Continental shelf

A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea. Much of the shelves were exposed during glacial periods and interglacial periods.

The shelf surrounding an island is known as an insular shelf.

The continental margin, between the continental shelf and the abyssal plain, comprises a steep continental slope followed by the flatter continental rise. Sediment from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope, called the continental rise. Extending as far as 500 km (310 mi) from the slope, it consists of thick sediments deposited by turbidity currents from the shelf and slope.[1] The continental rise's gradient is intermediate between the slope and the shelf.

Under the United Nations Convention on the Law of the Sea, the name continental shelf was given a legal definition as the stretch of the seabed adjacent to the shores of a particular country to which it belongs.

Geographical distribution

Elevation
  The global continental shelf, highlighted in cyan

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. The largest shelf – the Siberian Shelf in the Arctic Ocean – stretches to 1,500 kilometers (930 mi) in width. 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. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf. 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).[2] 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 (66 ft).[3]

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.[4] 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. Active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to the deep sea.[5]

Topography

Continental shelf

The shelf usually ends at a point of increasing slope[6] (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. The continental shelf and the slope are part of the continental margin.

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.

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.[7]

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°.[8] The slope is often cut with submarine canyons. The physical mechanisms involved in forming these canyons were not well understood until the 1960s.[9]

Sediments

The continental shelves are covered by terrigenous sediments; that is, those derived from erosion of the continents. 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.[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 accumulate 15–40 cm every millennium, much faster than deep-sea pelagic sediments.[12]

Biota

Continental shelves teem with life because of the sunlight available in shallow waters, in contrast to the biotic desert of the oceans' abyssal plain. 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.[13]

Though the shelves are usually fertile, if anoxic conditions prevail during sedimentation, the deposits may over geologic time become sources for fossil fuels.

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. Sovereign rights over their continental shelves up to a depth of 200 m (660 ft) or to a distance where the depth of waters admitted of resource exploitation 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. This was partly superseded by the 1982 United Nations Convention on the Law of the Sea.[14] which created the 200 nautical miles (370 km; 230 mi) 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, but no less than 200 nmi (370 km; 230 mi) and no more than 350 nmi (650 km; 400 mi) 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

Notes

  1. ^ Pinet 39, Gross 45.
  2. ^ Pinet, 37.
  3. ^ Pinet 36–37.
  4. ^ Pinet 35–36.
  5. ^ Pinet 90–93.
  6. ^ "shelf break – geology". Encyclopædia Britannica.
  7. ^ Gross 43.
  8. ^ Pinet 36, Gross 43.
  9. ^ Pinet 98, Gross 44.
  10. ^ Pinet 84–86, Gross 43.
  11. ^ Gross 121-22.
  12. ^ Gross 127.
  13. ^ Pinet 316-17, 418–19.
  14. ^ "Treaty Series – Convention on the Continental Shelf, 1958" (PDF). United Nations. 1958-04-29. Retrieved 2016-01-13. vol. 499, p. 311.

References

External links

Aegean Sea

The Aegean Sea ( or ; Greek: Αιγαίο Πέλαγος Aigaío Pélagos [eˈʝeo ˈpelaɣos] (listen); Turkish: Ege Denizi [eˈɟe deniˈzi]) is an elongated embayment of the Mediterranean Sea located between the Greek and Anatolian peninsulas i.e. between the mainlands of Greece and Turkey. In the north, the Aegean is connected to the Marmara Sea and Black Sea by the Dardanelles and Bosphorus. The Aegean Islands are within the sea and some bound it on its southern periphery, including Crete and Rhodes.

The sea was traditionally known as the Archipelago (in Ancient Greek, Ἀρχιπέλαγος, meaning "chief sea"), but in English the meaning of Archipelago has changed to refer to the Aegean Islands and, generally, to any island group.

Argentine Sea

The Argentine Sea (Spanish: Mar Argentino) is the sea within the continental shelf off the Argentine mainland.

Balaur gas field

The Balaur gas field natural gas field located on the continental shelf of the Black Sea. It was discovered in 2010 and developed by Sterling Resources. It will begin production in 2015 and will produce natural gas and condensates. The total proven reserves of the Balaur gas field are around 125 billion cubic feet (3.6 km³), and production is slated to be around 22 million cubic feet/day (0.62×106m³) in 2015.

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 ridges. The continental margin is the shallow water area found in proximity to continent. The continental margin consists of three different features: the continental rise, the continental slope, and the continental shelf. Continental margins constitute about 28% of the oceanic area.[1]

The continental shelf is the portion of the continental margin that transitions from the shore out towards to ocean. They are believed to make up 7 percent of the sea floor. The width of continental shelves worldwide varies from a 30 meters to 1500 kilometers. It is generally flat, and ends at the shelf break, where there is a drastic increase in slope angle. The mean slope of continental shelves worldwide is 0° 07’ degrees, and typically steeper closer to the coastline than it is near the shelf break. At the shelf break begins the continental slope, which can be one to five kilometers above the deep-ocean floor. The continental slope often exhibits features called submarine canyons. Submarine canyons often cut into the continental shelves deeply, with near vertical slopes, and continue to cut the morphology to the abyssal plain. The valleys are often V-shaped, and can sometime enlarge onto the continental shelf. At the base of the continental slope, there is a sudden decrease in slope, and the sea floor begins to level out towards the abyssal plain. This portion of the seafloor is called the continental rise, and marks the end of the continental margin.

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 Russia. Geologically, the extent of the shelf is defined as the entirety of the continental shelves adjacent to Russia's coast. In international law, however, the United Nations Convention on the Law of the Sea more narrowly defines the extent of the shelf as the seabed and subsoil of the submarine areas over which a state exercises sovereign rights.

The Siberian Shelf in the Arctic Ocean is the largest (and least explored) of the Russian shelves, a region of strategic importance because of its oil and natural gas reserves. Other parts of the Russian shelf are typically named after the corresponding seas: Barents Shelf (Barents Sea Shelf), Chukchi Shelf (Chukchi Sea Shelf), etc. With the exception of internal Russian seas, these geological shelves are shared with other countries which share the corresponding seas. For example, the Chukchi Shelf is shared between Russia and the United States according to the 1990 USA-USSR maritime boundary.

Exclusive economic zone

An exclusive economic zone (EEZ) is a sea zone prescribed by the United Nations Convention on the Law of the Sea over which a state has special rights regarding the exploration and use of marine resources, including energy production from water and wind. It stretches from the baseline out to 200 nautical miles (nmi) from its coast. In colloquial usage, the term may include the continental shelf. The term does not include either the territorial sea or the continental shelf beyond the 200 nmi limit. The difference between the territorial sea and the exclusive economic zone is that the first confers full sovereignty over the waters, whereas the second is merely a "sovereign right" which refers to the coastal state's rights below the surface of the sea. The surface waters, as can be seen in the map, are international waters.

James Shoal

James Shoal, also called Beting Serupai in Malaysia and Zengmu Reef (Chinese: 曾母暗沙; pinyin: Zēngmǔ Ànshā) in Greater China, is a small bank in the South China Sea, with a depth of 22 metres (72 ft), located about 45 nautical miles (83 km; 52 mi) off the Borneo coast of Malaysia. It is claimed by Malaysia, the People's Republic of China, and the Republic of China (Taiwan). The shoal and its surrounds are administered by Malaysia.

List of island countries

This is a list of island countries. An island is a land mass (smaller than a continent) that is surrounded by water. Many island countries are spread over an archipelago, as is the case with the Federated States of Micronesia and the Indonesia (both of which consist of thousands of islands). Others consist of a single island, such as Nauru, or part of an island, such as Haiti. Although Australia is designated as a continent, it is often referred to as an island, as it has no land borders. Some declared island countries are not universally recognized as politically independent, such as Northern Cyprus. Some states, such as Taiwan, officially claim to hold continental territories but are de facto limited to control over islands.

Lizard catshark

The lizard catshark (Schroederichthys saurisqualus) is a small shark species of the catshark family, Scyliorhinidae, found off the coast of southern Brazil on the upper continental shelf at depths of between 250 and 500 metres (820 and 1,640 ft).

Malaysia–Thailand border

The Malaysia–Thailand border consists of both a land boundary across the Malay Peninsula and maritime boundaries in the Straits of Malacca and the Gulf of Thailand/South China Sea. Malaysia lies to the south of the border while Thailand lies to the north. The Golok River forms the easternmost 95 km stretch of the land border.

The land border is based on the 1909 treaty between Thailand, then known as Siam, and the British which started to exert its influence over the northern Malay states of Kedah, Kelantan, Perlis, Perak and Terengganu in the early 20th century. The four states had earlier been under Siamese control. Four Malaysian states abut the border. They are (from west to east) Perlis, Kedah, Perak and Kelantan. The four Thai provinces which abut the border are (again from west to east) are Satun, Songkhla, Yala and Narathiwat.

Malaysia and Thailand have a territorial sea and a continental shelf boundary agreements for the Straits of Malacca which were signed in 1979 and 1971 respectively. The 1979 agreement also included Indonesia as a signatory as it also determined the common continental shelf border tripoint for the three countries. The 1979 agreement also established the territorial sea boundary in the Gulf of Thailand while a separate memorandum of understanding signed in 1979 established a short continental shelf boundary in the area. The boundary beyond that agreed is subject to dispute because of overlapping claims over the seabed. The overlapping claims led to the establishment of a joint development area in 1990 where both countries agreed to share mineral resources in a 7,250 square km wedge-shaped area.

Neritic zone

The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately 200 meters (660 ft) in depth.

From the point of view of marine biology it forms a relatively stable and well-illuminated environment for marine life, from plankton up to large fish and corals, while physical oceanography sees it as where the oceanic system interacts with the coast.

Norwegian continental shelf

The Norwegian continental shelf is the continental shelf over which Norway exercises sovereign rights as defined by the United Nations Convention on the Law of the Sea.The area of the shelf is four times the area of Norway mainland and constitutes about one-third of the Europe continental shelf. It is rich in petroleum and gas and it is the base of the petroleum economy of Norway.

Oceanic zone

The oceanic zone is typically defined as the area of the ocean lying beyond the continental shelf, but operationally is often referred to as beginning where the water depths drop to below 200 meters (656 feet), seaward from the coast to the open ocean.

It is the region of open sea beyond the edge of the continental shelf and includes 65% of the ocean’s completely open water. The oceanic zone has a wide array of undersea terrain, including crevices that are often deeper than Mt. Everest is tall, as well as deep-sea volcanoes and ocean basins. While it is often difficult for life to sustain itself in this type of environment, some species do thrive in the oceanic zone.

Outer Continental Shelf

The Outer Continental Shelf (OCS) is a peculiarity of the political geography of the United States. The OCS is the part of the internationally recognized continental shelf of the United States which does not fall under the jurisdictions of the individual U.S. States.

Patagonian Shelf

The Patagonian or Argentine Shelf is part of the South American continental shelf belonging to the Argentine Sea on the Atlantic seaboard, south of about 35°S. It adjoins the coasts of Uruguay, Argentina and the Falkland Islands.

Various authorities quote different dimensions of the shelf, depending on how they define its limits. Quoted statistics cites its area as being from 1.2 to 2.7 million square kilometres and its maximum width as being between 760 and 850 kilometres. The shelf itself can be divided into a 100 km band where the seabed slopes at about 1 m/km then a wide plain (250 to 450 km wide) where the seabed slopes gently to 200 m isobath. Apart from the Falklands Plateau (which lies to the east of the Falkland Islands), the seabed then falls by up to 10 m/km to 2000 m and more.

The Falklands Trough separates the Patagonian Shelf from the Scotia Arc.

Territorial claims in the Arctic

The Arctic consists of land, internal waters, territorial seas, exclusive economic zones (EEZs) and high seas. All land, internal waters, territorial seas and EEZs in the Arctic are under the jurisdiction of one of the eight Arctic coastal states: Canada, Norway, Russia, Denmark (via Greenland), Iceland, Sweden, Finland and the United States. International law regulates this area as with other portions of the Earth.

Under international law, the high seas including the North Pole and the region of the Arctic Ocean surrounding it, are not owned by any country. The five surrounding Arctic countries are limited to an exclusive economic zone (EEZ) of 200 nautical miles (370 km; 230 mi) adjacent to their coasts. The waters beyond the EEZs of the coastal states are considered the "high seas" (i.e. international waters). The sea bottom beyond the exclusive economic zones and confirmed extended continental shelf claims are considered to be the "heritage of all mankind" where exploration and exploitation of mineral resources is administered by the UN International Seabed Authority.

Upon ratification of the United Nations Convention on the Law of the Sea (UNCLOS), a country has a ten-year period to make claims to an extended continental shelf which, if validated, gives it exclusive rights to resources on or below the seabed of that extended shelf area. Norway, Russia, Canada, and Denmark launched projects to provide a basis for seabed claims on extended continental shelves beyond their exclusive economic zones. The United States has signed, but not yet ratified the UNCLOS.The status of certain portions of the Arctic sea region is in dispute for various reasons. Canada, Denmark, Norway, Russia, and the United States all regard parts of the Arctic seas as national waters (territorial waters out to 12 nautical miles (22 km)) or internal waters. There also are disputes regarding what passages constitute international seaways and rights to passage along them. There is one single disputed piece of land in the Arctic—Hans Island—which is disputed between Canada and Denmark because of its location in the middle of an international strait.

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 (see below), the contiguous zone, the exclusive economic zone and potentially the continental shelf. In a narrower sense, the term is used as a synonym for the territorial sea.

Tidal resonance

In oceanography, a tidal resonance occurs when the tide excites one of the resonant modes of the ocean.

The effect is most striking when a continental shelf is about a quarter wavelength wide. Then an incident tidal wave can be reinforced by reflections between the coast and the shelf edge, the result producing a much higher tidal range at the coast.

Famous examples of this effect are found in the Bay of Fundy, where the world's highest tides are reportedly found, and in the Bristol Channel. Less well known is Leaf Bay, part of Ungava Bay near the entrance of Hudson Strait (Canada), which has tides similar to those of the Bay of Fundy. Other resonant regions with large tides include the Patagonian Shelf and on the continental shelf of northwest Australia.Most of the resonant regions are also responsible for large fractions of the total amount of tidal energy dissipated in the oceans. Satellite altimeter data shows that the M2 tide dissipates approximately 2.5 TW, of which 261 GW is lost in the Hudson Bay complex, 208 GW on the European Shelves (including the Bristol Channel), 158 GW on the North-west Australian Shelf, 149 GW in the Yellow Sea and 112 GW on the Patagonian Shelf.

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 the international agreement that resulted from the third United Nations Conference on the Law of the Sea (UNCLOS III), which took place between 1973 and 1982. The Law of the Sea Convention defines the rights and responsibilities of nations with respect to their use of the world's oceans, establishing guidelines for businesses, the environment, and the management of marine natural resources. The Convention, concluded in 1982, replaced four 1958 treaties. UNCLOS came into force in 1994, a year after Guyana became the 60th nation to ratify the treaty. As of June 2016, 167 countries and the European Union have joined in the Convention. It is uncertain as to what extent the Convention codifies customary international law.

While the Secretary-General of the United Nations receives instruments of ratification and accession and the UN provides support for meetings of states party to the Convention, the UN has no direct operational role in the implementation of the Convention. There is, however, a role played by organizations such as the International Maritime Organization, the International Whaling Commission, and the International Seabed Authority (ISA). (The ISA was established by the UN Convention.)

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.