The Outer Limits of the Continental Shelf

CHAPTER 2 The Outer Limits of the Continental Shelf

2.1 Introduction

This chapter addresses the establishment of the outer limits of the continental shelf beyond 200 nm. Its main purpose is to define important concepts for the purposes of the book and to explain the main aspects of the delineation of the extended continental shelf. It gives a brief historical overview of the field and introduces the natural prolongation concept. Finally, the main provisions of UNCLOS regarding the establishment of the outer limits of the extended continental shelf are explained and a brief overview is given about coastal States rights and duties in the continental shelf.

2.2 What is the Continental Shelf?

The term continental shelf does not have the same meaning in international law as in science. The scientific meaning of the continental shelf refers to the platform on which the land lies while the legal definition does not only cover this platform but the whole continental margin, which not only consists of the continental shelf but also the rise and slope.1 In a more detailed way the legal continental shelf can generally be described as following:

Physically, the sea bed adjacent to a typical coast is usually considered to consist of three separate sections . . . First, the section that slopes down gradually from the low-water mark to the depth, averaging about 130 metres, at which the angle of declination increases markedly: this is the continental shelf proper. Second, the section bordering the shelf and having the steeper slope, going down to around 1,200 to 3,500 metres: this is known as the continental slope. Third, there is in many locations

1 The continental margin is the zone that separates ‘the thin oceanic crust of the deep ocean basins from the thick continental crust . . . The boundary between these crustal provinces marks the real physical outer edge of the prolongation of the continent beneath the ocean.’ Philip A. Symonds et al., ‘Characteristics of Continental Marginsʼ in Peter Cook & Chris Carleton (eds.) Continental Shelf Limits: The Scientific and Legal Interface (Oxford University Press 2000) 25, 25.

an area beyond the slope where the sea bed falls away more gradually and is composed mainly of sediments washed down from the continents. This is called the continental rise, and typically descends to a depth of around 3,500 to 5,500 metres. Together these three sections form the continental margin, which constitutes about one-fifth of the sea floor.2

Beyond the outer edge of the continental margin is the deep ocean floor which includes the oceanic features of the seafloor, such as ocean basins, abyssal plains, abyssal hills, mid-ocean ridges, fracture zones and seamounts. The main reason why there is a large interest in the establishment of the outer limits of the continental shelf is that in many places the continental margin is rich of natural resources suitable for exploitation, the most important being oil and gas. Other possible future energy sources, are also found there, ‘such as gas hydrate, a methane/water mixture frozen into the sediments’.3 It also ‘includes many types of sea-floor formations with metal and mineral resource potential, such as polymetallic nodules’ and biological resources used for medical and pharmaceutical purposes.4 The continental shelf as it is described in UNCLOS is a legal fiction. The continental shelf in the meaning of UNCLOS extends throughout the natural prolongation of the land territory to the outer edge of the continental margin or to a distance of 200 nm from the baselines where the outer edge does not extend up to that distance.5 The seabed itself has no role in the latter method, only distance. It must also be noted that the seabed within the territorial sea, which is of course part of the physical continental shelf, is not part of the legal continental shelf. In addition, as explained above, the provisions in UNCLOS regarding the continental shelf in fact include not only the continental shelf, but also the continental margin. It would therefore make more sense to use the continental margin concept instead of the continental shelf one. In fact ‘it would have been better to have adopted a more neutral concept such as “sub- marine area”. However the term “continental shelf” had such widespread usage that this was not practical, and it continues to be used today.’6

2 Robin Churchill & Vaughan Lowe, The Law of the Sea (3rd edn, Manchester University Press 1999) 141. 3 Huw Llewellyn, ‘The Commission on the Limits of the Continental Shelf: Joint Submission by France, Ireland, Spain and the United Kingdom’ (2007) 56 ICLQ 677, 680. 4 Ibid. 5 Article 76(1) of UNCLOS. 6 Donald R. Rothwell & Tim Stephens, The International Law of the Sea (Hart Publishing 2010) 103.