The continental shelf is the extended perimeter of each continent and associated coastal plain, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs. A continent is one of several large Landmasses on Earth. They are generally identified by Convention rather than any strict criteria with seven regions A coastal plain is an area of flat low-lying land adjacent to a seacoast and separated from the interior by other features An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets This article is about the body of water For other uses see SEA and Seas. Headlands and bays are two related features of the coastal environment

Contents 1 Topography 2 Geographical distribution 3 Sediments 4 Biota 5 Economic significance 6 See also 7 Footnotes 8 References 9 External links

Topography

The shelf usually ends at a point of increasing slope (called the shelf break). The sea floor below the break is the continental slope. Below the slope is the continental rise, which finally merges into the deep ocean floor, the abyssal plain. Abyssal plains are flat or very gently sloping areas of the deep Ocean basin floor The continental shelf and the slope are part of the continental margin. The continental margin is the zone of the Ocean floor that separates the thin Oceanic crust from thick Continental crust.

The shelf area is commonly subdivided into the inner continental shelf, mid continental shelf, and outer continental shelf, each with their specific geomorphology and marine biology. Geomorphology (from Greek: γη ge, "earth" μορφή morfé, "form" and λόγος Logos, "knowledge" Marine biology is the scientific study of living Organisms in the Ocean or other marine or Brackish bodies of water

The character of the shelf changes dramatically at the shelf break, where the continental slope begins. With a few exceptions, the shelf break is located at a remarkably uniform depth of roughly 140 m (460 ft); this is likely a hallmark of past ice ages, when sea level was lower than it is now. ^[1]

The continental slope is much steeper than the shelf; the average angle is 3°, but it can be as low as 1° or as high as 10°. ^[2] The slope is often cut with submarine canyons, features whose origin was mysterious for many years. A submarine canyon is a steep-sided Valley on the Sea floor of the Continental slope. ^[3]

The continental rise is below the slope, but landward of the abyssal plains. Its gradient is intermediate between the slope and the shelf, on the order of 0. 5-1°. ^[4] Extending as far as 500 km from the slope, it consists of thick sediments deposited by turbidity currents from the shelf and slope. A turbidity current or density current is a current of rapidly moving sediment-laden water moving down a slope through air water or another fluid Sediment cascades down the slope and accumulates as a pile of sediment at the base of the slope, called the continental rise. ^[5]

Geographical distribution

The width of the continental shelf varies considerably – it is not uncommon for an area to have virtually no shelf at all, particularly where the forward edge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone such as off the coast of Chile or the west coast of Sumatra. Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins The continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the Sumatra (also spelled Sumatera) is the sixth largest island in the world (approximately 470000 km² and is the largest island entirely in Indonesia (two The largest shelf – the Siberian Shelf in the Arctic Ocean – stretches to 1500 kilometers (930 miles) in width. The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region is the smallest and shallowest of the world's five major The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States The South China Sea lies over another extensive area of continental shelf, the Sunda Shelf, which joins Borneo, Sumatra, and Java to the Asian mainland. The South China Sea is a Marginal sea south of China. It is a part of the Pacific Ocean, encompassing an area from Singapore to the Geologically, the Sunda Shelf is an extension of the Continental shelf of Southeast Asia, covered during Interglacials by the South China Borneo is the third largest island in the world and is located at the centre of Maritime Southeast Asia. Java (Jawa is an Island of Indonesia and the site of its Capital city Jakarta. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf. The North Sea is a marginal, Epeiric sea of the Atlantic Ocean on the European Continental shelf. The Persian Gulf, in the Southwest Asian region is an extension of the The average width of continental shelves is about 80 km (50 mi). The depth of the shelf also varies, but is generally limited to water shallower than 150 m (490 ft). The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International ^[6] The slope of the shelf is usually quite low, on the order of 0. 5°; vertical relief is also minimal, at less than 20 m (65 ft). ^[7]

Though the continental shelf is treated as a physiographic province of the ocean, it is not part of the deep ocean basin proper, but the flooded margins of the continent. Physical geography (also known as geosystems or physiography) is one of the three major subfields of Geography. An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. ^[8] Passive continental margins such as most of the Atlantic coasts have wide and shallow shelves, made of thick sedimentary wedges derived from long erosion of a neighboring continent. The continental margin is the zone of the Ocean floor that separates the thin Oceanic crust from thick Continental crust. Active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to the deep sea. The continental margin is the zone of the Ocean floor that separates the thin Oceanic crust from thick Continental crust. An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer ^[9]

Sediments

The continental shelves are covered by terrigenous sediments; that is, those derived from erosion of the continents. In Oceanography, terrigenous Sediments are those derived from the erosion of rocks on land that is that are derived from terrestrial environments However, little of the sediment is from current rivers; some 60-70% of the sediment on the world's shelves is relict sediment, deposited during the last ice age, when sea level was 100-120 m lower than it is now. "Riverine" redirects here For the use of that term in Maritime geography, see there ^[10]

Sediments usually become increasingly fine with distance from the coast; sand is limited to shallow, wave-agitated waters, while silt and clays are deposited in quieter, deep water far offshore. ^[11] These shelf sediments accumulate at an average rate of 30 cm/1000 years, with a range from 15-40 cm. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth ^[12] Though slow by human standards, this rate is much faster than that for deep-sea pelagic sediments. Pelagic sediments, also known as marine sediments, are those that accumulate in the Abyssal plain of the deep ocean far away from terrestrial sources that provide

Biota

Combined with the sunlight available in shallow waters, the continental shelves teem with life compared to the biotic desert of the oceans' abyssal plain. Abyssal plains are flat or very gently sloping areas of the deep Ocean basin floor The pelagic (water column) environment of the continental shelf constitutes the neritic zone, and the benthic (sea floor) province of the shelf is the sublittoral zone. Any water in the sea that is not close to the bottom is in the pelagic zone. The neritic zone, also called the sublittoral zone, is the part of the ocean extending from the low tide mark to the edge of the Continental shelf, with a relatively The benthic zone is the ecological region at the lowest level of a Body of water such as an Ocean or a Lake, including the sediment surface and some sub-surface ^[13]

Though the shelves are usually fertile, if anoxic conditions in the sedimentary deposits prevail, the shelves may in geologic time become sources of fossil fuels. Oceanic anoxic events or Anoxic events occur when the Earth 's Oceans become completely depleted of oxygen (O2 below the surface levels The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust.

Economic significance

The relatively accessible continental shelf is the best understood part of the ocean floor. Most commercial exploitation from the sea, such as metallic-ore, non-metallic ore, and hydrocarbon extraction, takes place on the continental shelf. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. Sovereign rights over their continental shelves up to 350 nautical miles from the coast were claimed by the marine nations that signed the Convention on the Continental Shelf drawn up by the UN's International Law Commission in 1958 partly superseded by the 1982 United Nations Convention on the Law of the Sea. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. The International Law Commission was established by the United Nations General Assembly in 1948 for the "promotion of the progressive development of international law and Year 1982 ( MCMLXXXII) was a Common year starting on Friday (link displays the 1982 Gregorian calendar) The United Nations Convention on the Law of the Sea ( UNCLOS) also called the Law of the Sea Convention or the Law of the Sea treaty is the international agreement that resulted ^[14]

See also

• Baseline
• Continental shelf pump
• Continental shelf of Russia
• Exclusive economic zone
• International waters
• Land bridge
• Outer Continental Shelf
• Territorial waters
• Passive margin

Footnotes

References

• Gross, Grant M. Oceanography: A View of the Earth. Englewood Cliffs: Prentice-Hall, Inc. , 1972. ISBN 0-13-629659-9

• Pinet, Paul R. (1996) Invitation to Oceanography. St. Paul, MN: West Publishing Co. , 1996. ISBN 0-7637-2136-0 (3rd ed. )

External links

• Office of Naval Research: Ocean Regions: Continental Margin & Rise
• UNEP Shelf Programme

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