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November 7, 2013
Ocean Currents: Types, Causes & Circulation Pattern of Ocean Currents of the World
Ocean Currents: Ocean currents are large masses of surface water that circulate in regular patterns around the oceans, e.g.. the North Atlantic Drift, Labrador Current, Benguela Current, etc.
Based on temperature. Ocean currents can broadly be divided into two classes—the warm and the cold currents.
The Warm Currents: These are those currents which flow from the low latitudes in Tropical Zones towards the high latitudes in the Temperate and Sub-polar Zones. They bring warm water into cold water areas.
The Cold Currents: These currents have a lower surface temperature and bring cold water into warm water areas. These currents flow in the high latitudes from the Polar regions towards the low latitudes in the warm Equator region.
Based on their depth the ocean currents can also be divided into two categories:
The Surface Currents: These currents constitute about 10 per cent of all the water in the ocean, these waters are the upper 400 m of the ocean.
The Deep Water Currents: These currents make up the other 90 per cent of the ocean water. These waters move around the ocean basins due to variations in the density and gravity. Deep waters sinks into the deep ocean basins at high latitudes, where the temperatures arc cold enough to cause the density to increase.
Causes of Ocean Currents: The ocean currents have a circulation of water in a regular pattern around the oceans. The origin and nature of the movement of the currents arc related to the following factors:
(i) Level of Salinity: The higher the level of salinity of ocean water, the denser it is. Water with less salinity therefore flows, over the denser saline water. For example the Mediterranean Sea is more saline as compared to the Atlantic Ocean: so the Atlantic water flows into Mediterranean Sea's surface.
(ii) Temperature: The oceans near the tropics and Equator are much warmer than the ocean water in the polar or temperate regions. Therefore warm Equatorial water move towards poles as warm currents, while cold ocean currents move towards Equator as cold ocean currents.
(ill) The Earth s Rotation: Since the speed of rotation of the earth is maximum at the Equator, all moving bodies (winds and ocean currents) move in a clockwise direction in the Northern Hemisphere and anticlockwise direction In the Southern Hemisphere, e.g. Canary current and Gulf stream in Northern hemisphere and Peruvian and West Wind Drift in Southern hemisphere.
(iv) The Planetary Winds: The planetary winds play a dominant role on the flow of ocean currents.
(a) Trade Winds : Trade Winds blow between the Equator and the Tropics. These winds move Equatorial waters polewards and westwards. They warm the eastern coasts of continents. For example:
(i) The North-East Trade Winds move the North Equatorial Current to warm the eastern coasts of Japan as the Kuroshio Current.
(ii) The South-East Trade Winds drive the South Equatorial Current which warms the eastern coast of Australia as the warm East Australian Current.
(b) Westerlies: Westerlies blow in the temperate latitudes and result in a north-easterly flow of water in the Northern Hemisphere and the opposite In the Southern Hemisphere. For example:
(i) The Westerlies force the warm Gulf Stream to the western coast of Europe as the North Atlantic Drift.
(ii) They cause the cold West Wind Drift to flow towards the Equator as the Peru Current along South America and the Benguela Current along South Africa.
(c) Monsoon Winds: The strongest influence of prevailing winds on flow of current is seen in the North Indian Ocean. Due to the monsoon winds the direction of the currents change from south-west in summer to the north-east in winter.
(v) Land : A land mass obstructs the flow of water of an ocean current and diverts its movement. For example, at Cape Sao Roque the South Equatorial Current gets divided into two branches, one Joins North Equatorial current, the other becomes the Brazil current.
CIRCULATION PATTERN OF OCEAN CURRENTS
Ocean currents are greatly influenced by the stresses exerted by the prevailing winds and Coriolis force. The oceanic circulation pattern roughly corresponds to the Earth's atmospheric circulation pattern. The air circulation over the oceans in the middle latitudes Is mainly anti-cyclonic (more pronounced in the southern hemi-sphere than in the northern hemisphere). The oceanic circulation pattern also corresponds with the same. At higher latitudes, where the wind flow is mostly cyclonic, the oceanic circulation follows this pattern. In regions of pronounced monsoonal flow, the current movements are influenced by the monsoon winds. Due to the Coriolis force, the warm currents flow from low latitudes to move to the right in the northern hemisphere and to their left in the southern hemisphere. The cold waters of the Arctic and Antarctic circles move towards warmer water in tropical and equatorial regions, while the warm waters of the lower latitudes move pole wards.