The continental shelf
The continental shelf is the extension of a coastal State’s land territory under the sea. Under customary international law, as reflected in Article 76 of the 1982 Law of the Sea Convention (Convention), the continental shelf consists of the seabed and subsoil that extends (1) to the outer edge of the continental margin, or (2) to a distance of 200 nautical miles from the coast if the outer edge of the continental margin does not extend up to that distance. This legal definition is different from the geological definition of a continental shelf. The continental shelf is an important maritime zone that holds many resources and vital habitats for marine life.
The extended continental shelf (ECS)
The extended continental shelf, or ECS, refers to that portion of the continental shelf beyond 200 nautical miles from the coast (Figure 1). ECS is a term of convenience; under the Convention, the term “continental shelf” includes both continental shelf within and beyond 200 nautical miles.
Figure 1: Maritime zones under the international law of the sea. ECS is that portion of the continental shelf that extends beyond 200 nautical miles.
Determining the outer limits of the ECS
Determining the outer limits of the ECS is different from determining the extent of other maritime zones, such as the territorial sea and exclusive economic zone. These other maritime zone limits are determined based on a specified distance from the coastal baselines (Figure 1).
The outer limits of the ECS, however, depend on the geophysical characteristics of the seabed and subsoil. ECS limits are determined using complex provisions set forth under Article 76 of the Convention. (The text of Article 76 can be found here. ) A coastal State can use one of two formulas in any combination to determine the outer edge of its continental margin (Figure 2). Article 76 also contains two constraint lines (Figure 3). If the outer edge of the continental margin extends past the constraint lines, a coastal State can use either of the constraint lines to maximize its ECS. The outer limit of the continental shelf is determined by the combined use of Article 76’s formula lines and constraint lines.
As discussed in the Data Collection section of the U.S. ECS website, bathymetric and seismic data are needed to apply the formula and constraint lines.
Figure 2: Formula lines under Article 76 of the Law of the Sea Convention. A coastal State can use either formula to determine the outer edge of the continental margin.
Figure 3: Constraints under Article 76 of the Law of the Sea Convention. A coastal State can use either constraint to maximize the limits of its continental shelf.
Continental shelf rights
The sovereign rights and jurisdiction of a coastal State over its continental shelf are reflected in the Convention and include the following:
- Exploration, exploitation, conservation, and management of non-living resources (e.g., minerals and hydrocarbons)
- Exploration, exploitation, conservation, and management of living resources that are “sedentary species” (e.g., clams and corals)
- Regulating marine scientific research
- Construction, operation, and use of artificial islands, installations, and structures
- Delineating the course for laying pipelines
- Drilling for any purpose
- Prevention of marine pollution in connection with some activities
Distinction between the continental shelf and EEZ
The continental shelf and the exclusive economic zone (EEZ) are distinct maritime zones (Figure 1). The continental shelf includes only the seabed and subsoil, whereas the EEZ includes the water column. In addition, while the maximum extent of the EEZ is 200 nautical miles from the coast, the continental shelf may extend beyond 200 nautical miles, depending on the depth, shape, and geophysical characteristics of the seabed and sub-sea floor. The ECS is, therefore, not an extension of the EEZ. Some of the rights that a coastal State may exercise in the EEZ, especially rights to the resources of the water column (e.g., pelagic fisheries), do not apply to the ECS.