Table of Contents
Ocean Currents
A continuous general movement of ocean water in a specified direction is called an ocean current. These can be considered as a river running across the surface of the ocean.
Most surface currents carry water horizontally and vertically in the upper layer above the thermocline (you will learn about this later in this section). The water beneath the thermocline circulates as well, although at an extremely slow rate.
Based on these currents’ influence on the destination, they are classified as warm ocean currents and cold ocean currents. A warm stream is one that travels towards the pole in both hemispheres and transports warm water from lower to upper latitudes. A cold stream flows from the high latitudes to the tropics.
Ocean Currents Types
Ocean Currents are of the following types:
Based on Depth
Based on the depth, the ocean currents may be classified as surface currents and deep water currents:
Surface currents are those currents that circulate to a depth of 400m from the surface; they roughly constitute about 10 percent of all the water in the ocean.
Deepwater currents are caused due to changes in density and under the influence of gravity. They make up the other 90 percent of the ocean water.
The changes in the temperatures and salinity determine the density, which causes the vertical movement of water.
Deep waters sink into deep ocean basins at high latitudes when temperatures are cold enough to cause the density to rise.
Based on Temperature
Based on temperature, ocean currents are classified as cold currents and warm currents:
Cold currents transport cold water from high latitudes to low latitudes, bringing cold water into warm water areas. These currents are most commonly seen on the west coasts of continents at low and middle latitudes (in both hemispheres) and on the east coast at higher latitudes in the Northern Hemisphere.
Warm currents transport warm water from low to high latitudes and are most commonly seen on the east coasts of continents in the low and intermediate latitudes (true in both hemispheres). They can be found on the west coasts of continents at high latitudes in the northern hemisphere.
Ocean Currents Influence
1. Influence of Insolation
The water expands when heated by incoming solar radiation (insolation). As a result, the ocean water level at the equator is around 8 cm higher than in the middle latitudes. As a result, there is a minor gradient, and water flows down the slope.
2. Influence of Gravity
Gravity tends to pull the water down to pile and create gradient variation.
3. Influence of Temperature
Differences in the temperature of ocean waters at the equator and the poles influence the current movement. As warm water is lighter, it rises, and cold water is denser; it sinks. The warm equatorial waters move slowly along the surface towards the pole, while the heavier cold waters of the polar regions move along the bottom of the sea towards the equator.
4. Influence of Salinity
Based on the temperature, geographical area, the inflow of fresh water, etc., the salinity of ocean water varies from place to place. Waters of high salinity are denser than the waters of low salinity. Hence, high salinity waters sink and flow at the bottom towards low salinity waters. On the other hand, ocean waters of low salinity flow on the surface of ocean waters and move towards high salinity waters. For Example, in the partially enclosed Mediterranean Sea, there is a great difference in salinity between the waters of the open Atlantic Ocean and those of the Mediterranean Sea. The less saline water from the Atlantic Ocean flows into the Mediterranean Sea. However, this inflow is compensated by denser water that flows from the bottom of the Mediterranean to the Atlantic Ocean.
Influence Due to the Earth’s Rotation
Under the influence of the Coriolis force, the earth’s rotation deflects freely moving objects to the right, including ocean currents. This is a clockwise direction in the northern hemisphere (e.g., the direction of the Canaries and the Gulf Stream). It runs counter-clockwise in the southern hemisphere (for example, the Brazilian Current)
Influence of geographical Orientation: Crustal land masses block and affect the course of a current due to their geographical orientation. The Peruvian Current, for example, is formed when part of the West Wind Drift is diverted northwards by the tip of southern Chile.
Influence of the Trade Winds
The Trade Winds blow between the equator and the tropics, moving equatorial waters polewards and westwards and warming continents’ eastern shores. The North-East Trade Winds, for example, warm the southern and eastern shores of the United States by moving the North Equatorial Current and its derivatives, the Florida Current. The Westerlies blow in temperate latitudes.They result in a northeasterly movement of water in the northern hemisphere, driving the warm Gulf Stream to the western coast of Europe as the North Atlantic Drift. The westerlies are, however, less reliable than the ‘Trade Winds.’
The most significant effect on the flow of ocean currents is that of planetary winds. The North Indian Ocean has the best evidence of the prevailing winds’ impact on the current flows. The monsoon winds, which blow from the northeast during the winter and the southwest during the summer, completely modify the course of the currents.
Ocean Currents Atlantic Ocean
The North and South Equatorial Currents at the equator are constantly drifting from east to west under the influence of the consistent Trade Winds. The landmass in northeast Brazil splits the South Equatorial Current into the Cayenne Current, which flows down the coast of Guiana, and the Brazilian Current, which flows southwards along Brazil’s east coast.
The Cayenne Current is joined and reinforced by the North Equatorial Current in the North Atlantic Ocean, and it flows north-westward into the Caribbean Sea as a vast body of equatorial water. The Florida Current emerges from the Florida Strait between Florida and Cuba as part of the current entering Mexico’s Gulf. The balance of the equatorial water moves northeast of the Antilles, eventually joining the Gulf Stream off the coast of the United States of America. With a width of 35 to 100 miles, a depth of 2,000 feet, and a speed of three miles per hour, the Gulf Stream Drift is one of the most powerful ocean currents. The current follows the American coast and is subsequently redirected eastwards by the combined impact of the Westerlies and the earth’s rotation. The Gulf stream is known as the North Atlantic Drift as it gets to Europe. The warm equatorial water is carried to the European coasts by this current. The current branches in three directions from the North Atlantic: eastwards to Britain, northwards to the Arctic, and southwards along the Iberian coast.
According to oceanographic studies, about two-thirds of the water carried to the Arctic by the Gulf Stream is returned to the tropical latitudes each year as dense, cold Polar water that creeps southwards into the ocean bottoms. The Canaries Current, which flows southward, finally combines with the North Equatorial Current, completing the clockwise circuit in the North Atlantic Ocean.
There is no apparent current within this ring of currents in the centre of the Atlantic. This zone of negligible current leads to the formation of the Sargasso Sea. A massive amount of drifting seaweed forms the Sargasso Sea.
There are also currents that reach the North Atlantic from the Arctic areas, in addition to the clockwise circulation of the currents. The out-flowing arctic winds blow these chilly waters south. At the confluence point, the Irminger Current, which flows between Iceland and Greenland, cools the warm North Atlantic Drift. Between West Greenland and Baffin Island, the cold Labrador Current drifts south-eastwards until it meets the warm Gulf Stream off the coast of Newfoundland.
The circulation of the South Atlantic Ocean is similar to that of the North Atlantic Ocean. The circle is anti-clockwise, and the gathering of seaweed in the calm seas of the mid-South Atlantic is not as noticeable. At Cape Sao Roque, the South Equatorial Current splits into two branches, one heading south as the warm Brazilian Current. The pull of the prevailing Westerlies and the earth’s rotation accelerates the current eastwards, merging with the cold West Wind Drift as the South Atlantic Current. When the current reaches Africa’s west coast, it is rerouted northward as the frigid Benguela Current (the counterpart of the Canaries Current). It transports the West Wind Drift’s chilly polar waters to tropical latitudes. The Benguela Current rushes equatorward in a north-westerly direction, driven by the frequent South-East Trade Winds to join the South Equatorial Current. This completes the present circulation in the South Atlantic. The east-flowing Equatorial Counter Current lies between the North and South Equatorial Currents.
The circulation pattern in the Pacific is similar to that in the Atlantic, with some differences due to the Pacific’s larger size and more open nature. Correlate it to the Atlantic currents if you can.
Ocean Currents Indian Ocean
The South Indian Ocean’s currents form a circuit comparable to the Atlantic and Pacific Oceans. The Equatorial Current joins the West Wind Drift, which flows eastwards and turns equatorward as the West Australian Current, before turning southwards past Madagascar as the Agulhas or Mozambique Current.
Due to fluctuations in monsoon winds, the direction of currents in the North Indian Ocean completely reverses between summer and winter. During the summer, from June to October, when the South-West Monsoon is the dominating wind, the currents are blown south-westerly as the South-West Monsoon Drift.
This is reversed during the winter, commencing in December, when the North-East Monsoon Drift blows the currents from the northeast. The North Indian Ocean currents are the most striking example of the dominance of winds over ocean current circulation.
Ocean Currents Map
Below is the Map of Various Ocean Currents:
Cold Ocean Currents List
Here is the List of Cold Ocean Currents
| Cold Ocean Current | Region | Important or Additional Facts |
| Humboldt or Peruvian Current | South Pacific Ocean | Along the west coast of South America, The Peruvian current flows from the southernmost tip of Chile to northern Peru.
The Current is named after Prussian naturalist and Geographer- Alexander Von Humboldt. This large marine ecosystem which serves as the major nutrient system of the world is supported by this very low-salinity current. |
| Kurile or Oyashio Current | North Pacific Ocean | It flows south of the Arctic Ocean via the Bering Sea in the North Pacific Ocean while originating from the same Arctic Ocean.
This sub-arctic ocean current circulates in an anti-clockwise direction. To form the North Pacific Drift the cold Oyashio current collides with Kurioshio currents off the Japanese east. The currents are rich in nutrients.
|
| California Current | Pacific Ocean | It forms a part of the North Pacific Gyre.
The California Current is an extension of the Aleutian Current that flows along the west coast of North America in a southward direction. The region experiences a very strong Upwelling. |
| Antarctic Circumpolar Current | Southern Ocean | It is also known as West Wind Drift.
The current flows in a clockwise direction from east to west around Antarctica. The Antarctic Circumpolar Current is considered to be the largest ocean current in the world. |
| Labrador Current | North Atlantic Ocean | With the combination of warm Gulf Stream and cold Labrador Current is known for producing one of the richest fishing grounds in the world.
The Labrador Current meets the warm northward moving Gulf Stream with the Arctic Ocean after flowing south. |
| Canary Current | North Atlantic Ocean | The current is named after the Canary Islands.
The Canary Current, also known as Eastern Boundary Current, is a part of the North Atlantic Gyre. The region experiences Upwelling. |
| Eastern Greenland Current | Arctic Ocean & North Atlantic Ocean | The North Atlantic and the Arctic are directly connected by this current.
The Eastern Greenland Current is a Low salinity current that extends between Cape Farewell to Farm Strait. It also contributes to the highest sea-ice export out of the Arctic. The Eastern Greenland Current forms the major freshwater sink for the Arctic. |
| Benguela Current | South Atlantic Ocean | The Benguela Current forms the Eastern portion of the South Atlantic Ocean Gyre.
The Benguela Current forms the branch of West Wind Drift in the Southern Hemisphere. The current is characterised by high upwelling, the presence of an excellent fishing zone and low salinity. |
| Falkland Current | South Atlantic Ocean | The current has been named after the Falkland Islands.
The current is also known as Malvinas Current. The Falkland Current is a branch of the Antarctic Circumpolar Current. The Barzil-Malvinas Confluence zone is created by the mixing of the Falkland cold current and the warm Brazil current. This is also responsible for the region’s temperate climate. |
| Northeast Monsoon Current | North Indian Ocean | Indian North Equatorial Current flows southwest and west, crossing the Equator. |
| Somali Current | West Indian Ocean | The Current is deeply influenced by the monsoon.
The Somali Current is similar to the Gulf Stream in the Atlantic Ocean. The region experiences major upwelling. |
| Western Australian Current | Southern Ocean & South Indian Ocean | The current is also a part of the Antarctic Circumpolar Current.
The Western Australian Current is otherwise known as West Wind Drift. The Western Australian Current is a seasonal current- that is strong in summer and weak in winter. |
| South Indian Ocean Current | South Indian Ocean | The South Indian Ocean Current is similar to South Atlantic Current. |
Warm Ocean Currents List
Here is the list of Warm Ocean Currents
| List of Warm Warm Ocean Current | Region | Important or Additional Facts |
| North Equatorial Current | Pacific Ocean & Atlantic Ocean | Though the term “equatorial” has been used, it has no relation with the Equator.
The current forms the southern side of the clockwise subtropical gyre. The North Equatorial Current flows east to west between 10° N to 20°N. |
| Kuroshio Current | Pacific Ocean | The word “Kuroshio” refers to “Black Stream”. This is a western boundary current.
The average surface temperature of the current is warmer than the surrounding ocean. Due to this warm current, the temperature in Japan is regulated. It is similar to the Gulf Stream in the Atlantic Ocean as it is in the Pacific Ocean.
|
| North Pacific Current | Pacific Ocean | The North Pacific current circulates anti-clockwise direction along the Western North Pacific Ocean.
The current is formed when the Kuroshio current and the Oyashio current meet. |
| Alaskan Current | North Pacific Ocean | The northward diversion of a part of the North Pacific Ocean results in the formation of the Alaskan current.
Two large eddies are formed, known as Haida Eddies and Sitka Eddy |
| Equatorial Counter Current | Atlantic Ocean, Pacific Ocean, and the Indian Ocean | The current is also called North Equatorial Countercurrent.
This wind-driven current flows west to east between 3°N-10°N. |
| El Nino Current | Central & East-Central Equatorial Pacific | Speed and strength of ocean currents are deeply impacted by the occurrence of El Nino events. |
| Tsushima Current | Sea of Japan | It is a branch of Kuroshio Current. |
| South Equatorial Current | Atlantic Ocean, Pacific Ocean, and the Indian Ocean | Southern hemisphere counterpart of North Equatorial counter current.
Directly driven by trade winds blowing from east to west. |
| East Australian Current | South-Western Pacific Ocean | The East Australian Current transports the tropical marine fauna to habitats in sub-tropical regions along the southeast Australian coast. |
| Florida Current | South Atlantic Ocean & Caribbean Sea | The Florida current was discovered by Spanish explorer Juan Ponce de León in 1513.
The Florida current flows around Florida Peninsula and joins the Gulf Stream at Cape Hatteras. |
| Gulf Stream | North Atlantic Ocean | The Gulf Stream splits into North Atlantic Drift (crossing Northern Europe & southern stream) and Canary Current (recirculating of West Africa).
This is an intensified current driven mainly by wind stress. |
| Norwegian Current | North Sea (Atlantic Ocean) & Barents Sea (Arctic Ocean) | Norwegian Current is a branch of North Atlantic Drift and sometimes is also considered as an extension of the Gulf Stream.
This wedge-shaped current is one of the two dominant Arctic inflows of water. |
| Antilles Current | North Atlantic Ocean | The Antilles Current is a part of the North Atlantic gyre.
The Antilles current flows across the island chain which separates the Atlantic Ocean and the Caribbean Sea. |
| Irminger Current | North Atlantic Ocean | The current is named after the Danish vice-admiral Carl Ludvig Christian Irminger.
The Irminger current is a part of the North Atlantic subpolar gyre. |
| Brazilian Current | South Atlantic Ocean | The Brazilian current flows along the south coast of Brazil till Rio de la Palta.
The Brazilian current joins the cold Falkland Current at the Argentine Sea making it a temperate sea. |
| Mozambique Current | Indian Ocean | Large anti-cyclonic Mozambique channel eddies are formed.
The Mozambique current flows between the southeast country of Africa- Mozambique and the island of Madagascar in the Mozambique Channel. |
| Agulhas Current | South-West Indian Ocean | The Aghulas current flows south along the east coast of Africa.
This is the largest western boundary ocean current. |
| Southwest Monsoon Current | Indian Ocean | The current extends into the Arabian Sea and the Bay of Bengal.
The Indian Ocean is dominated by this current during the southwest monsoon season (June–October). |
Ocean Currents UPSC
A continuous general movement of ocean water in a specified direction is called an ocean current.
Ocean currents are the directional movement of seawater that is continuous and predictable. It is a massive movement of ocean water caused and influenced by a number of forces. They are similar to river flows in oceans. A solid understanding of this subject is required to help individuals pass competitive exams. On that note, we have covered this topic exclusively for students preparing for the UPSC and IAS exams.
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