ICSE IX GEOGRAPHY Importance of Oceans

DISTRIBUTION OF LAND AND WATER

It is important to understand the link between land and water and their distribution before we can get to know the importance of oceans.

The earth is a unique planet with abundant water. Water together with other conditions like temperature, etc. make life possible on this planet

Distribution of Land and Water

1.    The three-fourths of the surface of the earth are covered with water and one-fourth is land. The mean depth of the Hydrosphere is 3800 metres and it is five times the mean height of land which is 710 metres.

2.    There is much more land in the Northern Hemisphere than in the Southern Hemisphere.

3.    The main land masses generally taper towards the south. Europe and Asia which stretch east and west have three southern peninsulas tapering towards the south.

4.    North America is joined to South America by a narrow neck of land called the Isthmus of Panama. Eurasia is joined to Africa by the Isthmus of Suez. Through both these isthmuses canals have been dug.

5.    Around the North Pole there is an ocean, which is surrounded by the land masses of North America and Eurasia, but round the South Pole there is a land mass called Antarctica, which is covered with a very thick sheet of ice.

Three-fourths of surface of this earth is covered with water, is a great advantage. The ocean waters are the storehouse of heat and keep the earth warm. Had land been greater than water, it would have remained frozen. The ocean waters absorb the heat of the sun and hold it for a long time while land gets heated very quickly and becomes cold equally quickly.

OCEANS OF THE WORLD

All the oceans of the world are connected. They cover 361,000,000 sq. km out of the earth’s total surface of 501,000,00O sq. km.

The Atlantic Ocean

·        "S" shaped  with greatest length from north to south

·         It covers an area of about 82,160,000 sq. km.

·        The average depth of the ocean is between 3 and 5 km or 2,2OO fathoms (4092 metres). The greatest depth lies off the Dominican Republic and is 9,4OO metres.

·        There is an S shaped ridge running almost in the middle, called the Central Ridge which form most of the  islands of the Atlantic

·        The coastline is greatly broken and is bordered by the most fertile lands of Europe. The Atlantic Ocean is the biggest highway of commerce.

The Pacific Ocean 

·        The Pacific Ocean is oval in shape with greatest length from east to west.

·        It has North America and South America on its east and Asia and Australia on its west

·        It is the biggest ocean in the world and is double the size of the Atlantic Ocean. all the continents plus a another Africa can fit into the  Pacific.

·        There are greater deeps in this ocean than in the Atlantic. The greatest known depth of sea in the world is at the Mariana Trench, 320 Kms south-west of Guam.

·        It has a much shorter and regular coastline and fewer harbours than the Atlantic Ocean.

·        Its shores are bordered by less fertile and less commercial lands. It has consequently less commerce than the Atlantic Ocean. It has great resources of fish.

The Indian Ocean

·        The Suez Canal connects the Indian Ocean with the Mediterranean Sea, facilitating trade opportunities and growth

·        The greatest known depth of 7,067 metres lies in the Dunda Trench, south of Java.

The Arctic Ocean

·        Situated round the North Pole and remains perpetually frozen

·        It is connected to the Atlantic Ocean by the Eastern and Western Greenland Channels and to the Pacific Ocean by the Bering Strait

·        The Arctic strictly not an ocean as it is not navigable. it winds around the North Pole and is completely frozen in winter and covered with drifting ice for the rest of the year. Its separate existence and its area over 13 million sq km entitle it to an ocean.

The Antarctic Ocean

·        There are some geographers who regard the area around the continent of Antarctica as the Antarctic Ocean.

·         But most experts think that this part of the globe has no natural boundaries on the north, and consists largely of the southern extremities of the three major oceans-Pacific, Atlantic and Indian.

Sea is described as a salt water body usually on the margins of the continents.

The important seas are the Caribbean, Mediterranean, Bering, Arctic, Sea of Japan, Barents Sea, Kara Sea, East China Sea Andaman Sea, Arabian Sea and Red Sea.

The average depth of oceans is 380O m against average height of 840 m of the lithosphere.

·        The highest summit on land surface is Mount Everest - 8848 metres above sea level.

·        The deepest bottom of the ocean is Mariana Trench - 1 1,033 metres below sea level.

The difference in height between the greatest depth and the highest summit on surface of the earth is thus only 19.9 km. This is very small in relation to the earth's diameter.

CHIEF FEATURES OF THE OCEAN

The ocean basins and land surface are similar. There are submarine ridges, plateaus, canyons, plains and trenches. This is because these zones exist as a result of the interaction between tectonic activities, volcanic, erosional and depositional processes which are active on the surface of the earth. The main relief zones are - Continental shelf, Continental slope, Abyssal plain and Ocean Deeps.

Continental Shelf [most important part of the ocean floor for man]

·        Is the submerged part of land

·        Is adjacent to the coastline,

·        Is not more than 200 metres deep

Ø  Light penetrates in these shallow waters and the submarine vegetation grows

Ø  Fish food planktons are abundant making it the richest fishing grounds

Ø  The high tides are useful for commerce

Ø  The continental shelf in some parts of the world is rich in oil, coal, and sulphur and non-ferrous metals.

o   Undersea oil-fields in the Caspian Sea and the Gulf of Mexico. Off-shore exploration for oil is being done in India as well.

o   Tin mines off the Island of Sumatra.

Continental Slope

·        Is the outer edge of the continental shelf where the slope suddenly steepens at 35 to 61 metres per km

·        One end of the slope connects it with the continental shelf while the other one merges into the ocean floors.

·        The area occupied by continental slope is 8.5% of the total ocean area.

·        The continental slope consists of light continental rocks which overlie the dense rocks of ocean floors. (Hence, deposits of the coast, except some fine mud, do not reach the continental slope.)

Deep ocean floors

·        Deep Ocean Floors occupy two-thirds of the ocean surface.

·        Situated on the base of the continental slope.

·        The depth varies from 3,000 to 6,000 metres.

·        Many long zigzag ridges, plateaus, plains, volcanic summits, etc. exist on the basins.

·        Many mountain tops rise steeply from the ocean floors and emerge out of sea as islands. Such mountain tops are found in Indonesia and in the Pacific Ocean.

The Ocean Deeps

·        These are long deep trenches that are around 30,000 feet deep.

·        Most oceanic trenches are found in the Pacific Oceans. The deepest of which is the Mariana Trench which is about 36,000 feet deep.

·         Their depth is more than the highest peak on land, Mount Everest 29, 028 feet. Other deeps include the Mindanao deep 35,000 feet, Tonga trench 31,000 feet.

FEATURES OF OCEANS AND LANDS

Isostasic balance is the balance between upstanding continents and low lying ocean basins. Land-ocean features can be explained with reference to this isostasy.

Bay

·        A bay is a wide curving indentation in a coastline, usually lying between two headlands. Sometimes a recess occurs in the line of the coast as a result of pounding of water which eats away weak spots or soft rock and creates an inlet of water. This becomes a bay.

·        Sometimes the elliptical hollows may be alternated by hard and weak rocks. These are called cover or mini-bays.

Changes in the level of the sea relative to that of land may have a great effect on both, through the forces of emergence or submergence of land.

o   Bay of Bengal is an example of this isostatic adjustment and erosional forces.

o   Cape Cod Bay on the coast of Massachusetts in the North American continent is an excellent example of the work of long shore drifts of sea as well as isostasic adjustment.

 Man makes the best use of bays by converting them into harbours.

A headland jutting out into the sea is called a cape.

Gulf

Gulf is a deep inlet of the sea almost surrounded by land, with a narrow mouth.

·        Cut into continental masses, gulfs are usually made by subsidence.

·        The currents carrying dense suspensions of mud and sand may also fill deep crevasses in the continental block near the shoreline.

·        The Persian Gulf is an arm of Arabian Sea between Arabia and the Asian mainland. It is connected to the Arabian Sea by the Strait of Hormuz and the Gulf of Oman.

·        Other famous gulfs are Gulf of Mexico, Gulf of Guinea, Gulf of Alaska and Gulf of Aden.

Islands

An island is a tract of land completely surrounded by water.

Small rock outcrops, often, the summits of sea mounts (mountains in the sea) are also called islands.

o   Madagascar Island in the Indian Ocean measures 5, 90,000 square km.

o   Greenland is the world's largest island measuring 21, 75,000 sq. km.

o   New Guinea in South-west Pacific is the second largest island measuring 820,033 sq. km.

There are several factors responsible for formation of islands.

·        Tectonic activity including folding, faulting and volcanoes results in formation of large islands. Some of the islands in the Andaman and Nicobar group of islands are volcanic in origin.

·        Corals, with calcium carbonate skeletons form small islands like Lakshadweep islands

·        Denudation by sea wave forms small islands near sea coasts. The headland projecting into the sea may be separated from the mainland by erosion to form an island.

Strait

A strait is a narrow passage of water connecting two large bodies.

·        The Bering Strait was once a land bridge between Asia and North America. The Bering connects the Arctic Ocean with the Bering Sea and to the North Pacific Ocean Pacific Ocean. Its width is 85 km.

·        The Davis Strait separates Greenland from Baffin Island and links Baffin Bay with the North Atlantic Ocean.

Isthmus

An isthmus is a narrow stretch of land linking two landmasses and separating two water bodies.

·        The Isthmus of Suez joined Africa and Asia. After the construction of the Suez Canal it now joins the Mediterranean Sea and the Red Sea.

·        The Isthmus of Panama separated the Pacific and Atlantic Oceans and North America with South America. Panama Canal links the two oceans.

The oceans serve as a store house of chemical, biological and geological wealth, a means of transportation and communication and as a modifying factor in climatic environment.

Oceans and Food Resources

Oceans abound in plant and animal sea organisms which provide food and other products of value to man.

Man consumes as food

·        Fish, mollusks, crustaceans and many other edible forms of animal life.

·        Seaweeds used for an increasing number of purposes as human and animal food, in cooking and in textile industry.

Sea animals provide

·        Oil, fur, leather, glue, cattle feed

·        Marine plants and animals are used for making curative medicines.

Planktons are floating sea plants upto the depth of 200 m from sea level.

·        Planktons produce food through the process of photosynthesis.

·        Algae and diatoms are the most important members of this community.

·        They serve as food to marine organisms.

Fish form a rich source of food and nutrition to man It is the most abundant and widely used food.

·        For the world as a whole, fish now makes up more than 10 per cent of the total animal protein food that man consumes.

·        Herring, pilchard, sardine, cod, salmon, tuna, mackerel, haddock, constitute the bulk of the world fish catch.

·         Fishing is a well developed industry in many parts of the world. Advanced fishing nations use more efficient methods including trawling, drifting.

 The most important factor about the marine biological resources is that they are

·        Easily available

·        Inexhaustible

 Vitamins and Drug Resources

·        Marine pharmacology is a distinct discipline where marine pharmacologists use marine organisms (plants and animals) for vitamins and medicines to cure different diseases.

·        Marine pharmacologists are busy in investigating physiological, physical and chemical properties of marine organisms like crabs, sea weeds, sea cucumbers, barnacles, horseshoe crabs, sharks, cods, etc.

·        Shark oil and cod liver oil are already in use as energy tonics.

·        Cod liver oil is available in capsule form too.

Oceans and Mineral Resources

Oceans are the storehouses of a large number of useful metallic and non-metallic minerals. Minerals in sea-water include

·        Important minerals-common salt, magnesium and bromine.

·        Other important minerals petroleum, gas, manganese, phosphorite, sulphur, gold, platinum, diamonds, tin, iron, sand and gravel.

·        The main source of various minerals in the sea water is the land. The precipitation that falls on the land carries vast amounts of mineral material to the oceans on its return journey.

 Oceans and Petroleum

·        Petroleum and gas are the most important minerals obtained from the sea, accounting for more than 90 per cent of the total value of minerals obtained from the oceans.

·        Petroleum is found mainly in the continental shelves and slopes and in small ocean basins.

·        In India, the Bombay High is now an important oil source of India. At present, offshore petroleum lies in areas within 150 kilometers off the coasts and depths of 2,000 metres.

 Oceans and Energy

 The energy resources of the oceans come in various forms:

·        Tidal force

·        Energy from ocean temperature differences

·        Geothermal energy

1.    Tides are a source of great energy.

·        This energy is due to the rise and fall of the sea- water due to tide generating forces.

·        The powerful tidal waves release large amounts of energy when they strike against the shore.

·        The piston-like movement of tides can be tapped to run a generator and subsequently to produce electricity.

2.    Energy from ocean temperature differences

·        The principle underlying the generation of power from sea-water is based upon the difference in temperatures of surface and the sub-surface water.

·        The water at the bottom of the ocean is cold and at the surface is warm. The water at the surface of the sea in the tropical region may be 25°C to 30°C, while the deep waters in the same locality are 5°C. This thermal gradient of 25°C is powerful enough to run a generator that would ultimately produce electricity.

·        Floating generators have been designed in recent years in Belgium and Cuba

3.    Geothermal energy means the energy derived from the internal heat of the earth.

 Oceans Transport and Trade

The oceans, covering 71% of earth's surface

·        They provide the most important means of transport to man.

·        They have proved to be an invaluable link among the various nations.

·        Uses: Ocean transport is cheap because the water provides free highways needing less motive power. There are no obstructions such as gradients, which the land and inland water transportation encounter.

·        Obstacles: fog, icebergs, submerged reefs and storms.

Oceans belong to none and can be used by all. Therefore, the oceans as a highway have proved a boon for international trade.

 Oceans and Politics

Defence of the oceans has become equally important for maintaining peace and for use of their resources by the countries adjoining them.

·        Disputes arise between nations due to increasing importance of oceanic resources They differ on the territorial claims of sea-waters and on the ownership of their resources.

·        However, every country having a coastline has its own territorial waters and exclusive economic zone. High seas are to be kept free as common heritage of mankind.

The future uses of the oceans will include

·        Desalination

·        Deep-sea oil exploration and production

·        Deep-sea mining of strategic minerals

·        Production of power from the tides

·        Extraction of substances for vitamins and drugs for curing diseases from marine organisms.

 Oceans are to be checked to conserve rich marine life.

·        Oceans to be kept free from pollution

·        The spilling of oil from large petroleum tankers

·        Heavy concentration of toxic metallic contents

·        Addition of radio-active wastes from ships and nuclear explosions