13. Water (Oceans)

 NCERT Questions:

1. Multiple choice questions:

(i) Identify the element which is not a part of the hydrological cycle.

a) Evaporation

b) Hydration

c) Precipitation

d) Condensation

Ans. b)  Hydration

(ii) The average depth of continental slope varies between.

a) 2 – 20 m.

b) 200 – 2,000 m

c) 20 – 200 m

d) 2000 – 20,000 m

Ans. b) 200 – 2,000 m

(iii)  Which one of the following is not a minor relief feature in the ocean?

a) Sea Mount

b) Atoll

c) Oceanic Deep

d) Guyot

Ans. b) Atoll

(iv) Salinity is expressed as the amount of salt in grams dissolved in seawater per:

a) 10 gram

b) 1000 gram

c) 100 gram

d) 10,000 gram

Ans. b) 1000 gram

 (v) Which one of the following is the smallest ocean?

a) Indian Ocean

b) Arctic Ocean

c) Atlantic Ocean

d) Pacific Ocean

Ans. b)  Arctic Ocean

2. Answer the following questions in about 30 words.

(i)  Why do you call the Earth the blue planet?

Ans. Water is an essential component of all life forms that exist over the surface of the earth. The creatures on the Earth are lucky that it is a water planet; otherwise we all would have no existence. Water is a rare commodity in our solar system. There is no water on the sun or anywhere else in the solar system. The earth, fortunately, has an abandoned supply of water on its surface. Hence, our planet is called the Blue Planet.

(ii) What is a continental margin?

Ans. The continental margin is the extended portion of each continent occupied by relatively shallow seas and gulfs. It is the shallowest part of the ocean, showing an average gradient of one degree or even less. The shelf typically ends at a very steep slope called the shelf break. The width of the continental shelves varies from one ocean to another. The average width of continental shelves is about 80 km. The shells are almost absent or very narrow along some of the margins, like the coast of Chile, the west coast of Sumatra etc.

(iii) List out the deepest trenches of various oceans.

Ans. As many as 57 deeps have been explored so far. Of which 32 are in the Pacific Ocean, 19 in the Atlantic Ocean, and 6 in the Indian Ocean. Some important trenches of the world are as follows:

a) Mariana Trench: It is the world’s deepest trench. It lies in Pacific Ocean. It is 11,034 km below the ocean.

b) Puritonko Trench: It is the deepest trench in Atlantic Ocean.

c) Sunda Trench: It is the deepest trench in Indian Ocean.

(iv) What is a thermocline?

Ans. The temperature depth profile for the ocean water shows how the temperature decreases with the increasing depth. The profile shows a boundary region between the surface water of the ocean and the deeper layers. The boundary usually begins around 100 to 400 metres below the sea surface and extends several hundred of meters downward. This boundary region from where there is a rapid decrease of temperature is called the thermocline.

(v) When you move into the ocean, what thermal layers would you encounter? Why the temperature varies with depth?

Ans. The temperature structure of oceans over middle and low latitude can be described as a 3 layer system from surface to the bottom:

a) The first layer represents the top layer of warm oceanic water and it is about 500 m thick with temperatures ranging between 20˚ and 25˚ C. This layer within the tropical region is present throughout the year, but in mid-latitudes it develops only during summer.

b) The second layer, called the thermocline layer, lies below the first layer and is characterised by rapid decrease in temperature with increasing depth. The thermocline is 500 to 1000 metre thick.

c) The 3rd layer is very cold and extends up to the deep ocean floor. In the Arctic and Antarctic circles, the surface water temperatures are close to 0˚ C and so that temperature variation within the depth is very slight.

(vi) What is salinity of seawater?

Ans. Salinity is a term used to define the total content of dissolved salts in seawater. It is calculated as the amount of salt (in gram) dissolved in 1000gm (1 kg) of sea water. It is usually expressed as (parts per 1000) ‰ or ppt. Salinity is an important property of seawater. Salinity of 24.7% has been considered as the upper limit to demarcate brackish water. Salinity changes with depth, but the way it changes depends upon the location of the sea. Salinity at the surface increases by the loss of water to ice or evaporation or decreases by the input of fresh water, such as from the rivers. Salinity at depth is very much fixed because there is no way that water is lost or the salt is added.

3. Answer the following questions in about 150 words:

(i) How are various elements of the hydrological cycle interrelated?

Ans. Water is a cyclic resource. It can be used and reused. Water also undergoes a cycle from atmosphere, land surface and subsurface, and the organisms. About 71% of the planetary water is found in the oceans. The remaining is held as water, freshwater in glaciers and ice caps, groundwater sources, lakes, soil moisture atmosphere streams and within life. Nearly 59% of water that falls on land returns to the atmosphere through evaporation from over the oceans as well as from other places. The remainder runs off on the surface, infiltrates into the ground, or a part of it becomes glacier. The renewal water of the earth is constant, while the demand is increasing tremendously. This leads to the water crisis in different parts of the world, spatially and temporarily. The pollution of river water has further aggravated the crisis.

(ii) Examine the factors that influence the temperature distribution of the ocean.

Ans. The factors which affect the distribution of temperature of ocean water are:

a) Latitude: The temperature of surface water decreases from the equator towards the poles because the amount of insolation decreases pole word. The enclosed seas in the low latitudes record relatively higher temperature than the open seas; whereas the enclosed seas in the high latitudes have lower temperature than the open seas.

b) Unequal distribution of land and water: The Ocean in the northern hemisphere receives more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.

c) Prevailing wind: The winds blowing from the land towards the oceans drive warm surface water away from the coast, resulting in the upwelling of cold water from below. As a result, there is longitudinal variation in the temperature. On the contrary, the onshore winds spill up warm water near the coast and this raises the temperature.

d) Ocean currents: Warm ocean currents raise the temperature in cold areas, while the cold currents decrease the temperature in warm ocean areas. Eg. Gulf Stream raises the temperature near the eastern coast of North America and the West Coast of Europe. While the Labrador cold Current lower the temperature near the North East coast of North America.

e) Salinity: Saline water absorbs more heat and its temperature rises much higher than fresh water.

All these factors influence the temperature of the ocean currents locally.

Question Bank:

1. The smallest ocean is the:

a) Indian Ocean

b) Atlantic Ocean

c) Arctic question

d) Pacific Ocean

Ans. c) Arctic Ocean

Arctic Ocean is the smallest of the 4 oceans. It lies almost entirely above the Arctic Circle (66 ½˚ N). Nearly surrounded by land its only outlets are the barriers straight between Alaska and Russia, Davis Strait between Greenland and Canada and Denmark Strait and the Norwegian Sea between Greenland and Europe. The Arctic Ocean has an area of 14,090,000 km² and an average depth of, 3,658 metre off the continental shelf. The Arctic Ocean has the widest continental shelf of all the oceans.

2. Continental shelf is the:

a) Deepest part of the ocean

b) Widest part of the ocean

c) Longest part of the ocean

d) Shallowest part of the ocean

Ans. d) Shallowest part of the ocean

It has an average gradient of 1˚ or even less. It is the shallowest part of the ocean.

3. More than 10,000 seamounts and guyots exist in the:

a) Indian Ocean

b) Atlantic Ocean

c) Arctic Ocean

d) Pacific Ocean

Ans. d) Pacific Ocean

Guyots are flat topped seamount. It is estimated that more than 10,000 seamounts and guyots exist in the Pacific Ocean alone.

4. A mid ocean ridges is an underwater mountain system formed by:

a) Plate tectonics

b) Earthquake

c) Ocean currents

d) Submarine landslides

Ans. a) Plate tectonics

Mid Ocean Ridge is an underwater mountain system formed by plate tectonics and consequently is termed as divergent plate boundary.

5. Gulf of stream is an important current of Atlantic Ocean. It is a:

a) Cold current

b) Warm current

c) Important sea root

d) Important fishing ground

Ans. b) Warm current

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic drift, is a powerful, warm, and swift Atlantic Ocean current. It originates in the Gulf of Mexico, axis through the state of Florida, and follows the eastern coastline of the United States and Newfoundland before crossing the Atlantic Ocean.

6. The salinity increases with depth and there is a distinct zone called:

a) Isohaline

b) Halocline

c) Salocline

d) Thermocline

Ans. b) Halocline

Salinity generally, increases with depth and there is a distinct zone called the halocline, where salinity increases sharply. Other factors being constant, increasing salinity of sea water causes its density to increase.

7. A major portion of sea level is found at:

a) 10 – 12 kilometres below sea level

b) 6 – 9 kilometres below sea level

c) 3 – 6 kilometres below sea level

d) 1 – 2 kilometres below sea level

Ans.  c) 3 to 6 km below sea level

3 to 6 km below sea level ocean floor has varied and complex features.

8. Along the coast salinity is:

a) Lowered

b) Increased

c) Stable

d) Unaffected

Ans. a) Lowered

Along coast water has a lower salinity due to the vast amount of fresh water runoff pouring into the sea from rivers and streams.

9. The largest shelf is the:

a) Cost of Chile

b) Siberian shelf in the Arctic Ocean

c) West Coast of Sumatra

d) South China Sea

Ans. b) Siberian shelf in Arctic Ocean

Continental shelves surround all the continents. They extend from the mean level of low tide to the continental slope, the part of the seafloor that descends from the edge of a continental shelf to the ocean bottom.

10. An ocean current is flow of water:

a) Only in small water bodies

b) In a definite direction up to a considerable distance

c) Not affected by winds

d) In any direction to any distance

Ans. b) In a definite direction up to a considerable distance

The water at the ocean surface is moved primarily by winds. Large scales winds move in specific directions because they are affected by earth’s spin and the Coriolis Effect.  Because earth spins constantly, the winds blow in predictable direction. The winds are able to move the top 400 metres of the ocean in a predictable pattern too.

11. Which is the most saline lake in the world?

a) Lake Van

b) Don Jaun Pond

c) Great Lakes

d) Lake Ocombo

Ans. b) Don Jaun Pond

The most saline water body in the world is the Don Jaun Pond, located in Antarctica. The Don Jaun Pond has a salinity level of 44%.

12. The total volume of water found below the thermocline in the deep ocean is:

a) 5%

b) 45%

c) 60%

d) 90%

Ans. d) 90%

The boundary region from where there is a rapid decrease of temperature is called a thermocline. About 90% of the total volume of water is found below the thermocline in the deep ocean. In these zone temperature approaches 0˚ C.

13. The flattest and smoothest regions of the world are:

a) Trench

b) Atoll

c) Guyots

d) Sea Plain

Ans. Sea Plain

Sea Plain has a slope of less than one foot of elevation difference for each 1000 feet of distance. The lack of features is due to a thick blanket of sediment that covers most of the surface.

14. After Arctic Circle salinity decreases from:

a) 40 ‰to 39 ‰

b) 38 ‰ to 35 ‰

c) 35 ‰to 31 ‰

d) 30 ‰to 25 ‰

Ans. 35 ‰ to 31 ‰ it is due to the influx of melted water from the Arctic region.

15. The maximum temperature of the ocean is always at there:

a) Bank

b) Surface

c) Bed

d) Centre

Ans. b) Surface

The surface directly receives heat from the sun and this heat is transmitted to the lower section of the oceans through the process of convection.

16. Factors affecting ocean salinity is:

a) Coastal regions

b) Atmosphere

c) Plateau regions

d) Hill regions

Ans. a) Coastal regions

Factors affecting ocean salinity is coastal regions, wind, ocean currents, evaporation and precipitation.

17. Increasing salinity of seawater causes its density to:

a) Decrease

b) Fluctuate

c) Increase

d) Constant

Ans. c) Increase

The density of an object is the rotation of its mass to its volume. In sea water, the main dissolved constituents include sodium and chloride. Since, salt ions are heavier than water molecules, Sea water gets dense.

18. Europe is one of the most important fishing grounds because of their intermixing of:

a) Alaska current and Kuroshio current

b) Brazil current and Labrador current

c) Gulf Stream and Labrador current

d) Brazilian current and Falkland current

Ans. c) Gulf Stream and Labrador Current;

Europe is one of the most important fishing grounds because of the intermixing of Gulf Stream and Labrador Current.

19. A characteristic of continental shelves is that:

a) It ends at very gentle slope

b) It is the deepest part of the oceans

c) It has clay and silt

d) Sites of well-developed submarine canyons

Ans. a) It ends at very gentle slope

A characteristic of continental shelves is that it ends at very gentle slope. It is very shallow part of the ocean with gradient of 1˚ or even less.

20. Which of these oceans touches the shores of Asia on one side and that of North America on the other side?

a) Indian Ocean

b) Pacific Ocean

c) Atlantic Ocean

d) Antarctic Ocean

Ans. b) Pacific Ocean

Asia lies to western side of Pacific Ocean while America lies to the east of the Pacific Ocean.

21. Along the coasts salinity is:

a) Lowered

b) Increased

c) Stable

d) Unaffected

Ans. a) Lowered

Surface salinity is lowered in coastal regions because of the inflow of fresh water from rivers.

22. The coral reefs are a major characteristic of:

a) Indian Ocean

b) Pacific Ocean

c) Atlantic Ocean

d) Mediterranean Sea

Ans. b) Pacific Ocean

Pacific Ocean has the most coral reefs amongst all the oceans. There are about twice as many coral species in Pacific Ocean reefs as in Atlantic Ocean reefs.

23. Ocean current is:

a) Flow of water

b) Flow of water in definite direction up to a considerable distance

c) Flow of water in the oceans

d) Flow of water in rivers

Ans. b) Flow of water in definite direction up to a considerable distance

Ocean current is flow of water in definite direction up to a considerable distance.

24. Salinity refers to:

a) Total amount of sediments in the water

b) Total amount of impurities present in the water

c) Total amount of salt present in the water

d) Total amount of humidity

Ans. c) Total amount of salt present in the water

Salinity refers to the total amount of salt present in the water.

25. The average surface temperature of the ocean is

a) 23 ˚C

b) 27 ˚C

c) 25 ˚C

d) 15 ˚C

Ans. b) 27 ˚C

The average temperature of surface water of the ocean is above 27 ˚C and it gradually decreases from the equator towards the poles.

26. Minor relief feature of the ocean is:

a) Seamount

b) Ocean deep

c) Deep sea plain

d) Continental shelf

Ans. a) Seamount

A minor relief feature of the oceans is seamount.

27. The boundary in the water from where rapid decrease of temperature begins is called:

a) Thermal divide

b) Thermodynamics

c) Thermocline

d) Thermohaline

Ans. c) Thermocline

About 90% of the total volume of water is found below the thermocline in the deep ocean. In this zone, temperature approaches 0˚ C.

28. What is an atoll?

a) An island

b) A rock

c) A coral island with a narrow lake in the center

d) A coral reef

Ans. A coral island with a narrow lake in the center

Atolls are coral islands found in the tropical oceans consisting of coral reefs surrounding a central depression.

29. There are ____ deeps that have been discovered in the oceans:

a) 59

b) 57

c) 56

d) 52

Ans. 57

Ocean deeps are the deepest part of the ocean.

30. Continental shelves are a good source of:

a) Pearls

b) Gold

c) Fossil Fuels

d) Diamond

Ans. c) Fossil fuels

The continental shelf is the extended margin of each continent occupied by relatively shallow seas and curves. Massive sedimentary deposits received over a long time by the continental shelves, become the source of fossil fuels.

31. Trenches are a part of:

a) Ocean floor

b) Land surface

c) Land surface atmosphere

d) Desert areas

Ans. a) Ocean floor

Trenches are part of ocean floor.

32. The factors affecting the distribution of temperature of ocean water is:

a) Evaporation

b) Precipitation

c) Hydration

d) Ocean currents

Ans. Ocean currents; the factor affecting the distribution of temperature of ocean water is latitude, unequal distribution of land and water, prevailing winds, ocean currents.

33. Which one of the following is the smallest ocean?

a) Indian Ocean

b) Atlantic Ocean

c) Arctic Question

d) Pacific Ocean

Ans. Arctic Ocean is the smallest ocean in the world. It has an area of about 5.4 billion square miles.

34. The salinity increases with depth and there is a distinct zone called:

a) Isohaline

b) Halocline

c) Salocline

d) Salinity

Ans. b) Halocline

The salinity increases with depth and there is a distinct zone called Halocline.

35. An important factor affecting the salinity of the ocean water is:

a) Evaporation and precipitation rate

b) Influx of freshwater in the coastal regions

c) Ocean currents and winds

d) Temperature of the ocean waters

Ans. b) Influx of freshwater in the coastal regions

An important factor affecting the salinity of the ocean water is Influx of freshwater in the coastal regions from the rivers.

36. Salinity refers to the total amount of:

a) Sediments in the water

b) Impurities present in the water

c) Salt present in the water

d) Heat present in the water

Ans. c) Salt present in the water

Salinity is the saltiness or dissolved salt content of the body of water. It is a general term that is used to describe the levels of different salts, such as sodium chloride, magnesium and calcium sulphate and bicarbonates.

37. Highest saline lake in the Turkey is:

a) Lake van

b) Great Salt Lake

c) Great lake

d) Lake Ocombo

Ans. a) Lake Van

Lake Van is in Turkey and its salinity is 330‰.

38. The deepest hypersaline lake in the world is:

a) Black Sea

b) Baltic Sea

c) Red Sea

d) Dead Sea

Ans. d) Dead Sea

Salinity in Dead Sea is 238‰. The Dead Sea is 306 metre deep, the deepest hyper saline lake in the world with 34.2‰ salinity in 2011

39. Largest shelf – the Siberian shelf is:

a) In Arctic Circle

b) In arte K ocean in the Indian Ocean

c) In the Pacific Ocean

d) In the Atlantic Ocean

Ans. a) In the Arctic Ocean

The largest shelf the Siberian shelf is in the Arctic Ocean it stretches to 1500 kilometres in width. The width of the continental shelf varies considerably.  It is not uncommon for an area to have virtually no shelf at all.

40. Gulf Stream originates in the ______.

a) Atlantic Ocean

b) Pacific Ocean

c) Indian Ocean

d) Arctic Ocean

Ans. a) Atlantic Ocean;

Gulf Stream is a warm ocean current of the northern Atlantic Ocean to the eastern coast of North America. It originates in the Gulf of Mexico and, as the Florida current passes through the Straits of Florida and then flows northward along the South East coast of the United States. North of Cape Hatteras the Gulf Stream veers north-east word into the Atlantic Ocean, where it splits to form the North Atlantic drift and the Canary current.

41. Gulf Stream is an important _______ current.

a) Cool current

b) Warm current

c) Important sea route

d) Surface current

Ans. Warm current

Gulf Stream is an important warm current of Atlantic Ocean.

42. The average depth of continental slope varies between:

a) 2 to 20 metres

b) 200 to 3000 metres

c) 20 to 200 metre

d) 2000 to 20,000 metre

Ans. 200 to 3000 metres

Gradient of the slope region varies between 2˚ and 5˚. The depth of the slope region varies between 200 to 3000 metres. The slope boundary indicates the end of the continents. Canyons and trenches are observed in this region.

43. Total percentage of water in ice caps is:

a) 25%

b) 25%

c) 05%

d) 05%

Ans. c) 2.05%

The highest case is in oceans 97.25% followed by the ice caps i.e. 2.05%.

44. Identify the element which is not a part of the hydrological cycle:

a) Evaporation

b) Hydration

c) Precipitation

d) Condensation

Ans. b) Hydration

45. The average depth of continental slope varies between:

a) 2 to 20 metre

b) 200 to 2000 metre

c) 20 to 200 metre

d) 2000 to 20,000 metre

Ans. 200 to 2000 metre

46. Which one of the following is not a minor relief feature in the oceans?

a) Atoll

b) Seamount

c) Oceanic deep

d) Guyot

Ans. c) Oceanic deep or trenches

These are the deepest part of the oceans. The trenches are relatively steep sided, narrow basins.

47. Salinity is expressed as the amount of salt in grams dissolved in sea water per

a) 10 gram

b) 1000 gram

c) 100 gram

d) 10,000 gram

Ans. b) 1000 grams

48. Which one of the following is the smallest ocean?

a) Indian Ocean

b) Arctic Ocean

c) Atlantic Ocean

d) Pacific Ocean

Ans. b) Arctic Ocean

49. The circulation of water in hydrosphere is called:

a) Water cycle

b) Hydrological cycle

c) Life cycle

d) Atmospheric cycle

Ans. b) Hydrological cycle

The circulation of water in different forms i.e., the liquid solid and gaseous state is called hydrological cycle.

Short answer type questions:

1. Name the two fishing banks of the world.

Ans. The two major fishing banks of the world are:

a) The Dogger Bank North Sea

b) The Grand Bank Atlantic Ocean

2. Name the largest Barrier Reef of the world. Where is it located?

Ans. The largest Barrier Reef of the world is the Great Barrier Reef, which is located at the East Coast of Australia.

3. What is continuous evapotranspiration?

Ans. Evapotranspiration is the combined form of evaporation and plant transpiration to atmosphere. It can be expressed in millimetres per unit of time

4. What is hydrography?

Ans. Hydrography is the investigation of seas and other bodies of water including charting ocean surface, study of tides, currents etc.

5. What do you understand by the term atoll?

Ans. An atoll is a ring shaped coral reef, island, or series of eyelets. An atoll surrounds a body off water called a lagoon. Sometimes, atolls and lagoons protect a central island. Channels between islets connect a lagoon to the open ocean or sea. These are low islands found in the tropical oceans consisting of coral reefs surrounding a central depression. It may be a part of the sea (lagoon), or sometimes form enclosing a body or fresh or highly saline water.

6. What do you understand by the term reef?

Ans. Reef is a line of rocks in the tidal zone off a coast submerged in high water but partially uncovered in shallow water.

7. What is sea mounts or guyots?

Ans. Guyots are flat top sea mount. It is estimated that more than 10,000 sea mounts and guyots exist in the Pacific Ocean alone.

8. What is submarine canyon?

Ans. The submarine canyons are the deep gorges of the ocean bottom. They are sometimes found cutting across the continental shelves and slope, often extending from the mouths of large rivers. The Hudson Canyon is the best known submarine canyon in the world.

9. What is a submarine trench?

Ans. Submarine trench is a long, narrow and steep sided depression off the ocean bottom. It is generally some 3 to 5 km deeper than the surrounding ocean floor. It usually occurs at the base of continental slopes and along island arcs and is associated with active volcanoes and strong earthquakes.

10. What is continental rise?

Ans. The continental rise is an underwater feature found between the continental slope and the abyssal plane. The environment in the continental rise is quite unique, and many oceanographers study it extensively in the hopes of learning more about the ocean and geologic history.

11. What is continental slope?

Ans. Continental slope is the area which is extended from the continental shelf towards the bottom of the ocean. The gradient of the slope region varies between 2˚ to 5˚. The slope boundary indicates the end of the continents.

12. What is continental shelf?

Ans. Continental shelf is the extended margin of each continent occupied by relatively shallow seas and gulf. It is the shallowest part of the ocean. The width of the continental shelves varies from one ocean to another.

13. What are the various components of water cycle?

Ans. The various components of water cycle are as follows:

a) Water storage in the oceans

b) Water in the atmosphere

c) Water storage in ice and snow

d) Surface runoff

e) Groundwater storage

14. Name the major oceanic water bodies.

Ans. The major oceanic water bodies are as follows:

a) Pacific Ocean

b) Atlantic ocean

c) Indian Ocean

d) Arctic Ocean

15. Write a short note on ocean basin.

Ans. Ocean basin is an extensive region of the basin floor, generally lying in a depth range of 2500 to 6000 metres. It covers about 76.2% of the ocean areas. The ocean basin floor contains 3 types of features abyssal plains, oceanic rise and seamounts.

16. Write a note on the role of oceans in hydrological cycle.

Ans. Hydrological cycle is one of the most fundamental cycles that maintain life on the earth. Life on land sustains because of the transfer of water from the great ocean body to the land through the atmosphere. The hydrological cycle depends basically on the inter relationship between the circulation of ocean waters and that of the atmosphere.

17. Name the deepest trench of oceans.

Ans. Mariana Trench in Pacific Ocean is the deepest trench of the world. Its maximum depth is off about 11,033 meters.

18. Write a short note on the abyssal plain.

Ans. These are extensive plains that lie between the continental margins and mid-oceanic ridges. The abyssal plains are the areas where the continental sediments that move beyond the margins get deposited.

19. What are the various processes by which the water moves through the water cycle?

Ans. The multiple processes under which the water cycle moves are:

a) Evaporation and transpiration

b) Condensation

c) Precipitation

d) Infiltration

e) Run off

f) Subsurface runoff

20. What is salinity of sea water?

Ans. Salinity is the term used to define the total content of dissolved salts in sea water. It is calculated as the amount of salt (in grams) dissolved in 1000 gm (1 kg) of sea water. It is usually expressed as parts per 1000 (‰) or ppt.

21. Distinguish between the submarine trenches and the Canyon.

Ans.

22. What is continental margin?

Ans. Continental margin is the term which is commonly used for the transition between continental shores and deep sea basins. They include continental shelf, continental slope, continental rise and deep oceanic trenches.

23. Why do we call the earth blue planet?

Ans. Our planet earth is called the blue planet because of the availability of water in abundance. The water body covers more than 70% of the surface of the earth and the rest of the surface is covered with land area. If we try to look at the hemisphere wise distribution of sea water, it is seen that the northern hemisphere contains 43% of water and the southern hemisphere contains 57% of the total sea water.

24. What is thermocline?

Ans. Thermocline is the layer of the ocean after where there is a rapid decrease of temperature in the ocean water. The boundary region after which the rapid decrease of temperature is seen is called thermocline. The thermocline is 500 to 1000 metre thick.

25. How are various elements of the hydrological cycle interrelated?

Ans. Hydrological cycle is the cyclic movement of water containing basic continuous process like evaporation, condensation, precipitation and runoff.

26. What is a continental margin?

Ans. Continental margin is also called as continental shelf. It is called as margin because it is the extended margin of each continent occupied by relatively shallow seas and gulfs.

27. What is salinity of ocean water?

Ans. Salinity is the term used to define the total content of dissolved salts in sea water. It is calculated as the amount of salt in grams dissolved in 1000 grams or 1 kg of seawater. It is usually expressed as parts per 1000 (‰) salinity. It is an important property of sea water. All waters in nature, weather rain water or ocean water, contain dissolved mineral salts.

28. Write a note on the mid oceanic ridge?

Ans. Mid-Oceanic ridge is a great submarine mountain chain which is extended from the north of the Atlantic to the South of the Atlantic Ocean. The total length of the range is 64,000 kilometres and it also passes through the Indian Ocean towards the Australia and Antarctica and enters into the South Pacific Ocean.  On an average the ridge has a ranging between 2000 to 24,000 kilometres. There are various abyssal plains in the mid oceanic ridge.

29. What is a thermocline?

Ans. Thermocline is a boundary region from where there is a rapid decrease of temperature of the ocean water. About 90% of the total volume of water is found below the thermocline in the deep ocean. It is also the second layer of ocean water from surface to the bottom.

30. Examine the factors that influence the temperature distribution of the oceans?

Ans. The factors which affect the distribution of temperature of ocean water are:

Latitude the temperature of surface water decreases from the equator towards the poles because the amount of insolation decreases pole word.

Unequal distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.

Prevailing winds: The winds blowing from the land towards the ocean drive warm surface water away from the coast resulting in the upwelling of cold water from below. It results into the longitudinal variation in the temperature. Contrary to this the onshore winds pile up warm water near the coast and this raises the temperature.

Ocean currents: Warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas.

31. Define salinity. What are the factors that affect the distribution of salinity in the oceans?

Ans. Salinity is the term used to define the total content of dissolved salts in seawater. It is estimated that one cubic kilometre of sea water contains 41,000,000 tonnes of salt. The average salinity in sea water is about 35 parts per 1000.

Factors affecting salinity:

a) Availability of freshwater: Freshwater comes from river and the melting of snow. The addition of fresh water leads to the decrease in percentage of salinity in the ocean water.

b) Evaporation: Due to evaporation, fresh water of the water body is lost and the remaining sediments enhance the salinity of the water.

c) Ocean currents: The cold ocean currents which are generated because of the melting of the snow at the poles carry fresh water and flow towards the equator and degrade the amount of salinity at the tropical areas.

Distribution of salinity in the sea water: The distribution of salinity in the sea water can be defined in two ways:

i) Horizontal distribution

ii) Vertical distribution

The horizontal distribution of salinity in ocean can be divided into the following categories.

i) Horizontal distribution

a) Salinity in the open seas: it is determined by the various factors such as the currents etc. The salinity is highest in the tropics.

b) Salinity of partially enclosed sea: Partially enclosed sea like the Mediterranean Sea, Black Sea, Baltic Sea have comparatively high amount of salinity.

c) Salinity in the enclosed sea: The enclosed seas have highest amount of salinity. No river or water body merge into these seas so it is the main reason for the high amount of salinity in these areas.

ii) Vertical distribution

The vertical distribution of the salinity in the ocean can be determined by depth. With the increase in depth, the amount of salinity increases, so the addition of fresh water or the high amount of evaporation does not affect the vertical distribution of salinity.

32. What are the factors that influence temperature distribution of the ocean floor?

Ans. Ocean temperature is the most important factor which influences various movements of the ocean current. The major factors which control the ocean temperature are as follows:

Latitudes: Latitudes are among the few major factors that control the temperature difference in the oceans. The temperature of the surface water decreases from equator towards the poles because the Sun’s rays become more and more slanting towards the poles and thus the amount of insolation decreases towards the poles.

Uneven distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.

Prevailing winds: The winds blowing from land towards the ocean drive surface water away from the coast resulting into up-welling of cold bottom water from below.

Ocean currents: The warm ocean currents keep up the temperature in cold areas while the cold ocean current cool down the temperature in warmer areas. So the ocean currents play an important role in terms of ocean temperature.

Other reasons:  Local weather conditions also play an important role in the ocean temperature like local cyclones etc.

33. Distinguish between the features of the Pacific Ocean and the Indian Ocean.

Ans. The bottom relief of the Pacific and Indian Ocean are not similar, though the basic characteristics of these oceans are the same but still there are enough differences. The difference between the Pacific and the Indian Ocean can be explained as follows:

34. Distinguish between the continental shelf and the continental slope.

Ans. The continental shelf and the continental slope are the areas which are very close to each other. The differences between the continental shelf and the continental slope can be seen as follows:

35. Distinguish between seamount and guyots.

Ans.

36. What is the average temperature of the ocean surface water? Explain the distribution of temperature in the ocean water.

Ans. The temperature of ocean water varies from place to place. The average temperature of the ocean surface waters is about 17 ˚C (62.6 ˚ Fahrenheit).

Distribution of ocean temperature: The distribution of temperature in the oceans can be categorised into 2 ways:

a) Horizontal distribution

b) Vertical distribution

Horizontal distribution of temperature: The horizontal distribution of temperature is the amount of insolation received. The areas which are closer to the equator receive more insolation instead of the areas which are closer to the poles. The decrease in the temperature is of 0.5 degree per latitude till the poles.

The average temperature of the entire ocean is 17.2˚ Celsius. The average annual temperature for the northern hemisphere is 19.4˚ Celsius and for the southern hemisphere it is 6.1˚ Celsius.

Vertical distribution of temperature: In the oceans vertical distribution of temperature is more important phenomena in spite of the horizontal distribution of temperature. The temperature in the polar-regions remains low while the middle latitude and the low latitude regions have high variation in the temperature of ocean water.

Vertical temperature distribution can be described in 3 layers structure of the temperature in the oceans.

First layer: This layer within the tropics is present throughout the year but in mid-latitudes it develops only during summer. This is the warm layer which is 20˚ C to 25˚ C warm.

Second layer: This is known as the thermocline layer which is just below the first layer. The rapid decrease in temperature with the increase in depth is the major characteristic of this layer.

Third layer: This layer is very cold and extends up to the deep ocean floor. Most of the ocean water is contained in this layer.

37. Describe the bottom relief features of the ocean floor.

The ocean floor has variety of features related to the topography of the ocean bottom. Its vast extended landforms are fragmented in the ocean bottom. The geographers have divided the oceanic part of the earth into 4 oceans, namely the Pacific Ocean, the Atlantic Ocean, the Indian Ocean and the Arctic Ocean. The various seas bays gulfs and other inlets are part of these four large oceans.

Classification of ocean floor:

Broadly we can divide the ocean floor into 4 major divisions

a) The continental shelf

b) The continental slope

c) The deep sea plains

d) The oceanic deeps

a) The continental shelf: The continental shelf is slightly inclined, inundated zone which structurally forms the border of the continent. It has a gentle slope with the gradient of one degree or even less and its maximum depth is normally 200 metres. It covers about 7.6% in the world’s ocean.

b) The continental slope: At the edge of the continental shelf, the sea ward slope becomes steep all of a sudden. This position with steep slope is known as continental slope. The gradient of the slope varies from 2˚ to 5˚. It extends to a depth of about 3000 meters.

c) The deep sea plain: The deep sea planes are also known as the abyssal planes. The gradient of these planes are less than one degree. Their depth varies from 3000 to 6000 metres. These planes cover 40% of the total ocean floor.

d) Oceanic deeps or trenches: A trench is a long, narrow and steep sided depression on the ocean floor. Trenches are deepest part of the oceans with the usual depth of 6000 metres. So far 57 trenches have been found, out of which 32 are in Pacific Ocean. 19 in the Atlantic Ocean and 6 in the Indian Ocean. They occupy 1.2% area of the oceans.

e) Other features: In this category other minor bottom relief features are included they are:

i) Mid oceanic ridges

ii) Seamount

iii) Submarine canyons

iv) Atolls

v) Guyots

38. List out the deepest trenches of various oceans?

Ans. Various points that mark deepest points of oceans are:

Mariana Trench: better known as the deepest point on earth surface this trench lies in Pacific Ocean at Challenger Deep

Tonga Trench

Kuril Kamchatka Trench

Philippine Trench

Kermadec Trench

Puerto Rico Trench

South Sandwich trench

Ramanche trench

39. When you move into the ocean what thermal layers would you encounter? Why the temperature varies with depth?

Ans. The temperature structure of ocean water can be described as a three layer system from surface to the bottom:

The first layer represents the top layer of warm oceanic water and it is about 500 metre thick with temperatures ranging between 20˚ to 25˚ C.

The second layer called the thermocline layer is a boundary region from where there is a rapid decrease of temperature of the ocean water. The thermocline is 500 to 1000 metre thick. About 90% of the total volume of water is found below the thermocline in the deep ocean.

The third layer is very cold and extends up to the deep ocean floor.

40. Components of hydrological cycle:

Ans.

Runoff: It is the water flowing over the land making its way towards rivers lakes oceans etc.

Precipitation: It is the fall of moisture from atmosphere to the Earth’s surface in the form of rain hail snow sleet glaze drizzle snowflakes etc.

Evaporation: It is the conversion of natural liquids like water into gaseous form like water vapour

Condensation: It is the conversion of water vapour or the gas to a liquid.

Transpiration: It is evaporation taking place from any plant or greenery.  Example: water droplet on leave getting evaporated into atmosphere.

Evapotranspiration: It is the combination of evaporation and transpiration.

Infiltration: It is a process of filtration of water to the inner layers of soil based on its structure and nature.

Water cycle: Process of hydrological cycle starts at oceans. Water in oceans gets evaporated due to heat energy provided by sun and forms water vapour. This water vapour moves upward to higher altitudes forming clouds. Most of the clouds condense and precipitate in the form of rain, hail, snow, sleet. Some part of clouds move towards the land by winds. Precipitation causes the clouds to fall in form of water or snow on to the ground and even then some part of it evaporates back to atmosphere. Portion of water reaches the ground and enters the Earth’s surface infiltrating various layers of soil and enriching the moisture content as well as water table. Trees and plants send a portion of water from earth surface back to atmosphere through the process of transpiration. Once water percolates and infiltrates the Earth’s surface, run off is formed over the land, flowing through the contours of land heading towards rivers and lakes and finally joins into oceans.  Some amount of water is retained underground in the form of ground table storage. This cyclic process continues and has been going on for billions of years on earth.