The 1982 UN Convention on the Law of the Sea and the Outer Limit of the Continental Shelf: Some Practical Difficulties for Wide Margin States

Article 76 of the 1982 UN Convention on the Law of the Sea prescribes the method for defining the outer limit of the continental shelf where it extends beyond 200 nautical miles. This requires the positioning of at least one and possibly three features of the ocean floor: the foot of the slope (the point of maximum change of sea floor gradient); ´the Gardiner Line´ (the point where sediment thickness equals one percent of the distance back to the foot of the slope); and the 2500-metre isobath. Upon ratification of the Convention, each wide-margin state will have ten years in which to define its outer limit and to submit the result to a UN Commission for review. In order to implement the prescriptions of Article 76, most affected coastal states will probably first have to map in greater detail the bathymetry and sediment thickness of their continental margins. Operations of this sort are well within the capabilities of present technology in ice-free waters, but further development will be required before mapping operations can be conducted in areas like the Arctic polar pack. Problems are likely to arise from: the Convention´s ambiguous definition of what constitutes a ´natural component´ of the continental margin; a lack of procedural guidelines for defining the foot of the continental slope and the Gardiner Line; and uncertainties in the measurement of water depth and sediment thickness. In the absence of a higher authority to whom such questions may be referred, wide-margin states should seek a consensus for establishing a uniform and practical set of standards.