continental shelf(redirected from Continental shelf break)
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continental shelf:see oceanocean,
interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanography.
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relatively shallow submarine plain adjacent to the shores of the continents and genetically constituting a part of the continent. It was formerly assumed that its outer boundary was located at a depth of 200 m, but research conducted in the 1950’s and 1960’s demonstrated that its outer edge may be located at various depths, in some cases down to 1,500-2,000 m (for example, in the South Kuril trough of the Sea of Okhotsk and on the New Zealand submarine plateau).
the comparatively level part of the underwater margin of the continent adjacent to the coast and characterized by the same geological structure. The boundaries of the continental shelf are the shores of the sea or ocean and the shelf break (an abrupt increase of the declivity of the sea floor, the transition to the continental slope). The depth at the shelf break is close to 100–200 m, but in some cases reaches 500–1,500 m, for example, at the southern part of the Sea of Okhotsk and the shelf break of the New Zealand Shelf.
The continental shelf as a historical geological category has existed in all geological periods, prograding considerably in some, such as the Jurassic and Cretaceous periods, while retrograding in others, for example, the Permian and Devonian periods. The present geological epoch is characterized by a moderate development of the shelves.
The continental shelf is part of the underwater margin of the continent and has a continental crust. The coast and the shelf have similar geomorphological features. Various relict subaerial forms of relief and deposits are widespread, as are many traces of ancient shorelines, which indicate that the shelf formed primarily as a result of the inundation of the continental margins by the world ocean in postglacial times and as a result of recent tectonic subsidences of the earth’s surface. Also widespread are shelves formed as a result of the retreat of shores through the action of abrasion or as a result of the underwater accumulation of thick deposits of sediments near the continental margins.
The total area of continental shelves is about 32 million sq km. The largest shelf areas are found along the northern margin of Eurasia, where it is 1,500 km wide, in the Bering Sea, Hudson Bay, the South China Sea, and along the northern coast of Australia.
The continental shelf has been used for fishing and hunting sea mammals since ancient times; 92 percent of all the fish caught commercially are caught in shelf waters. Prospecting for minerals, especially petroleum and gas, has developed extensively in the shelf area. In 1975 petroleum extracted from the shelf accounted for 20 percent of all the petroleum extracted in the world; placer deposits of minerals, such as cassiterite, titano-magnetite, diamonds, and gold, are also exploited.
The international legal status of the continental shelf is regulated by a special convention adopted in Geneva in 1958. In the Convention on the Continental Shelf, the term “continental shelf” refers to “(a) the seabed and subsoil of the submarine areas adjacent to the coast but outside the area of the territorial sea, to a depth of 200 m or, beyond that limit, to where the depth of superjacent waters admits of the exploitation of the natural resources of the set area; (b) the seabed and subsoil of similar submarine areas adjacent to the coasts of islands.” The convention acknowledges the sovereign right of coastal states to explore and exploit the natural resources of the shelf, including mineral and other nonliving resources of the seabed and subsoil and living organisms attached to the seafloor or moving along it, such as corals, sponges, mussels, and crabs. Other states do not have the right to do this without the consent of the coastal state.
As a general principle, the boundary of the continental shelf is determined by agreement between interested states in conformity with the rules established by the convention. Such agreements have been concluded by the Soviet Union with Finland (May 20, 1965, and May 6, 1967) and with Poland (Aug. 28, 1969). In addition, the USSR, Poland, and the Democratic Republic of Germany signed a declaration on the continental shelf of the Baltic Sea on Oct. 23, 1968, which established the general principles for delineating the shelf in this region.
A special aspect of the legal status of the continental shelf is that it does not involve the legal status of the superjacent waters of the high seas and the air space above these waters. According to the convention, a coastal state has the right to build, maintain, and operate necessary structures and installations on the shelf and to create a 600-meter safety zone around such structures and installations, as well as to take any necessary steps to protect them. It is stipulated that these structures, installations, and safety zones must not be on important international sea-lanes.
REFERENCESLeont’ev, O. K. Dno okeana. Moscow, 1968.
Shepard, F. P. Morskaia geologiia, 2nd ed. Leningrad, 1969. (Translated from English.)
Kartirovanie shel’fov: Sb. st. Leningrad, 1974.
Problemy geologii shel’fa: Sb. st. Moscow, 1975.
Ostrovnye shel’fy tropicheskoi zony okeana. Moscow, 1975.
Khrustalev, Iu. P. Mineral’nye bogatstva Mirovogo okeana. Rostov-on-Don, 1975.
Slevich, S. B. Shel’f: Osvoenie i ispol’zovanie. Leningrad, 1977.
Molodtsov, S. V. Mezhdunarodno-pravovoi rezhim otkrytogo moría i kontinental’nogo shel’fa. Moscow, 1960.
Kalinkin, G. F., and Ia. A. Ostrovskii. Morskoe dno: komu ono prinadlezhif? Moscow, 1970.
Zhudro, A. K., and Iu. Kh. Dzhavad. Morskoe pravo. Moscow, 1974.