Introduction of Oceanography

General introduction: Oceanography

• The Earth’s surface is divided into two major types: oceanic, with a thin dense crust about 10 km thick, and continental, with a thick light crust of about 40 km which are also known as first-order relief features.
• The ocean and seas cover 70.8% of the surface of the earth, which amounts to approximately 361,254,000 km².
• The study of the ocean is oceanography which focuses on the study of the 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 the elevation of a relief.

Major Ocean relief features

• 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.
  • The average depth of the continental shelf is 200m.
  • The average slope of the continental shelf is 1 degree.
  • It covers approximately 7.5% of the total ocean cover.
  • Worlds 20% production of crude oil and natural gases have come from the continental shelf.
• Continental slope
  • The average slope of continental slope is 2 – 5 degrees.
  • It covers approximately 5.5% of the total ocean cover.
  • The percentage of the Continental slope in the Atlantic Ocean is 12.4%, in the Pacific Ocean 7%, and in the Indian Ocean, it is 6.5%.
• Continental Rise
  • The continental rise is slightly sloping between the continental slope and the deep seabed abyssal plain.
  • The average slope is 0.5 – 1 degree.
  • The average depth lies between 2000 – 3000m.
• Deep sea plain
  • The average depth of the deep sea plain lies between 3000 – 6000m.
  • It covers approximately 75.9% of the total ocean cover.
  • The percentage of deep-sea plain in the Pacific Ocean is 80.3%, in the Indian ocean 80.1% and in the Atlantic Ocean, it is 54.9%.
• Ocean Trench
  • The deepest part of the ocean.
  • Generally, trenches are found near to coastline and parallel to the coast.
  • The world’s deepest trench is the Mariana trench.
  • Normally the ocean trench depth is 5500m.
  • Plate tectonic theory is the most relevant theory for expanding the origin of ocean trenches.

Trench	Location	Depth
Mariana Trench	Pacific Ocean	10,984 m (36,037 ft)
Tonga Trench	Pacific Ocean	10,882 m (35,702 ft)
Philippine Trench	Pacific Ocean	10,545 m (34,596 ft)
Kuril–Kamchatka Trench	Pacific Ocean	10,542 m (34,587 ft)
Kermadec Trench	Pacific Ocean	10,047 m (32,963 ft)
Izu-Bonin Trench (Izu-Ogasawara Trench)	Pacific Ocean	9,810 m (32,190 ft)
Japan Trench	Pacific Ocean	10,375 m (34,039 ft)
Puerto Rico Trench	Atlantic Ocean	8,800 m (28,900 ft)
South Sandwich Trench	Atlantic Ocean	8,428 m (27,651 ft)
Peru–Chile Trench or Atacama Trench	Pacific Ocean	8,065 m (26,460 ft)

Minor Relief features

• Ridges: Mid-oceanic ridges or submarine stripes are underwater mountain systems formed by plate tectonics activities.

• 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).