International Laws of The Sea, The continental shelf and the Exclusive Economic Zone

Definition and Method of Drawing the Limits of the Continental Shelf

April 27, 2022July 25, 2022By Tan Pui Yen
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Definition and method of drawing the limits of the continental shelf

1. Evolution of the continental shelf as a legal concept

The Truman Proclamation of 1945 became a catalyst for a variety of titles or claims by various states to the seabed and subsoil adjacent to their territorial seas. However, these states did not use the term‘continental shelf’ as it is used today in the law of the sea. It was the First UN Conference on the Law of the Sea of 1958 (UNCLOS I) that defined the continental shelf to include:

“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 metres, or, beyond that limit, to where the depth of the superjacent waters admits of the exploitation of the natural resources of the said areas.”

When the Third UN Conference on the Law of the Sea (UNCLOS III) got underway, many states were in favour of extending coastal state control over ocean resources out to 200 miles from shore so that the outer limit of the shelf coincided with that of the EEZ, another maritime zone in the water column. However, a number of states persisted with their demand for a geographical shelf extending beyond 200 miles for wider economic jurisdiction.

Eventually, the 1982 Convention resolved conflicting claims, interpretations and measuring techniques by setting the 200-mile EEZ limit as the standard boundary of the continental shelf for seabed and subsoil exploitation. It also admitted the possibility of establishing a final limit going out 350 miles or further from the shores of certain coastal states, depending on certain geological criteria outlined in the Convention.

It also established a Commission on the Limits of the Continental Shelf (CLCS) to make recommendations regarding claims extending beyond 200 miles based on applications made by coastal states, which are required to submit data to the Commission to support their claim. 

2. Definition of the continental shelf and criteria for the establishment of its outer limits

Both the definition of the continental shelf and the criteria by which a coastal state may establish the outer limits of its continental shelf are set out in the 1982 Convention. In addition, UNCLOS III adopted on 29 August 1980 a ‘Statement of Understanding’ concerning a specific method applicable to such special features such as those to be found in the southern part of the Bay of Bengal.

To geologists, the term ‘continental shelf’ means that part of the continental margin that lies between the shoreline and the shelf break or, where there is no noticeable slope, between the shoreline and the point where the depth of the overlying water is approximately between 100 and 200 metres. However, the definition of the term provided in Article 76 of the 1982 Convention is a juridical one.

According to this juridical definition, the continental shelf of a coastal state comprises the submerged prolongation of the land territory of the coastal state – the seabed and subsoil of the submarine areas thatextend beyond its territorial sea to the outer edge of the continental margin, or to a distance of 200 nautical miles where the outer edge of the continental margin does not extend up to that distance.

The Convention makes it clear that the continental margin consists of the seabed and subsoil of the shelf, the slope and the rise. However, it does not include the deep ocean floor with its oceanic ridges, or the subsoil thereof, since they are declared as the common heritage of mankind and are governed by a separate set of rules under Part XI of the Convention.

In cases where the continental margin extends further than 200 miles, nations may claim jurisdiction up to 350 miles from the baseline or 100 miles from the 2,500-metre depth, depending on certain criteria such as the thickness of sedimentary deposits. The definition in Article 76(1) of the Convention reads as follows:

Article 76

Definition of the continental shelf

  1. The continental shelf of a coastal State comprises the seabed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a Distance of 200 nautical miles from the baselines from which the breadth of the territorial sea is measured where the outer edge of the continental margin does not extend up to that distance.

3. Method of drawing the outer limit of the continental shelf

As can be seen from the above definition of the continental shelf, the normal rule is that the continental shelf has, like the EEZ, a 200-mile limit from the baselines. However, unlike the EEZ, the continental shelf can extend beyond the 200-mile limit in certain cases, and the task of establishing how far the shelf can extend is complex. Wherever the continental margin extends beyond 200 nautical miles, a coastal state has the right to establish the outer limits of its juridical continental shelf by:

a) establishing the foot of the continental slope

b) meeting the requirements stated for the thickness of sedimentary rocks

c) satisfying geomorphological requirements

d) meeting distance and depth criteria

e) certain combinations of these methods.

Paragraphs 4–7 of Article 76 of the 1982 Convention prescribe the following method or formula for drawing the outer limit of the continental shelf:

Article 76

Definition of the continental shelf

4. a. For the purposes of this Convention, the coastal State shall establish the outer edge of the continental margin wherever the margin extends beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured, by either: 

i. a line delineated in accordance with paragraph 7 by reference to the outermost fixed points at each of which the thickness of sedimentary rocks is at least 1 per cent of the shortest distance from such point to the foot of the

continental slope; or 

ii. a line delineated in accordance with paragraph 7 by reference to fixed points not more than 60 nautical miles from the foot of the continental slope; or 

b. In the absence of evidence to the contrary, the foot of the continental slope shall be determined as the point of maximum change in the gradient at its base.

5. The fixed points comprising the line of the outer limits of the continental shelf on the seabed, drawn in accordance with paragraph 4(a)(i) and (ii), either shall not exceed 350 nautical miles from the baselines from which the breadth of the territorial sea is measured or shall not exceed 100 nautical miles from the 2,500 metre isobath, which is a line connecting the depth of 2,500 metres.

6. Notwithstanding the provisions of paragraph 5, on submarine ridges, the outer limit of the continental shelf shall not exceed 350 nautical miles from the baselines from which the breadth of the territorial sea is measured. This paragraph does not apply to submarine elevations that are natural components of the continental margin, such as its plateaux, rises, caps, banks and spurs.

7. The coastal State shall delineate the outer limits of its continental shelf, where that shelf extends beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured, by straight lines not exceeding 60 nautical miles in length, connecting fixed points, defined by coordinates of latitude and longitude.

4. Commission on the Limits of the Continental Shelf (CLCS)

In accordance with the provisions of Article 76, the 1982 Convention establishes a Commission on the Limits of the Continental Shelf (CLCS). Since all states have a right to a continental shelf up to the 200-mile point, the Commission is concerned only with an area between the 200-mile point and 350 miles, the maximum limit that a coastal state can claim as its continental shelf.

The Commission consists of 21 members who are experts in the field of geology, geophysics or hydrography, and are elected by states parties to the Convention from among their nationals, having due regard to the need to ensure equitable geographical representation. They serve in a personal capacity. They are elected for a term of five years and are eligible for re-election. 

The functions of the Commission are:

a) to consider data and other material submitted by coastal states concerning the outer limits of the continental shelf in areas where those limits extend beyond 200 nautical miles, and to make recommendations in accordance with Article 76 and the Statement of Understanding adopted on 29 August 1980 by UNCLOS III

b) if requested by a coastal state, to provide scientific and technical advice during the preparation of data to be submitted to the

Where a coastal state intends to establish the outer limits of its continental shelf beyond 200 nautical miles in accordance with Article 76, that state is required to submit particulars of such limits to the Commission and supporting scientific and technical data as soon as possible, but in any case within 10 years of the entry into force of the Convention for that state. The recommendations of the Commission are to be submitted in writing to the coastal state that made the submission and to the Secretary-General of the UN. This process is already underway and several states have now made applications, including the Russian Federation, Ireland, Brazil and Australia. Most recently (at the time of writing), the UK, France and Spain had made a joint application over a particular sector of the Atlantic Ocean, off the Bay of Biscay.

5. Activities of the Commission on the Limits of the Continental Shelf

The year 2008 witnessed a flurry of activity by some of the parties to the 1982 Convention on the Law of the Sea in order to meet the 10-year deadline to submit their claim to the Commission on the Limits of the Continental Shelf in respect of the establishment of the outer limits of the continental shelf beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured. Under the 1982 Convention, a coastal state is allowed to establish the outer limits of its continental shelf where it extends beyond 200 miles on the basis of a recommendation from the Commission.

Under Article 76 and Annex II to the 1982 Convention and the Statement of Understanding adopted on 29 August 1980 by UNCLOS III, the Commission is entrusted with the task of considering data and other material submitted by coastal states concerning the outer limits of the continental shelf in areas where those limits extend beyond 200 nautical miles, and to make recommendations. Article 4 of Annex II to the 1982 Convention requires any coastal state intending to establish the outer limits to its continental shelf beyond 200 nautical miles to submit particulars of such limits to the Commission along with supporting scientific and technical data as soon as possible, but in any case within 10 years of the entry into force of the Convention for that state.

Accordingly, Barbados, the UK, Indonesia, Japan, Mauritius, the Seychelles, Suriname and Myanmar submitted their claims to the Commission during 2008.

Responding to a 13 May 2009 deadline, some 69 states filed claims to oceanic territories along their coasts for an area extending more than 200 nautical miles from their baselines. 

It is expected that as many as 80 states may be able to substantiate a claim to an extension of their continental shelf. Critics have described this as yet another scramble for coastal state jurisdiction over the seabed.

As of 26 October 2017, a total of 78 submissions had been made to the Commission; the Commission has adopted 18 recommendations with regard to 17 coastal states covering either the whole country or certain territories of those states.

The 40th session of the Commission on the Limits of the Continental Shelf was held at United Nations Headquarters in March 2016. This 40th session attracted some attention in the media and in international legal circles because of its work on several sensitive submissions by some states, including by Argentina, which included the continental shelf off the Falkland Islands.

Besides two weeks of plenary meetings (8–12 February and 7–11 March), the Commission, working through its subcommissions, devoted five weeks to the technical examination of submissions at the Geographic Information Systems laboratories and other technical facilities of the Division for Ocean Affairs and the Law of the Sea.

The active subcommissions continued their work during this 40th session. These were the subcommissions established for consideration of the submissions made by Brazil in respect of the Brazilian Southern Region (partial revised submission); Norway in respect of Bouvetøya and Dronning Maud Land; South Africa in respect of the mainland of the territory of South Africa; the Federated States of Micronesia, Papua New Guinea and Solomon Islands, jointly, concerning the Ontong Java Plateau; France and South Africa, jointly, in the area of the Crozet Archipelago and the Prince Edward Islands; Kenya; Mauritius in the region of Rodrigues Island; Nigeria.

Some subcommissions met with the respective delegations. At the plenary level, the Commission adopted, without a vote, two sets of recommendations, namely the recommendations in respect to the submission made by Argentina, and… the submission made by Iceland in respect of the Ægir Basin area and in the western and southern parts of Reykjanes Ridge.

With regard to the recommendations in respect of the submission made by Argentina,… the Commission … decided that it was not in a position to consider and qualify those parts of the submission that were subject to dispute and those parts that were related to the continental shelf appurtenant to Antarctica (see CLCS/64, paras. 76 and 77 and CLCS/76, para. 57).

The Commission also continued, at the plenary level, its consideration of draft recommendations in respect to the submission made by the Cook Islands concerning the Manihiki Plateau, and commenced its consideration of draft recommendations in respect to the submission made by Uruguay.

The Russian Federation, headed by Sergei E. Donskoi, Minister for Natural Resources and Environment, presented its partial revised submission in respect of the Arctic Ocean before the plenary of the Commission. The Commission assigned the examination of the submission to the subcommission established to consider the submission made by the Russian Federation on 20 December 2001.

Also, the Commission established a new subcommission to consider the submission made by Seychelles concerning the Northern Plateau Region; the subcommission has now begun its work.

The Commission decided that it would hold three weeks of plenary meetings during the 43rd session in order to consider draft recommendations submitted to the plenary before the term of office of the current members expires in June 2017. 

Details of the 40th session will be reflected in the Statement by the Chairperson of the Commission on the Limits of the Continental Shelf on the progress of work in the Commission, which will be issued as document CLCS/93. (UN Division for Ocean Affairs and the Law of the Sea, 28 March 2016.

6. Summary and conclusions

Since the outer limit of the continental shelf can extend beyond the standard 200-mile limit in certain geological and geographical circumstances, the 1982 Convention on the Law of the Sea established a Commission on the Limits of the Continental Shelf.

Any coastal state claiming a limit of the continental shelf beyond 200 nautical miles from its baselines must submit information to the Commission. The coastal state must deposit with the Secretary-General of the UN charts and relevant information, including geodetic data, permanently describing the outer limits of its continental shelf. The task of the Commission is to make recommendations to coastal states on matters related to the establishment of the outer limits of their continental shelf. The limits of the shelf established by a coastal state on the basis of these recommendations are final and binding.

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