Notes Class 11 Chapter 6 Geography Maharashtra Board

Ocean Resources

Introduction

Oceans cover about 71% of the Earth’s surface and are vital for human survival, providing resources, energy, and supporting trade, transport, and tourism. The study of oceans began scientifically in the 19th century, with significant contributions from voyages like the British ship Challenger (1872-1876). The invention of the echo sounder in the 1920s revolutionized ocean floor mapping by using SONAR to measure depths. This chapter explores the structure of the ocean floor, its resources, and their importance to humanity, alongside challenges like marine pollution.

Structure of the Ocean Floor

The ocean floor has varied relief, similar to terrestrial landforms, including continental shelves, slopes, abyssal plains, trenches, ridges, and plateaus.

1. Continental Shelf

Definition: The submerged portion of continents bordering coastal areas, covered by shallow water (up to 180-200 m deep).

Characteristics:

• Occupies ~7.6% of the oceanic area.
• Broad, gently sloping plains; width varies (narrow along Chile, Sumatra; ~1500 km wide off Siberia).

Importance:

• Fishing: Sunlight penetration supports plankton growth, a key food source for fish. Rich fishing grounds include Grand Banks and Georges Bank (North America).
• Minerals: Contains oil and gas reserves (e.g., Mumbai High in the Arabian Sea), diamonds, chromite, ilmenite, magnetite, platinum, gold, phosphorite, sand, gravel, and silica.

Human Activities: Fishing, oil and gas extraction, and mineral mining.

2. Continental Slope

Definition: A steep drop following the continental shelf, with a gradient of 2°-5°.

Characteristics:

• Depth ranges from 200 m to 4000 m.
• Covers ~8.5% of the ocean area; considered the boundary of continents.
• Limited sediment deposition due to steepness.

Features:

• Methane hydrates (e.g., Krishna-Godavari basin, India).
• Submarine landslides, ocean canyons (e.g., Congo Canyon), and avalanche fans.

Significance: Limited resource extraction due to steep terrain but potential for methane hydrate mining.

3. Abyssal Plains

Definition: Vast, gently sloping plains beyond the continental slope.

Characteristics:

• Cover ~66% of the ocean floor.
• Formed by volcanic and tectonic activities; include seamounts, mountains, and plateaus.
• Sediments include wind-blown dust, volcanic ash, chemical precipitates, and meteorite fragments.

Resources:

• Manganese nodules containing iron, nickel, cobalt, and copper.
• Not currently mined but holds future potential.

Significance: Stable environment for sediment accumulation, supporting unique ecosystems.

4. Oceanic Trenches

Definition: Deep, narrow, steeply sloping depressions, the deepest parts of the ocean.

Characteristics:

• Shallow ones are called deeps; deeper ones are trenches (e.g., Mariana Trench, ~11 km; Java Trench, ~7.7 km).
• Found along plate boundaries, associated with volcanoes and earthquakes.

Challenges:

• Limited exploration due to extreme depth and remoteness.
• Only three humans have visited below 6000 m; knowledge derived from 1950s sampling campaigns.

Significance: Critical for understanding tectonic processes and extreme marine ecosystems.

5. Oceanic Ridges and Plateaus

Definition: Submerged mountain ranges (ridges) and flat-topped elevations (plateaus) on the ocean floor.

Characteristics:

• Ridges are hundreds of kilometers wide and thousands of kilometers long (e.g., Mid-Atlantic Ridge).
• Plateaus include Chagos Plateau (Indian Ocean).
• Peaks may emerge as islands (e.g., Hawaiian Islands).

Types of Oceanic Islands:

• Continental Islands: E.g., Madagascar (Indian Ocean).
• Volcanic Islands: E.g., Hawaiian Islands (Pacific Ocean).
• Coral Islands: E.g., Aldabra Islands (Indian Ocean).

Significance:

• Seamounts support unique ecosystems with high endemism, important for conservation.
• Islands and ridges are critical for biodiversity and geological studies.

6. Other Features

• Submarine canyons, valleys, and seamounts resemble terrestrial landforms like canyons and hills.
• Similarities with land: Both ocean and land relief are shaped by tectonic, volcanic, and erosional processes.

Ocean Resources

Ocean resources are classified into biotic (living) and abiotic (non-living) resources, found at various depths and critical for human use.

1. Biotic Resources

Marine Plants and Animals:

• Oceans host thousands of species, providing food (fish, molluscs, seaweeds) and products like oil, leather, glue, and cattle feed.
• Plankton: Microorganisms (phytoplankton and zooplankton) are the base of the marine food chain, supporting fish and whales.
• Coral Reefs: Major ecosystems (e.g., Great Barrier Reef, Australia, ~2010 km long), providing habitats and resources like pearls for medicine.
• Seaweeds: Used as food, fertilizers, and in skincare products.

Mangrove Vegetation:

• Found on tropical coasts (e.g., Sunderbans, India), providing food, shelter, and wood for fuel and furniture.
• Supports diverse fauna, including tigers in Sunderbans.

Significance: Essential for food security, pharmaceuticals, and coastal economies.

2. Abiotic Resources

Minerals:

• Sodium Chloride (Common Salt): Extracted from seawater, a major coastal industry.
• Potassium and Gypsum: Found in large quantities; gypsum is used for Plaster of Paris in construction.
• Petroleum and Natural Gas: Major resources on continental shelves (e.g., Mumbai High).
• Manganese Nodules: Found on abyssal plains, containing iron, nickel, cobalt, and copper.
• Other Minerals: Diamonds, chromite, ilmenite, magnetite, platinum, gold, phosphorite, sand, gravel, and silica.

Significance:

• Support industries like energy, construction, and manufacturing.
• Require advanced technology for deep-sea extraction while maintaining ecological balance.

Uses of Oceans

Oceans serve multiple purposes beyond resource extraction, including energy, water, trade, transport, and tourism.

1. Energy

Tidal Energy:

• Generated from the energy released by tides.
• Example: A tidal turbine in the Bay of Fundy, Nova Scotia (2016), powers 500 homes.
• Challenges: High installation costs and technological limitations.

Thermal Energy:

• Uses temperature differences between surface (25-30°C) and deep water (<5°C) to generate electricity.
• Example: Floating generators in Belgium and Cuba.

Significance: Renewable energy sources to reduce reliance on fossil fuels.

2. Drinking Water

Desalination:

• Process to remove salt from seawater for drinking and irrigation.
• Methods: Heating, freezing, or electrical processes.
• Used in countries like Saudi Arabia, Oman, UAE, Spain, Algeria, and Cyprus.
• India has desalination plants (locations can be researched online).

Challenges:

• High costs limit use in developing countries.
• Environmental impact: Harms marine life (e.g., plankton, baby fish) by suction into plants, disrupting food chains.

Significance: Critical for water-scarce regions, with potential for wider adoption.

3. Trade and Transport

Maritime Transport:

• Cheapest mode for transporting cargo and people.
• The Atlantic Ocean route is the busiest, connecting North America and Western Europe.

Significance: Facilitates global trade, supporting economic development.

4. Tourism

Forms: Cruises, scuba diving, fishing, beach tourism.

Growth: Increasingly popular, with resorts and marinas built in coastal areas.

Challenges:

• Large developments harm ocean habitats (e.g., coral reefs).
• Pollution from tourism activities affects marine ecosystems.

Significance: Boosts economies but requires sustainable practices to protect marine life.

Ownership of Oceans

Concept: Oceans lack visible boundaries, making ownership complex.

Law of the Sea:

• Informal agreement historically stated no one owns the oceans.
• UNCLOS (1982):
  • Territorial Sea: A country can claim 12 nautical miles from its coast.
  • Exclusive Economic Zone (EEZ): Extends 200 nautical miles, where a country has rights to resources (e.g., India’s manganese nodule mining rights).
  • Beyond EEZ: Resources are international, regulated by global institutions.

Significance: Balances national rights with global cooperation for resource use.

Marine Pollution

Sources:

• Oil spills from ships and coastal extraction.
• Industrial and urban waste, including radioactive matter and river effluents.
• Plastic pollution (e.g., a 30-year-old plastic bag found in Mariana Trench, 2018).
• Microplastics constitute over a third of ocean debris.

Impacts:

• Threatens marine life (e.g., plankton, fish, corals), disrupting food chains.
• Contaminated seafood affects human health.
• Degrades coastal tourism and water quality, impacting economies.

Future Risks:

• Growing human dependence on oceans for food, water, and minerals increases vulnerability to pollution.
• By mid-21st century, pollution could exacerbate food security issues.

Solutions:

• Reduce waste disposal and oil leaks.
• Promote sustainable resource extraction and tourism.
• International cooperation to regulate pollution.

Historical and Cultural Role of Oceans

Exploration:

• Early 15th century: Limited world knowledge; European and other navigators explored new lands.
• Challenger voyage (1872-1876): Provided insights into ocean depths and marine life.

Discoveries:

• Continents, countries, and islands (e.g., Madagascar, Hawaiian Islands) were mapped via ocean routes.

Cultural Exchange:

• Oceans facilitated the spread of trade, religions, and cultures, connecting civilizations.

Significance: Oceans shaped human history by enabling global exploration and interaction.

Key Features on the World Map

1. Chagos Range: Indian Ocean, south of Maldives (~6°S, 72°E).
2. Mariana Trench: Western Pacific Ocean, east of Mariana Islands (~11°N, 142°E).
3. Dogger Bank: North Sea, between UK and Denmark (~55°N, 2°E).
4. Mumbai High: Arabian Sea, off India’s west coast (~19°N, 71°E).
5. Sunda Deep: Indian Ocean, near Sunda Strait, Indonesia (~6°S, 105°E).
6. Grand Banks: North Atlantic Ocean, southeast of Newfoundland, Canada (~45°N, 50°W).

Sustainable Development

Need: Oceans are critical for food, energy, minerals, and water, especially as terrestrial resources deplete.

Challenges: Overexploitation and pollution threaten marine ecosystems.

Strategies:

• Use advanced technology for deep-sea resource extraction with minimal environmental impact.
• Implement sustainable tourism and fishing practices.
• Protect ecosystems like coral reefs and mangroves through conservation efforts.

Significance: Ensures long-term availability of ocean resources for future generations.

Exercises and Activities

Use Your Brain Power: Discuss how oceans facilitated major journeys, discoveries, and cultural exchanges in the last millennium.

Try This:

• Analyze Figure 6.1 (ocean floor diagram) to identify shallow areas, sediment deposition zones, and islands formed by submerged mountains.
• Compare ocean landforms with terrestrial ones.

Find Out:

• List Indian islands by type (continental, volcanic, coral).
• Identify locations of India’s desalination plants.
• Research Indian institutes studying oceans (e.g., National Institute of Oceanography).

Exercise Questions:

• Complete chains, correlations, and geographical reasons.
• Write short notes on EEZ, oceanic tourism, minerals, and continental slope.
• Discuss marine pollution, landform similarities, and sustainable tourism in detail.

Conclusion

Oceans are a treasure trove of resources and opportunities, from biotic and abiotic wealth to energy and tourism. Their exploration has shaped human history, and their sustainable use is crucial for future prosperity. However, challenges like pollution and limited knowledge of deep-sea environments require global cooperation and technological advancements to ensure oceans remain a viable resource for generations to come.