Ocean Bottom Topography
Continental Shelf
Continental shelf are extension of continents into the sea. It extends up to the depth of 200m. Its last limit is shelf break.
Importance
- Rich in biotic resources like fisheries. It is because
- Due to sallow depth, it absorbs abundant sunlight
- Photosynthesis take place up to the depth of 200m.
- It is abundant amount of dissolved oxygen.
- It is important region where cold and warm ocean currents meet, which makes the temperature ideal for the growth of phytoplankton's which make the base of marine food chain.
- Rich in fossil fuel resources.
- The larger concentration of fossil fuel resources in the world is concentrated on continental shelf either of present or of geological past.
- The West Asia which has largest oil reserves like in Saudi Arabia, UAE, Quat, Iran, Iraq are on continental shelf. Venezuela of South America (Lake Maracaibo), Libya and Nigeria in Africa, South China Sea in East Asia, Okhotsk Sea in Eastern Russia, Northern Black Sea of Russia and Ukraine, North Sea in West Europe between Norway and UK are prime examples.
- Rich in metallic minerals
- These are deposited by rivers during their delta and estuary formation.
- Very rich in biological diversity
- e.g. Mangroves and Corals
- Strategic Significance
- The sovereignty of a country extends up to 12 nautical miles from the base, contiguous zone up to 12 (24) nautical nautical miles and exclusive economic zone extends up to 200 nautical miles from the base line.
- It contributes in maintaining coastal ecosystem like coastal erosion, protection from Tsunami, tropical cyclones, etc.
Growing Importance of Artic Continental Shelf
Because of the growing importance of Artic Continental shelf various resource sharing issues have emerged between the northern countries, countries sharing their coast with Artic. However, for peaceful negotiation and cooperation, execution UNCLOS (United Nation Convection on the Laws of the Seas) Artic Council has formed and India has also been given the status of observer.
Importance of Artic CS
- Huge potential of oil and gas
- Russia and Norway are engaged in exploration.
- Huge potential of rare earth minerals as well as metallic minerals like nickel, cobalt, cooper, etc.
- Various high fishing grounds
- Melting of glaciers will open new trade routes which will connect Asia, Europe and North America more efficiently.
- It is important to study the heat balance of earth.
Why India is interested in Artic CS
- To meets its energy security
- Import oil and gas from Artic region in future
- To study impact of climate change.
- To take benefits of new trade routes.
- To avail the benefits of geopolitics of the Artic Region.
- To make optimum use of blue economy of Artic.
Continental Slope
It extends beyond shelf break towards the seaward side. It is the region of step slop thus the depth could be 3000-4000m
Importance
- It makes boundary between continents and the oceans.
- It has gad hydrate and other mineral resources.
- Influences ocean currents
- Many at times epicentre of earthquakes.
Continental Rise
It extends next to continental slope. It is formed due to deposition of the sediments which slide down along with continental slope.
Importance
- Great possibility of oil and gas.
- Support important marine ecosystem.
- These are found mostly along with the coast which has exposure to constructive plate margin.
Ocean Trenches
These are deepest part of the ocean which are formed due to plate convergence. e.g.
- Trenches of Pacific Ocean
- Mariana Trench
- It is situated east to Philippines in North-Western Pacific.
- It is deepest trench in the world, has depth of more than 11kms.
- Mindanao Trench
- It is situated between Philippines and Mariana Trench.
- Japan Trench
- East to Japan
- Kuril Trench
- East to Russia
- Peru-Chile Trench
- West to South America in South-Eastern Pacific.
- Tonga Trench
- North-east to Austrailia
- Mariana Trench
- Trenches of Indian Ocean
- Java/Sunda Trench
- Deepest of Indian Ocean, depth is more than 7000m.
- Java/Sunda Trench
- Trenches of Atlantic Ocean
- Puerto Rico Trench
- Romanche Trench
These are found along with destructive plate margin
Guyot
These are underwater plateaus, altitude less than 1000m, formed due to the erosion of sea mounts usually. Rich in biodiversity and minerals specially metallic ferrous and non-ferrous.
Sea Mounts
These are volcanic peaks, altitude more than 1000m. These are rich in biodiversity like coral, fishery. It affects ocean currents.
Mid-Oceanic Ridge
These are formed along with divergent plate boundary.
Ocean Temperature
Sources of Temperature
- Sun (most important)
- Underwater volcanism
- Organisms metabolism
- Pressure
- Water Movement (frictional heat)
Horizontal Distribution of Temperature
It refers to the variation of temperature from one place to another across the earth surface at the same latitude or between different regions.
Factors Affecting Horizontal Distribution of Temperature
- Latitude
- Temperature generally decreases from equator towards pole.
- Land and Water distribution
- Open areas have moderate temperature whereas coastal areas have relatively extreme temperature because of the influence of landmass.
- Size of the water bodies
- In tropical areas small waterbodies have higher temperature than the large water bodies. e.g. Red Sea has high temperature than the Arabian Sea.
- Whereas, in high latitudes/ polar region small water bodies have lower temperature than the large water bodies. e.g. Baltic Sea has lower temperature than the North Sea.
- Direction of Wind
- Offshore winds decrease temperature near the coast and onshore wind increase temperature near the coast due to upwelling and downwelling respectively.
- Ocean Currents
- Warm Ocean Current Increase temperature and cold ocean current decrease temperature. e.g. Norwegian Current, warm current makes Norway habitable but Labrador Current and East Greenland Current make Greenland example of cold desert.
Vertical Distribution of Temperature
In general, ocean water is broadly divided into three thermal zones.
- Surface Mixed layer
- It extends up to 200m depth on an average. Here temperature remains high but relatively uniform due to mixing of water caused by wind, waves and currents.
- Thermocline Zone
- It extends between to 200-1000m in open sea. In this temperature falls with steepest rate.
- Deep and Bottom Zone
- It extends below 1000m and extends up to bottom. Temperature usually remains 4°C.