Importance of Oceans Class 6 Geography Notes Maharashtra State Board
In the previous standard, we have studied the lithosphere and hydrosphere of the earth, the proportion of land and water on earth, and also the major oceans. Note the area of each ocean given in the following table.
| Ocean | Area in sq. km. |
| Pacific | 166,240,977 |
| Atlantic | 86,557,402 |
| Indian | 73,426,163 |
| Southern | 20,327,000 |
| Arctic | 13,224,479 |
The hydrosphere includes all the water bodies that exist on the earth. This covers all the oceans, seas, rivers and their tributaries, lakes, reservoirs and groundwater. Of the total global waters, 97.7% is contained in oceans.
We always see the living world around us. There is considerable diversity in the living world on land. The living world in the hydrosphere is many times greater than the living world on land. And it has a much greater diversity.
Use the following ingredients: One bowl of rice flakes (pohe). One teaspoon oil. One tomato and a small onion: diced. Chilli powder to taste. Mix all the ingredients well. Give the mixture to all your friends and ask them to taste it. Now add some salt to the mixture and taste it again.
Take some water in a steel dish. It is better if the water is from a borewell. Keep the water in direct sunlight. Do not remove the dish until all the water has evaporated. Observe the dish after the water has evaporated completely. What do you see? Taste the substance in the dish.
You must have noticed that after the water evaporates completely, a whitish layer is left in the dish. If you taste it, you will find that it is salty. You will realize that these are the salts in the water. In drinking water, the proportion of salts is quite low. Water from oceans and seas has a greater amount of salt. Hence it tastes salty.
There is abundant aquatic life in the oceans. From the microscopic plankton to huge whales, different types of living things are found in the oceans. Once they die, their remains accumulate in oceans. All rivers flowing from mountains or hilly areas finally meet the oceans. Sediments from eroded lands, trees, and bushes flowing with the water, dead remains, etc. enter the ocean with this river water. In both the above processes, the dead remains decompose, releasing various minerals and salts into the ocean water.
Volcanic eruptions occur on land. Similar volcanic eruptions take place in the ocean as well. During volcanic eruptions different minerals, ashes, salts, and gases are added to the water. This increases the level of salts and minerals in ocean water. Due to the continuous evaporation of oceanic waters, the proportion of salts increases. All these things make the ocean water salty. The salinity of ocean water is different in different places. Salinity is expressed in terms of mils (particles per thousand). The average salinity of oceanic waters is 35 o/oo. The Dead Sea is known to have the maximum salinity. Its salinity is 332 o/oo.
We obtain salt from the salty waters. Salt as a substance is obtained by constructing salt pans in the coastal areas. Salt is an item in our diet. Many minerals like phosphates, sulfates, iodine, etc. are also obtained from the sea. We depend on oceans to some extent for minerals.
Many of us include fish in our diet. We get fish from rivers, lakes, and seas. The proportion of fish in seas is much greater than of those in rivers and lakes. Catching marine animals is a large-scale activity the world over. It is one of the ancient occupations of human beings. Though food is the major purpose of this activity, marine animals are also used for the production of fertilizers, pharmaceuticals, and also in research.
In India, people mainly consume prawns (kolambi), clams (tisre), crabs, seerfish (surmai), mackerel (bangda), pomfret (paplet), Indian shark (mori), Indian salmon (ravas), etc. Many other types of marine animals are consumed in different parts of the world. The life of people from countries that have a coastline largely depends on the sea, especially if there are few other occupations. Seychelles, Mauritius, Maldives, etc. are some of these.
You must have realized from the above activity that there are differences in the temperature of different places on the earth. Similarly, there is a difference in the maximum and minimum temperatures. This difference is less in the coastal regions (nearness to the sea) while it is more in the regions far away from the sea (continentality).
This means that in regions close to the oceans, seas, or large reservoirs, there is not much of a difference in the temperature throughout the day. The main reason for this is the mixing of vapour released through the evaporation of water from these water bodies into the air. This vapour in the air absorbs and stores the heat released from the land. Hence, the temperature in coastal areas remains equable.
You have studied that the equatorial region receives near perpendicular sunrays. As a result, these areas get more heat whereas the polar regions receive highly slant rays. This differential heating creates an imbalance in the temperature of air in different parts. This leads to the formation of belts of high and low pressure on the earth. Winds blow due to pressure differences in these belts. These winds are called Planetary Winds. These winds move the oceanic water in the form of currents. These currents are warm currents or cold currents.
Warm currents move towards cold regions and cold currents move towards warm regions. This means ocean currents move from the equatorial region to polar regions and from polar regions to the equatorial region. This leads to the redistribution of heat on the earth. The cold currents moving towards the equatorial region make the temperature of coastal areas in that zone milder whereas the warm currents coming in the colder regions cause temperatures in coastal areas to rise. We have seen this in the figure.
The oceans act as the controller of global temperature in the two ways described above. The oceans have a vast expanse, therefore huge amounts of vapour get created. This process goes on continuously. From this vapour, the earth gets rainfall. Oceans are the source of rain. The rainwater flows through rivers and streams and finally flows back into oceans. This makes it clear that the beginning and end of the water cycle take place in the oceans.
As the regions close to the sea have an equable climate, the density of population is high in these areas. The coastal regions have always attracted man due to its climate, abundance of food, and various products obtained from the sea.
In the future, it will be possible to generate electricity with the help of oceanic waves and tides. It is possible to convert the saline ocean water into potable drinking water. This will reduce the scarcity of drinking water to some extent. The drinking water in the city of Dubai in the United Arab Emirates is being made available through this method.
In the swampy areas of the sea coast, and in the areas of estuaries, the soils are saline and the climate is humid. In such areas, mangrove forests with tivari and sundry grow well. The wood of mangrove trees is light and oily. It lasts longer. It is used as fuel and also for shipbuilding. The mangrove forests protect coastal areas from huge waves. These forests also protect the biodiversity in the coastal areas. If these forests are located near coastal towns, they are called the lungs of these towns.
Oceans and Resources
We have seen earlier that we obtain salt, fish, shells, and other products from the ocean. Besides these, we get minerals like iron, lead, cobalt, sodium, manganese, chromium, zinc, etc. from the ocean floor. We also get mineral oil and natural gas.
We get precious items like pearls, corals ornamental items like shells, as also medicinal plants from the seas.
Oceanic Transport
Oceans have provided us with the most economical option for transportation. Large-scale transport of goods is carried out with the help of ships, trawlers, boats, etc. International trade is carried out on a large scale using waterways. Countries like Spain, Norway, and Japan have a good coastline. Due to goods transport by ocean routes, these countries have gained importance.
Ocean currents are quite important in water transport. As far as possible water transport is carried out along ocean currents. They accelerate the speed of ships and also save fuel to a considerable extent. Water transport is conducted on a much higher scale as compared to other modes of transport. Hence, for the transport of bulky materials like coal, crude oil, raw materials, metallic minerals, food grains, etc. water transport is given preference.
Issues Related to Oceans
About 70.8% of the surface of the earth is occupied by water. In order to fulfill his requirements, man undertakes many activities. These lead to the production of huge amounts of different types of waste. These waste materials cause pollution. Pollution of oceanic waters is a major and serious issue that has developed in recent times.
- Oil Spills.
- Releasing the waste produced in the coastal cities into the seas.
- Materials thrown out from ships.
- Exploitative fishing.
- Cutting of mangrove forests in coastal areas.
- Disasters caused by the water mines.
- Sewage released by industries and cities.
- Excavations carried out in the seas.
All the things listed above lead to large-scale pollution of oceanic waters. Some coastal regions are proving to be death traps for aquatic animals. As a result, many aquatic animals are under the threat of being extinct e.g. the blue whale, some types of sea turtles, dolphins, etc. A larger proportion of the surface of the earth is occupied by water. Most of the water is salty. The living world in this salty water is suffering from the pollution caused by man. We must avoid this.
The proportion of water being greater than that of land, the earth is known as the water planet. Water in any form is a boon for the living world. Of all the planets known to man, the Earth is the only one which has a living world.
Southern Ocean:
The water body that extends from 60°S parallel to the coast of the Antarctic Continent is named the Southern Ocean.
Maharashtra State Board Class 6 Geography Notes Importance of Oceans can be used for revisiting and reinforcing previously learned content.