Ocean current definition
Ocean currents refers to the regular movement of large masses of surface water from one part of the ocean to another. The ocean water does not remain stationary in one place. The water of all the oceans and seas are flowing either as surface or under current.
Types of ocean currents
- Warm ocean current
- Cold ocean currents
Warm ocean currents: warm ocean current are currents that flow from the equatorial regions towards the poles with a relatively high surface temperature.
Cold ocean currents: cold ocean current are those currents that flow from the poles toward the equatorial region with a relatively low temperature.`
Causes of the ocean currents
Below are the causes of ocean currents:
- Rotation of the earth
- Difference of temperature
- Wind movement;
- Difference of evaporation
- Variation in depth
- Location of the landmass
Rotation of the earth
The earth rotation is responsible for the movement of ocean waters. The earth rotates from west to east and thereby causes ocean waters to deflect to the right , the deflection to the right causes the ocean water flows in a clockwise directions in the northern hemisphere and anticlockwise direction in the southern hemisphere.
Difference of temperature
The temperatures of the ocean waters at the equator is higher and therefore warmer and lighter than those at the tropic which in turn results in the expansion of the water in volume and thereby the water becomes lighter and the density also decreases. Thus, as a result of the differential distribution of temperature, the water at the equator flows on the ocean surface towards the poles, while the water at the poles is cold and denser thereby moving below at the bottom of the warm and lighter current towards the equator to fill the vacuum.
Difference of salinity
Water of high salinity is denser than water of low salinity. As a result of this, the water of low salinity often flow on the surface of waters of heavier salinity. A typical example of this is that of the Mediterranean region with a higher salinity than those of the Atlantic Ocean.
Variation in depth
The shallow ocean water becomes hot and light very quickly that it causes up-rise of the warm water resulting in a downward flow of the cold water current to occupy the place of the warm water. As a result of this, the upward and downward movement of the ocean water are created as currents.
Location of the landmass
Both cold and warm ocean currents flow in obedience to the transfiguration of the landmass and the topography. The landmass may deflect the current from the direction initially taken by the current to totally different directions.
Difference of evaporation
Much evaporation occurs in the hot regions of the ocean resulting in the decrease of water level. Comparatively cold water from the neighbouring less hot areas of the ocean move towards the more hot areas to maintain a balance in the ocean water.
Winds can cause the surface waters of the oceans to flow in a definite direction if the wind blow prevailingly from one direction. The north-east trades winds causes the surface waters of the Atlantic Ocean north of the equator to flow from eastern coast of USA landmass. On the other hand, the south east trade wind causes the equator to flow towards the south-eastern coasts of the South American landmass.
Distribution of ocean currents
The ocean currents are distributed into three parts on the basis of the location of the oceans. These are:
- The Atlantic Ocean Currents;
- The Pacific Ocean Currents;
- The Indian Ocean Currents.
The Atlantic Ocean Currents
Europe and Africa continents are all in the east of Atlantic while North America and South America are in the west. The equator divides the Atlantic Ocean into north and south part. However, the currents is then divided into two parts namely: South Atlantic Ocean Currents and North Atlantic Ocean Currents.
North Atlantic Ocean Currents
- North Equatorial Current: this is warm current that flows from east to west along the north of the equator under the influence of the rotation of the earth and the northeast trade winds is known as the North Equatorial Current.. After crossing the Mid-Atlantic, the northern part of the South Equatorial current meets the North Equatorial current. The North Equatorial current is divided into two branches. The first branch moves into the Gulf Stream taking a turn to the north. The second branch flows first into the Caribbean Sea and enters into the Gulf of Mexico.
- The Equatorial Counter Current: Between the North and South Equatorial currents, there is a weak current flowing from west to east and it is known as the Equatorial Counter Current. This is a warm current.
- The Gulf Stream: The Gulf Stream originates from the extended part of South and North Equatorial currents. This mixed current flows into the Caribbean Sea and is divided into two parts being hindered by the islands. One of the parts enters into the Gulf of Mexico. The speedy current of water from the Mississippi river of the United States of America enhances the speed of this current and flows through the narrow strait of Florida to North Atlantic. This is referred to as the Gulf Stream since it originates from the Gulf of Mexico, colour of the current is deep blue.
- At the Middle of the Atlantic, the depth and the temperature of the current decreases while the width increases and this current flows here at a speed of 2.5 kilometres per hour. As it flows towards the direction of north-east along the east coast of the United States of America, the Gulf Stream divides into three branches at the mid of the North Atlantic due to the influence of the westerlies.
- North Atlantic Stream
- West Greenland Current
- Canaries Current
- North Atlantic Stream: the first side of the Gulf Stream which is called the North Atlantic Stream, flows along the coast of West Europe, the British Islands and Norway into the North Sea as a warm current.
- West Greenland Current: the warm West Greenland Current, the second branch of Gulf Stream curving northward flows along the south of Iceland and Greenland and then flows through Davis Strait between Greenland and Baffin Island to the north.
- Guinea Current: the Guinea current, the second branch of Canaries Current, flows along the coast of Guinea of West Africa to the south up to the Equator; it then mixes with Equatorial Counter Current and flows into the Bay of Guinea. This is a cold current, the flow of different currents and cross currents along the sides of North Atlantic Ocean has caused in the centre of the ocean an area of stagnant sea often full of drifted branches of plants, grass, sea-weeds etc. and is called the Sargasso Sea.
- Canaries Current: the third branch of Gulf Stream which is known as the Canaries current flows and turns southward, it then flows along Portugal and the west coast of West Africa. The current is divided into two branches, the first branch curves south-west due to the influence of Trade Wind and being a cold current flows into North Equatorial Current.
- Labrador Current : these are two cold currents from the North Ocean which flow along the east and west of Greenland into the Atlantic Ocean. These two currents join in the north of Labrador Peninsula and taking the name of the Labrador Currents. Labrador current flows along the east coast of Newfoundland and the United States of America to the south. The Labrador current flowing south to New York is hindered by the warm Gulf Stream. The deep blue water of the Gulf Stream and the green water of the Labrador flow side by side in the opposite direction and the border of these two cross currents is called the ColdWall.
South Atlantic Ocean Currents
- The Antarctic Current: The cold water current from the Antarctic flows under the influence of the strong westerly wind moving from west to east direction. This is referred to as the Antarctic current it therefore enters into the Atlantic by the south of South America.
- South Equatorial Current: The South Equatorial Current originates from the extended part of the Benguela current. This current marches towards north-west up to the equator being influenced by the rotation of the earth and the south-east trade winds. This current is known as the South Equatorial Current as it flows to the south of the equator and it is a warm current.
- Benguela Current: the branch of the Antarctic current being deflected near the Cape of Good Hope flows to the north and turns towards the west side of South Africa. This current is known as the Benguela current. The current is cold since it comes from the cold current. It turns westward under the influence of the south-east trade winds and joins the South Equatorial current.
- Brazil Current: the part of South Equatorial current is referred to as Brazil current , it flows through the east coast of Brazil to the south-west. The current is warm since it starts from the warm current and flows through the tropical region, crossing theTropic of Capricorn, the current turns eastward gradually under the influence of westerly wind and meets the Antarctic current.
- Falkland Current: parts of the Antarctic current after flowing into the Atlantic Ocean turns north and flows northward along the coast of Falkland Island and Argentina, this is current is referred to as Falkland Current and it is a cold current.
Effects of ocean currents on climate
- Ocean currents modify the climate of an area by raising the temperature when it is cold and warm.
- The various warm currents of the ocean bring about regular rainfall to the coastlands
- Cold currents brings about reduction in temperature through the formation of coastal fogs.
- Cold currents bring about coastal fogs instead of actual rain and this is responsible forpoor visibility which poses danger to sailors on the high sea and aeroplane.
- In polar regions, warm currents enhance ports to be free from ice.
- Cold currents aids aridity of the landmass which they blow across.
- The meeting of warm and cold currents encourages the formation of plankton which is an essential food for fish.