Class 11 Geography Important Chapter 21 Temperature and Salinity of Ocean Water

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Class 11 Geography Important Chapter 21 Temperature and Salinity of Ocean Water

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Temperature and Salinity of Ocean Water

Chapter: 21

FIFTH UNIT : HYDROSPHERE

IMPORTANT QUESTION AND ANSWER

Answer The Following Questions:

1. What is the average surface temperature of ocean water?

Ans: The average surface temperature of the ocean is about 27°C.

2. What is the surface temperature of ocean water depending on location?

Ans: The surface temperature of ocean water varies between 30°C and 0°C, depending on the region.

3. What unit is used to measure salinity?

Ans: Salinity is measured in parts per thousand (%).

4. Which ocean has an average salinity of 36%?

Ans: The Atlantic Ocean has an average salinity of 36%.

5. Why does the deep layer of the ocean remain permanently cold?

Ans: The deep layer remains permanently cold because solar radiation does not reach the deeper parts, and the absence of winds and currents prevents heat mixing.

6. What are the three major layers of the ocean?

Ans: The three layers of the ocean are the surface layer, the thermocline layer, and the deep layer.

7. What is formed due to vertical temperature variation of ocean water?

Ans: Due to vertical temperature variation, a thermocline is formed.

8. What percentage of ocean water remains warm due to internal heat?

Ans: About 75% of ocean water lies below the thermocline and remains warm due to internal heat instead of solar radiation.

9. At what salinity is water called saline water?

Ans: Water is called saline water when its salinity is 24.7% or more.

10. Up to what depth does the surface temperature vary?

Ans: Surface temperature varies up to a depth of about 400 meters.

Long Question & Answer:

1. Explain the factors affecting the temperature of ocean water.

Ans: The main factors affecting ocean temperature are as follows.

(i) Latitude: Solar heating decreases from the Equator toward the poles. Therefore, surface temperature decreases as latitude increases.

(ii) Distribution of land and water: Seas enclosed by landmasses (like the Red Sea, Persian Gulf, Mediterranean Sea) are warmer than open oceans because they heat up more quickly. Such inland seas in the Northern Hemisphere show higher temperatures.

(iii) Wind direction: Offshore winds push warm surface water away from the coast, causing cold deep water to rise (upwelling). Onshore winds push warm surface water toward the coast, increasing coastal temperature. Therefore, temperature may vary more along longitude rather than latitude.

(iv) Ocean currents: Warm currents increase the temperature of the areas they pass, while cold currents reduce temperature. For example, the Gulf Stream warms parts of North America and Europe, while the Canary Current cools the western coast of Africa.

2. Explain the horizontal distribution of salinity with examples.

Ans: The horizontal distribution of salinity refers to the variation in the salinity of ocean water across different regions of the world. This variation occurs mainly due to differences in evaporation, rainfall, river discharge, and the direction of ocean currents. Areas with high evaporation and low rainfall, such as the Red Sea, have very high salinity levels that may reach up to 41‰. In contrast, regions near the mouths of large rivers like the Amazon, Congo, and Brahmaputra experience much lower salinity, sometimes falling below 20‰, because of the continuous inflow of freshwater. The Atlantic Ocean has an average salinity of about 36‰, with some central parts reaching above 37‰ due to high evaporation. In the Indian Ocean, the average salinity is around 35‰, but the Bay of Bengal shows a lower value of about 30‰ because numerous rivers drain freshwater into it. Conversely, the Arabian Sea has higher salinity due to intense evaporation. These regional differences in salinity influence ocean currents, climate conditions, and the marine ecosystem.