The United Nations Convention on the Law of the Sea subdivides ocean space into zones that lie under either the jurisdiction of a Coastal State or of the International Seabed Authority. Although most of this subdivision can be performed by relatively straightforward measurements of horizontal distance, delineating the Juridical Continental Shelf requires complying with the complex formula prescribed in Article 76 of the Convention. Article 76 requires the vertical measurement of depth and production of an isobath, and locating the Foot of the Slope, an elusive “geomorphic” seafloor feature that may not even exist. If it does not, and if its non-existence can be proven, then “evidence to the contrary” may be used to determine the location of a substitute line. In either case, sediment thickness must be measured seawards until a specified thickness is reached. Seaward extension of the Continental Shelf is not unlimited, since two constraints are prescribed: which constraint applies varies with the seafloor to some extent, since the presence of a “ridge” prohibits the use of one of them. What constitutes a ridge is not specified in the wording of the Convention, adding a further complication. Earth scientists are thus confronted with locating the 2500 m isobath, finding the Foot of the Slope or establishing that it does not exist and building a case for evidence to the contrary, measuring sediment thickness and establishing the geologic nature of seafloor ridges. From this, an Outer Limit to the Continental Shelf can be established.

Monahan, D. 2004. Altimetry applications to continental shelf delineation under the United Nations Convention on the Law of the Sea. Oceanography 17(1):75–82, https://doi.org/10.5670/oceanog.2004.69.

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