Q 1. Choose the correct option :
(a) In which ocean does the Labrador current flow?
(i) Pacific
(ii) South Atlantic
(iii) North Atlantic
(iv) Indian
(b) Which current out of the following flows in the Indian Ocean?
(i) East Australian Current
(ii) Peru current
(iii) South Polar current
(iv) Somali current
(c) Which factor out of the following does not affect the region along the coast?
(i) Precipitation
(ii) Temperature
(iii) Land breezes
(iv) Salinity
(d) Which of the following occurs in the area where the cold and warm currents meet?
(i) High temperature
(ii) Snow
(iii) Low temperature
(iv) Thick fog
(e) Which of these following currents flows from the northern polar region upto Antarctica?
(i) Warm Ocean currents
(ii) Surface Ocean currents
(iii) Cold Ocean currents
(iv) Deep Ocean currents
Q 2. Examine the given statements and correct the wrong ones.
(a) Ocean currents give specific direction and velocity to the water.
Ans. Correct.
(b) The deep ocean currents flow with high velocity.
Ans. Incorrect. The deep ocean currents flow with low velocity.
(c) Generally, surface ocean currents are formed in the equatorial regions.
Ans. Incorrect. Surface ocean currents move from equator to poles and vice versa.
(d) Ocean currents hold great importance for human life.
Ans. Correct.
(e) The movement of icebergs is not dangerous for water transport.
Ans. Incorrect. The movement of icebergs is dangerous for water transport as it comes along marine routes.
(f) Water becomes warm near Brazil due to ocean currents. On the other hand, it becomes cold near African coast.
Ans. Correct.
Q 3. Explain the effect of –
(a) Warm ocean currents on climate
Ans. (i) In cold regions where warm ocean currents flow, climate becomes warmer. (ii) In some regions, the amount of precipitation increases. For example, the warm ocean currents flowing near Western Europe, Southern Alaska, and Japanese coast, reduce the intensity of the winters there and make them warmer. (iii) As a result, these ports do not freeze in winters.
(b) Cold ocean currents on the movement of icebergs
Ans. (i) Due to cold currents, icebergs are carried away from the polar areas. (ii) If such icebergs come along the marine routes, they are hazardous to the ships.
(c) The shape of the coast line on ocean currents
Ans. (i) According to the shape of the coastline, the direction of the ocean current changes. (ii) The velocity of the ocean currents is around 2 to 10 km per hour.
(d) Meeting of warm and cold ocean currents
Ans. (i) At places where the cold and the warm currents meet, thick fog is formed. Such fogs create problems for transportation. (ii) Plankton, vegetation, algae, etc. are the food for the fish, grows in the regions where cold and warm currents meet. Therefore, fish come here in large numbers and breed. This has led to formation of large fishing grounds.
(e) The transportational capacity of ocean currents
Ans. (i) Ocean currents play a very important role in water transport (ii) Transportation done in the direction of the flow of current increases the speed and saves valuable fuel
(f) Deep ocean currents
Ans. (i) Deep ocean currents help in circulation of water (ii) Ocean water moves from the surface to the bottom and from the bottom to the surface. (iii) Warm water is transferred to the bottom from the surface and the nutrient-rich cold water is circulated to the surface.
Q 4. Look at the map of ocean currents and answer the following :
(For map refer to the textbook page no.31 Figure 5.4 : Ocean Currents)
(a) How does the Humboldt current affect the climate of the South American coast?
Ans. Humboldt or Peru Current is a cold current flowing northwards towards western coast of South America. Hence cold water flows into hot water causing dryness in the region as cool air has less moisture holding capacity.
(b) In which oceans are counter equatorial currents not observed and why?
Ans. Counter Equatorial currents are not observed in Indian Ocean due to the monsoonal winds.
(c) Which currents are absent in northern part of the Indian Ocean and why?
Ans. Cold Ocean currents cannot flow from pole to equator as Northern part of Indian Ocean is covered by land and hence cold currents are absent.
(d) In which regions do the cold and warm ocean currents meet?
Ans. Cold and warm currents meet in Grand Bank near the North American coast in Atlantic Ocean and Dogger Bank near the European coast.
Q 5. Answer the following questions:
(a) What are the reasons responsible for the formation of deep ocean currents?
Ans. (i) Deep Ocean currents are formed due to the differences in temperature and density of the water in different parts of the ocean. (ii) Warm water has lower salinity and density. Such water comes to the surface of the sea. (iii) Cold water with high density goes down. This movement causes the deep-sea water currents.
(b) What is the reason behind the dynamics of the ocean water?
Ans. (i) Difference in temperature and salinity leads to movements in ocean water. (ii) Planetary wind gives speed to the ocean currents causing warm and cold currents. (iii) Due to Rotation of the earth the ocean water moves in clockwise and anti-clockwise direction. (iv) Due to Continental structure the direction of the ocean currents change as per the alignment of the coastline.
(c) How do winds give direction to the ocean currents?
Ans. (i) Currents are pushed to long distances by the planetary winds. (ii) Under the influence of the Westerlies, in the midlatitudes, the ocean currents flow from west to east, but near the equator they flow from east to west. This leads to a circular pattern.
(d) Why do the ports in the eastern coast of Canada freeze in winter?
Ans. (i) Labrador is the cold ocean current flowing southwards along the eastern coast of Canada. (ii) The cold Labrador current transports icebergs from glaciers of Greenland Southwards. (iii) The relatively lower salinity of Labrador current makes the water susceptible to freezing. So, the ports in the eastern coast of Canada freeze in winter.