Ocean currents are the regular movements of water in the oceans. They move in a circular pattern around the oceans. Based on temperature and depth, ocean currents may be divided into the following divisons:
Based on temperature
These currents flow from low latitudes in the tropical zone towards the high latitudes in the temperate and sub-polar regions. These currents bring warm water to cold regions.
These currents flow from the polar regions to the equatorial regions. These currents bring cold water to warm regions.
Based on depth
These currents make about 10% of all water in the ocean.
Deep water currents:
These currents make about 90% of all water in the ocean.
Causes of Ocean Currents
Temperature affects the origin and nature of ocean currents. As equatorial and tropical regions are warm, the oceans lying near the Equator and the tropics are warmer than the oceans lying near the Polar Regions. Thus, the ocean currents from warm equatorial regions move towards the Polar Regions as warm currents. Similarly, the cold currents move from the Polar Regions to the equatorial regions as cold currents.
Level of Salinity:
Oceans with a higher level of salinity are denser than oceans with lower levels of salinity. Generally, the ocean currents are generated from areas of less salinity to areas of high salinity. Because the Mediterranean Sea is more saline than the Atlantic Ocean, most ocean currents flow from the Atlantic Ocean to the Mediterranean Sea.
Rotation of the Earth:
The Earth rotates from west to east. The speed of rotation of the Earth is maximum at the Equator. All the moving bodies move in a clockwise direction in the Northern Hemisphere and in an anti-clockwise in the Southern Hemisphere. This is also known as the Coriolis Effect.
Winds affect the ocean currents. The trade winds blow between the Equator and the Tropics. These winds thus move the equatorial water towards the poles. For example, the Southeast Trade Winds drift the equatorial current to the eastern coast of Australia as the warm East Australian Current.
A landform may influence the ocean currents. For example, the shape of various landmasses may obstruct the flow of water and influence its movement. For example, the South Equatorial Current gets deflected towards the Northern Hemisphere.
The circulation pattern of the ocean currents is influenced by the Earth’s atmospheric circulation pattern. At higher latitudes, the wind flow is cyclonic. Thus, the oceanic currents move in a cyclonic pattern. Similarly, in middle latitudes, air circulation is mainly anti-cyclonic. The currents thus move in an anticyclonic pattern.
Also Read Water Resources
Effects of Ocean Currents
Currents influence the climatic conditions of the regions in which they blow. The warm equatorial currents raise the temperature of the region in which they blow. Similarly, the cold currents lower the temperature of the places where they blow. For example, British Isles would have been extremely cold without the warm North Atlantic Drift. The hot climate of Peru is cooled by the cold Peru Current.
The winds blowing over warm currents pick up and carry moisture and bring rainfall. For example, the North Atlantic Drift brings rainfall in some areas located along the western coasts of Europe. On the contrary, cold currents do not bring rainfall and make the region cooler and drier. The Kalahari Desert hardly experiences rainfall because of the cold Benguela Current.
The meeting of the warm and cool currents results in the creation of fog. For example, the Japanese coast experiences heavy fog when the warm Kuroshio current meets the cold Oyashio current.
At times, the meeting line of a warm and a cold current may cause a violent storm. The hurricanes which occur off the coast of USA follow the line where the Gulf Stream merges with the Labrador Current.
The mixing of warm and cold currents results in the deposition of plankton. Therefore, at such places, fish can be found in abundance.
Currents help the ships to sail if they follow the directions of the currents.
Many warm currents keep the ports of Europe ice-free even during the winters. This helps in trade and commerce.
The ships face danger because of the fogs caused by the meeting of the warm currents with the cold currents. This has resulted in the wreckage of many ships in the past as they were not able to view icebergs because of poor visibility.