Here is a compilation of essays on ‘Ocean Currents’ for class 6, 7, 8, 9, and 10. Find paragraphs, long and short essays on ‘Ocean Currents’ especially written for school students.
Essay on Ocean Currents
- Essay on the Origin of Ocean Currents
- Essay on the Meaning of Ocean Currents
- Essay on the Causes of Ocean Currents
- Essay on Factors Controlling Ocean Currents
- Essay on the Currents of Various Oceans
- Essay on the Effects of Ocean Currents
Essay # 1. Origin of Ocean Currents:
the currents in the oceans are originated due to combined effects of several factors acting internally as well as externally. The factors, in fact, controlling the origin and other characteristics of ocean waters, rotational mechanism of the earth, external factors or atmospheric factors, topographic characteristics of the coasts and ocean basins.
i. Usually the direction of the currents is guided by the direction of the prevailing winds.
ii. The ocean currents, like the circulation of planetary winds, are deflected by the rotation of the earth according to Ferrel’s Law. Hence, the currents of the northern hemisphere are deflected towards the right and those in the southern hemisphere to the left.
iii. The shape of the landmasses helps in guiding the direction of the currents.
iv. The speed of the current in mid ocean is slow and it is speedy in coastal region.
v. Currents of warm water flow along the surface as surface currents and cold water currents flow along the ocean bed as bottom current.
Essay # 2. Meaning of Ocean Currents:
The movement of ocean water from one part to another takes place due to effects of the earth’s rotation, wind difference, salinity and density of sea water, etc. The movement of ocean water is called ocean current. It is to be noted that the waves are not currents because the movement of water does not take place in waves.
Ocean currents are more powerful of all the dynamics of oceanic waters because these drive oceanic water for thousands of kilometres away. The forward movement of surface water of the oceans under the influence of prevailing winds is called drift whereas the ocean current involves the movement of oceanic water in a definite direction with greater velocity.
Ocean stream involves movement of larger mass of ocean water like big rivers of the continent in a direction with greater velocity than drifts and currents.
Essay # 3. Causes of Ocean Currents:
Generally, the ocean currents take place for the following causes:
i. The earth rotates from the west to the east at a tremendous speed. As a result of this, water of the earth’s surface, particularly that of the middle part of the equatorial region, move from the east to the west.
ii. There are some planetary wind systems, namely the trades, westerlies and polar winds on the surface of the earth. They cause many of the surface currents.
iii. The water of the equatorial region is light or less dense because of high evaporation and high temperature. On the other hand, density of sea water is quite high in the cold region because of low temperature and low evaporation. So, water of this region is heavy. In order to remove the difference of density of sea water in these two regions, a circulation of water takes place.
iv. The salinity varies from one part of the ocean to another. It is quite possible that water with lower salinity could be lighter than water with higher salinity. This may result in a natural circulation of water.
It is to be noted that water in the equatorial region is hot and light and that of the polar region is cold and heavy. That is why, warm and light water of the equatorial regions flows towards the polar region along the surface. This is called warm current. Similarly cold and heavy water flow towards the equator along the ocean bed as bottom current. This is called cold current.
Thus water of the torrid region flows towards the rigid region, where it cools down, sinks and returns along the ocean bed as a bottom current towards the torrid region. It then rises to the surface again after being warm and light.
Essay # 4. Factors Controlling Ocean Currents:
The factors controlling the origin and other characteristics of ocean currents are: 1. Factors Related to the Rotation of the Earth 2. Factors Related to the Oceans 3. Factors Related to the Atmosphere 4. Factors Modifying Ocean Currents.
1. Factors Related to the Rotation of the Earth:
The rotation of the earth on its axis from west to east results in the genesis of deflective force or Coriolis force which deflects the general direction of ocean currents. For example, the currents flowing from equator towards the North Pole and from North Pole towards the equator are deflected to their right while the currents flowing north-south and south-north in the southern hemisphere are deflected towards their left.
The rotational force of the earth causes movement of ocean water near the equator in opposite direction to ‘the west to east rotation’ of the earth and thus equatorial currents are generated. These currents flow from east to west. Some ocean water moves in the direction of the rotation of the earth i.e., from west to east and thus counter equatorial currents are formed.
2. Factors Related to the Oceans:
Local variations in the physical properties of the ocean e.g., pressure gradient, temperature differences, salinity differences, density variations etc., generate ocean currents.
(i) Temperature Difference:
The amount of insolation received at the earth’s surface and consequent temperature decreases from equator towards the poles. Due to high temperature in the equatorial region the water density decreases because of greater expansion of water particles whereas the density of sea water becomes comparatively greater in the polar areas. Consequently, water moves due to expansion of volume from equatorial region (of higher temperature) to polar areas (colder areas) of relatively very low temperature.
There is movement of ocean water below the water surface in the form of subsurface current from colder polar areas to warmer equatorial areas in order to balance the loss of water in the equatorial areas. Thus, the pole-ward surface currents and equator ward subsurface currents form a complete circulatory system of ocean water. The Gulf Stream and Kuroshio warm currents moving from equator towards north are examples of such currents.
(ii) Salinity Difference:
Oceanic salinity affects the density of ocean water and density variation causes ocean currents. Salinity increases the density of ocean water. If two areas having equal temperature are characterized by varying salinity, the area of high salinity will have greater density than the area of low salinity.
The denser water sinks and moves as subsurface current whereas less saline water moves towards greater saline water as surface current. In other words, ocean currents on the water surface are generated from the areas of less salinity to the areas of greater salinity. Such system of surface and sub-surface currents caused by salinity variation is originated in open and enclosed seas.
For example, the current flowing from the Atlantic Ocean to the Mediterranean Sea via Gibralter Strait is caused because of salinity difference. In fact, the salinity of the Mediterranean Sea is much higher than the adjoining Atlantic Ocean.
Consequently, water sinks in the Mediterranean Sea. In order to compensate the loss of water Atlantic water flows as surface current into the Mediterranean Sea. The sinking water in the Mediterranean Sea moves as subsurface current towards the Atlantic Ocean. Similarly, such system of surface and subsurface currents is generated between the Red Sea and the Arabian Sea via Babel Mandeb Strait.
The salinity of the Baltic Sea is lowered due to the flow of fresh water by the rivers but the level of water is raised. With the result water moves northward as a surface current into the North Sea and subsurface current moves from the North Sea to the Baltic Sea.
(iii) Density Difference:
In fact, difference in the density of oceanic water is the main cause for the movement of oceanic water as ocean currents. Water density depends on a number of factors e.g., temperature, salinity, pressure etc. In other words, density is the function of temperature, air pressure and salinity. As a rule, water moves from the areas of lower density to the areas of higher density.
The density variation caused by temperature and salinity and resultant movement of oceanic water as ocean current has been explained just above. The density of water also decreases due to influx of freshwater resulting from melting of ice in the polar areas.
High density is caused due to significantly very low insolation in the polar areas but at some places density is lowered due to influx of melt-water. Consequently, cold water moves as cool current from polar areas towards the equator. East Greenland current is supposed to be caused by this factor.
It may be pointed out that the factors of pressure, temperature, salinity and density should be considered together and not separately. It may be summarized that low density water is lighter and hence expands and moves forward as surface current towards high density water where there is sinking of water. The high density water then moves as sub-surface current from greater density to lesser density below the water surface.
3. Factors Related to the Atmosphere:
Ocean currents are greatly influenced and controlled by atmospheric conditions like atmospheric pressure and its variation, wind direction, rainfall and evaporation etc.
(i) Air Pressure and Winds:
Air pressure on the oceanic water causes ocean currents through density variations. The areas of high atmospheric pressure are characterized by low volume of water and thus lowering of water level. Contrary to this the areas of low atmospheric pressure record higher volume of water and higher water level. Thus, water moves as surface current from the areas of higher water level (low pressure areas) to low water level areas (high pressure areas).
Prevailing or planetary winds (e.g. trade winds, westerlies and polar winds) play major roles in the origin of ocean currents. The wind blowing on the water surface also moves water in its direction due to its friction with the water. Most of the ocean currents of the world follow the direction of prevailing winds.
For example, equatorial currents flow westward under the influence of N.E. and S.E. trade winds. The Gulf Stream in the Atlantic and the Kuroshio in the Pacific move in north-eastern direction under the influence of the westerlies. There is seasonal change in the direction of currents in the Indian Ocean twice a year (after every 6 months) due to seasonal change in the direction of monsoon winds.
It has been commonly agreed by the majority of the scientists that friction caused by the wind sets the sea water in motion. Karl Zoppritz mathematically demonstrated in 1878 that a steady blowing wind through its friction with sea water can drag water in its direction. He further demonstrated that there is definite relationship between the direction of winds and ocean currents.
According to Karl Zoppritz the currents generated by wind force move the whole water mass from sea surface to the bottom in wind direction. Findlay has objected to this observation of Karl Zoppritz and has maintained that wind force is active only upto the depth of 30 to 36 feet and thus only the upper water layer moves as currents in the wind direction.
Since the density increases downward with increasing depth, the wind becomes ineffective in dragging sea water at greater depths. According to H.U. Sverdrup there is definite relationship between winds and velocity of currents. According to him the friction and the stress of the wind causing ocean currents is proportional to the square of the wind velocity. The velocity of ocean currents is 1.5% of the wind velocity. For example, if the wind blows at the velocity of 50 km per hour, the velocity of the resultant current would be 0.75 km per hour.
(ii) Rainfall and Evaporation:
The sea water level becomes relatively higher in the areas of low evaporation and high rainfall than those areas which record low rainfall but high evaporation. In fact, evaporation and rainfall are also related to oceanic salinity and density. Low evaporation coupled with high rainfall lowers the amount of salinity and thus reduces water density.
This mechanism results in the rise of sea level. On the other hand high evaporation and low rainfall increases salinity and water density and thus lowers the sea level. Thus, surface ocean currents are generated from the area of high water level to the area of low water level. Ocean currents are originated near the equator because of high water level caused by exceptionally heavy daily rainfall and relatively low evaporation.
Thus, ocean currents after being originated in low latitudes move towards high latitudes. Ocean currents are also generated in polar areas due to high water level resulting from low evaporation due to exceptionally low temperature and abundance of water due to melting of ice mass. These polar cold currents move towards low latitudes.
4. Factors Modifying Ocean Currents:
The direction of ocean currents is determined and deflected by prevailing winds, earth rotation, configuration of coastlines and bottom reliefs of the oceans.
(i) Direction, Shape and Configuration of Coast lines:
The disposition of coast line perpendicular to the natural flow direction of ocean currents obstructs them with the result the ocean currents start flowing parallel to the coast line. The equatorial current after being obstructed by the Brazilean coast is bifurcated into two branches. The northern branch, known as Gulf Stream, flows along the eastern coasts of the USA while the southern branch moves southward in the name of Brazil current parallel to the Brazilean coasts. In Indian Ocean monsoon currents closely follow the coastlines.
(ii) Bottom Reliefs:
The irregularities of the bottom reliefs of the oceans modify the ocean currents at the surface as well as at the bottom. According to Ekman the ocean currents tend to follow the bottom contours in the middle and high latitudes but they are independent of bottom reliefs in the low latitudes. The submarine ridges usually deflect the course of currents.
Generally, the ocean currents while crossing over a sub-marine ridge are deflected to the right in the northern hemisphere and to the left in the southern hemisphere. For example, the North Atlantic Drift (the extension of the Gulf Stream) is deflected to the right when it crosses over the Wyville Thompson Ridge.
Similarly, the north equatorial current is deflected to the right while crossing over the mid-Atlantic Ridge. The Antarctic Circum Polar Current, to the south and south-west of New Zealand, bends sharply north and south when it crosses Macquarie Ridge.
(iii) Seasonal Variations:
There is seasonal change in the directions of currents in some areas in response to seasonal change in weather conditions e.g. in the regions of monsoon climate as the currents of the Indian Ocean show seasonal changes in their flow directions. The monsoon drifts (currents) move east to west along the coast during north-east monsoon in winter season while these flow in north-eastern direction under the influence of south-west monsoon in summer season.
Essay # 5. Currents of Various Oceans:
Some important currents are discussed below:
i. Currents of the Atlantic Ocean:
On both sides of the equator in the Atlantic Ocean, two warm currents are found to move from east to west under the influence of north-east and south-east trade winds.
The current which flows along the north of the equator is known as the North Equatorial Current. The similar current that occurs on the south of equator is called the South Equatorial Current. The south equatorial current in its westward flow is divided into two parts near Cape Sao Roque of South America. Its southern branch is called Brazil Current. This current moves eastward from the south-eastern coast of Brazil and taking the name of South Atlantic Current, reaches the South African coast.
Near the Cape of Good Hope, it flows northwards along the west coast of South-Africa. This part of the current is cold and is called the Benguela Current. The main current moves into the Gulf of Mexico and then it joins with the Antilles Current. Since, this current emerges from the gulf, it is known as the Gulf Stream. It originates from the equatorial region and so, its water is warm (about 30°C).
The width of the current is 64 km and its average speed is 13 km per hour. The current spreads out in the mid Atlantic region to about 480 km. Here it is divided into three branches—one branch runs towards north-east, the second to the east, and the third goes on towards the southeast. The last one is known as the Canaries Current. This branch meets the North Equatorial current.
The North Equatorial current, Gulf Stream and the Canaries current after meeting at the centre of the North Atlantic Ocean form a big whirl of water and in the centre of it is the Saragasso Sea. This part contains stagnant water often full of drifted sea weeds.
The branch of the Gulf Stream which runs towards the north-east is drifted by the westerlies and flows along the coasts of Britain and Scandinavian. This is the North Atlantic Drift or Westerly Drift. This warm current helps to warm up Britain and Scandinavian countries and keeps their ports free from ice.
The cold Arctic Current flows from the Arctic Ocean to the Atlantic. It is divided into two branches; one branch moves below the Gulf Stream as a bottom current and meets the Canaries Current. The other flows along the coast of Greenland as Greenland Current towards the Labrador Coat of Canada. From this point it goes towards south as the Labrador Current.
In the south this current comes in contact with the warm Gulf Stream. This results in the formation of fogs in the area of contact of the two dissimilar currents. Here the difference of temperature of these two current is about 10°C. The zone of contact with dense fog is known as the Cold Wall.
Floating icebergs are brought by the Labrador Current from the polar region. The water becomes warm while it moves towards south and near Newsfoundland coast the icebergs rapidly melt. This results in the deposition of their load of mud and stones on the sea floor. Thus the coastal region off Newfoundland becomes shallower and is known as the Grand Banks. The region abounds in fishes.
ii. Currents of the Pacific Ocean:
On both sides of the equator in the Pacific Ocean too there are currents, flowing from the east to the west. They are North and South Equatorial Currents. The South Equatorial Current covers a distance of about 12,800 km from the west coast of South America to the east coast of Asia. This current is also known as the South Pacific Current and is coming from the American coast towards the west, a portion of the current flows to the south.
At 4° south latitude it is drifted by the West Indies towards the east along the coast of Peru. This current is known as the Peruvian Current or Humboldt Current. Then it meets the south equatorial current again. The main current divides near 180° longitude into two parts. The southern part is called the East Australian Current.
The West flowing branch enters the Indian Ocean between Australia and New Guinea. In the mid pacific, a current flows from the west to the east. This is the Equatorial Counter Current. Starting as a South-East Monsoon Current at the west coast of Central America, the North Equatorial Current flows westwards to reach Philippines Islands. Then it runs northwards along the east coast of Japan. This warm current is called the Kuroshio Current.
It is quite analogous of the gulf stream of the Atlantic. The Kuroshio Current ultimately flows to the coast of Canada. This portion is called the North Pacific Drift. One part of the north pacific drift moves towards the south to form the Californian Current and the other part flows towards the north to reach the Gulf of Alaska. This is called the Alaskan Current.
In the north-west of the Pacific, a cold current flow from the Arctic Ocean through the Bering Strait. It is called the Kamchatka Current in the strait of Kamchatka and the Oyashio Current in the west coast of Japan.
Fig. 5.8: Important ocean currents
iii. Currents of the Indian Ocean:
The north Indian ocean is land locked and the southern part is open. Therefore, north equatorial current of the Indian Ocean is not so pronounced as that of the Pacific or the Atlantic. Its south equatorial current is somewhat prominent. This current moves westward between Indonesia and to the coast of Madagascar.
Here, it divides into two parts. One part goes towards the north and the other towards the south. The southern part flows from south of the Islands of Madagascar and Africa as the Agulhas current. The northern portion flows around northern Madagascar and then through the Mozambique Channel as Mozambique current to reach subsequently the Agulhas Current.
One part of the current has bent toward the north-east to meet the Arabian Sea. This is called the South-West monsoon Drift current. It enters the Bay of Bengal after moving from the west coast of India. A branch of it moves to the coast of Sumatra to meet North equatorial current.
The south-west monsoon current flows in the Indian Ocean under the influence of the monsoon winds in summer. In winter, an ocean current flows from the Bay of Bengal to the coast of Africa under the influence of the north-east monsoon winds. This is called North-East monsoon drift current. There is an eastward moving equatorial counter current in the Indian ocean between the Monsoon current and the south equatorial current like the one in the pacific.
There are no prominent currents in either the Arctic or the Antarctic Ocean. The cold water of the Arctic current moves from the Arctic Ocean along the coast of Greenland and Berring Strait to the Atlantic and the Pacific Ocean respectively. In the Antarctic Ocean a current of cold water moves very slowly at latitude 60°S towards the north. It becomes a bit stronger under the influence of the westerly. This is called the Antarctic Drift.
Essay # 6. Effects of Ocean Currents:
i. Modification in the Coastal Climate:
Ocean currents while flowing along the coasts modify their weather conditions in a number of ways. The most effective impacts of ocean currents are seen on the temperature of affected coastal lands. The effects are both positive (beneficial) and negative (injurious) for flora and fauna. The warm currents, when they reach colder areas, do not allow their temperatures to fall rather they keep them relatively warmer in winter months.
The origin of ideal and favourable European type of climate of the western coasts of Europe is due to the effects of the north Atlantic warm current which is the extension of the Gulf Stream. The temperatures of the coastal countries (e.g., the Great Britain, Norway, Sweden, Denmark, Netherlands etc.) are higher during winter than the average temperatures for their respective latitudes.
The Gulf Stream, on the other hand, raises the temperature of Atlantic and Gulf coastal plains of the USA during summer months and causes and intensifies heat waves and thus becomes responsible for hazardous weather conditions. Sometimes, the temperature rises so rapidly that several people die of sun strokes.
The coastal lands of the east and south-east USA are not benefitted from the warming effects of the Gulf Stream during winter because the winds are off shore i.e., winds blow from the mainland towards the Atlantic Ocean.
Ocean currents help in maintaining the temperature balance of ocean water as the warm currents transport warm waters of the tropical zones to the colder areas of the temperate and polar zones and cold currents bring cold waters of high latitudes to the areas of low latitudes.
Thus, ocean currents help in bringing homogeneity in the distribution of temperature of ocean water and thus help in maintaining the horizontal heat balance of the earth because they transfer additional heat of low latitudes (area of surplus heat) to high latitudes (area of deficient heat).
Cold currents, on the other hand, lower down the temperature considerably of the affected areas and thus cause snowfall. Labrador, Kurile and Falkland cold currents are responsible for heavy snowfall in the affected areas during winters.
The winds blowing over warm currents pick up moisture and help in increasing the amount of precipitation in the affected coastal areas. For example, the North Atlantic Drift and Kuroshio Current bring in sufficient rainfall along the western coasts of Europe and eastern coasts of Japan respectively. On the other hand, cold currents discourage rainfall.
For example, Kalahari desert along the western coast of South Africa and Acatama desert along the western coast of South America owe their existence to some extent it to Benguela and Peru currents respectively but the arrival of El Nino current results in wet condition and four to six times more rainfall than the normal amount is received which makes the arid Peruvian coast lands green and there is rich harvest of cotton, banana, coconut etc.
The convergence of warm and cold currents causes dense fogs which pose obstacles in navigation. Such conditions are created near Newfoundland due to convergence of warm Gulf Stream and cold Labrador current and near the eastern coast of Japan due to convergence of Kuroshio warm current and Kurile (Oyashio) cold current.
ii. Effects on Fishing:
Ocean currents act as distributing agents of nutrients, oxygen and other elements necessary for the existence and survival of fishes. Ocean currents transport planktons from one area to the other area. These planktons are useful food for fishes. Gulf Stream carries planktons from Mexican Gulf to the coasts of Newfoundland and north-western Europe. It may be pointed out that many significant fishing grounds have developed in these areas. Sometimes, a few ocean currents destroy planktons. For example, El Nino current destroys planktons off the Peruvian coasts and causes several diseases resulting into mass deaths of fishes.
iii. Effects on Trade and Navigation:
Ocean currents determine major ocean routes for the navigation of commercial ships in ancient times but presently power-motored ships do not care for the ocean currents and prevailing winds. The occurrence of fogs due to convergence of warm and cold currents pose serious threats to navigation. Larger icebergs brought by cold currents (e.g., by Labrador and Falkland cold currents) damage ships.
iv. Effects on Human Life:
The relation between ocean currents and men is very ancient. Ocean currents serve the human race in a number of ways.
These are discussed below:
(1) From ancient time, the ocean currents and winds serve as natural power for international trade. The icebergs are often seen to be floating along the cold currents. So, the sailors generally avoid the cold currents and choose the warm current for safe sailing of their vessels. That is why, the North Atlantic Drift has been chosen as an ocean route which attracts the heaviest traffic of passengers and goods of the world.
(2) The cold climate of a country under the influence of a warm current becomes milder. For example, the sea round the British Isles and Scandinavia never gets frozen as the water is kept warm by the north Atlantic drift. Such climates are often healthy and invigorating. The ports which are free from ice during the winter are more useful for trade and commerce.
(3) The atmosphere over the cold currents is cold and so the coastal areas under the influence of cold currents are much colder. Thus the water of the St. Lawrence River are practically frozen during the winter owing to the influence of the cold Labrador Current which flows along the east coast of Canada. This affects navigation.
(4) Warm ocean currents may bring rainfall to the coastal regions. If a warm current flows along the coast, wind may take sufficient moisture. This wind may move to the land and cause rainfall. Similarly, a cold current may bring snowfall to the coastal area.
(5) The contact of two currents of different temperature often causes fog and violent storms. Such storms blow along the line of meeting of cold and warm currents. This causes hindrance to navigation.
(6) In the meeting place of cold and warm currents some shallow banks may be created by the deposition of mud and stones. The Grand Bank and Daggers Bank are the examples of this kind. These shallow banks offer ideal conditions for rich marine life. Because of the availability of planktons and oxygen, a large number of fishes gather here. For these reasons, the shallow banks are famous for fishing.
Thus, the ocean currents affect human life directly and indirectly.