GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-12
Water (Oceans)
1. Multiple Choice Questions
(i) Identify the element which is not a part of the hydrological cycle.
Answer: (b) Hydration
Explanation:
The hydrological cycle includes the continuous movement of water through evaporation, condensation, precipitation, infiltration, runoff and transpiration. Hydration is a chemical weathering process and is not a part of the hydrological cycle.
(ii) The average depth of continental slope varies between
Answer: (b) 200–2,000 m
Explanation:
The continental slope begins at the edge of the continental shelf at about 200 m depth and extends down to nearly 2,000 m, where it merges into the deep ocean basin.
(iii) Which one of the following is not a minor relief feature in the oceans?
Answer: (c) Oceanic Deep
Explanation:
Oceanic deeps (trenches) are major relief features of the ocean floor. Seamounts, guyots and atolls are classified as minor ocean relief features.
(iv) Salinity is expressed as the amount of salt in grams dissolved in sea water per
Answer: (b) 1,000 gm
Explanation:
Salinity is measured as the number of grams of dissolved salts present in 1,000 grams (1 kg) of seawater and is expressed in parts per thousand (‰ or ppt).
(v) Which one of the following is the smallest ocean?
Answer: (b) Arctic Ocean
Explanation:
The Arctic Ocean is the world's smallest and shallowest ocean. It is located around the North Pole and remains covered with sea ice for most of the year.
2. Answer the following questions in about 30 words.
(i) Why do we call the Earth a Blue Planet?
Answer:
The Earth is called the Blue Planet because about 71% of its surface is covered by oceans and seas. When viewed from space, this vast amount of water makes the Earth appear blue.
(ii) What is a continental margin?
Answer:
A continental margin is the submerged outer edge of a continent. It includes the continental shelf, continental slope and continental rise, forming the transition between the continent and the deep ocean basin.
(iii) List out the deepest trenches of various oceans.
Answer:
| Ocean | Deepest Trench |
|---|---|
| Pacific Ocean | Mariana Trench |
| Atlantic Ocean | Puerto Rico Trench |
| Indian Ocean | Java (Sunda) Trench |
| Arctic Ocean | Molloy Deep |
(iv) What is a thermocline?
Answer:
A thermocline is the middle layer of ocean water where the temperature decreases rapidly with increasing depth. It lies between the warm surface layer and the cold deep ocean water.
(v) When you move into the ocean what thermal layers would you encounter? Why does the temperature vary with depth?
Answer:
The three thermal layers of the ocean are:
- Surface mixed layer
- Thermocline
- Deep cold layer
Temperature decreases with depth because sunlight heats only the upper layers, while very little solar energy reaches deeper waters.
(vi) What is salinity of sea water?
Answer:
Salinity is the total amount of dissolved salts present in seawater. It is expressed as the number of grams of dissolved salts in 1,000 grams of seawater, usually in parts per thousand (‰).
3. Answer the following questions in about 150 words.
(i) How are various elements of the hydrological cycle interrelated?
Answer:
The hydrological cycle is a continuous circulation of water between the oceans, atmosphere and land. Solar energy causes water to evaporate from oceans, rivers, lakes and soil, while plants add moisture to the atmosphere through transpiration. The water vapour rises, cools and condenses to form clouds. When the clouds become saturated, precipitation occurs in the form of rain, snow or hail. A part of this water flows over the land as surface runoff into rivers and oceans, while another part infiltrates into the soil to recharge groundwater. Groundwater moves slowly and eventually reaches rivers, lakes or oceans. From these water bodies, evaporation begins again, completing the cycle. Thus, evaporation, condensation, precipitation, infiltration, groundwater flow, runoff and transpiration are closely connected processes. Any change in one component affects the entire hydrological cycle, maintaining the continuous movement and balance of water on the Earth.
(ii) Examine the factors that influence temperature distribution of the oceans.
Answer:
The temperature of ocean water varies from place to place due to several factors. Latitude is the most important factor because equatorial regions receive more direct solar radiation than polar regions. Ocean currents also influence temperature by transporting warm or cold water from one region to another. Prevailing winds help in mixing surface waters and modifying temperatures. Seasonal changes affect the amount of solar energy received throughout the year. Cloud cover influences the amount of sunlight reaching the ocean surface. Temperature also decreases with increasing depth because sunlight penetrates only the upper layers of the ocean. In enclosed seas, salinity and limited water circulation also affect temperature. The combined effect of these factors produces variations in ocean temperatures across different regions of the world.