Water (Oceans)


EXERCISES

1. Multiple choice questions.

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

(a) Evaporation (c) Precipitation

(b) Hydration (d) Condensation

Ans: (b) Hydration.

 (ii) The average depth of continental slope varies between

(a) 2–20m (c) 20–200m

(b) 200–2,000m (d) 2,000–20,000m

Ans: (c) 20–200m.

(iii) Which one of the following is not a minor relief feature in the oceans:

(a) Seamount (c) Oceanic Deep

(b) Atoll (d) Guyot

Ans: (c) Oceanic Deep.

(iv) Salinity is expressed as the amount of salt in grams dissolved in sea water per

(a) 10 gm (c) 100 gm

(b) 1,000 gm (d) 10,000 gm

Ans: (b) 1,000 gm.

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

(a) Indian Ocean (c) Atlantic Ocean

(b) Arctic Ocean (d) Pacific Ocean

Ans: (b) Arctic Ocean.

2. Answer the following questions in about 30 words.

(i) Why do we call the earth a Blue Planet?

Ans: We call Earth the Blue Planet because over 71% of its surface is covered by vast, shimmering oceans, making it appear blue from space!

(ii) What is a continental margin?

Ans: Imagine the edge of a continent where land dips gently into the deep ocean. That's a continental margin! It's like a transition zone, with shallow continental shelves giving way to steeper slopes and finally the abyssal plain. Think of it as Earth's underwater rim! 

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

Ans: Imagine where your continent smoothly meets the ocean depths. That's a continental margin! It's a gradual slope from shallow shelves to deep plains, like Earth's underwater edge. 

(iv) What is a thermocline?

Ans: Picture a watery blanket: warm on top, then suddenly chilly deeper down. That's a thermocline - a layer in oceans or lakes where temperature drops sharply with depth, separating warmer surface water from the colder depths below. 

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

Ans: Diving in? Brace for a thermal staircase! Warm sunlit surface, then a rapid chill (thermocline), followed by colder depths. Sunlight weakens, Earth's heat's faint, dense water layers play their part. A fascinating temperature story awaits! 

(vi) What is salinity of sea water?

Ans: Seawater packs a salty punch – about 3.5%, like 35 teaspoons in a 10-liter bucket. But watch out, it can vary depending on rivers, ice, and hidden corners of the ocean! ️

3. Answer the following questions in about 150 words.

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

Ans: The hydrological cycle is a beautiful dance of water, where elements are intricately linked:

*Evaporation: Sun's heat turns liquid water into vapor, lifting it skyward from oceans, lakes, and even plants.

*Condensation: As temperatures drop, vapor condenses, forming clouds – tiny water droplets or ice crystals.

*Precipitation: Clouds heavy with moisture release rain, snow, hail, or sleet back to Earth, replenishing water bodies and land.

*Infiltration & Runoff: Some rainwater soaks into the ground, replenishing groundwater, while some flows over land as surface runoff, feeding rivers and lakes.

*Surface & Groundwater Flow: Water journeys through rivers, streams, and underground, eventually reaching oceans – the cycle restarts!

    Each element relies on the others. Evaporation wouldn't happen without sunlight, and precipitation wouldn't exist without condensation. This continuous loop ensures water circulates through the atmosphere, land, and oceans, sustaining life and shaping our planet. 

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

Ans: The ocean's temperature isn't a uniform bath – it's a dynamic tapestry influenced by various factors:

1. Sunshine & Latitude:

*Sunlight Intensity: Near the equator, the sun's rays hit directly, warming the surface more intensely. As you move towards the poles, the angle of sunlight becomes shallower, spreading the heat over a larger area, resulting in cooler temperatures.

*Daylight Duration: Days are longer near the equator, receiving more solar energy than shorter days at higher latitudes. This contributes to the temperature difference.

2. Land & Water Distribution:

*Land Heats Up Faster: Land absorbs and releases heat quickly, so continents experience larger temperature swings than the ocean. Oceans act as heat reservoirs, moderating temperatures near coastlines.

*Unequal Distribution: The Northern Hemisphere has more landmass, absorbing more heat and warming its surrounding oceans compared to the Southern Hemisphere, which has predominantly water.

3. Ocean Currents:

*Warm Currents: Like giant conveyor belts, warm currents like the Gulf Stream transport heat from the tropics towards cooler regions, influencing their temperatures.

*Cold Currents: Conversely, cold currents like the Humboldt Current bring up frigid water from the depths, cooling surface temperatures and impacting nearby climates.


4. Winds & Upwelling:

*Wind Direction: Onshore winds push warm surface water towards land, warming the coast. Offshore winds can drive upwelling, bringing cold water from deeper layers to the surface, lowering temperatures.

*Evaporation & Cooling: Wind can also enhance evaporation, cooling the surface water as heat energy is used to convert liquid water to vapor.

5. Salinity:

*Salinity Affects Density: Salty water is denser and absorbs less heat than freshwater. Areas with high salinity, like the Mediterranean Sea, tend to be warmer due to reduced mixing with colder, less saline water.

    Understanding these factors unveils the ocean's intricate thermal dance, shaping marine ecosystems, influencing weather patterns, and ultimately impacting our planet's climate. Remember, next time you dip your toes in the ocean, you're experiencing the result of this fascinating interplay of forces!

Project Work

(i) Consult the atlas and show ocean floor relief on the outline of the world map.

(ii) Identify the areas of mid oceanic ridges from the Indian Ocean.


Answer By: Himashree Bora.