Genesis of the Concept of the Continental Shelf
Geologically, the continental shelf is an area adjacent to a continent or around an island extending from the low-water line to the depth at which there is usually a marked increase of slope to greater depth. Before World War II, natural resources in the seabed and its subsoil had attracted little interest between States. However, natural resources in the
seabed and its subsoil, in particular, an extensive reserve of oil, have attracted growing interest since World War II because of the increased demand for petrol. Furthermore, technological progress at the turn of the twentieth century enabled the continental shelf’s hydrocarbon resources to be extracted from the surface of the sea. Against that background, on 28 September 1945, the United States took the decisive step with the Truman Proclamation to extend its jurisdiction over the natural resources of the continental shelf. The Truman Proclamation declared:
Having Concern for the urgency of conserving and prudently utilizing its natural resources, the Government of the United States regards the natural resources of the subsoil and sea bed of the continental shelf beneath the high seas but contiguous to the coasts of the United States as appertaining to the United States, subject to its jurisdiction and control.
The unilateral action of the United States created a chain reaction, and many States unilaterally extended their jurisdiction towards the high seas. The Latin American States – which have virtually no continental shelf in a geological sense – claimed their full sovereignty over all the seabed at whatever depth and over all the adjacent seas at whatever depth, to a distance of 200 nautical miles. While State practice was not consistent until the early 1950s, the vast majority of States were prepared to agree to create a new zone relating to the exploitation of natural resources on the continental shelf with the passage of time.
Thus a legal regime governing the continental shelf was, for the first time, enshrined in the 1958 Geneva Convention on the Continental Shelf. In this regard, the ICJ, in the 1969 North Sea Continental Shelf cases, took the view that Articles 1 to 3 of the Convention on the Continental Shelf, which included the definition of the continental shelf, were ‘regarded as reflecting, or as crystallizing, received or at least emergent rules of customary international law relative to the continental shelf’. Today there is no doubt that the rights of the coastal State over the continental shelf are well established in customary international law.
Spatial Scope of the Continental Shelf
The landward limit of the continental shelf in the legal sense is the seaward limit of the territorial sea. In this respect, Article 1 of the Convention on the Continental Shelf stipulates that the continental shelf is the seabed and subsoil of the submarine areas adjacent to the coast but outside the area of the territorial sea. Similarly, Article 76(1) of the LOSC states that ‘the continental shelf of a coastal State comprises the seabed and subsoil of the submarine areas that extend beyond its territorial sea’. It follows that the continental shelf in a legal sense does not include the seabed of the territorial sea.
On the other hand, the seaward limit of the continental shelf needs careful consideration. Article 1(a) of the Geneva Convention on the Continental Shelf provides two criteria to locate the seaward limits of the continental shelf: the 200 metres isobath and the exploitability test. However, the exploitability test gave rise to a considerable degree of uncertainty because legal interpretation of the test may change according to the development of technology. In fact, the technological development during the 1960s made it possible to exploit the seabed at depths in excess of 1000 metres. It could be reasonably presumed that this capacity would progress further. In this regard, some argue that the concept of exploitability may be interpreted in relation to the most advanced standards of technology. If this is the case, according to an extreme interpretation, all the ocean floor of the world would eventually be divided among the coastal States. Hence it was hardly surprising that the precise limits of the continental shelf became a significant issue at UNCLOS III.
Negotiations at the Conference resulted in Article 76 of the LOSC. Article 76(1) provides two alternative criteria determining the outer limits of the continental shelf beyond 200 nautical miles:
The continental shelf of a coastal State comprises the seabed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance of 200 nautical miles from the baselines from which the breadth of the territorial sea is measured where the outer edge of the continental margin does not extend up to that distance.
In the 2012 Nicaragua/Colombia case, the ICJ considered that the definition of the continental shelf set out in Article 76(1) of the LOSC forms part of customary international law. Article 76(1) provides two criteria: (i) the limit of the outer edge of the continental margin (geological criterion), or (ii) a distance of 200 nautical miles (distance criterion). There is
little doubt that the distance criterion is closely linked to the concept of the EEZ. In accordance with the distance criterion, the coastal State has the continental shelf in a legal sense up to 200 nautical miles regardless of the configuration of the seabed. As a consequence, approximately 36 per cent of the total seabed is now under the national jurisdiction of the coastal State.
In relation to this, legal title over the continental shelf should be mentioned. Legal title can be defined as the criteria on the basis of which a State is legally empowered to exercise rights and jurisdiction over the marine areas adjacent to its coasts. According to the Truman Proclamation, the continental shelf ‘may be regarded as an extension of the landmass of the coastal nation and thus naturally appurtenant to it’. Noting this phrase, the ICJ, in the North Sea Continental Shelf cases, highlighted the concept of natural prolongation as a legal title over the continental shelf. On the other hand, the emergence of the concept of the 200-mile EEZ inevitably affected the legal title of the continental shelf. As noted, the EEZ is based on the distance criterion. In this regard, the ICJ, in the Libya/Malta case, pronounced:
Although there can be a continental shelf where there is no exclusive economic zone, there cannot be an exclusive economic zone without a corresponding continental shelf. It follows that, for juridical and practical reasons, the distance criterion must now apply to the continental shelf as well as to the exclusive economic zone.
In light of the dictum of the Court and Article 76 of the LOSC, it may be argued that currently the distance criterion is the legal title over the continental shelf up to 200 nautical miles, and the natural prolongation offers legal title over the shelf beyond 200 nautical miles.