A.4] Oceans and Marine Life

1. Four Oceans of the World

Key Facts:

• Pacific Ocean is the largest and deepest ocean, with the Mariana Trench (11,034 m) as its deepest point.
• Atlantic Ocean is known for its strong currents like the Gulf Stream.
• Indian Ocean is the warmest and has the highest salinity due to high evaporation and low precipitation.
• Arctic Ocean is the smallest and shallowest, with about 14% of its area covered by sea ice.

Important Terms:

• Hydrothermal vents: Found in the Pacific and Atlantic Oceans, support unique ecosystems.
• Thermohaline circulation: Drives ocean currents and is crucial for climate regulation.

2. Continental Shelf

• Definition: The submerged edge of a continent, extending from the coast to the shelf break.
• Depth: Usually less than 200 meters.
• Width: Varies from 50 to 1,000 km.
• Significance: Rich in marine life and natural resources (oil, gas, fish).
• Legal Status: Under the United Nations Convention on the Law of the Sea (UNCLOS), the exclusive economic zone (EEZ) extends 200 nautical miles from the coast.

Key Facts:

• The continental shelf is a critical area for fisheries and resource extraction.
• It is also known for its continental shelf break, where the shelf ends and the slope begins.

3. Continental Slope

• Definition: The steep incline from the continental shelf to the deep sea floor.
• Depth: Ranges from 200 to 3,000 meters.
• Gradient: Steeper than the shelf, typically 2–5%.
• Features: Includes submarine canyons and underwater landslides.
• Significance: Important for sediment transport and marine biodiversity.

Key Facts:

• The continental slope is often marked by submarine canyons, such as the Grand Canyon of the Atlantic.
• It serves as a transition zone between the continental shelf and the deep ocean.

4. Deep Sea Plains and Oceanic Deep

4.1 Deep Sea Plains

• Definition: Flat, open areas of the ocean floor beyond the continental slope.
• Depth: Typically 3,000–6,000 meters.
• Characteristics: Low relief, sparse life, and cold temperatures.
• Significance: Important for sedimentation and geological studies.

4.2 Oceanic Deep (Trenches)

• Definition: Deep, narrow depressions in the ocean floor.
• Depth: Exceeds 6,000 meters.
• Notable Trenches:
  • Mariana Trench (Pacific Ocean): 11,034 m (deepest point)
  • Trench of Japan (Pacific Ocean): 10,542 m
  • Kuril-Kamchatka Trench (Pacific Ocean): 10,542 m
  • Sunda Trench (Indian Ocean): 7,258 m
  • Peru-Chile Trench (Pacific Ocean): 8,065 m

Key Facts:

• Trenches are formed by subduction zones where one tectonic plate is forced beneath another.
• The Mariana Trench is the deepest part of the Earth’s oceans.
• Hydrothermal vents are often found near trenches and support unique ecosystems.

5. Biodiversity in Marine Environments

• Definition: The variety of life in the oceans, including flora, fauna, and microbial life.
• Key Zones:
  • Coastal zones: High biodiversity due to nutrient-rich waters.
  • Shelf seas: Support large fish populations and marine mammals.
  • Deep sea: Low light, high pressure, and unique species like anglerfish and giant squid.
• Important Ecosystems:
  • Coral reefs: Found in tropical regions; support 25% of marine species.
  • Kelp forests: Found in temperate regions; provide habitat for many species.
  • Hydrothermal vent ecosystems: Support chemosynthetic life, such as tube worms and extremophiles.

Key Facts:

• Coral reefs are among the most biodiverse ecosystems on Earth.
• Deep-sea ecosystems are less understood but contain unique and resilient species.
• Marine biodiversity is under threat from climate change, pollution, and overfishing.

Important Terms:

• Chemosynthesis: Process by which organisms produce energy from chemical reactions, common in deep-sea vents.
• Extremophiles: Organisms that thrive in extreme environments, such as hydrothermal vents.
• Biodiversity hotspots: Areas with high species richness and endemism, such as the Great Barrier Reef.

SSC & RRB Focus Points:

• Mariana Trench and its depth.
• Continental shelf and slope definitions.
• Importance of coral reefs and biodiversity.
• Key terms like hydrothermal vents and chemosynthesis.