Introduction of Oceanography


General introduction

  • The Earth’s surface is divided into major two types: oceanic, with a thin dense crust about 10 km thick, and continental, with a thick light crust about 40 km thick which are also known as first-order relief features.
  • The ocean and seas cover 70.8% of the surface of the earth, which amounts approximately to 361,254,000 km2.
  • The study of the ocean is oceanography which focuses on the study of physical properties and dynamics of the ocean.
  • The average depth of oceans is 3800m
  • Hypsographic or hypsometric curve is a technique used for measuring the ocean depth as well as elevation of a relief.

Major Ocean relief features

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  • Continental shelf
  • Continental slope
  • Continental rise
  • Deep sea plains
  • Deep ocean Trench
  • Continental shelf
    • The continental shelf extends seaward from the shore with an average gradient of 1 in 500.
    • Average depth of the continental shelf is 200m.
    • Average slope of the continental shelf is 1 degree.
    • It covers approximately 7.5% total ocean cover.
    • Worlds 20% production of crude oil and natural gases are come from continental shelf.
  • Continental slope
    • Average slope of continental slope is 2 – 5 degree.
    • Average depth of the continental slope is 3600 – 4000m.
    • It covers approximately 5.5% total ocean cover.
    • The percentage of Continental slope in Atlantic Ocean is 12.4%, in Pacific Ocean 7% and in Indian ocean it is 6.5%.
  • Continental Rise
    • The continental rise is slightly sloping between the continental slope and the deep seabed abyssal plain.
    • Average slope is 0.5 – 1 degree.
    • Average depth lies in between 2000 – 3000m.
  • Deep sea plain
    • Average depth of Deep sea plain lies between 3000 – 6000m.
    • It covers approximately 75.9% total ocean cover.
    • The percentage of deep sea plain in Pacific Ocean is 80.3%, in Indian ocean 80.1% and in Atlantic Ocean it is 54.9%.
  • Ocean Trench
    • Deepest part of the ocean.
    • Generally, trenches are found near to coast line and parallel to the coast.
    •  World’s deepest trench is mariana trench.
    • Normally the ocean trench depth is 5500m.
    • Plate tectonic theory is most relevant theory for expanding the origin of ocean trenches.
Mariana TrenchPacific Ocean10,984 m (36,037 ft)
Tonga TrenchPacific Ocean10,882 m (35,702 ft)
Philippine TrenchPacific Ocean10,545 m (34,596 ft)
Kuril–Kamchatka TrenchPacific Ocean10,542 m (34,587 ft)
Kermadec TrenchPacific Ocean10,047 m (32,963 ft)
Izu-Bonin Trench (Izu-Ogasawara Trench)Pacific Ocean9,810 m (32,190 ft)
Japan TrenchPacific Ocean10,375 m (34,039 ft)
Puerto Rico TrenchAtlantic Ocean8,800 m (28,900 ft)
South Sandwich TrenchAtlantic Ocean8,428 m (27,651 ft)
Peru–Chile Trench or Atacama TrenchPacific Ocean8,065 m (26,460 ft)
Source :- “So, How Deep Is the Mariana Trench?”, Chase Ocean Engineering Laboratory of the University of New Hampshire, 2014

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Minor Relief features

  • Ridges: Mid-oceanic ridges or submarine stripes are underwater mountain systems formed by plate tectonics activities.
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  • Seamounts: It is a mountain with pointed tops, rising from the beach that does not reach the surface of the sea.
  • Guyots: The flat-topped mountains (seamounts) are known as guyots, eg:- Kuko Guyot (estimated 24,600 km2), Suiko Guyot (estimated 20,220 km2), and the Pallada Guyot (estimated 13,680 km2).
  • Coral reefs: Coral reefs are formed by small animal colonies found in seawater that contain certain nutrients (calcium carbonate).

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