Maharashtra Board Class 11 Geography Chapter 6 Ocean Resources PDF Download

Ocean Resources

Use Your Brain Power

Collect information of the following and discuss in the class:

Major journeys carried out by explorers in the last millennium

Discovery of continents, countries and islands

Spread of culture, trade and religions

Comment on how oceans have played a major role in all the three points mentioned above.

Geographical Explanation

During discussion, you must have realised that in the early fifteenth century, only a small part of the whole world was known. Later on, besides Europeans, navigators from other parts of the world also sailed around the world and collected information about new lands. The scientific study of oceans began in the early nineteenth century. In this period an important voyage of discovery took place between 1872 and 1876 when the British ship 'Challenger' sailed around the world. It brought new information about the ocean depths and teeming life found in them. In 1920s, the Echo sounder came into regular use. With the help of this technique, the map makers began to map different ocean floors. Today, many nations are involved in the study of the oceans.

Do You Know?

The Echo Sounder is a type of SONAR (Sound Navigation and Ranging) device. It is used determining the depth of the sea bed or detecting objects in deep water by measuring the time taken for sound echoes to travel.

Try This

Look at figure 6.1 and answer the following question.

1) What does the figure show?

2) In which part of the figure is the ocean shallow? Which human activities can be carried out here?

3) In which part does deposition of sediments occur?

4) Where in the figure do you find islands formed due to submerged mountains?

5) Label the figure with correct names of landforms.

6) Compare these features with the landforms on the earth.

Teacher's Note

Oceans are very deep and have different levels. Just like mountains and valleys on land, oceans also have many underwater mountains and deep trenches.

Exam Trick

Remember: Continental shelf = shallow water near coast. It is like the beach area in the ocean.

Points to Remember

Ocean floor has different parts like shelf, slope, plains and trenches.
Continental shelf is shallow and has fish.
Deeper parts have mountains and trenches.
Echo sounder helps measure ocean depth.
Different landforms exist underwater just like on land.

Geographical Explanation

Now, recall the relief of the ocean floor and its parts such as continental shelf, continental slope, abyssal plain and deeps or trenches.

The Structure Of Ocean Floor

These days, not only are the surface or coastal areas of the ocean exploited but even advanced research is being carried out to see how the deeper part of the oceans can be useful to mankind.

i) The Continental Shelf

The portion of the continents that is submerged under water and borders the coastal areas is known as a continental shelf. The continental shelf is of great importance to man. This part occupies about 7.6% of the oceanic area. They are broad, shallow and gently-sloping plains covered by water. The continental shelf does not extend into the ocean uniformly. Near some coasts, it is narrow while in some parts it may extend for hundreds of kilometres. For example, they are almost absent or very narrow along the coasts of Chile, Sumatra etc. while the Siberian coast near the Arctic Ocean is around 1500 km in width. Generally, its depth from the sea level is about 180 to 200 m.

As the sunlight reaches this part of the ocean bed, it is rich in plankton. These millions of microscopic organisms found in sea water are an important food for fish. Millions of fishes thrive here. The shelf has some of the richest fishing grounds in the world, such as the Grand Banks and Georges Bank in North America. In fact, the fish caught in the continental shelf form the backbone of the fisheries industry the world wide.

The continental shelves contain the world's largest reservoirs of natural oil and gas. For example, the Mumbai High in Arabian sea. Besides oil and gas, minerals are also found here. The concentrated minerals are often in large enough quantities to be minable. Examples are diamonds, chromite, ilmenite, magnetite, platinum, gold and phosphorite deposits. Sand, gravel aggregates and industrial silica sand are the most important of hard minerals now extracted in the near offshore zone.

Teacher's Note

Continental shelf is the underwater land near the coast. In India, the Mumbai High oil field is located on the continental shelf in the Arabian Sea.

Exam Trick

Remember: Continental shelf = fish + oil + minerals. All three important things are found here together.

Points to Remember

Continental shelf is shallow and covered by water.
Sunlight reaches here so plankton grows.
Fish are abundant in this area.
Oil and gas are found here.
Important minerals like diamonds and gold exist here.

ii) Continental Slope

After the extent of continental shelf is over, there is a sharp drop in the ocean floor. The gradient of slope in this region can be between 2° to 5° This is called continental slope. The depth of this slope extends from 200 m up to 4000 meters from sea level.

Due to its steepness, the continental slope stretches over a limited area. The deposition of sediments is also limited in this part. The continental slopes are generally considered as boundaries of continents. It covers about 8.5 percent of total ocean area. Methane hydrate, a compound of water and methane, is present on the continental slopes. e.g. The Krishna-Godavari offshore basin covering an area of 1400 km², is rich in methane hydrate. On the slope, we find many traces of submarine landslide activity, ocean canyons and huge avalanche fans. For example, Congo Canyon is a submarine canyon found near Africa.

iii) Abyssal Plains

Beyond the continental slope, lie the abyssal plains. They stretch over great distances. Over these plains, there are features such as sea mounds, mountains and plateaus. They have gentle slope and cover about 66 percent of the oceanic floor area. The relief on the plain is produced by volcanic and tectonic activities. Other components of the abyssal plain sediment include wind-blown dust, volcanic ash, chemical precipitates and occasional meteorite fragments.

The abyssal plains are often littered with nodules of manganese containing varying amounts of iron, nickel, cobalt, and copper. These pea to potato-sized nodules are formed by the precipitation of minerals from the seawater onto bones or rock fragments. Currently, the deposits of manganese nodules are not being mined from the ocean floor, but it is possible that they could be collected and used in the future.

Teacher's Note

Abyssal plains are the flat areas far below the ocean surface. They cover most of the ocean floor and are very deep.

Exam Trick

Remember: Abyssal = very deep. Abyssal plains cover 66 percent of ocean floor - this is the biggest part.

Points to Remember

Abyssal plains are very deep flat areas.
They cover 66 percent of ocean floor.
Mountains and plateaus are found here.
Manganese nodules are present here.
These nodules may be mined in the future.

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