1. Introduction
Continental shelf claims beyond 200 nautical miles (NM) have recently seen evolving judicial practice that appears to narrow what coastal States may claim under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS).Footnote 1 Article 76 defines a State’s continental shelf to consist of seabed and subsoil that extend beyond its territorial sea ‘through the natural prolongation of its land territory to the outer edge of the continental margin’ or, in cases where that natural prolongation does not reach 200 NM, to a limit of 200 NM from baselines (the distance criterion).Footnote 2
First, a State must demonstrate its entitlement to the continental shelf in a given area, i.e. that it has a legal right to it, based on scientific (geological, geomorphological, sediment thickness) and legal criteria under Article 76. Following a determination of entitlement, if two or more States’ entitlements overlap, the delimitation phase determines where the boundary line between them lies, according to Article 83 UNCLOS.
As will be discussed in Section 2.1, historically, natural prolongation played a central role under international law, especially before UNCLOS, to assert entitlement to the outer continental shelf beyond 200 NM: the State had to show its landmass continued beneath the sea, both geologically and geomorphologically.Footnote 3 However, as explained in Section 2.2, UNCLOS adjusted that formula: Article 76 retains natural prolongation, but also provides that where the continental margin does not extend that far, entitlement is satisfied by the 200 NM distance rule.
Recently, judicial practice has developed two interrelated constraints on continental shelf claims beyond 200 NM. The first constraint relates to the assessment of entitlement. Natural prolongation is increasingly interpreted in a less demanding way, subordinate to the distance criterion. In several cases, tribunals have held that natural prolongation is not an independent and separate requirement in all circumstances, especially where scientific evidence is hard to establish.Footnote 4 Distance has been given primacy or at least treated as an equal basis that may override geological objections in certain scenarios.
The second constraint is apparent in relation to delimitation. Once entitlement is established (by whichever basis), courts tend to use the same method of delimitation for areas beyond 200 NM as they do within 200 NM, effectively treating the outer shelf as a legal extension of inner shelf claims. The delimitation line drawn within 200 NM is merely extended seaward, rather than being reshaped to reflect more precisely geological or morphological differences at greater depths. In effect, beyond 200 NM claims become subordinate to what is decided closer to land. For example, in Nicaragua v Colombia (2023), the International Court of Justice (ICJ) stated that:
… under customary international law, a State’s entitlement to a continental shelf beyond 200 nautical miles from the baselines from which the breadth of its territorial sea is measured may not extend within 200 nautical miles from the baselines of another State.Footnote 5
This illustrates that the legal status and extent of the continental shelf beyond 200 NM are constrained by, and must yield to, the established 200 NM entitlements of neighbouring States.
These developments essentially mean that the outer continental shelf is being subordinated, i.e. being treated as less significant or constrained by, what happens within 200 NM. Although Article 76 UNCLOS mandates that natural prolongation is a basis for entitlement beyond 200 NM, judicial practice appears to be weakening its role, or interpreting it more loosely; and delimitation is being conducted with a unity of approach that does not distinguish between inner and outer continental shelf in terms of method.
This approach has also created a split between the concept of the geological continental shelf as used by the Commission on the Limits of the Continental Shelf (CLCS) and the legal continental shelf, as preferred by judicial bodies. This dichotomous understanding is contrary to the definition of the continental shelf prescribed in UNCLOS because, in the legal context, the extended continental shelf is founded upon the geological and morphological natural prolongation.
As the legal basis of an entitlement is crucial to the process of maritime delimitation,Footnote 6 this article aims to examine this trend in detail. It will first outline the role of natural prolongation historically and in Article 76 UNCLOS (Section 2), before examining how natural prolongation is currently being interpreted by courts and tribunalsFootnote 7 in entitlement claims beyond 200 NM in Section 3. Section 4 will analyse how delimitation beyond 200 NM is being carried out in comparison to delimitation within 200 NM. Section 5 examines the implications of these constraints, discussing the implications for State practice, the CLCS and whether these practices are consistent with the text of UNCLOS (especially Article 76).
In so doing, this article argues that while entitlement and delimitation remain legally distinct, judicial practice is converging toward a model in which natural prolongation is more constrained than UNCLOS might suggest, and delimitation beyond 200 NM is not being treated as a qualitatively different process, but rather a seaward extension of what has been decided up to 200 NM. This results in a narrowing of claims to the continental shelf beyond 200 NM, with consequences both for coastal States seeking extended rights and for the evolution of maritime boundary delimitation.
2. Natural prolongation as the legal basis of entitlement to the continental shelf
2.1. The rise of the principle of natural prolongation
The principle of natural prolongation was first proposed by the ICJ in the North Sea Continental Shelf Cases. The ICJ was requested to decide the principles and rules of international law applicable to the delimitation as between the parties of areas of the continental shelf in the North Sea.Footnote 8 In order to determine a coastal State’s rights to, and the extent of, the continental shelf, the ICJ stated that:
the most fundamental of all the rules of law relating to the continental shelf … namely the rights of the coastal State in respect of the area of continental shelf that constitutes a natural prolongation of its land territory into and under the sea exist ipso facto and ab initio, by virtue of its sovereignty over the land, and as an extension of it.Footnote 9
The method proposed by Germany to determine a just and equitable share of the continental shelf area, and the equidistance method proposed by Denmark and the Netherlands, were considered inconsistent with this fundamental rule because they would inequitably apportion continental shelf areas forming the natural prolongation of one State to another.Footnote 10 As natural prolongation conferred title to the continental shelf ipso facto and ab initio,Footnote 11 it was considered to play a more fundamental role than proximity in determining entitlement to the continental shelf, and was recognised as ‘a prime element in the delimitation process’.Footnote 12 The link between the physical fact of natural prolongation and the law of the continental shelf was stressed by the ICJ,Footnote 13 since ‘the quality of appurtenance or prolongation can only be identified by reference to physical fact, making geomorphological or perhaps geological considerations paramount’.Footnote 14
Consequently, natural prolongation formed the basis for a coastal State to claim an entitlement over continental shelf areas, and the justification for having a legal continental shelf was reliant upon the existence of a geological continental shelf.Footnote 15
2.2. The rule for entitlement to the continental shelf in Article 76 UNCLOS
Drafted after the North Sea Continental Shelf Cases in which natural prolongation was linked to geological facts, UNCLOS formulated its rule for the definition of the continental shelf on the basis of the principle of natural prolongation. Article 76 stipulates that:
The continental shelf of a coastal State comprises the sea-bed 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.Footnote 16
This indicates that within 200 NM of the coast,Footnote 17 an entitlement to the continental shelf should be only defined by distance, and ‘there is no reason to ascribe any role to geological or geophysical factors within that distance either in verifying the legal title of the States concerned or in proceeding to a delimitation as between their claims’.Footnote 18 However, the concept of natural prolongation is not completely superseded by distance;Footnote 19 it still retains its role as a legal basis for the continental shelf beyond 200 NM,Footnote 20 where the emphasis is on geological and geomorphological continuity.Footnote 21 As for where natural prolongation ends, the rules on this are contained in Article 76(4)–(6), and include considerations of geology, geophysics and hydrography. There are three steps: first, the location of the foot of the continental slope (FOS) must be determined (Article 76(4)(b)); second, a line must be drawn from the FOS by either applying the sediment thickness criterion (Article 76(4)(a)(i)) or the 60 NM distance criterion (Article 76(4)(a)(ii)); and, third, the line must not exceed 350 NM from the baselines or 100 NM from the 2,500 metre isobath (which is a line connecting the depth of 2,500 metres) (Article 76(5)).
The above provisions clearly show that the determination of an entitlement to the continental shelf beyond 200 NM and the delineation of its outer limits are not only legal processes but are also intertwined with morphological and geological questions. The CLCS, composed of experts in the field of geology, geophysics and hydrography,Footnote 22 was established not only to provide an interpretation of Article 76 in the Scientific and Technical Guidelines of the CLCS (Guidelines),Footnote 23 but also to consider the data and other material submitted by coastal States and to make recommendations concerning the outer limits of the continental shelf beyond 200 NM.Footnote 24 As reflected in the Guidelines and the recommendations, the CLCS favours a comprehensive examination of the proof of entitlement over the continental shelf and the method of delineating the outer limits of the continental shelfFootnote 25 and, at each stage, requires the support of scientific and technical information, such as geomorphological, geological, bathymetric or geodetic data.Footnote 26 The functioning of the CLCS thus helps States determine whether they are entitled to continental shelves beyond 200 NM and the respective outer limits thereof in a manner which respects both scientific and legal principles. If States could submit information to the CLCS and wait for their recommendation on the limits of the continental shelf prior to submitting a dispute concerning such delimitation to an international judicial body, this would ease the burden faced by judicial bodies in making such determinations. These are generally composed of jurists who are ill-equipped to handle the complex technical and scientific questions that arise in judicial practice. As will be examined in Section 3, the CLCS has not been as helpful as anticipated, but instead has caused some difficulty in determining an entitlement beyond 200 NM.
Article 76 UNCLOS, and thus natural prolongation and an analysis of the geological and morphological aspects of natural prolongation, remains the legal basis for the determination of the continental shelf beyond 200 NM. Together UNCLOS and the Guidelines provide detailed methods for determining the existence of natural prolongation and delineating its outer limits. Ideally, the assessment of scientific data and the issuance of recommendations by the CLCS would relieve international judicial bodies of the burden of examining these complex technical matters. However, in practice, most maritime delimitations are being carried out in the absence of recommendations from the CLCS.Footnote 27
3. Determination of entitlement to the continental shelf beyond 200 NM in maritime delimitation cases
The ICJ, the International Tribunal for the Law of the Sea (ITLOS), the Special Chamber of ITLOS and arbitral tribunals constituted under Annex VII UNCLOS have expressed a range of views on natural prolongation and on entitlement to the continental shelf beyond 200 NM. Their opinions can be categorised into six different approaches.
3.1. Natural prolongation not considered to be an independent legal basis of entitlement
ITLOS first outlined its approach to the natural prolongation assessment in the Bay of Bengal (Bangladesh/Myanmar) case. Surprisingly, it did not accept that natural prolongation ‘constitutes a separate and independent criterion a coastal State must satisfy in order to be entitled to a continental shelf beyond 200 NM’.Footnote 28 Instead, it decided that ‘entitlement to a continental shelf beyond 200 nm should be determined by reference to the outer edge of the continental margin’.Footnote 29 By highlighting the significance of the outer edge of the continental margin, ITLOS seemed to disregard the need for a natural prolongation on which entitlement to the outer continental shelf is founded.
This is inconsistent with Article 76 UNCLOS. As interpreted by the CLCS in its Guidelines, a coastal State has to satisfy the test of appurtenance, designed to determine its legal entitlement to delineate the outer limits of the continental shelf, to prove that ‘natural prolongation of its land territory to the outer edge of the continental margin extends beyond a line delineated at a distance of 200 nautical miles from the baselines’.Footnote 30 The CLCS adheres to the formulae set out in Article 76(4) for delineating the outer edge of the continental margin when interpreting the test of appurtenance.Footnote 31 This could explain why ITLOS emphasised the outer edge of the continental margin while paying little attention to natural prolongation. However, the CLCS interpretation does not mean that natural prolongation should be neglected. In practice, when examining whether the test of appurtenance has been satisfied, the CLCS has adopted two requirements that need to be met: first, based on the location of the base of continental slope (BOS) and that of the FOS, the outer edge of the continental margin should extend beyond 200 NM; and, second, the BOS and the FOS should be located within the submerged prolongation of the landmass of the coastal State.Footnote 32
For example, in its 2011 recommendations to Brazil concerning the Northern Brazilian and Fernando de Noronha Ridges Region, the CLCS found that Brazil did not ‘satisfy the test of appurtenance from the Northern Brazilian Ridge to extend the outer limit of its continental shelf beyond 200 nautical miles’Footnote 33 because the Northern Brazilian Ridge ‘lacks a continuous natural prolongation of the morphology and geology from the continental land mass of Brazil and its continental shelf and slope’.Footnote 34 The CLCS further suggested that Brazil relocate the BOS ‘at a depth of approximately 3,000 m identified as the proper natural prolongation from the land mass of Brazil’.Footnote 35 Similarly, in its 2012 recommendations to Japan in respect of the Mogi Seamount Region, the CLCS determined that the Mogi Seamount was part of the deep ocean floorFootnote 36 rather than part of the continental margin of Japan.Footnote 37 Consequently, the Mogi Seamount should not form the BOS and ‘any FOS point at the base of the continental margin in this Region will lie within the Izu-Ogasawara Trench’,Footnote 38 which did not extend beyond the 200 NM limit. The CLCS thus concluded that, in respect of the Mogi Seamount Region, the test of appurtenance was not satisfied, and therefore ‘Japan is not entitled to delineate the outer limits of its continental shelf beyond 200 NM’.Footnote 39
It can be summarised from the recommendations of the CLCS that without natural prolongation, reference to the outer edge of the continental margin alone cannot entitle a coastal State to the extended continental shelf. Therefore, natural prolongation from the landmass of a coastal State to the outer edge of its continental margin is still of vital significance and ought not to be ignored.Footnote 40 This renders the ITLOS statement in Bay of Bengal (Bangladesh/Myanmar) an inaccurate reflection of the law, relying as it does only on the outer edge of the continental margin.Footnote 41 It is more accurate to say that the outer edge of the continental margin is ‘an essential element in determining the extent of the continental shelf’,Footnote 42 although it is not the only element that matters.
3.2. Treating adjacent shelves alike
An identical geological condition shared by adjacent States has facilitated the confirmation of the existence of an entitlement beyond 200 NM. In the Ghana/Côte d’Ivoire case, the Special Chamber ruled that both Ghana and Côte d’Ivoire were entitled to continental shelves beyond 200 NM.Footnote 43 This was because Ghana had already received recommendations from the CLCS confirming the existence of an entitlement beyond 200 NM.Footnote 44 As Côte d’Ivoire’s geological situation described in its amended submission to the CLCSFootnote 45 was ‘identical to that of Ghana’,Footnote 46 the Special Chamber believed that Côte d’Ivoire would similarly receive affirmative recommendations from the CLCS confirming the existence of a continental shelf beyond 200 NM.Footnote 47 On the face of it, it seems rational for the Special Chamber to arrive at this conclusion based on the similarity of the two States’ geology. However, upon examination of the submissions by Ghana and Côte d’Ivoire to the CLCS and the recommendations issued to Ghana, it is concerning that an identical geological scenario can be brought before the CLCS by a State intentionally claiming parts of the same extended continental shelf area in their submission.
Côte d’Ivoire made its original submission to the CLCS in 2009,Footnote 48 and it later lodged an amended submission to the CLCS in 2016, two years after Ghana received its recommendations. Comparing the original and revised continental shelf areas claimed by Côte d’Ivoire,Footnote 49 it is clear that Côte d’Ivoire prolonged its continental shelf claims eastwards, extending into Ghana’s continental shelf areas, the existence and outer limits of which had already been verified by the CLCS.Footnote 50 As claimed by Ghana, due to this amended submission, ‘the entitlements of Ghana and Côte d’Ivoire in the outer continental shelf are now said to overlap, whereas previously there was no overlap’.Footnote 51 In addition, the locations of four outer limit points of Côte d’Ivoire were ‘almost at the same places as Ghana’s outer limit points’,Footnote 52 and the newly added FOS points claimed by Côte d’Ivoire were approximately the same as the ones used by Ghana. For instance, one FOS point was in the same location and was ‘determined along the same bathymetric profile (A2075L03) as one that was previously accepted’ in Ghana’s recommendations,Footnote 53 and the location of another was close to another of Ghana’s accepted FOS points.Footnote 54
The affirmative recommendations by the CLCS on the existence of an entitlement to and the location of the outer limits of the same extended continental shelf area are likely to explain why the Special Chamber was confident that Côte d’Ivoire had an entitlement to the continental shelf beyond 200 NM. In this case, the method adopted by the Special Chamber, relying on geological and geomorphological similarity and on the conclusions of the CLCS, is consistent with Article 76 UNCLOS. However, this method is unique to its circumstances and cannot be universally applied. Even if the creation of an overlap beyond 200 NM was somewhat artificial, Côte d’Ivoire still succeeded in proving the existence of an entitlement, with the potential to prompt positive recommendations from the CLCS, which indeed were eventually issued in 2020.Footnote 55
3.3. The existence of significant uncertainty
In the absence of recommendations from the CLCS, judicial bodies have taken on the task of determining the existence of an extended continental shelf themselves, but with the caveat that they would not undertake such a delimitation in the event of ‘significant uncertainty’. This approach was first proposed by ITLOS in the Bay of Bengal (Bangladesh/Myanmar) case where it held that ‘notwithstanding the overlapping areas indicated in the submissions of the Parties to the Commission, the Tribunal would have been hesitant to proceed with the delimitation of the area beyond 200 NM had it concluded that there was significant uncertainty as to the existence of a continental margin in the area in question’.Footnote 56 No significant uncertainty was found in this case because of the unique situation of the Bay of Bengal, the entire seafloor of which was covered by a thick layer of sedimentary rocks.Footnote 57 As this was supported by uncontested scientific evidence, ITLOS safely concluded that ‘both Bangladesh and Myanmar have entitlements to a continental shelf extending beyond 200 NM’.Footnote 58
The Special Chamber in the Mauritius/Maldives case applied what it referred to as ‘the standard of significant uncertainty’.Footnote 59 In order to determine whether a significant uncertainty existed concerning the entitlement of Mauritius to an extended continental shelf, the Special Chamber examined the three routes for natural prolongation to the critical FOS proposed by Mauritius in justification of its claim. As the first route passed through the 200-NM continental shelf of the Maldives, it was considered impermissible because ‘a coastal State must demonstrate a natural prolongation of its submerged land territory to the outer edge of its continental margin beyond 200 NM’,Footnote 60 and so it could not ‘form a basis for Mauritius’ natural prolongation to the critical foot of slope point and thus for its entitlement to the continental shelf beyond 200 NM’.Footnote 61 This finding was consistent with CLCS recommendations.Footnote 62
As far as the other two routes were concerned, because there was a fundamental disagreement concerning whether the existence of a natural prolongation could be established from the territory of Mauritius across the Chagos Trough to the critical FOS point,Footnote 63 the Special Chamber concluded that there was significant uncertainty, such that it was not in a position to determine whether Mauritius had an entitlement to an extended continental shelf in the Northern Chagos Archipelago Region.Footnote 64
Relying on the significant uncertainty standard to avoid determining the existence of natural prolongation also conforms to CLCS practice. For example, in the recommendations to the Cook Islands concerning the Manihiki Plateau, the CLCS explained that, ‘due to the lack of conclusive geological and geophysical data and information, and the resulting uncertainties in the tectonic hypothesis’,Footnote 65 it was difficult to ‘substantiate the natural prolongation of the landmass beyond the High Plateau’,Footnote 66 and ‘the Danger Islands Troughs represent a geological/structural discontinuity across the Manihiki Plateau, particularly between the High and Western plateaus’.Footnote 67
It can be inferred that the Special Chamber attached some importance to natural prolongation meaning that it should not be simply ignored in maritime delimitation cases concerning the continental shelf beyond 200 NM. However, applying the standard of significant uncertainty does not require judicial bodies to examine scientific and technical evidence in support of natural prolongation; rather, courts and tribunals should only ascertain whether they can rule out the significant possibility that there is morphological and geological discontinuity. This seemingly modifies the method of determining an entitlement: rather than seeking positive confirmation of the existence of natural prolongation, the tribunal seeks to ensure that there is no significant uncertainty. The latter approach has the advantage of preventing ‘conflicts between the view of the CLCS and that of ITLOS’,Footnote 68 and of avoiding ‘prejudice to the Area, which is the common heritage of humankind’.Footnote 69
3.4. Agreement upon the existence of an entitlement
The entitlement to the continental shelf beyond 200 NM is sometimes confirmed through mutual agreement between States. In the Bay of Bengal (Bangladesh v India) case, the arbitral tribunal acknowledged that Bangladesh and India agreed that they both had entitlements beyond 200 NM.Footnote 70 The tribunal noted that ‘neither may claim a superior entitlement based on geological or geomorphological factors in the overlapping area’.Footnote 71 Relying purely upon the agreement between the disputing States concerning their undisputed entitlements to continental shelves beyond 200 NM, this method neglects the geological and morphological continuity which is required to prove the existence of natural prolongation and also sets aside relevant scientific and technical data normally requested by the CLCS when examining submissions. Such reliance on ‘agreement rather than scientific proof’ amounts to allowing States to agree on technical issues, whilst disregarding the fact that ‘proof of entitlement can only be determined in accordance with Article 76 UNCLOS, not by agreement between the parties’.Footnote 72
The ICJ took a similar approach in the Somalia v Kenya case, verifying the entitlements on the basis of the agreement between States. As ‘neither Party questions the existence of the other Party’s entitlement to a continental shelf beyond 200 nautical miles or the extent of that claim’,Footnote 73 it was able to proceed to ‘delimit the maritime boundary between them in the Indian Ocean up to the outer limit of the continental shelf’.Footnote 74 However, in contrast to the tribunal in Bangladesh v India, the ICJ explicitly stressed that the entitlement to the continental shelf beyond 200 NM should depend on ‘geological and geomorphological criteria, subject to the constraints set out in Article 76, paragraph 5’.Footnote 75 However, the ICJ did not examine whether there was a geological and geomorphological continuity extending to the outer edge of the continental margin in order to confirm the existence of entitlements; rather, it noted that, as reflected in submissions made by Somalia and Kenya,Footnote 76 ‘in most of the area of overlapping claims beyond 200 nautical miles, both Parties claim that their continental shelf extends to a maximum distance of 350 nautical miles’.Footnote 77 This was criticised by Judge Robinson who said that, ‘by delimiting on the presumption that the Parties are entitled to a shelf up to 350 nautical miles, the Court has replaced the geological and geomorphological criteria required by the Convention for such an entitlement with a simple distance criterion of a maximum of 350 nautical miles’.Footnote 78 The existence and the extent of extended continental shelves have thus been verified simply through States’ agreement. It should also be noted that such an agreement—focused on fundamental questions of entitlement—does not amount to an agreement reached between States concerning delimitation issues.
3.5. The relationship between natural prolongation and the distance criterion
In Nicaragua v Colombia (2023), instead of directly delimiting the precise course of the maritime boundary, the ICJ addressed two preliminary questions, the first of which concerned the priority between the claims based on the distance criterion and those based on natural prolongation: under customary international law, may a State’s entitlement to a continental shelf beyond 200 NM from the baselines from which the breadth of its territorial sea is measured extend within 200 NM of the baselines of another State?Footnote 79
By referring to the travaux préparatoires of UNCLOSFootnote 80 and States’ submissions to the CLCS, the ICJ was satisfied that the practice of States was ‘sufficiently widespread and uniform for the purpose of the identification of customary international law’,Footnote 81 and that the State practice before the CLCS was considered to be indicative of opinio juris.Footnote 82 As a consequence, the ICJ decided for the first time that ‘under customary international law, a State’s entitlement to a continental shelf beyond 200 nautical miles from the baselines from which the breadth of its territorial sea is measured may not extend within 200 nautical miles from the baselines of another State’.Footnote 83 It followed that ‘Nicaragua is not entitled to an extended continental shelf within 200 nautical miles from the baselines of Colombia’s mainland coast’.Footnote 84 Accordingly, given that no overlapping entitlements existed, the ICJ did not have to undertake a delimitation.Footnote 85
When comparing the interpretation of the ICJ and that of the CLCS, a difference of approach emerges. The ICJ method affords priority to the distance criterion over natural prolongation, whereas the CLCS treats them equally at the entitlement phase and the extent of natural prolongation is only constrained when determining the outer limits. In the 2011 recommendations concerning the joint submissions made by Mauritius and Seychelles relating to the Mascarene Plateau, the CLCS confirmed that, ‘in the western area of the Mascarene Plateau region, the outer edge of the continental margin of the two coastal States overlaps with the 200 NM limits of Mauritius’.Footnote 86 After assessing the application of the relevant constraint criteria, the CLCS acknowledged that ‘the two coastal States have entitlement to continental shelf beyond 200 NM arising from this part of the western margin of the Mascarene Plateau that extends up to the adjacent 200 NM limits of Mauritius’.Footnote 87 The CLCS finally noted that ‘in the western area of the Mascarene Plateau region the two coastal States have demonstrated the overlap of the outer edge of the continental margin with the 200 NM limits of Mauritius’,Footnote 88 and that they ‘have entitlement to continental shelf beyond 200 NM that extends up to the 200 NM limits of Mauritius’.Footnote 89
It can be inferred from the recommendations that, as regards entitlement, the CLCS, Mauritius and Seychelles all held open the possibility that the extended continental shelf area shared by both States could extend into the inner continental shelf of Mauritius, thus resulting in an overlap. The CLCS cannot conduct a delimitation itself, and its functioning and recommendations cannot cause prejudice to delimitation. Considering the scrupulous attitude that the CLCS has taken towards the ‘non-prejudice clause’,Footnote 90 it would be surprising if the CLCS were to remain silent in the event of an invalid overlap, and thus it can be assumed that the CLCS did acknowledge there to be an overlap where it extends within 200 NM of another State’s baseline. If the priority to the inner continental shelf nullified an extended continental shelf at the entitlement phase, even mutual consent between Mauritius and Seychelles could not validate such an overlap.
The conflicting attitudes taken by the CLCS and judicial bodies add another level of complexity for States when claiming their entitlements, and it appears that, both capable of interpreting and applying Article 76 UNCLOS, the CLCS and judicial bodies have gradually developed their own understandings and their opinions sometimes conflict with each other.
3.6. A procedural precondition for the identification of the entitlement
A submission to the CLCS by coastal States is recognised by international judicial bodies as a procedural precondition for the identification of an entitlement to the continental shelf beyond 200 NM. In Nicaragua v Colombia (2012), the ICJ observed that, as Nicaragua had only submitted preliminary information to the CLCS instead of a formal submission,Footnote 91 Nicaragua could not establish ‘a continental margin that extends far enough to overlap with Colombia’s 200-nautical-mile entitlement to the continental shelf, measured from Colombia’s mainland coast’.Footnote 92 The ICJ thus did not delimit the continental shelf between Nicaragua and Colombia as requested by Nicaragua. The ICJ reiterated this precondition in Nicaragua v Colombia (2016), saying that ‘delimitation of the continental shelf beyond 200 nautical miles from the Nicaraguan coast was conditional on the submission by Nicaragua of information on the limits of its continental shelf beyond 200 nautical miles, provided for in paragraph 8 of Article 76 of UNCLOS, to the CLCS’.Footnote 93 Since a formal submission was made by Nicaragua in 2013,Footnote 94 the ICJ considered that ‘the condition imposed by it in its 2012 Judgment in order for it to be able to examine the claim of Nicaragua contained in final submission I(3) has been fulfilled in the present case’,Footnote 95 and that ‘it is not precluded by the res judicata principle from ruling on the Application submitted by Nicaragua on 16 September 2013’.Footnote 96
Making a submission to the CLCS can improve the credibility of the claim that a State has an entitlement to a continental shelf beyond 200 NM,Footnote 97 but it should not be a mandatory prerequisite. As in Mauritius/Maldives, the Special Chamber did not consider that ‘there is any rule requiring that a submission be made prior to the institution of delimitation proceedings’.Footnote 98. This opinion is strengthened by the fact that, in some situations, the absence of submissions might not prevent the identification of an entitlement. For instance, due to the uncontested scientific evidence regarding the unique nature of the Bay of Bengal, namely the thick layer of sedimentary rocks covering the entire floor of the bay, even if Bangladesh and Myanmar had not made a submission to the CLCS, ITLOS could still have confirmed the existence of their entitlements beyond 200 NM.Footnote 99 Moreover, submission to the CLCS does not always guarantee the existence of the entitlement. As mentioned in Section 3.1 and as reflected in the recommendations,Footnote 100 during the CLCS examination, some claims may not pass the test of appurtenance and thus the coastal State has no entitlement to the extended continental shelf in the area in question.Footnote 101
3.7. Reflections on the different approaches in maritime delimitation cases
As judicial practice can be divided into six different approaches, it is clear that there is no universally applicable method of determining the existence of an entitlement in the absence of a CLCS recommendation. Some methods still pay attention to the existence of a physical natural prolongation and to supportive geological and geomorphological data, which is consistent with Article 76 and CLCS recommendations, while others simply rely on the existence of a legal agreement, which is a questionable approach. It might be concluded that, from a scientific perspective, natural prolongation still plays a crucial role whereas, from a legal perspective, it retains only a symbolic role.
This begs the question: why has there been a divergence in jurisprudence and practice? States’ entitlements to different maritime areas derive from the same axiom of international law: the land dominates the sea.Footnote 102 As ‘the land is the legal source of the power which a State may exercise over territorial extensions to seaward’,Footnote 103 continental shelf rights are considered to be ‘legally both an emanation from and an automatic adjunct of the territorial sovereignty of the coastal State’.Footnote 104 The connection between the landmass of a coastal State and its right to the continental shelf has been strengthened through ‘the projection of the coasts or the coastal fronts’Footnote 105 since coastal projections generate maritime claims in the seaward direction. The axiom has thus developed into: ‘the land dominates the sea through “closeness”’,Footnote 106 which is reflected in the provisions of UNCLOS which provide that the breadth of each maritime zone is measured from the baselines.Footnote 107
The principle of natural prolongation and the distance criterion as being the legal basis of the continental shelf consequently both derived from this axiom. It thus seems rational for judicial bodies to trace back to the most fundamental principle that authorises maritime entitlements to States, namely ‘the land dominates the sea’, when having difficulty in confirming an entitlement beyond 200 NM based upon natural prolongation.Footnote 108 This might explain why alternative methods are adopted and why supplementary elements, such as coastal projections, are considered. Furthermore, the emphasis on the ‘closeness’ can explain the precedence given to the legal entitlement to the continental shelf within 200 NM over that beyond 200 NM. However, being located further from the coast does not preclude entitlement to the extended continental shelf. Natural prolongation can facilitate such entitlement based on the actual geological and morphological continuity of the seabed and subsoil from the land territory to the outer edge of the continental margin, the existence of which is not required for the inner continental shelf. The definition contained in Article 76(1)Footnote 109 indicates that the extended continental shelf is of equal status to the inner continental shelf, but the conclusion reached by the ICJ in Nicaragua v Colombia (2023) conflicts with this, implying that the inner continental shelf is of greater importance.
This leads to a second question: how can an overlap be found to exist in the absence of an enquiry into substantive geological and morphological evidence supporting it? Here, the notion of adjacency appears to offer an explanation. For States with adjacent coasts, it is likely that the projections of the adjacent coasts overlap, including the continental shelf within and beyond 200 NM. When reviewing the CLCS recommendations which have been issued in relation to the four joint submissions, all of them concern States with adjacent coasts.Footnote 110 States’ natural prolongations extend in the same direction with the seaward projections from baselines and, more importantly, parts of their natural prolongations overlap. Therefore, for adjacent States, this factual ‘adjacency’ makes it highly likely that parts of their extended continental shelves overlap with those of their neighbouring States. This might explain why judicial bodies have proceeded to delimit the extended continental shelf between adjacent States.
4. Subordinating delimitation of the continental shelf beyond 200 NM to that within 200 NM
Given the limitations to the application of natural prolongation as a determining factor and the detachment of geological prolongation from the legal concept of the continental shelf, this section examines how judicial bodies proceed to delimit the continental shelf beyond 200 NM under such circumstances. In contrast to the varying approaches adopted in the entitlement phase, the selection and application of delimitation methods beyond 200 NM appear fairly consistent. It can be inferred from judicial practice that, by relying upon the concept of a single continental shelf, the delimitation method used for the continental shelf beyond 200 NM remains the same as that used within 200 NM, and the delimitation line beyond 200 NM is merely a seaward extension of the line used within 200 NM.
4.1. The current approach adopted in judicial practice
In the four delimitation cases that have arisen in the past two decades, courts and tribunals have found it appropriate to extend seawards the delimitation line between adjacent States for the exclusive economic zone (EEZ) and the continental shelf within 200 NM in order to delimit the continental shelf beyond 200 NM.Footnote 111 For instance, in 2012 ITLOS decided in Bay of Bengal (Bangladesh/Myanmar) that ‘the adjusted equidistance line delimiting both the exclusive economic zone and the continental shelf within 200 NM … continues in the same direction beyond the 200 NM limit of Bangladesh until it reaches the area where the rights of third States may be affected’.Footnote 112
This seaward extension was justified based on the concept of a single continental shelf, an idea implicit in Articles 76, 77 and 83 UNCLOS, which make no distinction between the inner and extended shelf. This was noted by ITLOS, which observed that these provisions refer to the continental shelf ‘in its entirety without any distinction being made between the shelf within 200 NM and the shelf beyond that limit’.Footnote 113 The concept of a single continental shelf was first articulated by the arbitral tribunal in 2006 in the Barbados v Trinidad and Tobago case. It stated: ‘in any event there is in law only a single “continental shelf” rather than an inner continental shelf and a separate extended or outer continental shelf’.Footnote 114 This was intended to confirm the jurisdiction concerning ‘the delimitation of the maritime boundary in relation to that part of the continental shelf extending beyond 200 NM’.Footnote 115
This concept was later used to support the idea that the delimitation method for the continental shelf beyond 200 NM should remain the same as that within 200 NM. For example, the arbitral tribunal in Bay of Bengal (Bangladesh v India) in 2014 said that, because there is only a single continental shelf, ‘the appropriate method for delimiting the continental shelf remains the same, irrespective of whether the area to be delimited lies within or beyond 200 NM’.Footnote 116 In 2017 the Special Chamber in the Ghana/Côte d’Ivoire case also considered it ‘inappropriate to make a distinction between the continental shelf within and beyond 200 nm as far as the delimitation methodology is concerned’.Footnote 117
By emphasising the uniformity of the continental shelf and not differentiating between the continental shelf within 200 NM and that beyond 200 NM, judicial bodies have thus been able to justify the application of the equidistance/relevant circumstances method to delimit the continental shelf beyond 200 NM, i.e. the standard approach used to delimit the continental shelf (and EEZ) to achieve an equitable result. First a line is drawn using the equidistance principle, which is then adjusted as necessary to account for relevant circumstances which might render that line inequitable, e.g. coastal length disparities, shape of the coastline, presence of islands etc.Footnote 118 In Black Sea (Romania v Ukraine) in 2009, the ICJ added a third stage to test the adjusted line to ensure the result is not grossly disproportionate to the relative lengths of the parties’ coasts and that it achieves an equitable outcome.Footnote 119 It is indeed true that the delimitations of the continental shelf both within and beyond 200 NM pursue the same goal, which is to achieve an equitable solution.Footnote 120
The application of the equidistance method has been further legitimised by the judicial ‘redefinition’ of natural prolongation. As analysed in Section 3, natural prolongation is no longer considered to be an exclusive basis for entitlement, and the natural boundary derived from geological and geophysical prolongation is no longer being applied in the delimitation beyond 200 NM,Footnote 121 thus detaching natural prolongation from the continental shelf beyond 200 NM. This detachment allows judicial bodies to transform the geological and geomorphological continental shelf beyond 200 NM into a featureless legal unit.Footnote 122 In such circumstances, it is easy for courts and tribunals to extend the delimitation line beyond 200 NM, and thus subordinate the delimitation of the continental shelf beyond 200 NM to that within 200 NM.
4.2. Reflections on the equidistance/relevant circumstances approach
The application of the equidistance/relevant circumstances method to the delimitation of the extended continental shelf is clearly entrenched in judicial practice. The method is ‘based on objective, geographical criteria, while at the same time taking into account any relevant circumstances bearing on the equitableness of the maritime boundary’.Footnote 123 This method has been gradually developed through international jurisprudenceFootnote 124 and has been adopted in the majority of delimitation cases.Footnote 125
There are two reasons why this method is considered the most suitable for delimiting maritime areas within 200 NM. The first reason is its ability to achieve an equitable solution, as evidenced in a number of past cases.Footnote 126 As prescribed in Articles 74 and 83 UNCLOS, reaching an equitable solution is the core goal of every delimitation of the EEZ and the continental shelf. It has also been emphasised in delimitation cases that ‘the goal of achieving an equitable result must be the paramount consideration guiding the action of the Tribunal’.Footnote 127 The equidistance/relevant circumstances method is considered capable of achieving this goal within 200 NM mainly because of its connection to the basis of entitlement and the relationship between the continental shelf and the EEZ within 200 NM.Footnote 128 The second reason is that the application of the equidistance/relevant circumstances method can ensure a degree of predictability, transparency and consistency,Footnote 129 which are also objectives to be strived for in the maritime delimitation process.Footnote 130 As a result, the equidistance/relevant circumstances method has been recognised as being ‘the best combination between certainty and an equitable result, as an expression of equity infra legem’.Footnote 131
For the delimitation of the continental shelf beyond 200 NM, courts and tribunals have continued to apply the equidistance/relevant circumstances method. The justifications for this application are less evident, particularly given that its use is at the expense of denying the unique geological and morphological characteristics of natural prolongation and, consequently, the conflation of the continental shelf within and beyond 200 NM. The application of the equidistance/relevant circumstances method beyond 200 NM could have been more logically founded if such application had been based on the detailed information of the outer limits of the continental shelf recommended by the CLCS. Still, applying the same delimitation method within and beyond 200 NM has achieved the goals of consistency and predictability, even though it has been done artificially. A question is raised here: if the delimitation method for the extended continental shelf is applied by depriving it of its uniqueness, can this method still achieve a substantive equitable solution or merely an abstract one? It might be further argued that ‘the crystallization of equitable considerations bolsters consistency, but that benefit comes at an underappreciated cost: the loss of equity itself’.Footnote 132
Despite these considerations, it cannot be denied that the ICJ and other tribunals have ‘had a major impact on the clarification of the principles and rules of delimitation’,Footnote 133 and have contributed to the development of the delimitation rule of the continental shelf beyond 200 NM.
5. The implications of these constraints
The constraints added to the continental shelf beyond 200 NM, both at the entitlement level and in the delimitation process, will have broader implications. First, State claims submitted to the CLCS will be invalid if they extend into another State’s inner continental shelf. For instance, the Republic of Korea in 2012 sent a submission to the CLCS concerning the outer limits of the continental shelf beyond 200 NM in respect of the East China Sea.Footnote 134 In 2013, it claimed that, as UNCLOS did not prioritise the distance criterion over natural prolongation, Japan could not ‘use its entitlement based on the distance criterion to negate Korea’s entitlement based on geomorphological considerations’.Footnote 135 This argument could no longer stand following the ICJ’s pronouncement in Nicaragua v Colombia and, consequently, any claims of entitlement and to outer limits dependent upon it also become invalid.
Since the extended continental shelf area claimed by the Republic of Korea also falls within the Japan–Korea Joint Development Zone (JDZ),Footnote 136 Korea’s interests in the JDZ are also affected. As the JDZ serves as ‘a provisional arrangement to manage peacefully the disputed continental shelf’,Footnote 137 which expires in 2028, the unresolved delimitation of the continental shelf is now a live issue. As the distance criterion has priority over natural prolongation, it can be expected that a large part of the originally claimed overlapping area will cease to overlap and instead will fall within the jurisdiction of Japan. One possible modification is to narrow the JDZ by excluding the Republic of Korea’s extended continental shelf area which intrudes upon Japan’s inner continental shelf.Footnote 138 Consequently, for the Republic of Korea and States with similar claims, the constraint on the continental shelf beyond 200 NM is definitely to their disadvantage both in respect of the delineation of the outer limits beyond 200 NM and in respect of the delimitation of the continental shelf. If they were to submit their dispute to judicial bodies for delimitation, the current claim of Korea which extends into the inner continental shelf of Japan would be considered invalid on the basis of the rule in Nicaragua v Colombia. Meanwhile, for States like Japan, their insistence on the distance criterion and the continental shelf within 200 NM gives them an advantage, as even without submitting the dispute to a judicial body, Japan could invoke the ICJ judgment to justify its claim and nullify that part of Korea’s claim.
With respect to future dispute settlement proceedings, it can be expected that international judicial bodies will follow the tendency to restrict the continental shelf beyond 200 NM and give priority to the continental shelf within 200 NM. The equidistance/relevant circumstances method will continue to be applied to the delimitation of the continental shelf beyond 200 NM between adjacent States. What remains unclear is how judicial bodies will deal with the delimitation beyond 200 NM between opposite States.Footnote 139
As regards the work of the CLCS, it is highly likely that the CLCS will keep focusing on examining the scientific attributes of the continental shelf and, at the same time, implicitly accept new rules established by international judicial bodies. The priority given to the distance criterion will not affect the evaluation of technical data and evidence by the CLCS. It is the submitting States who will be affected by the divergent roles and different interpretations of Article 76 between the CLCS and tribunals since they are participants in both procedures. For instance, after receiving judgments in 2012 and 2014,Footnote 140 in 2020 Bangladesh submitted a revised submission to the CLCS which superseded its 2011 submission in its entirety.Footnote 141 Bangladesh claimed that the amended outer limits:
give effect to the Bangladesh/Myanmar Judgement by the ITLOS that delimits a maritime boundary between Bangladesh and Myanmar including where it extends beyond 200 M measured from the relevant territorial sea baselines, and the Bangladesh/India Award by the Arbitral Tribunal, which delimits a maritime boundary between Bangladesh and India including where it extends beyond 200 M measured from the relevant territorial sea baselines.Footnote 142
As judicial decisions are not a replacement for CLCS recommendations, Bangladesh still needs to obtain a positive recommendation from the CLCS to confirm that its outer limits are in conformity with Article 76, which is time-consuming and would now appear to be somewhat redundant. A positive recommendation is more useful if it can be issued prior to the delimitation process, as was the case with that of Ghana.
For the legal regime of the continental shelf, as priority has been given to the distance criterion over natural prolongation, contrary to Article 76(1) UNCLOS the continental shelf beyond 200 NM does not receive equal treatment to that within 200 NM. Considering the difference between the practice of judicial bodies and that of the CLCS concerning Article 76, concerns remain that no consistent interpretation of the legal regime of the continental shelf has been developed. There is a split between the scientific aspect of the continental shelf focused on by the CLCS and the legal aspect of the continental shelf favoured by judicial bodies. This division is clearly unexpected and contrary to the definition contained in Article 76.
6. Conclusion
In recent years two restrictions on the continental shelf beyond 200 NM have developed as a result of judicial practice. As regards the legal basis of entitlement, natural prolongation has not been treated in the manner contemplated by the ICJ in the North Sea Continental Shelf Cases or provided for in Article 76 UNCLOS. Following the denial of natural prolongation as an independent basis of entitlement, judicial bodies have not adopted a method that accords with UNCLOS but, rather, have chosen to apply relatively liberal methodologies to confirm the existence of an extended continental shelf. However, it should be borne in mind that, even when applying these methods, judicial bodies have considered the possibility of the existence of geological and geomorphological natural prolongation rather than completely ignoring the scientific aspects embedded in the concept of the continental shelf. The prioritising of the distance criterion over natural prolongation adds another level of complexity to the issue. It should also be noted that a discrepancy has been created between the interpretations by judicial bodies and those of the CLCS concerning natural prolongation and the determination of the entitlement to the continental shelf beyond 200 NM.
The second restriction that has developed relates to the maritime delimitation of the continental shelf beyond 200 NM, which no longer takes account of geological and geomorphological aspects when drawing a delimitation line beyond 200 NM, and further loses its independence by effectively collapsing into the method for determining maritime boundaries within 200 NM.
This restrictive approach, which courts have adopted in relation to the continental shelf beyond 200 NM, impacts not only coastal States’ delineation and delimitation processes, but also the legal regime of the continental shelf itself. It seems that judicial bodies interpret the continental shelf beyond 200 NM in a way that does not accurately reflect Article 76 but, rather, in a way that is judicially convenient and seeks to guarantee an equitable solution in the absence of recommendations from the CLCS.
Acknowledgments
The author wishes to sincerely thank the anonymous reviewers for their constructive comments.
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