Water (Oceans)

Distribution of Water on Earth

• Total Water: About 71% of the Earth’s surface is covered by water.
• Breakdown:
  • Oceans: 97.3% (saline water).
  • Freshwater: 2.7% (ice caps, glaciers, groundwater, rivers, lakes).
• Example:
  • The Pacific Ocean is the largest ocean, covering about 30% of the Earth’s surface.

Composition of Ocean Water

• Salinity:
  • Definition: The amount of dissolved salts in seawater, measured in parts per thousand (‰).
  • Average Salinity: 35‰ (35 grams of salt per 1000 grams of water).
  • Factors Affecting Salinity:
    • Evaporation: Increases salinity (e.g., Red Sea has high salinity due to high evaporation).
    • Precipitation: Decreases salinity (e.g., Equatorial regions have lower salinity due to heavy rainfall).
    • Freshwater Inflow: Rivers reduce salinity near their mouths (e.g., Ganges-Brahmaputra delta).
  • Example:
    • The Dead Sea has a salinity of 340‰, making it one of the saltiest water bodies.
• Dissolved Gases:
  • Oxygen, carbon dioxide, and nitrogen are present in ocean water.
  • Example: Oxygen levels are higher near the surface due to photosynthesis by marine plants.

Temperature of Ocean Water

• Factors Affecting Temperature:
  1. Latitude: Temperature decreases from the equator to the poles.
     • Example: Equatorial regions have warmer waters (around 25-30°C), while polar regions are near freezing.
  2. Depth: Temperature decreases with depth.
     • Example: The thermocline layer (200-1000m) shows a rapid decrease in temperature.
  3. Ocean Currents: Warm currents raise temperatures, while cold currents lower them.
     • Example: The Gulf Stream warms the eastern coast of the USA.

Ocean Currents

• Definition: Continuous, directed movements of seawater generated by forces like wind, temperature, and salinity differences.
• Types:
  • Warm Currents: Flow from the equator to the poles, raising temperatures.
    • Example: Gulf Stream, North Atlantic Drift.
  • Cold Currents: Flow from the poles to the equator, lowering temperatures.
    • Example: Labrador Current, Humboldt Current.
• Causes:
  • Wind: Trade winds and westerlies drive surface currents.
  • Coriolis Effect: Deflects currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
  • Temperature and Salinity: Differences create density-driven currents (thermohaline circulation).
• Example:
  • The Gulf Stream influences the climate of Western Europe, making it warmer than other regions at similar latitudes.

Tides

• Definition: Periodic rise and fall of sea levels caused by the gravitational pull of the moon and sun.
• Types:
  • Spring Tides: Occur during full moon and new moon when the sun, moon, and Earth are aligned.
    • Example: Higher high tides and lower low tides.
  • Neap Tides: Occur during the first and third quarters of the moon when the sun and moon are at right angles.
    • Example: Moderate tides.
• Significance:
  • Navigation, fishing, and tidal energy generation.
  • Example: The Bay of Fundy (Canada) has the highest tides in the world, reaching up to 16 meters.

Waves

• Definition: Rhythmic rise and fall of ocean water caused by wind energy transfer.
• Characteristics:
  • Crest: Highest point of a wave.
  • Trough: Lowest point of a wave.
  • Wavelength: Distance between two consecutive crests or troughs.
• Example:
  • Tsunamis are large waves caused by underwater earthquakes or volcanic eruptions.

Ocean Resources

• Biological Resources:
  • Fish, shellfish, seaweed, and other marine organisms.
  • Example: The fishing industry in Japan and Norway relies heavily on ocean resources.
• Mineral Resources:
  • Salt, magnesium, and hydrocarbons (oil and natural gas).
  • Example: Offshore oil drilling in the Gulf of Mexico.
• Energy Resources:
  • Tidal energy, wave energy, and ocean thermal energy conversion (OTEC).
  • Example: The Rance Tidal Power Station in France generates electricity from tidal energy.

Ocean Pollution

• Sources:
  • Industrial waste, oil spills, plastic waste, and agricultural runoff.
• Impacts:
  • Harm to marine life, coral reef destruction, and disruption of food chains.
• Example:
  • The Great Pacific Garbage Patch is a massive accumulation of plastic waste in the Pacific Ocean.

International Efforts for Ocean Conservation

• UNCLOS (United Nations Convention on the Law of the Sea):
  • Establishes guidelines for the use of ocean resources and conservation.
• Marine Protected Areas (MPAs):
  • Designated areas to conserve marine biodiversity.
  • Example: The Great Barrier Reef Marine Park in Australia.

MCQ PRACTICE

1. Consider the following statements regarding ocean salinity:

1. High evaporation increases ocean salinity.
2. The salinity of equatorial regions is higher than that of subtropical regions.
3. River inflows can reduce salinity near coastal areas.

Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 1 and 3 only
Explanation: High evaporation increases salinity, and river inflows reduce it near coastal areas. However, equatorial regions have lower salinity than subtropical areas due to heavy rainfall.

2. Which of the following factors influence ocean currents?

1. Wind patterns
2. Coriolis effect
3. Ocean salinity
4. Earth’s rotation

Select the correct answer using the codes given below:
(a) 1, 2, and 3 only
(b) 2, 3, and 4 only
(c) 1, 3, and 4 only
(d) 1, 2, 3, and 4

Answer: (d) 1, 2, 3, and 4
Explanation: Ocean currents are influenced by global wind patterns, the Coriolis effect (caused by Earth’s rotation), differences in water salinity, and temperature gradients.

3. Consider the following statements about the Gulf Stream:

1. It is a warm ocean current in the Atlantic Ocean.
2. It helps moderate the climate of Western Europe.
3. It originates in the Southern Hemisphere and flows towards North America.

Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3

Answer: (a) 1 and 2 only
Explanation: The Gulf Stream is a warm ocean current in the North Atlantic, influencing the climate of Western Europe. It originates near the Gulf of Mexico and moves towards Europe, not from the Southern Hemisphere.

4. Which of the following statements regarding tides is/are correct?

1. Spring tides occur only during the summer season.
2. Neap tides occur when the Sun, Earth, and Moon form a right angle.
3. Tides are influenced by both the gravitational pull of the Moon and the Sun.

Select the correct answer using the codes given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3

Answer: (b) 2 and 3 only
Explanation: Spring tides occur during full and new moons, not just in summer. Neap tides happen when the Sun, Moon, and Earth form a right angle, and tides are influenced by both the Moon and the Sun.

5. Consider the following statements about ocean waves:

1. Wind is the primary factor behind the formation of ocean waves.
2. Tsunamis are caused by wind activity in deep oceans.
3. The highest point of a wave is called the crest.

Which of the statements given above is/are correct?
(a) 1 and 3 only
(b) 2 and 3 only
(c) 1, 2, and 3
(d) 1 only

Answer: (a) 1 and 3 only
Explanation: Wind drives normal ocean waves, while tsunamis are caused by underwater earthquakes or volcanic activity. The highest point of a wave is called the crest.

6. Which of the following statements about ocean resources is/are correct?

1. The ocean is a major source of hydrocarbons such as oil and natural gas.
2. Marine fisheries contribute significantly to global food production.
3. The deep ocean contains valuable minerals like manganese nodules and polymetallic sulfides.

Select the correct answer using the codes given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3

Answer: (d) 1, 2, and 3
Explanation: Oceans provide hydrocarbons, fisheries contribute significantly to food supply, and deep-sea mining yields minerals like manganese nodules and polymetallic sulfides.

7. Consider the following statements about ocean pollution:

1. The Great Pacific Garbage Patch consists mainly of plastic waste.
2. Oil spills have long-term ecological consequences on marine ecosystems.
3. Agricultural runoff containing fertilizers does not affect ocean pollution.

Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3

Answer: (a) 1 and 2 only
Explanation: The Great Pacific Garbage Patch is a massive accumulation of plastic waste. Oil spills damage marine ecosystems, but agricultural runoff (fertilizers, pesticides) also contributes to ocean pollution, making statement 3 incorrect.

8. Which of the following statements regarding ocean temperature is/are correct?

1. Ocean temperature decreases with increasing latitude.
2. The thermocline is the layer where temperature drops rapidly with depth.
3. Warm ocean currents always originate from the poles and move toward the equator.

Select the correct answer using the codes given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3

Answer: (a) 1 and 2 only
Explanation: Ocean temperature decreases with latitude, and the thermocline is the zone where temperature drops rapidly. Warm ocean currents originate near the equator, not the poles.

9. Consider the following international efforts for ocean conservation:

1. The United Nations Convention on the Law of the Sea (UNCLOS) regulates marine resource use.
2. Marine Protected Areas (MPAs) are designated to conserve marine biodiversity.
3. The International Whaling Commission focuses on sustainable deep-sea mining.

Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3

Answer: (a) 1 and 2 only
Explanation: UNCLOS sets laws for ocean resource use, and MPAs protect marine biodiversity. The International Whaling Commission (IWC) regulates whaling, not deep-sea mining.

10. Which of the following statements about the distribution of water on Earth is/are correct?

1. More than 97% of Earth’s water is saline.
2. The majority of Earth’s freshwater is found in rivers and lakes.
3. Glaciers and ice caps store the largest proportion of Earth’s freshwater.

Select the correct answer using the codes given below:
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 1 and 3 only
Explanation: Over 97% of Earth’s water is saline. Most freshwater is stored in glaciers and ice caps, not in rivers and lakes.