Introduction to Oceans

Introduction-

• Oceans basin covers approximately 70.8% of earth surface and Continents cover 29.2% of earth surface. 

• The southern hemisphere is dominated by oceans and covers 80.4% of the area and Northern hemisphere contains most of the land but it is also dominated by oceans and covers approximately 60% of the area. 

• The centre of land Hemisphere -in the city of Nantes, France.

• The centre of Water Hemisphere - New Zealand's Bounty Islands in the Pacific Ocean. 

Division of Water on Earths surface-

Oceans(97.23%)>Ice caps(2.05 %)>Glaciers and Ground water (0.68%)>Lakes(0.01%)>Soil Moisture (0.005%)>Atmosphere (0.001%)>Streams and rivers(0.0001%)>Biosphere(0.00004%). 

Process through which water enters into our surroundings-

• Water in oceans through -Evaporation,Evapotranspiration,Sublimation.

Water in the atmosphere-

• Condensation and Precipitation. 

Water storage in ice and snow-

• Snowmelt runoff to streams. 

Relief of ocean floor-

Hypsographic curve represent the distribution of earths surface with depth and the elevation. 

1.Continental Shelf-

• Continental shelf  is the shallow submerged extension of continent .

• Depth : between 120 to 370 metres.

• It is the shallowest part of the ocean and its shows an average gradient of 1° or even less.

• They constitutes the 7.5% of the total area of the oceans.

• Shelf break is a very steep slope continental shelf ends .

• They are very narrow or almost absent along some of the margins like the west coast of Sumatra, the coasts of Chile, etc.

• On the contrary, there are some regions which have very large continental shelf for example -the Siberian shelf in the Arctic Ocean, the largest in the world, stretches to 1,500 km in width.

• There is Massive sedimentary deposits on the continental shelves and therefore they are source of fossil fuels.

• They are formed due to submergence of a part of a continent,relative rise in sea level and Sedimentary deposits brought down by rivers. 

In India -

• The continental shelf off the western coast of India is much lesser than that of the eastern coast.

• The west coast has a much wider shelf in the northern region that extends to some 300 km in the Bombay Offshore Region.

• The vast shelf width in this region has been attributed to the tectonic setting of the region.

• The shelf narrows down from north to south along the west coast.

• One of the striking features of the continental shelf is the presence of submarine canyons which extend to the continental slope. 

Example-  Godavari Canyon. 

Some of the Examples are as below-

• Great Banks around Newfoundland.

• Coral reef shelf  at Queensland, Australia.

• Glaciated shelf Surrounding Greenland.

• Siberian shelf in the Arctic Ocean.

Importance-

• Presence of microscopic plants and animals like planktons.

• Source of many  fishes, mineral like sand ,gravel etc.

The continental slope-

• The continental slope acts as the bridge between the continental shelf and the ocean basins.

• The gradient of the slope region varies between 2-5°and depth of this region varies between 200 and 3,000 m.

• They are potential sites for economic minerals.

• The seaward edge of the continental slope loses gradient at this depth which gives rise to continental rise.

Continental rise-

• At the base of the continental slope, a high bathymetric region is termed as continental rise.

• For the legal demarcation of the Exclusive Economic Zone (EEZ) of a country, the thickness of sediments at the continental rise is very important.

• A 1% sediment thickness is the criteria to extend the EEZ of any country beyond a legal limit of 200 nautical miles (nm).

Deep Sea Plain/Abyssal Plains. -

• Abyssal plains are extremely flat and featureless plains of the deepocean floorand are likely the most level areas on the earth.

• They have different submarine geographical features like plateaus, hills, guyots and seamounts.

• The submarine ridges which have the steep side-slopes reach the sea level and and they sometimes project above the water surface and they appear as islands. Example - Mid Atlantic ridge.

• The floor of the abyssal plain is covered by sediments. These sediments are called oozes.

• There are some of the open seas which do not support enough life to produce ooze on the floor.

• Red Clay is one of the sediment that covers them.

Submarine Ridges-

• There is also similar mountain system beneath the ocean water as that on the surface of the earth .

• These oceanic mountains are known as submarine ridges.

• They are linear belts occurring near the middle of the oceans and are also called mid-oceanic ridges.

• All the mid oceanic ridges constitute a world-wide system which is interconnected from ocean to ocean.

• The Mid-Atlantic Ridge is the largest continuous submerged mountain ridge which runs from north to south in the Atlantic-Ocean. It is in the shape of S. 

Seamounts and Guyots-

• Undersea mountains formed by volcanic activity are called Seamounts.

• Sometimes they rise above the sea in the form of  isolated Islands. Hawaii and Tahiti Islands are the exposed tops of volcanoes. 

Note- The Laccadive Islands of India were formed during the northward migration of Indian Plate after its recent break up during Early Jurassic Period. 

Guyot: Volcano rising above the ocean floor whose top has been flattened by erosion and is covered by water is called Guyot. 

Atoll -

• They are type of  low islands found in the tropical oceans which consists of coral reefs surrounding a central depression. 

Oceanic Deeps or Trenches-

• They are the one of the deepest parts of the oceans.

• The trenches have relatively have steep sides with narrow basins.

• These deeps and trenches are 3-5 km deeper than the surrounding ocean floor.

• Example- Mariana Trench located to the west of Philippines in the North Pacific Ocean is the deepest trench (11,000 metres) and it is also known as Challenger Deep(its lowest point). 

• These are generally located parallel to the coasts facing mountains and along the islands. In general they are  found close to the continents, particularly in the Pacific Ocean.

• They helps to study the movement of earth plates. 

• Majority of them are located in Pacific ocean. 

Relief Features of Different Oceans-

1.Pacific Ocean

• The Pacific Ocean covers one-third of the area of the earth and largest ocean of the world.

Extension-

•  It extends from the coast of Asia in the west to America in the east  and  Bering Strait in the north to the Cape Adare (Antarctica Continent) in the South.

• The oceanic surface in general is uniform, with broad gentle swells and depressions.

• It has a broad triangular shape.

• Nearly All along the coast the folded mountains are found parallel to it.

• The centers of both the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean.

Different Basins of Pacific oceans-

Philippine basin –

• It is situated east of Philippine Islands. 

Aleutian basin –

• It is Located north of the Aleutian island. 

West Caroline basin-

• Located at east of Philippine basin.

Fiji basin –

• Located south of Fiji Island. 

East Australian basin –  

• It is compact and circular in form. 

South-eastern Pacific basin –  

• It extends west of Peru and Chile with Baver deep.

Pacific Antarctic basin-

• It extends south-west of Chile.

South Australian or Jeffrey’s basin –

• longitudinal basin extending south of Australia.

Tasman Basin -

• It is located between New Zealand and eastern Australia. 

Deeps and Trenches-

Total 32 deeps are recorded in the Pacific, out of which most of them are in the trenches. 

Other Trenches includes-

Ryukyu

Bonin

Yap Palau

New Hebbrides

Soloman

Islands and Land mass of Pacific Ocean-

• Pacific Ocean roughly consists of around 25,000 islands.

The islands which are located entirely within the Pacific Ocean can be divided into three major groups which are known as-

Micronesia, Melanesia and Polynesia.

Micronesia-

• It  lies north of the equator and west of the International Date Line.

• It includes the Mariana Islands in the northwest, the Caroline Islands in the center, the Marshall Islands to the east and the islands of Kiribati in the southeast.

Melanesia-

• It is located  to the southwest and includes New Guinea( the world's second largest island after Greenland and by far the largest of the Pacific islands).

• The other main Melanesian groups from north to south are the Bismarck Archipelago, the Solomon Islands, Santa Cruz, Vanuatu, Fiji and New Caledonia.

Polynesia

• Polynesian Triangle :there are three different regions which when connected with each other ,forms the Polynesian triangle and these regions are  Hawaii, New Zealand, and Easter Island.

• The other main island groups located within the Polynesian Triangle are Samoa, Tonga , Tokelau, Niue, Wallis and Futuna, the Cook Islands, Tuvalu, , and French Polynesia.

Different Islands-

Continental islands-

• the Aleutians, the Kurils, the Ryukyus, Taiwan, the Malay Archipelago (including New Guinea), and New Zealand. 

Coral islands-

• The Marianas, the Marshalls, the Carolines, Kiribati (Gilbert Islands), and Tuvalu (Ellice Islands) etc.

Marginal seas of the Pacific Ocean

Sea of Okhotsk. 

South China Sea. 

Tasman Sea. 

Yellow Sea. 

Bering Sea. 

Celebes Sea. 

Coral Sea. 

East China Sea. 

Philippine Sea. 

Sea of Japan. 

Division of Pacific ocean-

North and Central Pacific-

• It is characterized by maximum depth and a large number of deeps, trenches and islands.

• Some of the trenches are- Aleutian,Kuril etc.

• The central pacific is the largest and the most geologically stable portion. 

West and South-West region-

• The western Pacific region is delineated by a discontinuous chain of oceanic trenches, which extends from the north at the Aleutian Trench, down through the Kuril and Japan trenches, and continues southward towards the Tonga and Kermadec trenches.

• The boundary of this region lies towards the seaward side and ends in the vicinity of the northeast of North Island, New Zealand.

Eastern and south Eastern Pacific

• Eastern pacific extend from Alaska to Tierra del Fuego.

• It runs parallel to American mountain system with narrow continental shelf.

• The Tonga and Atacama trenches are some of the trenches.

Important Ridges of Pacific oceans-

• East pacific ridge.

• Cocos ridge.

• San Felix Juan Fernandes ridge.

• Hawaiian ridge.

• Chattam rise.

• Tasmania ridge.

• Norfolk island ridge.

• Caroline-Solomon ridge etc.

The Atlantic Ocean-

• In term of size ,the Atlantic Ocean is the Earth's second-largest ocean.

• It covers approximately 20 percent of Earth's surface and it covers approximately 29 percent of water surface area.

• It is of S Shape.

• The region stretches longitudinally from the east, covering Europe and Africa, to the west, including the Americas..

Continental Shelf-

• It has prominent continental shelf and this continental shelf have varying widths.

• The length of the continental shelf is maximum in Northern Atlantic coasts. 

• Grand banks continental shelf is the most productive continental shelf in the world due to fishing. 

Seamounts and guyots

• They are present in significant numbers but not as significant as in pacific ocean and some of them have formed the islands. 

• Examples - Pico Island of Azores, Gape Verde Islands, Canary Islands etc..

Important trenches of The Atlantic oceans

• Devil's Hole (North Sea).

• Faroe–Shetland Channel.

• The Gully (Atlantic).

• Hellenic Trench.

• Kings Trough.

• Milwaukee Deep.

• Norwegian trench . 

• Puerto Rico Trench(the deepest part of the Atlantic Ocean ).

• Romanche Trench.

• South Sandwich Trench.

• Tongue of the Ocean.

Important islands of The Atlantic ocean-

• Cape Verde Islands. 

• Azores. 

• Canary Islands (Spain). 

• Savage Islands (Portugal). 

• The Bahamas. 

• Barbados. 

• Bermuda (UK). 

• Newfoundland (Canada). 

• Oak Island (Canada). 

• Sable Island (Canada). 

• Bouvet Island (Norway). 

• Falkland Islands (UK) etc.

Mid-Atlantic Ridge

• The most distinctive characteristic of the Atlantic Ocean is the Mid-Atlantic Ridge, which extends from north to south and runs parallel to the 'S' shape of the ocean.

• The Mid-Atlantic Ridge divides the Atlantic longitudinally into two-halves, in each of which a series of basins are delimited by secondary, transverse ridges.

Some of the Basins of The Atlantic Ocean-

Guinea basin-

• The elongated shape landmass, positioned between Guinea Ridge and Sierra Leone Rise, stretches in a northeast to southwest direction.

Angola basin -

• It is located between the equator and 30°S latitude.

Labrador basin -

• It extends between the continental shelf of Greenland in the north and Newfoundland Rise in the south. 

Brazilian basin -

• It is confined between the equator and 30°S latitude and east coast of Brazil in the west and Para Rise in the east.

Spanish basin -

• It is located between the mid- Atlantic Ridge and Iberian Peninsula. It is bordered by Azores Rise in the south. 

North and South Canary basin -

• It consist of two almost circular basins. 

Cape Verde basin -

• It is located between the mid- Altlantic Ridge and west African coast. 

Marginal seas of the Atlantic Ocean-

• Gulf of Mexico.

• Hudson Bay.

• Irish Sea.

• Labrador Sea.

• Argentine Sea.

• Caribbean Sea.

• English Channel.

• North Sea.

• Norwegian Sea.

• Scotia Sea etc.

Important rise/ridges of The Atlantic ocean

• Newfoundland rise.

• Azores rise.

• Sierra leone rise.

• Parra rise.

• Walvis rise.

• Guinea rise.

The Indian Ocean-

• The Indian Ocean is the third-largest ocean of the world.

• It covers 19.8% of the water on Earth's surface.

• The Indian ocean is the most intricate of the three significant oceans on the planet. It is geologically the most youthful and also the smallest in size.

• The Indian Ocean is surrounded by Asia to the north, Africa to the west, and Australia to the east, with its southern boundary being the Southern Ocean or Antarctica.

Continental Shelves-

• The continental shelf extends to an average width of about 120 km in the Indian Ocean, with its widest points off Mumbai (Bombay) on the western coast of India and off northwestern Australia.

• There is wide range of variation in the continental shelves of the Indian Ocean. 

Mid Oceanic Ridges-

• The oceanic ridges that run through the middle of the ocean take the shape of an inverted Y on the ocean floor. The starting point of this Y is the Carlsberg Ridge, which is situated in the upper northwest of the ocean floor in the Arabian Sea. From there, the ridge turns southwards, passing by the Chagos-Laccadive Plateau, and eventually becoming the Mid-Indian (or Central Indian) Ridge.

• Towards the southeastern region of Madagascar, the ridge splits into two branches. The Southwest Indian Ridge moves towards the southwest direction and eventually merges with the Atlantic-Indian Ridge located south of Africa. Meanwhile, the Southeast Indian Ridge trends towards the east and finally links with the Pacific-Antarctic Ridge situated south of Tasmania.

Ninety - east Ridge-

• It is also located here  which is the longest and straightest in the world ocean. 

Some of the Important ridges are-

Seychelles – Mauritius ridge-

• It bifurcates from the main ridge around 18°S latitude near Mauritius Island. 

Socotra-Chagos Ridge-

• It is also known as Carlesbreg Ridge emerges from the central ridge at 5°S latitude and extends in northwesterly direction upto Gardafuli Peninsula of N. E. Africa. 

Madagascar Ridge -

• It stretches from the southern tip of Madagascar (Malagasy) to 40°S latitude.

• Its further southward extension is known as Prince Edward – Crozet Ridge.

• Ninety East Ridge(already discussed above). 

Important basins-

Atlantic- Indian – Antarctic basin-

• It is in fact the eastward continuation of Atlantic – Antarctic Basin. 

Eastern Indian-Antarctic basin -

• It is located between Amsterdam – St. Paul Plateau and Indian-Antarctic Ridge in the north and north-east and Antarctica in the south.

West Australian basin -

• It is the most extensive basin and forms rectangular shape surrounded by S.E. Indian Ridge in the south – west, Ninety East Ridge in the west, continental shelves of Java-Sumatra in the north-east and the continental shelf of west Australia. 

Oman basin -

• It faces the Gulf of Oman and is spread over the extensive continental shelf. 

Arabian basin -

• It is located in almost circular shape between Laccadive-Chagos ridge and Socotra – Chagos Ridge. 

Somali basin -

• It is bordered by Socotra – Chagos ridge in the north-west.

Mauritius basin -

• It is located between S.W. Indian Ridge and South Madagascar Ridge. 

Mascarene basin -

• It is of oval shape extends between Madagascar and Seychelles – Mauritius Ridge. 

Agulhas-Natal basin -

• It is an elongated basin which is bordered by Madagascar ridge in the north. 

Mid-Indian basin -

• It is bordered by the central ridge in the west and the south-west, by Ninety East Ridge in the east and by the Bengal plateau in the north.

Marginal seas of the Indian Ocean

• Andaman Sea.

• Arabian Sea.

• Bay of Bengal.

• Java Sea.

• Persian Gulf.

• Red Sea.

• Sea of Zanj.

Important Trenches of Indian Ocean-

• Diamantina Fracture Zone.

• Dordrecht Deep.

• Java trench.

• Sumatra Trench.

• Sunda Trench.

Factual Questions on The Oceans

What is the world's largest ocean?

Answer: The Pacific Ocean.

Which ocean has the largest volume of water?

Answer: The Pacific Ocean has the largest volume of water.

What is the deepest part of the ocean and how deep is it?

Answer: The deepest part of the ocean is the Challenger Deep in the Mariana Trench, which is about 36,070 feet (10,994 meters) deep.

What is a seamount?

Answer: A seamount is an underwater mountain that rises at least 1,000 meters above the seafloor.

What is a mid-ocean ridge?

Answer: A mid-ocean ridge is an underwater mountain range that runs through the middle of an ocean.

What is a continental shelf?

Answer: A continental shelf is a shallow underwater area that extends from a continent's shoreline to the point where the slope becomes steep.

What is a continental slope?

Answer: A continental slope is the steep gradient that leads from the continental shelf down to the ocean floor.

What is a hydrothermal vent?

Answer: A hydrothermal vent is an opening in the seafloor where hot water and minerals are released into the ocean.

What is an atoll?

Answer: An atoll is a ring-shaped coral reef that surrounds a lagoon.