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Brief Overview of UNCLOS During the course of a series of meetings that lasted from 1973 to 1982, the nations of the world produced the United Nations Convention on the Law of the Sea (UNCLOS) (United Nations, 1983), a document that has been described as the result of probably the most prolonged and intense multinational negotiations in history. UNCLOS completely changed the character of the entire marine sector, and rests as the foundation on which all subsequent international and national marine legislation has been built (Miles, 1999). Before this exercise, ocean space was essentially divided into two zones: Coastal States’ sovereignty was absolute over a fringing Territorial Sea beyond which Freedom of the High Seas was held to be absolute. This was increasingly being challenged through isolated actions like the declaration of Fishing Zones. UNCLOS expanded the concept of two zones by the further subdivision of ocean space into several zones fringing continents, archipelagos and islands. Jurisdiction of Coastal States was extended, with powers being phased down through several successive zones at specified distances offshore, resulting in a much greater portion of the seafloor falling within national jurisdiction. Successively seawards, these zones are the 12 nm wide Territorial Sea, the 24 nm Contiguous Zone, the 200 nm Exclusive Economic Zone and the Continental Shelf, whose width is variable and has to be determined through a combination of measurement and judgement as discussed below. Introduction 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. Modern ship-borne instruments can collect the types of data appropriate to resolving this boundary: the question, one exacerbated by the requirement to submit a claim within ten years of ratification, is whether they can collect enough of it to produce a wellfounded claim. Because ships are limited in their speed, as well as by weather and by cost, it is possible that some Coastal States will not be able to assemble appropriate amounts of data within the time limit. Dave Monahan Canadian Hydrographic Service • Ottawa, Ontario Canada University of New Brunswick • Fredericton, New Brunswick Canada

Altimetry Applications to Continental Shelf Delineation Under the United Nations Convention on the Law of the Sea