Unit 1
Ocean and Seas
(Solved Exercise)
2. Write short answer to the following questions:
(i) Define gulf.
A large but narrow part of ocean which invades farther inland is called gulf, i.e., Persian Gulf of Mexico, etc.
(ii) Differentiate between spring and neap tides.
Spring Tides
The combined gravitation of Sun and Moon creates very high tides in the sea. These are called spring tides.
Neap Tides
When the Moon and Sun are perpendicular to each other with reference to the Earth. Gravitation of both bodies counter act each other resulting in the creation of low tides in the seas. These are called neap tides.
(iii) Differentiate between ocean and sea.
Ocean is huge body of salt water on the Earth’s surface whereas sea is the part of ocean partly enclosed by land. OR The largest body of water on the surface of the Earth is called ocean and an adjacent smaller body of water located on the margins of the ocean is called sea.
(iv) What is the difference between strait and isthmus?
Strait
A narrow channel of water which connects two large bodies of water i.e. oceans or seas is called strait i.e. Strait of Gibraltar which connects Atlantic Ocean with Mediterranean Sea.
Isthmus
A narrow strip of land which connects two large masses of land and separates two water bodies is called an isthmus, i.e. Isthmus of Panama connects north and South American continents.
(v) What is meant by ocean current?
Permanent flow of Ocean water in a specific direction (like river flow on land) is called ocean current.
(vi) Give two major threats that oceans are facing now a days.
- Global warming is causing alterations in ocean composition
- Spilling of oil from the ships is polluting the oceans.
(vii) Differentiate between Bay and Gulf.
Gulf
A large but narrow part of ocean which invades farther inland is called gulf, i.e., Persian Gulf of Mexico, etc.
Bay
Contrary to gulf, large and vast part of ocean which invades farther inland is called bay, i.e., Bay of Bengal and Hudson Bay etc.
3. Write detailed answer to the following questions:
(i) Discuss characteristics of some important oceans.
(i) Pacific Ocean
- Pacific Ocean is the largest ocean of the world.
- Its area is about 166 million square kilometres.
- Its average depth is about 4280 metres.
- Pacific Ocean is located between four continents, Asia and Australia in the west, north and South America in the east.
- Panama Canal which links Pacific Ocean with the Atlantic Ocean is among the important trade routes in the world.
(ii) Atlantic Ocean
- Atlantic Ocean is the second largest ocean.
- Its area is about 82 million square kilometres.
- Its average depth is about 3900 metres.
- Atlantic Ocean is also located between four continents, north and South America in the west, Europe and Africa in the east.
- It is also the most important and busiest trade route of the world.
(iii) Indian Ocean
- Indian Ocean is the third largest ocean.
- Its area is about 73 million square kilometres’
- Its average depth is 3900 metres.
- It is located between Africa in the west, Asia on the north, Australia on the east, and Antarctic Ocean in the south.
- It has become an important trade route between western and eastern hemispheres due to the construction of Suez Canal which links Red Sea with the Mediterranean Sea through Indian Ocean.
(ii) Evaluate the importance of oceans.
The importance of oceans can be summarized in following points:
- Oceans have a great potential for wave and tidal power.
- Oceans have vital economic importance due to tourism, particularly island-countries like Sri Lanka.
- Oceans are a source of minerals like oil, gas and salt.
- Oceans are rich source of fishes.
- Oceans are the world highways.
- Transportation of oil, minerals, consumer goods and food are transported through oceans.
(iii) How ocean act as a source of food?
The oceans have always been a source of food for human. But until now only about one percent of mankind’s food comes from the sea and much of it is fish. Oceans have always been an important and reliable source of food.
The importance of seafood in the human diet varies greatly around the world. One of the main services provided by the oceans to human societies is the service of food. So, the utilization of fish and aquaculture resources should be made sustainable in order to safeguard future benefits.
(IV) Explain the role of marine biodiversity on our environment.
Marine biodiversity may be determined as because the variety of life found in the ocean and seas.
The role of marine biodiversity in our environment can be discussed in following points:
- The ocean is one of the main bank/reservoirs of the world’s biodiversity. It constitutes over 90% of the habitable space on the planet and contains some 250,000 known species.
- The ocean, and the life therein, are critical to the healthy functioning of the planet, supplying half of the oxygen we breathe and absorbing annually about 20% of the anthropogenic carbon dioxide (CO2) emitted into the atmosphere.
- The fishery and aquaculture sectors are a source of income for hundreds of millions of people, especially in low-income families.
- It is contributing directly and indirectly in t foot security.
- Marin ecosystem provide many services for coastal communities around the world such as livelihoods, clean water, forest products etc.
(v) What are the causes of ocean currents?
Following are the major causes of current circulation:
(a) Permanent Winds
The most important cause of current circulation are permanent winds. Winds force the ocean water to circulate in their general direction.
(b) Salinity of Oceanic Water
Salinity variation also a causes of the ocean water to circulation. Water of inland seas is more saline than the water of open seas and oceans. So more saline water due to its higher density sinks downwards while less saline water moves upwards. This variation of salinity causes current circulation.
(c) Temperature of the Oceanic Water
Temperature difference is another cause of current circulation. Warmer water of equatorial regions moves upwards, while colder water of polar regions sinks downwards due to greater density.