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A continental shelf is a portion of a
continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of th ...

continent
that is submerged under an area of relatively shallow water known as a shelf sea. Much of these shelves were exposed by drops in sea level during
glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( or ) is a persistent body of dense ice that is constantly movi ...
s. The shelf surrounding an
island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll (), sometimes known as a coral atoll, i ...

island
is known as an insular shelf. The
continental margin The continental margin is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schemat ...
, between the continental shelf and the
abyssal plain Depiction of the abyssal zone in relation to other major oceanic zones">oceanic_zone.html" ;"title="abyssal zone in relation to other major oceanic zone">abyssal zone in relation to other major oceanic zones An abyssal plain is an underwater pl ...
, comprises a steep continental slope, surrounded by the flatter
continental rise The continental rise is a low-relief zone of accumulated sediments Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring ...
, in which
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope. Extending as far as 500 km (310 mi) from the slope, it consists of thick sediments deposited by
turbidity current 350 px, Longitudinal section through an underwater turbidity current A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that ...
s from the shelf and slope. The
continental rise The continental rise is a low-relief zone of accumulated sediments Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring ...
's
gradient In vector calculus Vector calculus, or vector analysis, is concerned with differentiation Differentiation may refer to: Business * Differentiation (economics), the process of making a product different from other similar products * Prod ...
is intermediate between the gradients of the slope and the shelf. Under the
United Nations Convention on the Law of the Sea 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 an international agreement A treaty is a formal legally binding written agreement between actors in intern ...

United Nations Convention on the Law of the Sea
, the name continental shelf was given a legal definition as the stretch of the
seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

seabed
adjacent to the shores of a particular country to which it belongs.


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
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. The continental shelf and the slope are part of the
continental margin The continental margin is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schemat ...
. The shelf area is commonly subdivided into the ''inner continental shelf'', ''mid continental shelf'', and ''outer continental shelf'', each with their specific
geomorphology incised into shale at the foot of the North Caineville Plateau, Utah, within the pass carved by the Fremont River (Utah), Fremont River and known as the Blue Gate. Grove Karl Gilbert, GK Gilbert studied the landscapes of this area in great detail, ...

geomorphology
and
marine biology Marine biology is the scientific study of the biology of marine life Marine life, sea life, or ocean life is the plants, animals, and other organisms that live in the Seawater, salt water of the sea or ocean, or the brackish water of coast ...
. 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 ; this is likely a hallmark of past ice ages, when sea level was lower than it is now. 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°. The slope is often cut with
submarine canyon A submarine canyon is a steep-sided cut into the of the , sometimes extending well onto the , having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km, from canyon floor to canyon rim, as with the . Just ...

submarine canyon
s. The physical mechanisms involved in forming these canyons were not well understood until the 1960s.


Geographical distribution

Continental shelves cover an area of about 27 million km2, equal to about 7% of the surface area of the oceans.Continental shelf – Blue Habitats
/ref> 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 350px, The thickness of Crust (geology)#Earth's crust, Earth's crust (km) Continental crust is the layer of Igneous rock, igneous, Sedimentary rock, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallo ...
in an offshore
subduction zone Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate This is a list of tectonic plates on Earth's surface. Tec ...

subduction zone
such as off the coast of
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern ...

Chile
or the west coast of
Sumatra Sumatra is one of the Sunda Islands The Sunda Islands are a group of islands in the Malay Archipelago. They consist of the Greater Sunda Islands The Greater Sunda Islands are four tropical islands situated within Southeast Asia S ...

Sumatra
. The largest shelf – the Siberian Shelf in the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major s. It spans an area of approximately and is also known as the coldest of all the oceans. The (IHO) recognizes it as an ocean, although some call it the Arctic Medit ...

Arctic Ocean
– stretches to in width. The
South China Sea The South China Sea is a marginal sea This is a list of seas of the World Ocean The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97 ...

South China Sea
lies over another extensive area of continental shelf, the
Sunda Shelf Geologically Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into t ...

Sunda Shelf
, which joins
Borneo Borneo (; id, Kalimantan) is the third-List of islands by area, largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java Is ...

Borneo
, Sumatra, and
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
to the Asian mainland. Other familiar bodies of water that overlie continental shelves are the
North Sea The North Sea is a sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
and the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of , ) is a in . The body of water is an extension of the () through the and lies between to the northeast and the to the southwest.United Nations Group of Exper ...
. The average width of continental shelves is about . The depth of the shelf also varies, but is generally limited to water shallower than . The slope of the shelf is usually quite low, on the order of 0.5°; vertical relief is also minimal, at less than . Though the continental shelf is treated as a
physiographic Physical geography (also known as physiography) is one of the two fields of geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabita ...
province of the
ocean The ocean (also the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
, it is not part of the deep ocean basin proper, but the flooded margins of the continent. such as most of the coasts have wide and shallow shelves, made of thick sedimentary wedges derived from long erosion of a neighboring continent. Active continental margins have narrow, relatively steep shelves, due to frequent
earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth Earth is the third planet from the Sun and the only astronomical object known ...

earthquake
s that move sediment to the deep sea.


Sediments

The continental shelves are covered by
terrigenous sediment In oceanography Oceanography (compound of the Greek words ὠκεανός meaning "ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

river
s; 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. 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. These accumulate 15–40 cm every millennium, much faster than deep-sea
pelagic sediment Pelagic sediment or pelagite is a fine-grained sediment Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mas ...
s.


Shelf seas

Shelf seas refer to the ocean waters on the continental shelf. Their motion is controlled by the combined influences of the
tide Tides are the rise and fall of sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of ...

tide
s, wind-forcing and brackish water formed from river inflows ( Regions of Freshwater Influence). These regions can often be biologically highly productive due to mixing caused by the shallower waters and the enhanced current speeds. Despite covering only about 8% of Earth's ocean surface area, shelf seas support 15-20% of global primary productivity. While the
North Sea The North Sea is a sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
is one of the better studied shelf seas, it is not necessarily representative of all shelf seas as there is a wide variety of behaviours to be found.
Indian Ocean The Indian Ocean is the third-largest of the world's five ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Another definition is "any of the large ...

Indian Ocean
shelf seas are dominated by major river systems including the
Ganges The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma River, Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian ...

Ganges
and
Indus#REDIRECT Indus River
{{Redirect category shell, {{R from move {{R from miscapitalisation {{R unprintworthy ...

Indus
rivers. The shelf seas around
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
are complicated because the submerged continent of
Zealandia Zealandia (prounounced ), also known as ( Māori) or Tasmantis, is an almost entirely submerged mass of continental crust 350px, The thickness of Crust (geology)#Earth's crust, Earth's crust (km) Continental crust is the layer of Igneous ...
creates wide plateaus. Shelf seas around
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
and the shores of the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major s. It spans an area of approximately and is also known as the coldest of all the oceans. The (IHO) recognizes it as an ocean, although some call it the Arctic Medit ...

Arctic Ocean
are influenced by
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...

sea ice
production and
polynya A polynya () is an area of open water surrounded by sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice cove ...
. There is evidence that changing wind, rainfall, and regional ocean currents in a warming ocean are having an effect on some shelf seas. Improved data collection via Integrated Ocean Observing Systems in shelf sea regions is making identification of these changes possible.


Biota

Continental shelves teem with life because of the sunlight available in shallow waters, in contrast to the biotic desert of the oceans'
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. The
pelagic The pelagic zone consists of the water column A water column is a concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy ...
(water column) environment of the continental shelf constitutes the
neritic zone The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated environment for marine ...
, and the
benthic The benthic zone is the ecological region at the lowest level of a body of water ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the Kingdom of Norway, is a Nordic countries, Nordic ...
(sea floor) province of the shelf is the
sublittoral zone The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated environment for marine ...
. The shelves make up less than ten percent of the ocean, and a rough estimate suggest that only about 30% of the continental shelf sea floor receives enough sunlight to allow benthic photosynthesis. Though the shelves are usually fertile, if
anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of disso ...
conditions prevail during sedimentation, the deposits may over
geologic time Geology (from the Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). ...

geologic time
become
sources Source or subsource or ''variation'', may refer to: Research * Historical document * Historical source * Source (intelligence) or subsource, typically a confidential provider of non open-source intelligence * Source (journalism), a person, public ...
for
fossil fuel A fossil fuel is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structure ...
s.


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 In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
extraction, takes place on the continental shelf. Sovereign rights over their continental shelves down to a depth of or to a distance where the depth of waters admitted of
resource exploitation The exploitation of natural resources is the use of natural resource , Malaysia is an example of undisturbed natural resource. Waterfalls provide spring water for humans, animals and plants for survival and also habitat for marine organisms. The ...
were claimed by the marine nations that signed the
Convention on the Continental Shelf The Convention on the Continental Shelf was an international treaty created to codify the rules of international law relating to continental shelf, continental shelves. The treaty, after entering into force 10 June 1964, established the rights of ...
drawn up by the UN's
International Law Commission The International Law Commission (ILC) is a body of experts responsible for helping develop and codify international law International law, also known as public international law and law of nations, is the set of rules, norms, and standards gen ...
in 1958. This was partly superseded by the 1982
United Nations Convention on the Law of the Sea 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 an international agreement A treaty is a formal legally binding written agreement between actors in intern ...

United Nations Convention on the Law of the Sea
. which created the exclusive economic zone, plus continental shelf rights for states with physical continental shelves that extend beyond that distance. The legal definition of a continental shelf differs significantly from the geological definition. UNCLOS states that the shelf extends to the limit of the
continental margin The continental margin is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schemat ...
, but no less than and no more than from the baseline. Thus inhabited volcanic islands such as the Canaries, which have no actual continental shelf, nonetheless have a legal continental shelf, whereas uninhabitable islands have no shelf.


See also

* Baseline * Continental island *
Continental shelf of Russia The continental shelf of Russia (also called the Russian continental shelf or the Arctic shelf in the Arctic region) is a continental shelf adjacent to the Russian Federation. Geologically, the extent of the shelf is defined as the entirety of the c ...
* Continental shelf pump * Exclusive economic zone *
International waters The terms international waters or trans-boundary waters apply where any of the following types of bodies of water (or their drainage basins) transcend international boundaries: oceans, large marine ecosystems, enclosed or semi-enclosed region ...

International waters
*
Land bridge In biogeography Biogeography is the study of the distribution of species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A sp ...
*
Outer Continental Shelf upright=1.20, Map of the Outer Continental Shelf The Outer Continental Shelf (OCS) is a feature of the geography of the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a ...
*
Passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate Continental margin, margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Contin ...

Passive margin
* Region of freshwater influence *
Territorial waters The term territorial waters is sometimes used informally to refer to any area of water over which a state has jurisdiction, including internal waters, the territorial sea, the contiguous zone, the exclusive economic zone and potentially the ...


Notes


References

* * * * * * * * * * * * * * * * * * *


External links


Office of Naval Research: Ocean Regions: Continental Margin & Rise

UNEP Shelf Programme

GEBCO world map 2014

Anna Cavnar, ''Accountability and the Commission on the Limits of the Continental Shelf: Deciding Who Owns the Ocean Floor''
{{Authority control Aquatic ecology Physical oceanography Aquatic biomes Coastal geography Coastal and oceanic landforms
Law of the sea This category is for articles on the Law of the Sea, a body of public international law dealing with navigational rights, mineral rights, jurisdiction over coastal waters and international law governing relationships between nations. For articl ...
Bodies of water {{See also, Limnology Compare to :Landforms and :Wetlands Bodies of water may exist within land areas or within other bodies of water and may be natural, man-made or a combination. Water Physical geography Hydrography Natural resources, +Water A ...
Oceanographical terminology