For example, the warm ocean currents flowing along with the coastal areas of Western Europe, Southern Alaska and Japan increases the temperature in the coastal areas along with which they flow. As its effect, the ports in the coastal areas of Western Europe, Southern Alaska and Japan do not freeze in winter.
  • Gulf stream, Agulhas, Somali, etc. are some of the Warm ocean currents.

Therefore, the ocean currents lead to redistribution of water on the earth from the poles to the equator and from equator to the poles.

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Types of ocean currents on the basis of the depth :

  • On the basis of the depth, the ocean currents can also be divided into surface ocean currents and deep ocean currents.

Horizontal (Surface) Ocean Current :

  • The flow on the surface of the ocean moves only 10% of the oceanic water.
  • The ocean current found up to 500 metres of depth from the surface of the sea, is called surface ocean current.
  • The discharge of water in the oceans is measured in Sverdrup unit. 1 Sverdrup discharge means 1 million cu.m./ second discharge of ocean water.
  • The horizontal flow of ocean water occurs as warm and cold currents.

Effects of Ocean Surface Currents on Human life :

(i) Effect on climate :

  • Warm ocean currents increase the amount of precipitation and temperature in the coastal regions.
  • For example, warm ocean currents flowing along with the coastal areas of Western Europe, increases the temperature of coastal areas of Western Europe.
  • Due to Labrador cold current, the temperature of sea water near the eastern coast of Canada decreases. As its effect, the ports in the eastern coast of Canada freeze in winter.
  • Fog is found at the meeting point of warm and cold ocean currents. Example : Newfoundland island

(ii) Effects on marine life :

  • Due to the ocean currents, ocean water keeps moving. As its effect, marine life and its ecosystem is developed.
  • In regions where cold and warm currents meet, plankton, vegetation, algae, etc. grow. This is food for the fish. Therefore, large number of fish came here and breed.
  • This has, in turn, led to formation of large fishing grounds. Examples : Grand Bank near the North American coast in Atlantic Ocean and Dogger Bank near the European coast are some of the examples.

(iii) Effect on water transportation :

  • If the transportation is done according to the flow of ocean currents, the speed of the ships increase and the fuel is saved too.
  • Near the coasts where cold currents flow, the amount of precipitation is low. For example, in Peru, Chile and the arid desert of South-West Africa.
  • Dense fog at the meeting point of cold and warm ocean currents and movement of icebergs due to cold ocean currents are hazardous to the water transportation.

Deep Ocean Currents :

Deep Ocean Currents :

  • The ocean current found below 500 metres of depth from the surface of the sea, is called deep water ocean current.
  • The difference in the temperature and density of seawater, leads to its circulation and the deep ocean currents are formed. This circulation is known as thermohaline circulation.
  • Deep water currents flow continuously like rivers below the surface of oceans.
  • Generally, the surface water near Greenland and the continent of Europe, moves in downward direction. At the depth, this water moves to the Antarctica. From Antarctica, this water moves to the surface.
  • The deep ocean currents redistributes the water and it takes nearly 500 years to complete. This movement of water is also known as conveyor belt.

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Importance of deep ocean currents :

  • Deep ocean currents lead to movement of sea Water on a large scale.
  • Due to thermohaline circulatiorn, the warm ocean water moves from the surface to the bottom and nutrient rich cold ocean water from the bottom to the surface.
Remember :

  • The ocean currents do not flow very close to the coast. They flow near the lower limit of the continental shelf.
  • Even though the velocity of the ocean currents is less, the water carried by them is immense.
  • Under the influence of the westerlies, in the mid-latitudes, the ocean currents flow from west to east, but near the equator they flow from east to west. This leads to a circular pattern.

The ocean currents of the Indian ocean :

The ocean currents of the Indian ocean :

  • There is similarity between the patterns of the ocean currents of the Pacific and Atlantic Ocean but the flow of the ocean currents of the Indian Ocean are different.
  • The Indian Ocean is land-locked in the north. The equator divides this ocean into two parts- northern and southern.
  • The Monsoon winds influence this ocean tremendously. These winds change their direction according to the season.
  • In the northern part of the Indian Ocean, currents flow in clockwise direction in summer while in winter they flow in the opposite direction due to reversal of Monsoon winds
  • Cold currents are absent in the northern part of the Indian Ocean. The northern part of Indian Ocean is included in the temperate zone. So cold currents are absent in the northern part of the Indian Ocean.

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Useful links :

Main Page : - Maharashtra Board Class 8th Geography   - All chapters notes, solutions, videos, test, pdf.

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