Ocean Currents

Ocean Currents

Ocean Current - It is the general movement of surface water of the ocean in a definite direction over a long distance. It is like a river channel in the ocean near to the surface.

Types of Ocean Current 

Based on the direction in which the ocean current moves, it is divided into two categories -

1. Warm Ocean Current - moving from Equatorial region to Polar region (i.e., moving from lower latitude to higher latitude)
2. Cold Ocean Current - moving from Polar region to Equatorial region (i.e., moving from higher latitude to lower latitude)

Factors influencing the Ocean Currents -

1.   Wind - (Winds drag away the surface water)

• Steady blowing winds drag the surface water in its direction and brings about the surface flow and steadily sets water currents in motion.

2.   Variation - (Variation in temperature, pressure, density, salinity, etc induced the movement of water)

• The variations in temperature or pressure or density or salinity causes the water to move and reduce the variation and to acquire uniformity. Such differences guide the movement of Oceanic Currents.

3.   Coriolis Force - (causes deflection in Ocean Currents)

• Coriolis force causes the Oceanic Current to deflect right in the Northern hemisphere and left in the Southern hemisphere.

4.   Shape of the Coastline - (Coastline directs the Ocean Current)

• Shape of the coastline modifies the Ocean Currents.

Ocean Currents of Atlantic Ocean

Source: Clear IAS

Source: Clear IAS

• In Equatorial region the trade winds drives the surface water westward resulting in North Equatorial current and South Equatorial current.
• The merging of these two currents along the western side causes Equatorial counter current which flows from west to east in between.
• The South Equatorial current gets bi-furcated near to the Brazil coast and the northern part joins the North Equatorial current
• The combined water flows towards the Caribbean islands.
• Some of the parts of this current flows on the eastern side of the Caribbean as Antilles current and the rest of the water enters Caribbean sea and then Gulf of Mexico.
• The current coming out of the Gulf merges with Antilles current and flows along the coast of Florida as Florida Current.
• Along the eastern coast of USA, it is known as Gulf Stream.
• Beyond the Newfoundland island (Canada), Gulf Stream turns right under the combined effect of westerlies and Coriolis force and flows as North Atlantic drift.
• North Atlantic drift crosses the Atlantic ocean and reaches the eastern side and gets bi-furcated equally into two parts.
• The northern part moves along the coast of England and Norway as North Atlantic Drift and enters in the Arctic ocean as Norwegian current.
• These waters near to the coast of Iceland (east coast) are called Irminger Current. 
• The southern bi-furcated part flows towards the equator as cold Canary Current and joins the North Equatorial current and completes the circulation.
• Significance - 
• The warm North Atlantic current to the east of England and Norway, makes the coast of England and Norway ice free even during the winter.
• Also, because of the cold Canary Current, the western coast of Africa remains dry (desert).
• In North Atlantic Ocean the continuous circulation of water in clockwise direction results in slow movement of water within, which is known as Gyre (Gyre is the slowly moving water body which is completely surrounded by circular oceanic currents on all sides). In this part of North Atlantic Ocean within the Gyre, a type of seaweed grows in large quantity which is known as Sargasso. Therefore, the sea is also known as Sargasso sea.
• There are two cold ocean currents also flowing in North Atlantic Ocean -

1. East Greenland Current flowing between Greenland and Iceland which merges with the North Atlantic drift. (It provides one of the best fishing band in the world)
2. Labrador Current flowing between Canada and Greenland which merges with the Gulf Stream. (It provides one of the best fishing band in the world)

• The southern branch of South Equatorial current moves along the eastern coast of Brazil as Brazilian Current. 
• At the higher latitudes, the Brazilian Current gets deflected towards left and flows as South Atlantic Current.
• The absence of landmass and strong westerlies causes the continuous flow of water without any obstruction at mid-latitude from west to east in Southern hemisphere surrounding the Antarctica as Cold West Wind drift.
• The South Atlantic current merges with the West Wind drift.
• Near to the Cape of Good hope, the South Atlantic current is diverted north as Cold Benguela Current which joins the South Equatorial current.
• The Cold Falkland Current flows near the south-east coast of South America and merges with the Brazilian current near to the Falkland island.

Ocean Currents of Pacific Ocean

Source: Clear IAS

Source: Clear IAS

• Along the equatorial region, North Equatorial current and South Equatorial current flow from east to west and Counter Equatorial current flows from west to east.
• The North Equatorial current turns northward and flows along Philippines and Japan as Kuroshio Current.
• Kuroshio current turns right and crosses the Pacific Ocean as North Pacific Current.
• North Pacific current is bi-furcated into warm Alaska Current along Canada and Alaska and cold California Current along the western USA which merges with North Equatorial current.
• The two cold currents which merge (near Japan coast) with Kuroshio current are -

1. Oyashio Current which merges near Kamchatka and Shakhalen island.
2. Okhotsk Current which merges near Shakhalen island.

• The South Equatorial current turns south and moves across eastern coast of Australia as East Australian Current which turns towards the left as South Pacific Current and joins the cold West Wind drift.
• Near the south western coast of South America, it turns north as cold Peru or Humboldt Current, which flows north and joins the South Equatorial current.

Ocean Currents of Indian Ocean

Source: Clear IAS

Source: Clear IAS

In South Indian Ocean 

• The South Equatorial Current upon reaching the western part turns southwards and gets bi-furcated by Madagascar.
• The current flowing between Madagascar and Mozambique is called Mozambique Current.
• The confluence of current beyond Madagascar is called as Agulhas Current which turns eastwards and merges with West Wind Drift.
• Upon reaching the western tip of the Australia, a branch of this current turns north and flows as West Australian Current which joins the South Equatorial current.

In North Indian Ocean 

Because of the presence of huge landmass, the currents of North Indian Ocean are bit different and also because of the phenomenon called Monsoon which is characterised by the seasonal reversal of winds, the ocean currents of North Indian Ocean shows peculiar characteristics.

• During winter, the North Equatorial Current flows westward above the equator and Equatorial Counter Current flows between the North and South Equatorial current.
• The north-east Monsoon drives the water of the Bay of Bengal and Arabian sea to circulate in anti-clockwise direction which is known as North-east Monsoon drift.
• In Summer, the entire waters of the North Atlantic Ocean comes under the influence of south-west Monsoon producing a clockwise flow of South-west Monsoon drift. 
• At this time there is no North Equatorial and Counter Equatorial currents.

Significance of Ocean Currents -

1. The cold current along the west coasts in the Sub-tropics suppresses the precipitation leading to the formation of deserts.
2. The eastern coast of continents in Sub-tropical regions are under the influence of warm ocean current which helps in receiving more rainfall which results in formation of more cyclonic disturbances.
• Example - Gulf Stream along the USA and Kuroshio Current along the East Asia (Japan, Korean islands, etc)
3. The western coast of the continents along the temperate region experience mild winters and ice free ports due to the influence of warm ocean currents.
• Example - North Atlantic drift along British and Norway
4. The condition where warm ocean current meets with the cold ocean current is very ideal for the formation of fishing banks.
• Example - North-eastern coast of USA where Gulf Stream meets with Labrador Current results in the formation of one of the best fishing bands in the world like Grand bank, Gorges bank, etc. Also, near to the Japan where Kuroshio Current meets with Oyashio Current, one of the best fishing banks.
5. The cold ocean currents are the zones of upwelling which helps in fish growth (along the coasts/Continental shelf).
• Example - Humboldt Current along the Peru coast
6. Ocean currents help in the global distribution of temperature and salinity.
7. The merging of warm and cold ocean currents result in the formation of fog which might obstruct the navigation.

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