Ocean deposits and Coral Reefs

Ocean deposits and Coral Reefs

Ocean deposits can be classified into 4 major categories -

1.   Lithogenous/Terrigenous deposits -

• Deposits which are derived from land.
• For example - Sand, Gravel, Silt, Mud, etc

2.   Biogenous/Organic deposits - 

• Deposits which are derived from various life forms.
• For example - Shell, Corals, Ooze, etc
• Ooze - Ooze is the deposition of dead micro-organism in sea. It is the shelly skeleton remains of micro-organisms and marine animals.
• Ooze are of two types -

1. Siliceous Ooze - Ooze which is rich in Silica content
2. Calcareous Ooze - Ooze which is rich in Calcium content

3.   Hydrogenous/Inorganic deposits - 

• Deposits which are inorganic in nature.
• For example - Red Clay, Polymetallic nodules, Mineral salts, Evaporite, etc.

Polymetallic nodules

4.   Cosmogenous deposits -

• Deposits which are derived from space/space debris.
• For example - Meteoritic debris

Coral Reefs

• Corals are huge masses of limestone or dolomite accumulated by lime secreting organism known as Coral Polyps.
• They are developed due to the symbiotic relationship between Coral Polyps and an algae called Zooxanthellae. 
• Coral reefs provide habitat to nearby 31 Phyla of animals, leading to rich biodiversity. Therefore, it is also known as 'Rainforest of Ocean'.
• Coral reefs are found along the ocean floor near to the continental shelf.

Types of Coral Reefs -

1.   Reef Building corals (Tropical & Sub-tropical regions)

2.   Cold water corals (along the ocean bottoms)

Reef building corals (Coral reefs) 

• Reef building corals are commonly known as Coral reefs.
• Conditions required -
• Temperature - 20℃ or above
• Latitude - found between 30° N and 30° S
• Depth - 200-250 ft
• Sediments - Water must be sediment free, i.e. clean and clear water
• Salinity - Salinity should be average
• Sub-marine platform - A sub-marine platform like Sea Mounts, Guyots, etc is required on which Corals can grow
• Because of the above reasons Coral reefs are not found along the eastern coast of India (because of huge sediment deposits from many Himalayan rivers)
• Also, Coral reefs are not found along the western margin of the continent due to the presence of Cold ocean current.

Stages of Coral Reefs/Types of Coral Reefs

1.   Fringing reefs 

• They are directly attached to a shore or border it with an intervening shallow channel or lagoon.
• Example - Greater Caribbean region

2.   Barrier reefs 

• They are separated from a mainland or island shores by a deep channel or lagoon.
• Example - Great Barrier reef (Australia)

3.   Atoll reefs 

• They are circular coral reefs developed surrounding a sea mountain or a guyot or an island.
• Example - The islands of Pacific ocean and Lakshadweep

Distribution of Coral reefs 

• Corals are found in Atlantic, Indian and Pacific Ocean.
• Atlantic Ocean -
• around Caribbean sea
• Gulf of Mexico
• Indian Ocean -
• around Red sea
• Persian Gulf
• Western and Southern Indian Ocean
• Along African eastern coast
• Maldives
• Andaman & Nicobar
• Pacific Oceans -
• Islands of Southern Pacific Ocean
• Hawaii island
• Coral triangle in Western Pacific Ocean (located between Indonesia, Philippines, Malaysia and Australia)

Coral Bleaching 

• Corals receives their colouration from the algae in the symbiotic relationship.
• Coral bleaching refers to the loss of colours of corals due to stress induced by the expulsion of symbiotic algae.
• Major event of coral bleaching happened in Indian Ocean during 1997-98.
• Coral bleaching happened in Great Barrier Reef, Australia because of El Nino (2014) in 2014-17.
• Factors which led to Coral Bleaching 
• △ Temperature
• △ Salinity
• Increase in sediments
• Acidification of Ocean Water
• Pollution
• Increase in the number of cyclones
• El Nino which affects the normal weather pattern

Significance of Coral Reefs 

• Coral reefs provide habitat to a number of species.
• They are used as jewels, ornaments, etc.
• They are best spot for fishing activities.
• Coral reefs act as an indicator of global temperature change (in ocean water).
• Economical benefit - Tourism

Previous Article - Salinity of the Ocean 

Next Article - Ocean currents

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Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own. 

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