mariana trench

Zones in the Ocean

  • Scientists have divided the ocean into five main layers. These layers, known as “zones”, extend from the surface to the most extreme depths.
    • Epipelagic Zone –
      • The surface layer of the ocean is known as the epipelagic zone.
      • It extends from thesurface to 200 meters (656 feet).
      • It is also known as the sunlight zonebecause this is where most of the visible light exists.
    • MesopelagicZone 
      • Below the epipelagic zone is the mesopelagic zone, extending from 200 meters (656 feet) to 1,000 meters (3,281 feet).
      • The mesopelagic zone is sometimes referred to as the twilight zone or the midwater zone.
      • The light that penetrates to this depth is extremely faint.
      • Bioluminescent creatures(visible light produced by the creatures themselves) starts appearing in this zone.
    • Bathypelagic Zone 
      • This zone extends from 1,000 meters (3,281 feet) down to 4,000 meters (13,124 feet).
      • It is sometimes referred to as the midnight zone or the dark zone.
    • Abyssopelagic Zone –
      • It is also known as the abyssal zoneor simply as the abyss.
      • It extends from4,000 meters (13,124 feet) to 6,000 meters (19,686 feet).
      • The water temperature is near freezing, and there is no light at all.
    • Hadalpelagic Zone –
      • This layer extends from 6,000 meters (19,686 feet) to the bottom of the deepest parts of the ocean.
      • These areas are mostly found in deep water trenches and canyons.
      • The deepest point in the ocean is located in the Mariana Trench off the coast of Japan at 35,797 feet (10,911 meters).
      • The temperature of the water is just above freezing, and the pressure is 800 times as that on the surface.
      • In spite of the pressure and temperature, life can still be found here.

Oceanic Trenches

Deep-sea trench, also called oceanic trench, any long, narrow, steep-sided depression in the ocean bottom in which occur the maximum oceanic depths, approximately 7,300 to more than 11,000 meters (24,000 to 36,000 feet). They typically form in locations where one tectonic plate subducts under another.

Deep-sea trenches generally lie seaward of and parallel to adjacent island arcs or mountain ranges of the continental margins. They are closely associated with and found in subduction zones—that is, locations where a lithospheric plate bearing oceanic crust slides down into the upper mantle under the force of gravity. The result is a topographic depression where the oceanic plate comes in contact with the overriding plate, which may be either oceanic or continental. If the overriding plate is oceanic, an island arc develops. The trench forms an arc in plan view, and islands with explosive volcanoes develop on the overriding plate. If the overriding plate is continental, a marginal trench forms where the topographic depression appears to follow the outline of the continental margin. Explosive volcanoes are found there too.

  • The Five Deeps Expedition is the first manned expedition to the deepest points in each of the world’s five oceans.

Five spots in oceans where the expedition will go are:

  • Puerto Rico Trench(Atlantic Ocean)
  • South Sandwich Trench(Southern Ocean)
  • Java Trench(Indian Ocean)
  • Challenger Deep(Pacific Ocean)
  • Molloy Deep(Arctic Ocean)

List of Trenches

Pacific Ocean

·         Challanger Deep (Mariana)

·         Tonga

·         Galathea

·         Kuril-Kamchatka

·         Karmadec

·         Richards Deep (Aleutian)

Atlantic Ocean

·         Puerto Rico

·         South Sandwich

·         Romanche

Indian Ocean

·         Diamentina

·         Java

Arctic Ocean

·         Litke Deep

  •     South China Sea-Manila Trench
  •     Southern Ocean, Australia- Murray Canyon
  •     Mediterranean- Calypso (Hellenic)
  •     Banda Sea- Weber Deep
  •     CaribbeanCaymon Trough

India’s Deep Ocean Mission

  • Union Ministry of Earth Sciences, Government of India has also launched a ‘Deep Ocean Mission’ for exploration of polymetallic nodules in the Central Indian Ocean Basin.
  • Polymetallic nodules contain multiple metals like copper, nickel, cobalt, manganese, iron, lead, zinc, aluminum, silver, gold, and platinum, etc. in variable constitutions and are precipitate of hot fluids from upwelling hot magma from the deep interior of the oceanic crust.
  • Of these, cobalt, copper, and nickel are of much importance and in great demand in India as cobalt is used extensively in medical treatment and nickel in batteries.
  • It will reduce India’s dependence on imports of cobalt and other rare earth metals.

Source- NCERTs/Britannica/Internet

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