General Awareness Oceanography
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Oceanography

Ocean of the World

An ocean is body of saline water that comprises 72 % of Earth's hydrosphere. The ocean contains 97%, of Earth's water and oceanographers have stated that less than 5% of the world ocean has been explored.

Following are the major oceans, which are arranged in descending order by area :

`text (Pacific Ocean)`

• This ocean is the largest ocean or water body of the world and extended from Arctic Ocean to Antarctic Ocean. The ocean is bounded by Asia and Australia in the West and the South and North America in the East.

• The equator sub-divides the Pacific Ocean into North and South Pacific Ocean. The Marina Trench in the Western-North Pacific is the deepest point in the world (10911 metres).

`text( Atlantic Ocean )`

• This ocean ts second largest of the world's oceans and slightly more than half of the pacific ocean. The ocean occupies an elongated, S-shape basin which extending longitudinally between Eurasia and Africa to the East and South and North America to the West.

• The equatorial counter current sub-divides the ocean into North and South Atlantic Ocean at about 8° North.

`text(Indian Ocean)`

• This ocean is third largest ocean in the world. It is bounded by Asia on the North, Africa on the West, Australia on the East and Antarctica on the South.

• The India ocean contain> approximately 20% of the water on the Earth's surface.

`text( Antarctic Ocean )`

It is the fourth largest ocean in the world. It is also known as Southern Ocean, the South Pole Ocean, is a large body of water encircling the continent of Antarctica. The ocean is particularly covered with ice.

`text( Arctic Ocean )`

It is the smallest and shallowest of the world's five major oceans. It is located mostly in Arctic North Polar region and completely surrounded by Eurasia and North America. The ocean is partly covered by sea ice throughout the year and almost completely in winter.

Deepest Points of the Ocean

Ocean Deepest Point
Pacific Mariana Trench
Atlantic Puerto Rico french
Indian Java Trench
Arctic Eurasian Basin

Relief Features of the Oceans

`text(Continental Shelf)`

• The shallow sub-merged extension of the continent is called the continental shelf. It extends to a depth of 100 fathoms (1 fathoms = 1.8 m).

• Average width 70 km; average slope 17 feet/mile or about 1°. Continental shelf covers 7.5% area of the oceans. It extends over 13.3% (If the Atlantic Ocean 5.7% of Pacific Ocean and 4.2% of Indian Ocean.

• If mountains extend along the coast, the shelf will be narrower. About 20 % , petrol and gas are found here. They also provide the richest fishing ground in the world.

`text( Continental Slope)`

• Extends seawards from the continental shelf. It has depth of 200-2000 fathoms (3660 m) and average slope of 20 to 50 degrees.

• The boundary between shelf and slope is known as Andesite Line, names, after the Andesite Rock. They cover about 8.5% of the total ocean area.

`text( Continental Rise)`

It is an area at the foot of the slope, slightly rising due to the accumulation of debris transported over the slope. It has average slope of 0.5° to 1° and oil deposits are found here.

`text(Abyssal or the Deep Sea Plains)`

• It is the deepest and most extensive part of the oceanic floor. It has average depth of 3000 m to 6000 m. It covers about 75.9% of total oceanic area.

• Parts of the Abyssal plains are occupied by raised ridges or submarine mountains and by very deep trenches or canyons.

`text(Deeps/Trenches)`

• Trenches are narrow and steep sides depressions. It are formed, when two plates of the Earth's crust are moving together and one is being pushed down below the other.
• Marina trench (challenger deep) is the deepest trench in the world situated in the NW Pacific oceans, near Philippines. It is more than 11 km deep.

`text(Oceanic Ridges)`

• Oceanic ridges are formed by the volcanic activity along the spreading boundary of plates.

• It is thousands of km long and hundreds of km wide mountain range on the oceanic floor.

• Their summits may rise above the sea level in the form of Islands i.e., Iceland, Azores Island.

`text(Coral Reefs)`

It are formed due to accumulation and the compaction of skeletons of lime secreting organisms known as coral polyps. Corals are found mainly in the tropical oceans and seas because they require high mean annual temperature of ranging between 20°C to 25°C. Corals do not live in deeper waters due to lack of sufficient sunlight and oxygen.

On the basis of nature, shape and mode of occurrence , the coral reefs is classified into three types :

(i) Fringing Reefs - It develop along the continental margins or along the islands.

- The seaward slope is steep and vertical while the landward slope is gentle.
- They are usually attached to the coastal land, but occasionally they are separated from the shore by a shallow and narrow lagoon called 'Boat Channel'.
- This type of reefs are found near Rameshwaram in the Gulf of Mannar.

(ii) Barrier Reefs :- Largest coral reefs off the coastal platform, but parallel to them.

- The reef lies at a distance away from the coast. Hence, a broad lagoon develops between the reef and the shore.
- The Great Barriers Reef of Australia is the largest barrier reef in the ·world.

(iii) Atoll :- A reef of narrow growing corals of horse shoe shape and crowned with palm trees is called an atoll.

- It is formed around an islands or in an elliptical form on a submarine platform.
- Funafuti atoll of Tuvalu is a famous atoll.

Waves

Waves are the oscillatory movements in water mainly produced by winds, manifested by an alternate rise and fall of the sea surface. The waves are the important agents of erosion in the coastal regions, where they carve out various land forms like caves, bays, gulfs, capes and cliffs.

• Seismic waves or tsunamis are the waves caused by earthquakes in volcanic eruptions in the sea bottom.

• The tsunamis, which hit the coast in South-East Asia on 26th December, 2004, caused havoc in that region.

Ocean Currents

• An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon it, such as breaking waves, wind, coriolis effect, temperature and salinity differences and tides caused by the gravitation pull of the Moon and the Sun.

• Ocean currents circulate in clockwise direction in Northern hemisphere and in anti-clock wise direction in Southern hemisphere.

Ocean currents are of two topics :

(i) Warm Currents The ocean currents flowing from lower latitude to higher latitude are known as warm Currents .

(ii) Cold Currents The ocean currents flowing from higher latitude to lower latitude are known as Cold Currents.

• At places where cold current and warm current meets fishing is very favourable. e.g. New found land is favourable for fishing due to meeting of Labrador Current and North Atlantic Drift.

Currents of North Pacific Ocean

`text( Warm Currents)`

• North Equatorial Current : It flows Westwards from the Western coast of Mexico to the Philippines.

• Kuroshio Current : It is an extension of North Equatorial Current near Japan Coast. It flows towards North.

• Alaska Current It flows along the coast of British Columbia and the AIaska Peninsula.

`text(Cold Currents)`

• Oyashio Current : It flows down from Bering sea towards Japan from North pole and it joins Kuroshio currents.

• Okhotsk Current and Kurd Current : It flows down from sea of Okhotsk and joins Kuroshio current to the North of Japan.

• West Wind Drift It flows towards Alaska.

• Californian Current It is an extension of Alaskan currents. It joins finally North Equatorial current and completes clockwise circulation of water.

Currents of South Pacific Ocean

`text(Warm Currents)`

• East Australian Current or Great Barrier Current : It flows towards East coast of Australia from equator towards Pole.

• South Equatorial Current : It originates due to South-East trade winds and flows Westwards and bifurcates near New Guinea.

• Counter Equatorial Current It extends upto Panama Bay. It flows exactly on equator from West to East.

`text(Cold Currents)`

• Peruvian Current (Humboldt current) : It flows from South towards equator on the coast of Chile and Peru.

• West Wind Drift : It flows from Tasmania to Chile coast of South America.

Currents of North Atlantic Ocean

`text(Warm Currents)`

• North Equatorial Current : It is present between Equator and 10°N.

• Cayenne Current It flows adjacent to French Guinea and enters into Caribbean Sea and Gulf of Mexico.

• Florida Current : Cayenne current near Florida (US Coast) is called Florida Current.

• Antilles Current : It flows to the East of West Indies and other islands.

• Gulf Stream : It flows from US coast towards North West Europe under the influence of Westerly winds.

• North Atlantic Drift Gulf Stream bifurcates into
- North Atlantic Drift (warm).
- West Wind Drift (cold) and Canaries current (cold).

`text(Cold Currents )`

• Labrador Current It originates in Baffin Bay and Davis Strait and merges with Gulf Stream near Newfoundland. Newfoundland is a famous zone of fishing, commonly known as Grand Bank.

• Irminger Current or Greenland Current It flows between Greenland and Iceland and merges with North Atlantic drift.

• Canaries Current It flows along the Western coast of North Africa between Madeira Cape Verde and it joins North equatorial current.

• West Wind Drift It flows clockwise from West to East around Antarctica.

Currents of South Atlantic Ocean

`text(Warm Currents)`

• South Equatorial Current: It flows between equator and 10° S

• Brazilian Current : It flows to the East coast of Brazil from equator towards pole.

`text(Cold Currents)`

• Falkland Current : It flows along the South-East coast of South America from South to North.

• Benguela Current : It flows from South to North near the 'Cape of Good Hope'.

• West Wind Drift : It is continuance of Brazilian and Falkland current.

• Guinea Current : It flows near Coast of Guinea (Africa).

Current of the Indian Ocean

• The Asiatic Monsoon influences the currents of the North Indian Ocean, while the currents of South Indian ocean are influenced by the atmosphere's anticyclonic circulation.

• North Equatorial Current : The current flows from East to West and upon reaching the East coast of Africa, a good portion turns Southward, crosses the equator and becomes the Mozambique current.

• Mozambique Current : The Mozambique current flows South along the East coast of Africa from the vicinity of the equator to about 35°, where it becomes Agulhas Stream.

• Agulhas Stream : The Agulhas stream flows Westward along the South-West of Madagascar and joins the Mozambique current along the East African coast.

• West Wind Drift Current : It flows across the Indian ocean to the waters South-West of Australia.

• North-East Monsoon Drift : It flows along the coast of India during winter.

• South-West Monsoon Drift : It flows along the coast of India during Summer.

• South Equatorial Current : It is a significant Pacific, Atlantic and Indian ocean current that flows East-West between the equator and about 20° South.

• Somalia Current : It is an ocean boundary current that runs along the coast of Somalia and Aman in the Western Indian ocean and is analogous to the Gulf Stream in the Atlantic Ocean.
 
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