A. Natural Prolongation Constitutes the Entitlement to Continental Shelf Beyond 200 nm

The proclamation on continental shelves made by President Truman of the United States in 1945 was regarded as the first clear assertion of the idea that a continental shelf belongs to the coastal state, justified on the basis of contiguity and reasonableness.Footnote ⁹ After the US, many other states made similar unilateral declarations, claiming rights or even full sovereignty over the continental shelf. Although state practice was inconsistent during the 1950s, it was generally accepted that coastal states should enjoy certain rights over their continental shelf by the 1958 Geneva Conference. And the 1958 Continental Shelf Convention set out two criteria in defining the scope of rights over the continental shelf, namely, the 200-metre isobaths 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.Footnote ¹⁰ The 1982 UNCLOS redefined the concept of continental shelf and provided two criteria for deciding costal states’ entitlements to a continental shelf, which are natural prolongation and 200 nm distance criterion.

The notion of natural prolongation was first introduced in the North Sea case and was regarded as the sole basis in determining the entitlement to a continental shelf.Footnote ¹¹ After Article 76(1) of the UNCLOS introduced the 200 nm distance criterion, both natural prolongation and the distance criterion constitute the entitlement to a continental shelf. The Libya/Malta case indicates, and most writers agree, “that today coastal States may claim an area of 200 nm beyond the baselines”.Footnote ¹² And in terms of the continental shelf beyond 200 nm, natural prolongation serves as the legal basis in determining coastal states’ entitlements to the shelf, which is supported by Article 76(1) and its drafting history, as well as relevant international judicial practice and state practice.

The text of Article 76, paragraph 1, has long been acknowledged as the definition of the continental shelf and contains two criteria in determining entitlements to the continental shelf: natural prolongation and distance.Footnote ¹³ The International Court of Justice (ICJ) remarked in the Libya/Malta case that “the concepts of natural prolongation and distance are therefore not opposed but complementary; and both remain essential elements in the juridical concept of the continental shelf”.Footnote ¹⁴ Since both criteria are “essential elements” in the continental shelf, how are they applied in determining entitlement to a continental shelf? We can say that the distance criterion can only be applied by states for rights over the continental shelf within 200 nm, while states with a broad continental shelf which extends beyond the 200 nm distance should base their entitlements on the natural prolongation criterion. This view is also echoed in the works of some scholars. For instance, Dr Yoshifumi Tanaka wrote that “currently the distance criterion is the legal title over the continental shelf up to 200 nm and the natural prolongation offers legal title over the shelf beyond 200 nm”.Footnote ¹⁵ And to understand “complementary”, one could conclude that only if a state's natural continental margin is narrower than 200 miles does the distance criterion come into operation.Footnote ¹⁶ However, this does not imply an approach to divide the legal titles into one within and one beyond 200 nm. Instead, it means that a coastal state could base its rights over the continental shelf on natural prolongation where it extends beyond 200 nm, including the parts within and outside 200 nm.Footnote ¹⁷

The drafting history of the UNCLOS sheds light on how the UNCLOS came to recognize natural prolongation as a basis for legal entitlement to the continental shelf beyond 200 nm. In fact, the final text of Article 76(1) could be regarded as a compromise between countries advocating the 200 nm distance criterion and those proposing natural prolongation as the primary criterion. During the Third UN Conference on the Law of the Sea (the Conference), the delegations could hardly agree on one single criterion to determine entitlement to the continental shelf.Footnote ¹⁸ One of the early proposals submitted by Canada, Chile, Iceland, India, Indonesia, Mauritius, Mexico, New Zealand, and Norway (the Nine-State Proposal) clearly expressed each country's concern about the continental shelf beyond 200 nm. Particularly, the Proposal defined the continental shelf with reference to a 200 nautical mile distance criterion and as the “natural prolongation of the coastal State's land territory where such natural prolongation extends beyond 200 miles”.Footnote ¹⁹ The countries recognized that natural prolongation provided the basis for rights over the continental shelf beyond 200 nm, which reflected the observation of the ICJ in the North Sea case. In addition, strong support for natural prolongation can be traced back to debates over whether the legal regime of the continental shelf should be absorbed by the newly introduced legal regime of the exclusive economic zone (EEZ). During these debates, countries with broad continental shelves argued that their rights to the continental shelf beyond 200 nm should be safeguarded. The legal basis for their claim was natural prolongation extending beyond 200 nm. At the 18th Meeting of the Second Session during the Conference, the delegation from Venezuela emphasized that “it would be sufficient to state that the continental shelf was the natural prolongation of the continental and island territory of the coastal State, and to establish clearly that prolongation might extend, in some cases, beyond 200 miles”.Footnote ²⁰ Furthermore, during the 19th Meeting of the Second Session, “the exercise of sovereign rights by the coastal State over the natural prolongation of its land territory where such prolongation extended beyond 200 miles” was considered to be one of the essential elements for constructive discussions leading to general agreement.Footnote ²¹ This also indicates that protecting rights over the continental shelf beyond 200 nm based on natural prolongation was a major issue for countries with broad continental shelves. Consequently, as a compromise between broad-margin countries and narrow-margin countries, the final text of Article 76(1), although without specific clarification, could be regarded as embracing two criteria concerning entitlements to the continental shelf.

International judicial practice also provides support for natural prolongation as a basis for entitlement to the continental shelf beyond 200 nm. In the Barbados/Trinidad and Tobago case, the Arbitral Tribunal discussed the relationship between natural prolongation and distance criterion and stated:

This restatement of the observation in the Libya/Malta case raises the question of understanding the “complementary roles” of natural prolongation and the distance criterion. In actual fact, natural prolongation is the only basis of the coastal states’ entitlement to the continental shelf beyond 200 nm. Otherwise, the “complementary” aspect of the above concept could not be understood precisely. Furthermore, as the first case on the delimitation of the continental shelf beyond 200 nm, the Tribunal decided in the Barbados/Trinidad and Tobago case that it had the jurisdiction to delimit such a continental shelf (although it did not do so in the end). This jurisdiction is based on the recognition that the continental shelf is “a single continental shelf rather than an inner continental shelf and a separate extended or outer continental shelf”.Footnote ²³ In this respect, the entitlement to the whole continental shelf shall be single too. Thus, natural prolongation as entitlement governs the entire continental shelf, including the parts within and beyond 200 nm.

State practice also confirms that natural prolongation has been applied as a legal title to the continental shelf beyond 200 nm. This principle was first reflected in the work of the Commission on the Limits of the Continental Shelf (CLCS) with regard to the establishment of the outer limit of the continental shelf. The Scientific and Technical Guidelines on the Limits of the Continental Shelf (hereinafter Guidelines), adopted by the CLCS in 1999,Footnote ²⁴ provide guidance for coastal states to delineate the outer limit of the continental shelf. Paragraph 2.2.3 of the Guidelines states:

According to one scholar, in order to make recommendations on the submissions by coastal states, to the extent the CLCS accepts, a coastal state's proposed outer limit of the continental shelf presupposes that the entire continental shelf from the territorial sea onwards to its outer limits is a natural prolongation of its land territory.Footnote ²⁵

State practice shows that proof of the existence of natural prolongation is highlighted in the preparatory work for submission to the CLCS. For example, the scientific work launched by Denmark emphasized proving the existence of natural prolongation. Two features of interest to Denmark in the central Arctic Ocean are the Lomonosov Ridge and the Morris Jessup Rise, the latter located to the northeast of Greenland with a jut out into the Amundsen Basin. Based on scientific research, these features are “assumed natural prolongations of northern Greenland”.Footnote ²⁶ Also, in the Joint Submission by France, Ireland, Spain, and the United Kingdom submitted on 19 May 2006, the coastal states presented various maps showing the geography, geology, and geomorphology of the Celtic Sea and Bay of Biscay area. This data demonstrated a wide shelf region along the submerged geological features known as the Celtic Shelf, the Goban Spur, the Armorican Margins, and the deeper and more seaward Union Basin. The joint submission also presented considerable scientific and technical data to establish that these features are a natural prolongation of the land territory of the four states within Article 76(1).Footnote ²⁷

The proof of the existence of natural prolongation can also be disputed in some circumstances. For instance, Russia's submission to the CLCS on 20 December 2001 was concerned with four different areas: the Arctic Ocean, the Barents Sea, the Bering Sea, and the Sea of Okhotsk. Five countries (the US, Japan, Denmark, Norway, and Canada) reacted to the executive summary of the Russian submission. The US, in particular, pointed out that there were major flaws related to the continental shelf in the Arctic Ocean. The American comments discussed the characteristics of the two ridges included in the outer limit lines as defined in the Russian submission, suggesting that these do not form a natural prolongation in the sense of Article 76(1).Footnote ²⁸

In short, natural prolongation is recognized as the basis for delimiting the continental shelf beyond 200 nm, which has been confirmed by both state and international judicial practice. However, this status of natural prolongation was questioned in the Judgment of the Bangladesh/Myanmar case, which cast doubts on natural prolongation as a legal title to the continental shelf beyond 200 nm.

B. Reflections on the ITLOS Interpretation of Natural Prolongation

In deciding the dispute between Bangladesh and Myanmar over the meaning of natural prolongation, the ITLOS carried out its interpretation from different perspectives. It is thus important to analyze and glean insights from the Court's interpretation.

The ITLOS's starting point was the meaning of Article 76. According to the Tribunal, “the outer edge of the continental margin” from paragraph 1 is an essential element in determining the extent of the continental shelf, because the continental shelf of a coastal state can extend either to a distance of 200 nm or to the outer edge of the continental margin, depending on where the outer edge is situated.Footnote ²⁹ The Tribunal then went through paragraphs 3 and 4, stating that, while the notion of the outer edge of the continental margin was elaborated upon, no such elaboration of “natural prolongation” is found in the subsequent paragraphs. The Tribunal also found that paragraph 4 introduces specific formulae to enable the coastal states to establish precisely the outer edge of the continental margin, but natural prolongation was never actually defined.

By stating that natural prolongation had never been defined, the Tribunal seemed to imply that the concept of natural prolongation was uncertain, especially compared to the specifically and technically defined notion of the outer edge of the continental margin. However, the notion of natural prolongation should not be so quickly regarded as uncertain, considering the origin of the concept of natural prolongation, which was based on geological and geomorphological facts.

These differences are best understood in the light of the historical background. Natural prolongation was more a geographical term than a legal term when it was adopted in the text of Article 76 at the Conference.Footnote ³⁰ When the Conference employed the notion of natural prolongation, it relied on the North Sea decision, where the ICJ observed that the natural prolongation of landmass into the sea “already appertaining to it” should determine the rights of a coastal state over the continental shelf.Footnote ³¹ Thus, the reason why natural prolongation had not been defined is that Article 76 presupposed that a geographical definition would be relevant. This could be confirmed by subsequent paragraphs 4, 5, and 6, where geological and scientific formulae were used to define how to establish the limits of the continental shelf. As Judge Lucky points out, Article 76 must be construed as a whole and not in part.Footnote ³² Besides, the lack of a precise definition is not a reason to undermine the status of natural prolongation. As Judge Gao pointed out in his Separate Opinion, the concept of a “common heritage of mankind” is enshrined in the Preamble of the Convention, but nowhere in the Convention is a clear and precise definition of the concept found. Yet that does not prevent it from being one of the most important legal principles of the entire Convention, as well as the basis for Part XI on the Area.Footnote ³³

From a historical perspective, the Tribunal commented that the notion of natural prolongation was employed as a concept to lend support to the trend towards expanding national jurisdiction over the continental margin; thus, the notion of natural prolongation and that of continental margin under Article 76, paragraphs 1 and 4, refers to the same area.Footnote ³⁴ This observation is true in itself because the judicial concept of continental shelf refers to the same area as the concept of continental margin except for the area of territorial sea.Footnote ³⁵ However, this observation contradicts the Tribunal's earlier statement, that “the notion of the outer edge of the continental margin is an essential element in determining the extent of the continental shelf”.Footnote ³⁶ Since the outer edge of the continental margin coincides with the extent of the natural prolongation, it is unclear which of these two notions is “essential in determining the extent of the continental shelf”.

In fact, the idea of natural prolongation was originally introduced by the ICJ in the North Sea case to describe the continuity of the landmass within the territory of a coastal state to the adjacent submarine area. This continuity provides a basis for the entitlement under the doctrine of “land dominates the sea”.Footnote ³⁷ Actually, the requirement of continuity is included in the definition because the plain meaning of the word “prolongation” includes the stipulation that natural, submerged prolongation of land territory or landmass to the outer edge of the continental margin must be unbroken from land.Footnote ³⁸ The origin of natural prolongation implies that it is a concept relying on geology and geomorphology. The definition of the legal continental margin under Article 76 also indicates that geological and geomorphological factors are relevant. This includes the submerged prolongation of the landmass of the coastal state, and consists of the seabed and subsoil (geological terms) of the shelf, the slope, and the rise (geomorphological terms).Footnote ³⁹ Unlike the interpretation of the Tribunal, although natural prolongation is not elaborated upon in the subsequent paragraphs of Article 76, the idea of “continuity” is reflected not only in paragraph 1, but also in paragraph 3. Therefore, the meaning of natural prolongation cannot be construed in isolation. The words that follow “natural prolongation” are “of its land territory to the outer edge of the continental margin”, and it is therefore crucial to establish whether the landmass continues to the outer edge of the continental margin.Footnote ⁴⁰ Further to this point, the continuity of the land territory to the outer edge of the continental margin cannot be ignored. Without geological and geomorphological continuity from its landmass, one would wonder how the jurisdiction of a coastal state could jump so far to the outer edge of the continental margin as even 350 nm, just as Judge Gao observes.Footnote ⁴¹

The Tribunal further based its observation on the purpose of Article 76, stating that the principal object of Article 76 is to define the precise outer limits of the continental shelf, beyond which lies the Area.Footnote ⁴² This finding is also true since Article 76 establishes substantive rules and procedural mechanisms that aim to guarantee stable continental shelf limits.Footnote ⁴³ However, it was less reasonable for the Tribunal to make the following conclusions: “the Tribunal finds it difficult to accept that natural prolongation referred to in article 76, paragraph 1, constitutes a separate and independent criterion a coastal State must satisfy in order to be entitled to a continental shelf beyond 200 nm.”Footnote ⁴⁴ This is because establishment of the continental shelf's outer limits is not the only purpose of Article 76. Article 76(1) provides the definition of the continental shelf and thus “lays down the foundation for the continental shelf regime”Footnote ⁴⁵ by setting out two criteria in determining the entitlements to the continental shelf. Unlike the complex scientific and technical procedures for deciding the precise outer limits of the shelf in the paragraphs that follow, paragraph 1 provides coastal states with a legal basis for claiming rights over the continental shelf, either up to 200 nm or extending beyond the 200 nm limit. The continental shelf to which a coastal state is entitled is the natural prolongation of the landmass continuing to the outer limits of the continental shelf as specified in Article 76, paragraphs 4, 5, and 6.Footnote ⁴⁶ Even though the establishment of the outer limits of the continental shelf is one of Article 76's principal purposes, the definition of continental shelf and criteria for deciding on the entitlements are also essential.

The Tribunal then cited the Guidelines to demonstrate what constitutes the entitlement to the continental shelf beyond 200 nm. Paragraph 2.2.6 of the Guidelines says: “the provisions contained in paragraph 4(a)(i) and (ii), defined as the formulae lines, and paragraph 4(b), to determine whether a coastal State is entitled to delineate the outer limits of the continental shelf beyond 200 nm”, and “2.2.8 … then a coastal State is entitled to delineate the outer limits of the continental shelf as prescribed by the provisions contained in article 76, paragraphs 4 to 10”.Footnote ⁴⁷ Finally the Tribunal reached its conclusion:

By quoting the stipulations in the Guidelines, the Tribunal seemed to base its reasoning on the scientific and technical criteria adopted by the CLCS. But this decision raises some questions. First, the CLCS is a technical body established to provide scientific and technical assistance for coastal states seeking to establish the outer limits of the continental shelf. One should bear in mind that legal work is not only outside the expertise of the CLCS, but also is not within its mandate as laid down under the UNCLOS.Footnote ⁴⁹ Although the Guidelines aim to “clarify its interpretation of scientific, technical, and legal terms contained in the Convention” (paragraph 1.3), the Guidelines themselves are not legally binding. Thus the Guidelines do not have the same status as those Articles in the Convention. In addition, the CLCS, though tasked to consider the data and other material as well as to make recommendations, does not have any competence to determine a coastal state's title to the continental shelf.Footnote ⁵⁰ In this sense, the Guidelines should not be seen as a legal document deciding entitlement to a continental shelf beyond 200 nm, as this task falls under the authority of the UNCLOS, in particular Article 76.

In fact, the Guidelines recognize the role of natural prolongation as the basis for entitlement to the continental shelf beyond 200 nm. Paragraph 2.1.1 reads: “Article 76, paragraph 1, establishes the right of coastal States to determine the outer limits of the continental shelf by means of two criteria based on either natural prolongation or distance”. Furthermore, under the “test of appurtenance”, paragraph 2.2.4 states:

According to paragraph 2.2.2 of the Guidelines, the test of appurtenance is designed to “determine the legal entitlement of a coastal State to delineate the outer limits of the continental shelf throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance to 200 nm”. This test is applied because the Guidelines acknowledge that a positive proof of the entitlement to delineate the extended continental shelf precedes the implementation of the methods to be applied in the delineation.Footnote ⁵¹ That is to say, in applying the rules described in paragraphs 4 to 10, the existence of natural prolongation must first be demonstrated before delineation of the outer limits of the continental shelf takes place.

However, it should be pointed out that the wording of the Guidelines is somewhat vague.Footnote ⁵² This is because, even though the Guidelines recognize that, under the test of appurtenance, demonstrating the existence of natural prolongation extending beyond 200 nm should come before establishing the outer limit of the continental shelf, it also requires the Commission to use the provisions contained in paragraph 4(a)(i) and (ii) and paragraph 4(b) to determine whether a coastal state is entitled to delineate the outer limits of the continental shelf beyond 200 nm, which was quoted by the Tribunal in the Bangladesh/Myanmar case. These two statements seem to contradict each other.

It should be noted that there is a distinction between entitlement to the continental shelf beyond 200 nm and the establishment of the outer limits of the continental margin. Article 76, paragraph 1 sets out the legal entitlement to the continental shelf, while paragraph 4 prescribes the procedures used to locate the exact scope of such entitlement, which is the limit of the continental margin. Even if the main purpose of Article 76 is to establish the precise limit of the outer edge of the continental margin, the establishment of that limit would not jeopardize the entitlement of the continental shelf of the coastal states. As is repeated in the jurisprudence of international courts and tribunals, entitlement to the continental shelf is based on the title of the coastal state over the land,Footnote ⁵³ which is considered “inherent” to the coastal states. The Judgment of the Bangladesh/Myanmar case itself rightly states that “the existence of entitlement does not depend on the establishment of the outer limits of the continental shelf by the coastal State”.Footnote ⁵⁴ Moreover, since Article 76 contains both the general definition of the continental shelf and the specific rules to define the outer limits, it confirms that entitlement to the continental shelf is not dependent on the establishment of outer limits.Footnote ⁵⁵ As paragraph 2.2.5 of the Guidelines stipulates:

Thus one should not overestimate the legal connotation of the Guidelines, especially when the wording seems to contain inner contradictions. Accordingly, the paragraphs quoted by the Tribunal are hardly convincing when studied against the whole background of the test of appurtenance.

By analyzing the reasoning part of the Judgment, one realizes that the Tribunal seems to avoid explaining the exact status of natural prolongation. On the one hand, although it rejects natural prolongation as the “independent and separate” criterion that must be satisfied, the Tribunal does not make clear whether natural prolongation should be considered as a criterion in determining a continental shelf. And if natural prolongation is a criterion, to what extent does it play its role? On the other hand, by stating that Article 76(4) should be satisfied to determine the entitlement to a continental shelf beyond 200 nm, the Tribunal seems to regard Article 76(4) as an independent criterion that is decisive in determining the entitlement to that area. However, this may lead to legal confusion, since the content of Article 76(4) is to provide scientific and technical guidance for coastal states to establish the outer limit of a continental shelf, while Article 76(1) lays down the legal basis for coastal states’ rights over the continental shelf, no matter whether within or beyond 200 nm. The Tribunal leaves these questions open.

In addition, the Tribunal seems to elevate the formulae in Article 76(4) over the notion of natural prolongation in Article 76(1). By emphasizing the decisive role of Article 76(4) while weakening the role of natural prolongation, the Tribunal seemed to ignore the relationship between natural prolongation in paragraph 1 and the formulae in paragraph 4. Articles 76(1) and 76(4) address the same issue from different perspectives and should be of equal importance. Article 76(1) defines the continental shelf as the natural prolongation of a coastal state's land territory to the outer edge of the continental margin. While referring to the same area as the natural prolongation, continental margin is defined by Articles 76(3) and 76(4), at a general level and then at an operational level, respectively.Footnote ⁵⁶ To be more specific, the definition in Article 76(1) provides the legal basis for entitlement to the continental shelf while Article 76(4) prescribes specific methods to locate the exact position of the outer limit of the continental shelf. The criterion of natural prolongation is a general rule while Article 76(4) offers operational methods to determine the exact extent of the natural prolongation.

As we know, a decision of international courts or tribunals is only a “subsidiary means for the determination of rules of law”Footnote ⁵⁷ and has no binding precedential value. Its reasoning must be convincing if future judges and arbitrators are to feel compelled to apply the derived rules of law.Footnote ⁵⁸

A. Different Roles of Natural Prolongation in Maritime Delimitation

A close analysis of the cases before international courts and tribunals suggests that, although widely used, natural prolongation represents different meanings in jurisprudence, playing different roles in each unique case, and sometimes even carrying different meanings in the same case.Footnote ⁶¹

When first introduced in the North Sea case, natural prolongation was regarded as the sole basis of the coastal states’ rights over the continental shelf.Footnote ⁶² Based on this observation, the Court concluded:

It could be clearly seen that the Court tried to connect the basis of the title with the delimitation process. “The most natural extension” cited above indicates that the Court adopted a declaratory conceptual approach, which means that the object of delimitation is to find out what was already appertained to that state. In other words, this approach is based on the perception that the entitlements to the continental shelf are not competing titles.Footnote ⁶⁴ The delimitation aims to “recognize” the boundary between coastal states rather than “delimiting” it on the basis of conflicts of entitlements. In this respect, natural prolongation was used in two senses: the entitlement and the delimitation result. And it should also be noted that the notion of natural prolongation used in the North Sea case relates mostly to the physical phenomenon, since the Court stated that “what confers the ipso jure title … is the fact that the submarine areas concerned may be deemed to be actually part of the territory over which the coastal State already has dominion”.Footnote ⁶⁵ It can be seen from the Court's approach that the legal continental shelf is closely tied up with the scientific continental shelf, since the Court reasoned that the physical shelf justified title to the legal shelf.Footnote ⁶⁶

However, in the aftermath of the North Sea case, the concept of natural prolongation went through a change and played a different role in maritime delimitation. The most significant change was the “divorce” between the scientific and legal concept of prolongation. In the Tunisia/Libya case, the Court reaffirmed that “the natural prolongation of the coastal State is a basis of its legal title to continental shelf rights”Footnote ⁶⁷ was a principle. However, at the same time, the Court also pointed out that “identification of natural prolongation may, where the geographical circumstances are appropriate, have an important role to play in defining an equitable delimitation, in view of its significance as the justification of continental shelf rights in some cases”.Footnote ⁶⁸ The Court's position in regarding the notion of natural prolongation as a principle that is applicable only in some cases is a problem, the only solution to which is that the notion of natural prolongation was used in a different sense. To be specific, when the Court stated natural prolongation as the legal basis of title, it was not referring to a physical or scientific area. This is confirmed by the Court's observation that “the fact that the legal concept [natural prolongation], while it derived from the natural phenomenon, pursued its own development”.Footnote ⁶⁹ However, it should be noted that the divorce of the scientific and legal concepts does not lead to the conclusion that the physical phenomenon of natural prolongation would not carry weight in the delimitation of a continental shelf any more. In fact, it could be concluded from the passages cited above that natural prolongation could play a significant role in delimiting a continental shelf, since the Court observed that “identification of natural prolongation may, where the geographical circumstances are appropriate, have an important role to play in defining an equitable delimitation”.Footnote ⁷⁰ In the Anglo-French Footnote ⁷¹ case, the Court seemed to adopt the same approach. The Tribunal in Anglo-French noted that “the force of the cardinal principle of natural prolongation is not absolute, but may be subject to qualifications”,Footnote ⁷² and such qualifications may refer to the circumstance where there is “a separation of continental shelves”.Footnote ⁷³ Also, in the Tunisia/Libya case, the Court seemed to define “appropriate geographical circumstances” as situations where there is a “marked disruption or discontinuance of the sea-bed”, which indicates “the limits of two separate continental shelves, or two separate natural prolongations”.Footnote ⁷⁴ Consequently, in the both cases, the judicial practice tends to consider that natural prolongation, when referred to as a physical phenomenon, could play a role in delimiting a continental shelf where geographical circumstances are appropriate. And this role has a primary status, implicit in the Court's statement that “it must first examine what such principles [equitable principles] entail, divorced from the concept of natural prolongation which has been found not to be applied for purposes of delimitation in this case”.Footnote ⁷⁵

After years of evolution in jurisprudence, the concept of natural prolongation is now used in the UNCLOS to define the concept of continental shelf, but the meaning of natural prolongation used here differs from what it used to be. As discussed above, the notion of continental shelf used in Article 76, paragraph 1, is one of the two criteria used to decide entitlement to a continental shelf. However, the exact contention of natural prolongation has departed from its initial form. According to a United Nations study on the continental shelf, the provisions of Article 76, paragraphs 1 and 3 “reaffirm the legal concept of the continental shelf and its link with the physical fact of the natural prolongation”, and the prolongation must be “shelf, slope, and rise”, that is, continental margin.Footnote ⁷⁶ The ITLOS adopts the same idea in the Bangladesh/Myanmar case when it states that “the notion of natural prolongation and that of continental margin under article 76, paragraphs 1 and 4, refer to the same area”.Footnote ⁷⁷ Thus, the concept of natural prolongation in Article 76, paragraph 1 “forms the basis for the juridical definition of the continental shelf”.Footnote ⁷⁸ While natural prolongation remains the entitlement to the continental shelf, its contention has changed from a physical factor to a more juridical definition. As some scholars point out, “the first article of Part VI, article 76, defines the continental shelf in a manner which is scientifically based, legally defensible, and politically acceptable”.Footnote ⁷⁹ This definition, consequently, confirms the divorce between the legal concept of natural prolongation and the scientific concept; it was also accepted by judicial practice. In the Gulf of Maine case, the Chamber affirmed that “legal title to certain maritime or submarine areas is always and exclusively the effect of a legal operation”.Footnote ⁸⁰

Despite the changes in the role of natural prolongation in continental shelf delimitation, the original geological and geomorphological concepts of natural prolongation still play a role in the delimitation of a continental shelf. In the North Sea case, after regarding natural prolongation as the sole basis of legal title to a continental shelf, the Court, after stating “balancing the factors in question … [requires] various aspects … [to] be taken into account”, emphasized that “the institution of the continental shelf has arisen out of the recognition of a physical fact”, and that geological criteria “can provide adequate bases for decision adapted to the factual situation”.Footnote ⁸¹ Also, in the Tunisia/Libya case, while the Court regarded the physical structure of the seabed of the Pelagian Block as the natural prolongation common to both parties, which means that there does not exist any element which interrupts the continuity of the continental shelf, the Court still held:

Following this statement, the Court made it clear that “the physical factor constituting the natural prolongation is not taken as a legal title, but as one of several circumstances considered to be the elements of an equitable solution”.Footnote ⁸³ In this aspect, the Court considered that natural prolongation had dual roles, namely the legal title and the relevant circumstance affecting the delimitation, with each carrying different meanings. While the former refers to the submarine area over which the coastal states may claim rights, the latter is understood as the physical factors of the seabed, that is, geological and geomorphological factors.

As the Libya/Malta case has established, geological and geomorphological factors shall not be taken into account when “title depends solely on the distance from the coasts of the claimant States of any areas of seabed claimed by way of continental shelf”.Footnote ⁸⁴ It is not difficult to understand this observation since the relevant circumstances are influenced by the basis of title. It is said that the ICJ used the basis of title as a means of limiting the range of factors which might have been relevant to the delimitation.Footnote ⁸⁵ The Court in the Libya/Malta case firmly rejected geological and geomorphological factors as relevant circumstances because there is no reason why “a factor which has no part to play in the establishment of title should be taken into account as a relevant circumstance for the purposes of delimitation”.Footnote ⁸⁶ It should be noted that in the Libya/Malta case, the distance between Libya and Malta is less than 200 nm. In other words, neither country could claim rights over the continental shelf beyond 200 nm; thus the distance criterion comes into play as the sole legal basis in determining entitlement to the continental shelf. After the Libya/Malta case, natural prolongation as geological and geomorphological factors hardly appeared in the judgments or awards of international judicial practice, mainly due to the reason that title influences the relevant circumstances considered in the maritime delimitation.Footnote ⁸⁷

However, the reasoning applied in delimitating the continental shelf beyond 200 nm and within 200 nm is different. In delimiting the continental shelf beyond 200 nm, natural prolongation as geological and geomorphological factors should be regarded as a relevant circumstance in the delimiting process.

B. Natural Prolongation as a Relevant Circumstance of Delimitation Beyond 200 nm

International judicial practice has demonstrated clearly that relevant circumstances are those factors that may be taken into account to affect the final boundary of a maritime delimitation. Just as Evans rightly points out:

The reason why natural prolongation, referred to as geological and geomorphological factors, should be regarded as a relevant circumstance arises out of two widely recognized principles: first, the factors taken into account shall be those “pertinent to the institution of the continental shelf”,Footnote ⁸⁹ and second, the non-encroachment principle.

During the decades of development in the law of maritime delimitation, the attitudes of international courts and tribunals towards the term “relevant circumstances” underwent a significant change. Post Libya/Malta, the international courts and tribunals shifted away from the position that “there is no legal limit to the considerations which States may take account of for the purposes of making sure that they apply equitable procedures”Footnote ⁹⁰ in the North Sea case, and tended to restrict the categories of relevant circumstances that may be taken into account in maritime delimitation. Recent judicial practice shows that the difficulty lies in reconciling the relevant circumstances and the basis of title. Following the proliferation of the single maritime delimitation, a neutral criterion that favours neither the continental shelf nor the EEZ is preferred in deciding the maritime boundary, as geological and geomorphological factors are only concerned with the legal regime of the continental shelf and not with extent of the EEZ. The Permanent Court of Arbitration (PCA) also observed that “international judicial organs would apply a neutral criterion concerning the coastal geography which favoured neither the continental shelf nor the EEZ”.Footnote ⁹¹ Therefore, there was a “natural reluctance on the part of courts and tribunals to give preference to those elements more closely connected to the continental shelf over those more closely related to the EEZ or vice versa”.Footnote ⁹² After the Libya/Malta case, almost all the parties before the ICJ and the PCA requested a single maritime delimitation, so it is not surprising that geological and geomorphological factors were hardly concerned.Footnote ⁹³

However, the rationale to exclude geological and geomorphological factors within 200 nm does not apply to areas beyond 200 nm.Footnote ⁹⁴ As analyzed above, natural prolongation remains the legal basis of entitlement to a continental shelf beyond 200 nm. Thus, the geological and geomorphological aspects of natural prolongation constitute the relevant circumstances that should be taken into consideration in the delimitation of a continental shelf beyond 200 nm. Even though the notion of natural prolongation defined in Article 76, paragraph 1 refers to a juridical concept, its physical connotation has not been totally detached. When applied to a continental shelf beyond 200 nm, natural prolongation is definitely used as a geological and a geomorphological concept, as seen from the work of the CLCS. In determining whether a coastal state is likely to be entitled to establish a continental shelf limit beyond 200 nm, the coastal state shall determine whether a natural prolongation exists, according to the stipulations set out in the Guidelines. And the prolongation is “morphologically continuous with or geologically connected to the landmass”.Footnote ⁹⁵ As a result, it is said that geological and geomorphological elements are the source of the entitlement to the continental shelf beyond 200 nm, thus delimitation of overlapping areas within this zone might be governed by principles other than the ones established for the delimitation of the area within 200 nm.Footnote ⁹⁶ Hence, it is only natural to include geological and geomorphological factors in delimiting a continental shelf beyond 200 nm because these physical features of the seabed form the underlying legal basis for entitlement to this area. In fact, while the Court in the Libya/Malta case erased natural prolongation as a factor as far as the EEZ was concerned, it also left open the possibility that international law might deem geological and geomorphological factors relevant to the delimitation of the outer continental shelf.Footnote ⁹⁷ Just as the Court stated, the applicable law and the method to be used in such areas should be adopted in a “manner consistent with the concepts underlying the attribution of legal title”.Footnote ⁹⁸ Since the jurisprudence has emphasized that the “legal concept of continental shelf could itself be fundamentally changed by the introduction of considerations strange to its nature”,Footnote ⁹⁹ it is only logical to take geological and geomorphological elements into account since these are two of the most important factors that relate to the nature of a continental shelf beyond 200 nm.

Second, the non-encroachment principle, developed in international cases, also confirms that natural prolongation as a geological and geomorphological factor should be respected in delimitation beyond 200 nm. This principle originated in the North Sea case and states that “the continental shelf of any State must be the natural prolongation of its land territory and must not encroach upon what is the natural prolongation of the territory of another State”.Footnote ¹⁰⁰ This statement reflects that “the principles of natural prolongation and non-encroachment are complementary, and that their definitions are inextricably intertwined”.Footnote ¹⁰¹ From the original meaning of the non-encroachment principle, it could be seen that what the Court try to avoid encroaching on is the area over which the coastal states already enjoy entitlement. Recent judicial practice indicates that the non-encroachment principle is still applied in this aspect. In the Jan Mayen case in 1993, the ICJ referred to the non-encroachment principle when examining the geographical context of the area to identify the required adjustment of the provisional equidistance line. The ICJ stated:

Since recent decisions have placed more emphasis on entitlement through the intermediary of the coast,Footnote ¹⁰³ the non-encroachment principle is increasingly applied in the sense of avoiding encroachment on the coastal projections of the state. This was also the case in the Barbados/Trinidad and Tobago case, where the Tribunal mentioned several criteria which emerged as the requirements of equity, including “[t]he principle that delimitation should avoid the encroachment by one party on the natural prolongation of the other or its equivalent in respect of the EEZ”.Footnote ¹⁰⁴ This recognition of non-encroachment's importance could mean that the ICJ or the PCA is still trying to hold on to the natural prolongation principle.Footnote ¹⁰⁵ Since natural prolongation is the entitlement to a continental shelf beyond 200 nm, and geological and geomorphological conditions are decisive factors in deciding the scope of this entitlement, avoiding encroachment on the natural prolongation of a coastal state in the delimitation of a continental shelf beyond 200 nm should also be a requirement of an equitable solution.

As to what extent or in what way natural prolongation as a geological and geomorphological factor plays a role in the delimitation of a continental shelf beyond 200 nm, it is left to the decision of the international courts and tribunals or states. Since maritime delimitation makes a general distinction between opposite states and adjacent states, it may be easier to address the issue by reviewing the geological and geomorphological factors separately in these two different situations. While state practice may provide some guidance in the former case where the states are opposite, the Bangladesh/Myanmar case sheds some light on the latter case.

When states lie opposite each other and either of them relies on the natural prolongation doctrine, the issue could be potentially complex as the states may refer to different geological and/or geomorphological data, suggesting different evidence of the condition of the disputed area. In such situations, even if the related issues are complex and difficult, it is still suggested that if a natural geological “boundary” is found to exist within the disputed area, this may form part of the basis of a negotiated settlement, together with other relevant geographical considerations.Footnote ¹⁰⁶ In any case, it is still left to parties to decide whether, and to what extent, they will consider natural prolongation as a geological or geomorphological factor in a maritime delimitation agreement. Furthermore, it is also open to any state, favoured by the evidence of natural prolongation, to argue that natural prolongation should be considered in delimiting any seabed boundary more than 200 nm from the coast.Footnote ¹⁰⁷ Australia relied on the natural prolongation argument as well as on geological and geomorphological factors when finalizing its maritime boundary with its geographically opposite states. The maritime boundary between Australia and Indonesia is a case in point. The delimitation line of the continental shelf lies beyond 200 nm from Australian territory, but within 200 nm of Indonesia's baselines.Footnote ¹⁰⁸ Up till now, international judicial organs have not decided a maritime delimitation dispute concerning overlapping entitlements beyond 200 nm between opposite states, since normally a coastal state shall make a submission to the CLCS to establish the outer limit of a continental margin, demonstrating its entitlement to a continental shelf beyond 200 nm. It is unlikely that international courts or tribunals would delimit a maritime boundary between opposite states when the outer limit of continental margin is not settled.Footnote ¹⁰⁹

In cases where the states are adjacent to each other, it seems that the issue is less complicated than that between opposite states. This is because it is probable that the prolongation of the shelf from the territorial sea baseline to the outer limits will be based on similar geological and geophysical evidence in the boundary region, while the claims to a continental shelf may be based on entirely different geological and geophysical evidence between opposite states.Footnote ¹¹⁰ The Bangladesh/Myanmar case represents the first case concerning the delimitation of a continental shelf beyond 200 nm dealt with by an international tribunal. It also concerns natural prolongation as a geological and geomorphological factor in the delimitation of a continental shelf beyond 200 nm. So it is of value to have a close analysis on how the Tribunal considers these factors.

Bangladesh contended that the geology and geomorphology of the seabed and subsoil are relevant circumstances in the delimitation of continental shelf beyond 200 nm. Bangladesh also relied on the geological and geomorphological continuity between its land territory and the entire seabed of the Bay of the Bengal. Myanmar, on the other side, did not dispute the scientific evidence provided by Bangladesh, but did believe that natural prolongation should not be interpreted as a geological concept. Myanmar argued that natural prolongation is only a legal concept, which could only be demonstrated by the application of the formulae set out in Article 76(4) of the UNCLOS.Footnote ¹¹¹ In other words, once satisfying this formula, natural prolongation as a geological and geomorphological factor that represents the continuity between the landmass and the seabed is not relevant in the delimitation process.

The Tribunal held that the “significant geological discontinuity” proposed by Bangladesh was irrelevant in that case. Similarly, the ITLOS also found that the geographical origin of the sedimentary rocks of the continental margin was of no relevance to the present delimitation. The latter observation is in line with the present geological realities. If the origin of the sedimentary rocks of a relevant continental shelf is a consideration, then Nepal and China might have as much claim to the seabed of the Bay of Bengal as the riparian states.Footnote ¹¹² It is considered generally acceptable to focus on the present geological realities, but to not consider the origin of the sedimentary rocks. However, as for the former observation, the Tribunal did not provide further reasoning. But some considerations behind the Decision of the Tribunal might be revealed from the declaration of the Judges:

The Tribunal seems to decline to consider the role of natural prolongation based on geology and geomorphology simply to avoid the uncertainty of the delimitation. However, this reasoning is not persuasive. In fact, there will always be uncertainty between the parties since certain issues are in dispute, especially about geological and geomorphological factors. The Tribunal might want to avoid “an unsettling effect” by refraining from accepting the idea of natural prolongation based on geological and related factors. However, in doing so, the Tribunal missed a valuable chance to clarify whether and to what extent geological and geomorphological factors should play a role in the delimitation of a continental shelf beyond 200 nm. Also, this consideration might lead to such a situation that “the Tribunal could only decide over things that have been agreed between the parties, which is hardly possible during the judicial proceedings”.Footnote ¹¹⁴ In this respect, the exclusion of natural prolongation may not provide efficient guidance for future cases because it does not provide much detail about its reasoning. Indeed, the justifications for the Tribunal's decision should be strengthened, as pointed out by Judge Wolfrum: “some additional reasoning might have enhanced its being fully accepted by other international courts and tribunals.”Footnote ¹¹⁵

It should also be noted that although the geological natural prolongation is not taken into account in the Bangladesh/Myanmar case, it does not mean that future cases will follow this practice. Every case has a unique geophysical background and whether a factor should be taken into account is based on a case-by-case approach.Footnote ¹¹⁶

Nevertheless, from the exclusion of the geological and geomorphological factors in the Bangladesh/Myanmar case, it could be seen that the attitude of the Tribunal towards such scientific facts is very cautious. International judicial practice has shown its unwillingness to decide a maritime boundary purely based on complicated scientific evidence. Moreover, scientific evidence adduced by different states can even be contradictory. Suppose there is a trench or a trough, lying beyond 200 nm from a coastal state's baselines, that separates the continental shelf geomorphologically or geologically between states that may be opposite or adjacent to each other. Should international courts or tribunals follow this natural boundary? If not, to what extent should such geological and geomorphological factors play a part in the delimitation process? As such, it is necessary to discuss the relationship between the natural prolongation as a geological and geomorphological factor and the “natural boundary”.

C. Natural Prolongation and the Issue of “Natural Boundary”

After the North Sea case, international courts and tribunals departed from their original position that natural prolongation as physically based fact is decisive in maritime delimitation, and made it clear that “the boundary results from a rule of law and not from any intrinsic merit in the purely physical fact”.Footnote ¹¹⁷ Also, international courts and tribunals would not normally rely on the geological or geomorphological evidence presented by either party. Just as the ICJ stated in the Tunisia/Libya case, where the Court was “invited to choose between two interpretations of natural prolongation as geological concept”, that “for legal purposes it is not possible to define the areas of continental shelf … by reference solely or mainly to geological considerations”.Footnote ¹¹⁸ This is mainly due to the fact that, nowadays, international courts and tribunals regard maritime delimitation as a “legal operation”, and what the courts and tribunals do is delimit the overlapping areas, not recognize the existence of a natural prolongation, which in many situations is even impossible to define. Scientific work is out of the courts’ and the tribunals’ expertise.

However, this position does not jeopardize the fact that delimitation should respect nature, a point confirmed by international judicial practice. The long-established principle that “there can never be any question of completely refashioning nature”Footnote ¹¹⁹ was originally stated in the North Sea case, and has never been questioned. And recent practice also emphasized this principle when delimiting a maritime boundary. In the Suriname/Guyana case in 2007, the Tribunal emphasized that “international courts and tribunals dealing with maritime delimitation should be mindful of not remaking or wholly refashioning nature, but should in a sense respect nature”.Footnote ¹²⁰ This position of international practice is rather clear. However, it is unclear what the Court meant when it firmly stated “delimitation should in a sense respect nature” and to what extent this position was related to natural prolongation as a geological and geomorphological factor in the delimitation of a continental shelf beyond 200 nm.

To address the connotation of “respect for nature”, there are two possible perspectives. First, from cases in international maritime delimitation, it is clearly seen that delimitation should not “completely” refashion nature. By this, international courts and tribunals may mean that delimitation would inevitably refashion nature, according to the law, but such refashioning shall not go against nature entirely. As Weil points out, “Law … take[s] account of the facts of nature, attributing certain effects to them, but these effects will always be determined by the law”.Footnote ¹²¹ On the one hand, certainty of the geographical situation in the disputed area is a given, as settled by nature, and this constitutes the basis on which the court or tribunal can decide.Footnote ¹²² On the other hand, what the court or tribunal is actually doing is applying maritime delimitation law to determine the final boundary between the disputed parties. Normally, the final boundary would reflect the certainty of the geographical situation in the given area. By doing this, the court or tribunal is trying to “strike the difficult balance between the safety of respect for nature and the temptation to rewrite geography so as to impose their own idea of justice”.Footnote ¹²³ Hence this principle is two-fold: conforming to nature while changing it.

Second, the idea of “respect for nature” has also been associated with the concept of “equity”. It has been established that “equity does not necessarily imply equality” in the early stages of maritime delimitation case-law. Following this statement, the Court in the North Sea case observed that “there can never be any question of completely refashioning nature … there could be a question of rendering the situation of a State with an extensive coastline similar to that of a State with a restricted coastline”.Footnote ¹²⁴ In other words, delimitation does not seek to “make equal what nature has made unequal”.Footnote ¹²⁵ In this respect, since geological and geomorphological aspects of natural prolongation play an important role in deciding the scope of the coastal states’ entitlement to a continental shelf, such natural factors should not be ignored in the delimiting process. As a significant geological discontinuity may separate two different continental shelves, the entitlement to a continental shelf of the corresponding state is also different. Therefore, the treatment given to wide-margin states should be different from the treatment given to narrow-margin states, since they base their entitlement differently and have different geophysical conditions. As Professor Gao wrote, what equity requires is giving equal or quasi-equal treatment to states with equal or quasi-equal geographical situations, while giving unequal treatment to states with unequal natural situations.Footnote ¹²⁶ Given the different conditions of the respective natural prolongation of each country, a state possessing natural prolongation lying beyond 200 nm can legitimately claim rights over its whole natural prolongation, based on geological and geomorphological evidence. If such factors are not considered, the delimitation of a continental shelf beyond 200 nm will go against nature, and thus depart from the “respect for nature” principle.

However, this does not mean that it is necessary to establish a maritime boundary based on a natural boundary. There are different ways to give effect to natural prolongation as a geological and geomorphological factor. In a situation where the distance between two opposite states is more than 400 nm and where there is a fundamental discontinuity lying outside the 200 nm zone of both states, the physical factor is determinative of entitlement and therefore delimits the shelf accordingly.Footnote ¹²⁷ The situation is more complicated where the distance between two opposite states is less than 400 nm, with one state claiming its right over the continental shelf beyond 200 nm based on natural prolongation, while the other state's continental shelf does not extend beyond the 200 nm limit. This situation creates a difficult problem, and how the conflicts of entitlements will be dealt with remains unclear.Footnote ¹²⁸ However, state practice shows that agreements between coastal states may produce innovative solutions to this kind of boundary delimitation.Footnote ¹²⁹ In the 1997 Australia-Indonesia boundary treaty, as mentioned above, the segment of the seabed boundary from point A51 to A79 is an equidistant line between the outer limit of Australia's natural prolongation and the 200 nautical mile limit from the Indonesian coast.Footnote ¹³⁰ By this arrangement, Australia secured significant areas of seabed under Indonesian waters.Footnote ¹³¹ This was also the position of Nicaragua in the Nicaragua v. Colombia case. The ICJ did not consider this argument because the Court decided that it could not determine the delimitation issue before the outer limit of Nicaragua's continental margin could be established.Footnote ¹³² However, this possibility is still open and of value in solving disputes between states in such a situation.

Since delimitation is a legal operation, giving effect to natural prolongation as a geological and geomorphological factor should be in line with the principles and rules of maritime delimitation. Natural prolongation as a geological and geomorphological factor should be considered in the delimitation of a continental shelf beyond 200 nm; but to what extent is left to international law and to agreements between states. What this paper is trying to argue is that in any situation such factors should not be totally ignored without persuasive reasoning or compelling reasons.