Ocean Currents Class 8 Geography Notes Maharashtra Board

Ocean Currents Class 8 Geography Notes Maharashtra State Board

Keep the large metal tray on a stand. Fill it with water. After the water becomes still, leave the sequins in them. After some time, the sequins will start floating in the water and become still too. Observe all these things. After some time, light the spirit lamp and place it below one corner of the tray. Observe what happens.
Ocean Currents Class 8 Geography Notes Maharashtra Board 1
It will occur to you that as the temperature of water increases, the plastic sequins move from one place to another. As the temperature rises, the density of water decreases and it becomes lighter. And, therefore, the water having a lower temperature which is heavier replaces the water with a higher temperature. After some time, the sequins start moving in a circular motion. There is movement of these sequins because of the flow of water.
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A very strange incident occurred in the Pacific Ocean in the year 1992. A cargo ship sailed towards America from Hong Kong. While traveling through the Pacific Ocean, near the Hawaii Islands, a container full of toys fell into the ocean and broke. Around 28000 rubber toys started floating on the ocean. This incident occurred on 10th January 1992. Now a strange thing happened. After around 10 months, on 16th November 1992, some of these toys reached the coast of Alaska. Some of them crossed the Bering Strait and moved upto the Arctic Ocean by the year 2000. Some of them also floated to the Atlantic Ocean from the Arctic. Some of these reached the eastern coast of America in 2003 and some of the toys had even reached the European coast by 2007. From the Hawaii Islands, some toys took the route to Australia!
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The ocean water can be divided into two parts: depth-surface water and deep water.

  • The upper layer extends upto 500 meters from the sea level.
  • Below 500 meters depth.

The region from sea level to the depth of 500 m. is considered to be surface water. Sunlight can reach this depth. The movements in this layer occur mainly due to differences in temperature and salinity. The planetary winds give speed to the ocean currents.

Ocean Currents Class 8 Geography Notes Maharashtra Board

Horizontal (Surface) Ocean Current:
The flow on the surface of the ocean moves only 10% of the oceanic water. The surface flow is considered up to 500 meters of depth. The discharge of water in the oceans is measured in the Sverdrup unit. It is equivalent to 1 million cu.m./second discharge. The horizontal flow of ocean water occurs as warm and cold currents. These currents flow from the equator to the poles and from the poles to the equator. These currents are pushed to long distances by the planetary winds. As a result, the ocean waters flow from the equator to both the poles and vice versa. You have studied the map given in the figure earlier.
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The Ocean Currents of the Indian Ocean:
There is a similarity between the patterns of the ocean currents of the Pacific and Atlantic Ocean but the flow of the ocean currents of the Indian Ocean are different. The Indian Ocean is landlocked in the north. The equator divides this ocean into two parts- northern and southern. The Monsoon winds influence this ocean tremendously. These winds change their direction according to the season. In the northern part of the Indian Ocean, currents flow in a clockwise direction in summer while in winter they flow in the opposite direction due to the reversal of Monsson Winds.

We have studied that ocean currents are formed due to differences in temperature, density, and planetary winds. In addition, the following reasons are also responsible for the direction of the flow of ocean currents and their velocity.

  • Rotation of the Earth: Because of the rotation of the earth, the ocean currents move in a clockwise direction in the Northern Hemisphere and an anti-clockwise direction in the Southern Hemisphere.
  • Continental Structure: According to the alignment of the coastline, the direction of the ocean current changes. The velocity of the ocean currents is around 2 to 10 km per hour. The ocean currents are divided into two types currents and warm currents.

Ocean Currents Class 8 Geography Notes Maharashtra Board

Effects of Ocean Surface Currents on Human Life:
Ocean currents especially affect the climate of the regions having proximity to the sea. In cold regions where warm ocean currents flow, the climate becomes warmer. In some regions, the amount of precipitation increases. For example, the warm ocean currents flowing near Western Europe, Southern Alaska, and the Japanese coast, reduce the intensity of the winters there and make them warmer. As a result, these ports do not freeze in winter.
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Had ocean currents been absent, the ocean water would have remained still. In such waters, the biotic components would have been devoid of food. Consequently, marine life and its ecosystems would have been limited in its extent. In regions where cold and warm currents meet, plankton, vegetation, algae, etc. grow. This is food for the fish. Therefore, fish come here in large numbers and breed. This has, in turn, led to the formation of large fishing grounds. Grand Bank near the North American coast in the Atlantic Ocean and Dogger Bank near the European coast are some examples.

Concerning water transport too, ocean currents are very important. If the transportation is done according to the flow of ocean currents, the speed of the ships increases and the fuel is saved too. Near the coasts where cold currents flow, the amount of precipitation is low. For example, in Peru, Chile, and the arid desert of South-West Africa. At places where the cold and the warm currents meet, thick fog is formed. Such fogs create problems for transportation. The warm Gulf Stream and the cold Labrador currents meet near the Newfoundland island. This leads to dense fog. Because of the cold currents, icebergs are carried away from the polar areas. If such icebergs come along the marine routes, they are hazardous to the ships.

Deep Ocean Currents:
Water currents beyond a depth of 500 meters are known as deep water/ocean currents. These currents are formed due to the differences in temperature and density of the water in different parts of the ocean. This is known as thermohaline circulation. These currents flow till the sea-bed of the ocean. They flow like rivers continuously below the surface of the sea. The difference in temperatures of various parts of the ocean is the major reason behind the deep-sea currents. Warm water has lower salinity and density. Such water comes to the surface of the sea. Cold water with high density goes down. This movement causes deep sea water currents. Generally, the surface water near Greenland and Europe moves to more depths. This water moves to the Antarctica at these depths. Later the water moves to the surface. Thus, the redistribution of ocean water keeps occurring. This redistribution takes around 500 years to complete. This type of movement is also known as a conveyor belt.
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Importance of Deep Ocean Currents:
Due to thermohaline circulation, the movement of seawater occurs on a large scale. Because of this circulation, ocean water moves from the surface to the bottom and from the bottom to the surface. Warm water is transferred to the bottom from the surface and the nutrient-rich cold water is circulated to the surface. This circular pattern of the movements of the ocean currents gives rise to certain peculiar features in the ocean. They are called gyres.

Ocean Currents Class 8 Geography Notes Maharashtra Board

The Sargasso Sea in the Atlantic Ocean is such an example. It is marked by the circular patterns of ocean currents. It does not have land boundaries and is only surrounded by ocean currents. It gets its name from the Sargassum seaweed. The water is still here. This sea is 1100 km wide and 3200km long. The ocean currents do not flow very close to the coast. They flow near the lower limit of the continental shelf. Even though the velocity of the ocean currents is less, the water carried by them is immense. Under the influence of the Westerlies, in the mid-latitudes, the ocean currents flow from west to east, but near the equator, they flow from east to west. This leads to a circular pattern.

Well-maintained Maharashtra State Board Class 8 Geography Notes Ocean Currents can serve as a reference for lifelong learning.

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