These are unconsolidated sediments deposited on the ocean floor. They are of two types: –
- Terrigenous deposits (deposits derived from land; found mainly on the continental shelves and slopes), and
- Pelagic deposits (found over deep sea plains and the deeps.
A) Terrigenous Deposits
- They are inorganic deposits (compounds not containing carbon) derived from disintegrated rock material (due to weathering and water erosion).
- The proportion of organic matter (in the form of shells, corals and skeletons) is quite negligible.
- The disintegrated rock material is carried from land to the sea mainly by running water.
- The terrigenous deposits are found mainly on the continental shelves and slopes.
- Except for fine volcanic ash, little terrigenous material is carried on to the sea surface.
B) Pelagic Deposits
- Pelagic deposits cover nearly 75% of the total sea floor.
- The pelagic deposits consist of both organic (remains of plants and animals) and inorganic material.
- Organic material is in the form of liquid mud called ooze which contains remnants of shells and skeletons.
- Inorganic material is in the form of red clay which is of volcanic origin.
- The chief constituents of red clay are silicon and aluminium dioxide.
- The red clay is the most widely spread pelagic deposit of the sea floor.
- The red clay covers more than half of the Pacific floor.
- Both metallic and non-metallic resources are found in seas.
- Most of these minerals are carried from land to sea by running water.
- The remaining are formed from to undersea volcanism and detritus (leftover parts) of marine organisms.
- At present, mining of only a handful of marine mineral resources is economically viable.
- Among them are offshore oil and natural gas, extraction of sodium chloride, salts of magnesium and bromine, etc.
A) Mineral deposits found on continental shelves and slopes
- Sands are mined to extract calcium carbonate along the Bahamas coast.
- Coral sands are mined in Hawaii and Fiji for calcium carbonate.
B) Marine Placer deposits
- A placer deposit is an accumulation of valuable heavy minerals that have been weathered and eroded from their source rocks.
- As a result of their high density, placer minerals accumulate just few kilometres away from their source rocks.
- Marine placers deposits accumulate on the continual shelves very close to the shoreline.
- The most economically important of placer minerals are cassiterite (ore of tin), ilmenite (titanium), rutile (titanium), zircon (zirconium), chromite (chromium), monazite (thorium), magnetite (iron), gold and diamonds.
- The beach sands of western India, coastal Brazil, Australia have zircon, monazite (thorium is extractedfrom monazite sands found across the Kerala coast).
- Kerala’s placer deposits contain 90 per cent of the world’s monazite reserves.
- Placer diamonds are mainly mined in shelf sediments along the west coast of South Africa and Namibia.
- Gold placers occur along the coast of Alaska on the East Pacific shelf.
- The tin ore, cassiterite, a residue of granite weathering, occurs in the shelf of South East Asia.
C) Marine hydrocarbon deposits
- Huge quantities of hydrocarbons can be formed only at depths within organic-rich layers greater than 1500m.
- Formation of exploitable reservoirs of hydrocarbons requires migration (from their source rocks) to geological traps comprising a porous reservoir rocks and overlain by an impermeable horizon.
- Common geological traps for hydrocarbons include shales, salt domes (evaporites; also rich in sulphur), and anticlinal folds of permeable and non-permeable strata.
- In addition to liquid hydrocarbons, natural gas is also common.
- Of the estimated reserves of oil worldwide at the beginning of the 21st Century, which is one trillion barrels about 252 billion barrels (25%) lie in marine environments.
- Similarly, the total worldwide resources of natural gas are estimated at about 4,000 trillion cubic feet, of which about 26 per cent are marine.
- These reserves of oil and gas are located as subsurface deposits almost exclusively on the continental shelves.
- The abyssal plains probably contain insufficient thickness of sediments (less than 1 km) to yield hydrocarbon accumulations.
- Of the twenty-five largest offshore production fields, eight are in the Persian Gulf and eight others are in the North Sea (here hydrocarbons are available at a shallow depth).
- The remaining ones are located in the Gulf of Mexico, East Asia (South China Sea), South Asia, etc.
- The western coast of India has shown promising reserves.
- Besides oil, submerged coal deposits are to be found in the coast of Maharashtra in India.
Challenges in harnessing marine hydrocarbon resources
- The cost of production from deep marine environments is economically unviable considering the present demand.
- Gas and oil exploration increase the risk of marine pollution from accidental oil spills. Existing response technologies are inadequate to contain and recover spills.
D) Marine manganese nodules (Polymetallic nodules) and crusts
- Manganese nodules are concentrations of iron and manganese oxides, that can contain economically valuable concentrations of manganese (~30%),nickel (1.25-1.5%), copper (~1%) and cobalt (~0.25%).
- Other constituents include iron (6%), silicon (5%) and aluminium (3%).
- They are thought to have formed from the precipitation of metals from seawater, hot springs associated with volcanic activity and metal hydroxides through the activity of microorganisms.
- Their abundance, composition, and their occurrence as loose material lying on the surface of the seabed make nodules potentially attractive to future mining.
- Manganese-rich crusts, similar in composition to the nodules, occur on rocky outcrops.
- The top ten countries that have the greatest resource potential of nodules and crusts are the United States of America, Madagascar, Brazil, Antarctica, Argentina, Japan, South Africa, Canada and India.
- Papua New Guinea is one of the few places where nodules were located in shallow waters.
- However, the expense of bringing the ore up to the surface proved to be expensive.
E) Central Indian Ocean Basin (CIOB)
- Manganese nodules in Indian Ocean cover a large area, over 10 million sq. km.
- Large areas in the basins east of the Central Indian Ridge (ridge along the Reunion Hotspot) contains nodules with a high percentage of manganese, nickel and copper.
- India has exclusive rights to explore polymetallic nodules from seabed in Central Indian Ocean Basin (CIOB).
- These rights are over 75000 sq. km of area in international waters allocated by International Seabed Authority for developmental activities for polymetallic nodules.
- Difficulty and expense of developing and operating mining technology that could economically remove the nodules from depths of five or six kilometres.
- Continuing availability of the key minerals from land-based sources like nickel at market prices.
- Mining is not economically viable for the next two decades.
MARINE GAS HYDRATE DEPOSITS
- Gas hydrate is an icy crystalline compound located at great ocean depths and in shallow polar waters.
- It is composed of gas molecules, normally methane, encaged within water molecules.
- At great ocean depths due to cold temperatures and high ocean pressure gas hydrate remain solid.
- The source of the dissolved gas is from the breakdown of organic matter trapped within marine sediment.
- Hence, gas hydrate deposits are likely to occur everywhere the seafloor exceeds 500 m (or 300 m in high latitudes), and where there is a source of unoxidsed organic carbon in marine sediments.
- On dissociation at standard atmospheric pressure, gas hydrate yields approximately 164 times its own volume of methane gas.
- Gas hydrates are estimated to hold many times more methane than presently exists in the atmosphere and up to twice the amount of energy of all fossil carbon-based fuels combined.
- Gas hydrates are known from the Atlantic and Pacific margins of both North and South America, especially at equatorial latitudes.
Challenges in economic exploitation of gas hydrate deposits
- Harnessing methane from gas hydrates is extremely challenging as they are stored deep in the ocean.
- Methane hydrates break at higher temperatures and lower pressures, presenting a challenge in the mining.(Methane is a greenhouse gas that traps heat twenty times more competently than carbon dioxide)
- Gas hydrate reservoirs are extremely sensitive as their mining could unlock excess methane into atmosphere that can catastrophically accentuate global warming.
- Once they hit warmer waters and lower pressures, they break down into methane gas.
- The driving force behind the release of methane gas is the warming of oceans worldwide.
Natural gas hydrate in North Indian Ocean
- 2016: ONGC discovered large, highly enriched accumulations of natural gas hydrate in the Bay of Bengal.
- ONGC plans to start pilot production from its discovery from 2017.
A) Energy from Tides
- The tides, during rise and fall, release a lot of energy by striking against the shore. This piston action can be used to operate a turbine and produce electricity.
- The USA, the CIS, Japan and France are producing power from tides.
B) Ocean Thermal Energy Conversion (OTEC)
- In tropical seas, the surface temperature is about 25 °C to 30 °C, while the sub-surface temperature is 5 °C.
- This vertical difference of 25 °C is enough to generate electricity.
- Belgium and Cuba are producing power in this way.
- 2008: An experimental 1MW plant at Kulasekarapattinam in Tamil Nadu was set up.
C) Geothermal Energy
- Tapping heat from fracture zones and active volcanoes undersea.
- Several desalination technologies are in operation, but as yet they are not being used on a large scale, as they are costly.
Technologies adopted in desalinization of sea water
- Electrodialysis employs iron-selective membranes for the desalination of brackish water.
- Flash distillation technique is in use in Saudi Arabia, Kuwait, Island, Pakistan, Chile, and India.
- Reverse osmosis is the most widely used method. Suitable osmotic membranes are used which reject salts and allow water to pass through when sea water is put under high pressure.
- At the base of the food chain are the planktons—phytoplankton and zoo-planktons. These are the food for many marine animal species.
- Benthos (sea surface) resources include animals such as crustaceans (prawn, shrimp, crab, lobster) and shellfish or molluscs (mussels, oysters).
- Marine animals provide oil, fur, leather, glue and cattle feed.
- Marine plants and animals are used in curative medicine.
- Seafoods are of high nutritional value.
- Edible fish are of three main types, based on the location of habitat.
- Pelagic fish (mackerel, herring, anchovies, tuna) breed near the surface of seas.
- Demersal fish (haddock, cod, halibut, sole in the temperate region, and snapper and garoupa in tropical waters) feed on or near the sea bed of the continental shelf.
- Then there are the migratory anadromous fish (salmon) that live in the sea but move into fresh water of coastal rivers every year.
- Whales are mammals of the ocean and have been caught not only for food but for industrial and medicinal purposes as well.
- Algae such as sea lettuces are used in soups and salads and for flavouring.
- Kelp can be cultivated for producing methane gas and used as an energy source by bioconversion.
- Brown algae produce algin, which is used as stabilisers in the paints industry, to strengthen ceramics, and to thicken jams.
- Red algae provide agar and carrageenan. Agar is an important medium for bacterial culture in research.It is also an ingredient in desserts and pharmaceutical products.
- Carrageenan is used as a stabiliser and emulsifier in ice-creams, and in cosmetics and medicines.
UNITED NATIONS INTERNATIONAL CONFERENCES ON THE LAW OF THE SEA (UNCLOS)
- UNCLOS is an international agreement that defines the rights and responsibilities of nations where use of the oceans’ waters by them is concerned.
- UNCLOS deal with aspects like delimitation, control of environmental pollution, commercial activities in the seas, technology transfer and settlement of disputes between States with reference to ocean matters.
- It also creates a legal regime for controlling mineral resource exploitation in deep seabed areas beyond national jurisdiction, through an International Seabed Authority.
- The UNCLOS came into force in the year 1994. It has been signed by more than 150 countries.
- The USA has signed the treaty but has not ratified it.
- UNCLOS uses a consensus process rather than a majority vote to discourage groups of nation-states dominating negotiations.
- Four main decisions have been widely accepted since 1978.
A) Territorial waters
- Territorial waters are those waters over which a state has full sovereignty
- Territorial waters extend for 19 km (12 miles) from the coast.
- Territorial waters include fjords, estuaries and land between the mainland and offshore islands in the internal waters.
B) Contiguous Zone or Pursuit Zone
- A further contiguous zone of 19 km is recognized in which the coastal state can act against those who break the law (smugglers, pirates, illegal immigrants etc.) within the true territorial waters.
- This, in other words, is a pursuit zone.
C) Exclusive Economic Zone (EEZ)
- Exclusive economic zone (EEZ) starts at the same baseline as the territorial waters.
- EEZ extend for 320-km (200-mile) from the baseline.
- Within the EEZ the coastal state has the right to exploit all economic resources — fish, minerals, oil and gas and energy production.
- The state may extend these rights to the edge of the shelf — as much as 1280 km (800 miles) in some cases — though this does not include rights to the sea itself beyond the 320 km EEZ.
- Land-locked and geographically disadvantaged states can participate on an equitable basis in exploiting an appropriate part of the surplus of the living resources of the EEZs of coastal states.
- In the EEZ and on the continental shelf, all marine scientific research is subject to relevant coastal State’s consent. The coastal states, in turn, are expected to grant consent for peaceful purposes to other States.
D) High Seas
- Beyond all the zones in which individual countries can claim control are the high seas.
- The high seas are free for navigation by vessels of all nations.
- The oceans may also be used freely for the laying of submarine cables, and the airspace over them is also free.
- The oceans may also be freely fished by all nations, though some international agreements seek to control overfishing, which endangers some species.
- The States must share with the international community part of the revenue derived from exploiting resources on the continental shelf extending beyond 200 miles.
- Special protection should be accorded to highly migratory species of fish and sea mammals.