The United Nations Convention on the Law of the Sea (UNCLOS) provides that a coastal State has jurisdiction and sovereign rights over the continental shelf, which is the natural prolongation of its land territory. According to the regime of continental shelf under UNCLOS Article 76, the continental shelf of a coastal State may, based on the geomorphological and geological conditions of its continental margin, extend to a distance of 350 nm, or even farther, from the baselines from which the breadth of its territorial sea is measured. The outer limits of the continental shelf serve as the outermost boundary within which a coastal State may enjoy and exercise sovereign rights over the natural resources. In other words, such outer limits concern the sovereign rights of the coastal State.
In the recent two decades, the gradual discovery of hydrothermal sulfide deposits and biological genetic resources, which are of great economic value, in the mid-ocean ridge regions, brought such regions to the forefront of the scramble for continental shelves between coastal States. A coastal State may, by invoking the ridge provisions, extend the outer limits of its continental shelf beyond 200 nautical miles. In this context, the issue of ridges has become a hot topic in the delimitation of extended continental shelf.
Faced with the imprecise terminology of Article 76(submarine elevations and ridges, and ridges of deep ocean floor present an array of definitional uncertainties), with the nonspecific wording of the Scientific and Technical Guidelines of the Commission on the Limits of the Continental Shelf (hereinafter referred to as the “Guidelines”), a coastal State needs to develop its own evaluations of whether the provisions related to ridges as invoked in its continental shelf submission are reasonable or not. Given the enormous economic interests involved, some coastal States tend to broadly interpret the ridge provisions, pursuing to extend its continental shelf to the maximum extent and further to maximize its maritime rights and interests. The outer limits of the continental shelf of a coastal State represent the outermost boundary within which that State enjoy sovereign jurisdiction, and also the line separating national continental shelf from international seabed. The scope of the international seabed area (hereinafter referred to as the “Area”) is determined, ultimately, by the delineation of the outer limits of continental shelf of each coastal State. That is to say, the outer limits of continental shelf of each coastal State is crucial in the determination of the scope of the Area. UNCLOS Article 136 articulates that the Area and its resources are the common heritage of mankind. Therefore, the extension of continental shelf would, necessarily, affect the common heritage of mankind, and also China’s rights over the resources in the deep ocean. Against this background, it is necessary to pay great attentions to the issue of ridges in continental shelf delimitation. The paper, by examining some typical submissions of extended continental shelf involving ridge provisions, explores the concrete principles on the application of such provisions, aiming to protect the maritime rights and interests of China.
II.An Overview of the UNCLOS Provisions Concerning Ridges
A. The Concept of Ridge under the UNCLOS
The term “ridge” is originally a concept of natural science, specifically, a term used in geomorphology describing the topographic characteristics of the seafloor. However, the UNCLOS, for the purpose of limiting a State’s extension of its continental shelf, lays down some provisions concerning the ridges, which are contained in paragraphs 3 and 6 of Article 76. Pursuant to the UNCLOS, the extent of continental shelf that different types of ridges may generate varies from each other. That is to say, the issue of ridge relates to the maritime and political boundary where a State enjoys sovereign rights. In this connection, the term “ridge” under the UNCLOS has acquired a legal sense. The three types of ridges under Article 76, namely oceanic ridges of the deep ocean floor, submarine ridges and submarine elevations, although originally a concept in science, have become a part of the UNCLOS. Therefore, their application and interpretation should follow the rules of international law. And the three types of ridges, as legal terms, have their own legal status and entitlements.
Article 76(3) prescribes that the continental margin does not include the deep ocean floor with its oceanic ridges or the subsoil thereof. This provision implies that an oceanic ridge of the deep ocean floor cannot generate a continental shelf beyond 200 nautical miles. Article 76, paragraph 6 imposes some restrictions on the application of the provisions under paragraph 5 with respect to submarine ridges. Paragraph 6 provides that notwithstanding the provisions of paragraph 5,“on submarine ridges, the outer limit of the continental shelf shall not exceed 350 nautical miles from the baselines from which the breadth of the territorial sea is measured.” Consequently, on submarine ridges, a coastal State may not extend its continental shelf by applying the depth constraint constructed at 100 nautical miles from the 2500 meter isobath. This restriction does not apply to “submarine elevations that are natural components of the continental margin, such as its plateaux, rises, caps, banks and spurs.” Paragraph 6 fails to directly define the term “submarine ridge”, however, it differentiates “submarine ridges” from “submarine elevations that are natural components of the continental margin”. Referring to this differentiation and the provision of paragraph 3 on ridges of deep ocean floor, we can describe submarine ridges as a part of the natural prolongation of the land territory of the coastal State, but not natural components of the continental margin. These ridges may be divided into two categories: one is the ridge which is originated from the continental margin and extends to the deep ocean seabed area; and the other is the submarine ridge which is not connected with the land mass but supports the island chain.
It should be mentioned that the examples of submarine elevations listed in paragraph 6, namely,“plateaux, rises, caps, banks and spurs”, are not exhausted and complete. Such names reflect more about their geomorphological characteristics, rather than their origins or geological compositions, because one principle governing the naming of a submarine feature is that the name of the feature merely describes its geomorphological characteristics, rather than its origin or geological composition, and many geomorphological features have acquired their names long before their geological characteristics are known to the world. For example, names such as ridge, rise and seamount can be used to call some submarine features that are components of the deep ocean floor, and also be used to call features which are components of the continental margin. Notably, continental margin and deep ocean seafloor are greatly different in origin and geological composition, which complicates the extension of continental shelf based on the geomorphological characteristics of submarine features. However, if a feature can be proved to be a natural component of the continental margin, whatever its name is, be it ridge, plateau, rise or any other names, then the second sentence of paragraph 6 explicitly prescribes that the provision laid out in the first sentence should not apply to the feature. The Guidelines also points out that the distinction between the “submarine elevations” and “submarine ridges” or “oceanic ridges” shall not be based on their geographical denominations and names used so far in the preparation of the published maps and charts and other relevant literature.
In this context, when the delimitation of continental shelf between coastal States involves ridges, the categorization of such ridges would need to be reviewed. However, disputes would arise concerning the classification of ridges and the choosing of which criterion to limit the scope of extended continental shelf, since the three types of ridges (i.e., oceanic ridges of deep ocean floor, submarine ridges and elevations) are subject to separate provisions regarding the maximum outer limit. Considering the provisions of paragraphs 3 and 6, we can know that: if a ridge is categorized as an oceanic ridge of deep ocean floor, then it cannot become a component of the continental margin, and as such cannot generate a continental shelf beyond 200 nautical miles; if a ridge is considered a submarine ridge, then the outer limit of its continental shelf shall not exceed 350 nautical miles; if a ridge is regarded a submarine elevation that is a natural component of the continental margin, then the depth constraint constructed at 100 nautical miles from the 2,500 meter isobath would apply.
B. The Distinction of Different Types of Ridges
The classification of ridges under the UNCLOS relates to the outer limits of continental shelf of a coastal State. As a term under the UNCLOS, ridge has already become a legal term. However, the distinction of ridges, for the purpose of Article 76, should be made on the basis of scientific evidence taking into account the appropriate provisions of the Guidelines. This implies that, to decide the type of a ridge, one still needs to conduct thorough geomorphologic and geological research to consider its geomorphologic features and geologic origin.
The Guidelines defines eight types of ridges associated with UNCLOS Article 76, according to the geological processes of their formation. It also specifies that this categorization of ridges is not exhaustive and complete owing to the variety of the tectonic settings of the sea floor. Even if the ridges composed of basaltic rocks may be considered to be of oceanic origin, there are known examples where such ridges infringe the continental margin and hence make their defining difficult. As it is difficult and complex to define the types of ridges, the Commission on the Limits of the Continental Shelf (hereinafter the “CLCS” or the “Commission”) felt it appropriate that the issue of ridges be examined on a case-by-case basis. Anyway, the Commission believed that in cases of ridges its view shall be based on geological composition and morphology of ridges and their relation to the continental margin, and continuity of ridges.
Due to the imprecise terminology of ridges (submarine elevations, submarine ridges and ridges of deep ocean floor), and the complex causes of their formation, it is difficult to apply the ridge provisions in practice. Many scholars have conducted research on this issue.
Cdr. Nuno Sérgio Marques Antunes (Portuguese Navy), member of the Committee on the Legal Issues of the Outer Continental Shelf of the International Law Association, expressed his views on how to distinguish the three types of ridges. He stated that taking paragraphs 1,3 and 6 of Article 76 into consideration, the following definitions can be put forward:
A “submarine elevation” is a natural component of a continental margin, being thus necessarily a part of the submerged natural prolongation of the land territory.
A “submarine ridge” is not a natural component of a continental margin, but it is a part of the submerged natural prolongation of a land territory.
An “oceanic ridge” is neither a natural component of a continental margin, nor a part of the submerged natural prolongation of a land territory.
The distinction above uses a language that is typically legal. It reflects the contents of the relevant legal provisions. Since the implementation of Article 76 entails the recourse to scientific-technical data, such definitions can be translated into a more scientific language:
(a)“Submarine elevations” are typically composed of continental crust, and they are part of the geomorphic continental margin. This definition has a two-fold requirement: geological continuity with (or linkage to) the geological continental margin; and geomorphic continuity;
(b)“Submarine ridges” may be distinguished from “submarine elevations” in the following ways: they are in principle composed of oceanic crust (although they may also be partly formed by an amalgam of materials, which reflects their complex origin). In this category, there is only one relevant requirement: geomorphic continuity;
(c)“Oceanic ridges” are elevations of the seafloor that can in no way be considered as submerged natural prolongation of a territory. They are, both in geomorphic and geological terms, completely detached from any land masses.
Symonds (Australia), a member of the CLCS, et al., in light of the tectonic setting where ridge-like seafloor highs are formed, categorize them into: a) spreading ridges, fracture zone ridges, microcontinents, oceanic plateaus and hotspot ridges in divergent settings; b) convergent ridges and accreted ridges in convergent settings. Accreted ridges are subdivided into five varieties, including island arcs, remnant arcs, hotspot chains, fracture zone ridges, and spreading ridges. The following types of ridges are closely pertinent to the delineation of extended continental shelf:
(a)ridges formed by plate separation, upwelling and intrusion of magma into and extrusion of magma through the crust. The topography of mid-ocean ridges varies depending on the rates of sea floor spreading along the ridges. Fast spreading ridges, such as the East Pacific Rise, have axial highs present at the crest and much smoother flanks. Slow-spreading ridges, such as Southwest Indian Ridge, are characterized by a rift valley at the crest.
(b)Ridges formed along transform faults and created as an inherent part of the sea floor spreading process. Such ridges are created in the same of period when the mid-ocean ridges are formed. In the sea floor spreading process, different sections of the plate spread at different rates, where faults are produced, running perpendicular to the spreading ridges, and valleys and precipices are formed along transform faults.
(c)Ridges formed by later tectonic activity resulting in uplift of oceanic crust.
(d)Hotspot ridges, which are seafloor highs formed by volcanic activity related to the movement of crust over a hot spot.
(e)Ridges formed by regional excessive volcanism related to plumes of anomalously hot mantle, i.e., plateaux formed by large igneous provinces (LIP) which are also produced by mantle plumes. However, different from hotspot ridges, such submarine plateaux are huge rock masses consisting mainly of basic rocks caused by the intrusion and eruption of magma, when large mushroom-shaped heads of mantle plumes reach the earth’s surface.
(f)Ridges associated with active plate boundaries and the formation of island arc systems, which are also called intra-oceanic arcs. Intra-oceanic arcs may be formed when oceanic crust collides with each other on convergent plate boundaries. They could occur as remnant and active volcanic arcs resulted from the subduction of plates. And back-arc basins could be formed between remnant and active volcanic arcs.
(g)Microcontinents formed by rifting (extension and thinning) of continental crust. Microcontinents are the continental fragments produced during plate separation, and they are surrounded by oceanic basins. As for some microcon- tinents, they are largely submerged underwater, and some parts above water become islands.
Tomasz explored two approaches to enlightening the ambiguity between the three types of ridges:
Definitional interpretation. The International Hydrographic Organization (IHO) defines “oceanic ridge” as “a long elevation of the sea floor with either irregular or smooth topography and steep sides.”“Submarine ridge” is defined as “an elongated elevation of the sea floor, with either irregular or relatively smooth topography and steep sides, which constitutes a natural prolongation of land territory.” The term “submarine elevation” has never been included in any oceanographic or legal dictionaries. Article 76(6) sets out that submarine elevations are natural components of the continental margin, such as its plateaux, rises, caps, banks and spurs. According to the IHO,“cap” is a “feature with a rounded cap- like top. Also defined as a plateau or flat area of considerable extent, dropping off abruptly on one or more sides.”“Bank” is “an elevation of the sea floor located on a continental (or an island) shelf, over which the depth of water is relatively shallow”. A “rise” is defined as “a broad elevation that rises gently and generally smoothly from the sea floor.”“Oceanic plateau” is “a flat or nearly flat elevation of considerable areal extent, dropping off abruptly on one or more sides.”“Spur” is “a subordinate elevation, ridge or rise projecting outward from a larger feature.”法小宝
Definitions based on morphology fail to provide a satisfactory answer to the differences between submarine elevations, submarine ridges and oceanic ridges. The CLCS explained the geologic origins of submarine elevations in the following words:
(a)in the active margins, a natural process by which a continent grows is the accretion of sediments and crustal material of oceanic, island arc or continental origin onto the continental margin. Therefore, any crustal fragment or sedimentary wedge that is accreted to the continental margin should be regarded as a natural component of that continental margin;
(b)in the passive margins, the natural process by which a continent breaks up prior to the separation by seafloor spreading involves thinning, extension and rifting of the continental crust and extensive intrusion of magma into and extensive extrusion of magma through that crust. This process adds to the growth of the continents. Therefore, seafloor highs that are formed by this breakup process should be regarded as natural components of the continental margin where such highs constitute an integral part of the prolongation of the land mass.
However, the distinction between the three remains unclear in terms of the definitional standards.
Historical interpretation. The drafting history of Article 76 highlights the intention of there being a difference between oceanic ridges, submarine ridges and submarine elevations that are natural components of the continental margin. The creation of the notion of submarine ridge was intended to address cases where island States were situated on mid-ocean ridges. Russia proposed to set a 350-nautical-mile limit for submarine ridges to exclude excessive extension of the shelf by delimitating the foot of slope around mid-ocean ridges by the island States. The Chairman of Negotiating Group 6 of the Third UN Conference on the Law of the Sea incorporated the proposals, which were raised by each delegation on the issue of ridges, into the final text of Article 76, paragraphs 3 and 6. It is originally intended to limit the excessive extension of continental shelf along ridges, particularly in cases where an island mass is located on the ridge.
III.A Study on the Practical Delimitation of Extended Continental Shelf Relating to the Ridge Provisions
The issue of continental shelf beyond 200 nautical miles relating to ridges is one of most complex and contentious parts of UNCLOS Article 76. A coastal State may extend, by invoking the ridge provisions under Article 76, its continental shelf to the maximum extent. For example, when a ridge-like seafloor high is considered as a submarine elevation that is a natural component of the continental margin, the coastal State concerned may extend its continental shelf to the extent possible, by applying the 2500 m isobath +100 nautical mile constraint criterion. Many coastal States, in their Submissions, attempt to extend their extended continental shelf to the maximum scope by applying the ridge provisions, based on the topographical and geological conditions of the claimed areas.
A.Delimitation Practices of Coastal States
As to 31 May 2017, the coastal States had formally filed 77 Submissions, among which 49 are associated with ridges.
Up to now, the CLCS has reviewed 24 Submissions, including the Submissions by Russian Federation and its Partial Revised Submission in Respect of the Okhotsk Sea, the Submission by Barbados and its Revised Submission, the Submissions by Brazil, by Ireland, by New Zealand, by Australia, by Norway, by Mexico, by France, by the United Kingdom of Great Britain and Northern Ireland (UK), by Indonesia, by Japan, by the Philippines, by Suriname, by France in Respect of the Areas of the French Antilles and the Kerguelen Islands, by Ghana, by Denmark in the Area North of the Faroe Islands, by Pakistan, by Argentina, and by Iceland, as well as the Joint Submissions by France, Ireland, Spain and the UK, and by the Republic of Mauritius and the Republic of Seychelles. Among the 24 reviewed Submissions (including two revised Submissions),10 involve the issue of ridges.
Table 1Reviewed Submissions Involving the Application of the Ridge Provisions
│No. │Submissi│The issue │Claims of the coastal │Recommendations of the CLC│
│ │on │of ridges │State │S │
│ │ │involved │ │ │
│1 │Submissi│Involving │Russia alleged that th│The Commission was of the │
│ │on by Ru│the classi│e Lomonosov Ridge │view that the evidence pro│
│ │ssia │fication o│and the Mendeleev Ridg│vided by Russia in respect│
│ │ │f the Lomo│e were the natural com│ of this region was not su│
│ │ │nosov Ridg│ponents of Russian con│fficient, therefore it rec│
│ │ │e and the │tinental margin (i.e.,│ommended to Russia to prov│
│ │ │Mendeleev │ submarine elevation).│ide more solid supporting │
│ │ │Ridge in t│ It requested the Comm│data. │
│ │ │he Arctic │ission to recognize a │ │
│ │ │Ocean │sea floor of 1,200,000│ │
│ │ │ │ km2, including the No│ │
│ │ │ │rth Pole, to be the pr│ │
│ │ │ │olongation of the cont│ │
│ │ │ │inental shelf of Russi│ │
│ │ │ │a. │ │
│ │Submissi│Involving │Brazil claimed that th│The Commission concluded f│
│ │on by Br│the classi│e Vitória-Trindade Ri│rom a geological perspecti│
│ │azil │fication o│dge was a natural comp│ve that the Vitória-Trind│
│ │ │f the Vit │onent of Brazilian con│ade Ridge was a seamount c│
│ │ │ória-Trin│tinental margin (i.e.,│hain situated on the deep │
│ │ │dade Ridge│ submarine elevation),│ocean floor caused by hot │
│ │ │ │ which should be consi│spot effect. The evidence │
│ │ │ │dered as the natural p│submitted by Brazil is ins│
│ │ │ │rolongation of the Bra│ufficient to prove that th│
│ │ │ │zilian continental she│e ridge was a submarine el│
│ │ │ │lf. │evation. In light of the a│
│ │ │ │ │vailable data, the Commiss│
│ │ │ │ │ion considered that it was│
│ │ │ │ │ a submarine ridge, whose │
│ │ │ │ │outer limit of continental│
│ │ │ │ │ shelf cannot exceed 350 n│
│ │ │ │ │autical miles. The Commiss│
│ │ │ │ │ion recommended to Brazil │
│ │ │ │ │to make a revised Submissi│
│ │ │ │ │on in respect of the outer│
│ │ │ │ │ limits of its continental│
│ │ │ │ │ shelf beyond 200 nautical│
│ │ │ │ │ miles in the Vitória-Tri│
│ │ │ │ │ndade Region. │
│3 │Submissi│Involving │Australia claimed that│(a)Argo Region, Great Aust│
│ │on by Au│the classi│ the Kerguelen Plateau│ralian Bight Region, Macqu│
│ │stralia │fication o│, Lord Howe Rise, Macq│arie │
│ │ │f Kerguele│uarie Ridge, Naturalis│Ridge Region and Three Kin│
│ │ │n Plateau,│te Plateau, South Tasm│gs Ridge Region: the Commi│
│ │ │ Lord Howe│an Rise, Three Kings R│ssion approved the part of│
│ │ │ Rise, Mac│idge, and Wallaby and │ the Submission concerning│
│ │ │quarie Rid│Exmouth Plateaus were │ these regions; │
│ │ │ge, Natura│the natural components│(b)Australian Antarctic Te│
│ │ │liste Plat│ of Australian contine│rritory: the Commission de│
│ │ │eau, South│ntal margin (i.e., sub│cided not to consider the │
│ │ │ Tasman Ri│marine elevations), wh│part of the Submission con│
│ │ │se, Three │ich should be regarded│cerning this territory; │
│ │ │Kings Ridg│ as the natural prolon│(c)Kerguelen Plateau Regio│
│ │ │e, and Wal│gation of Australian c│n and Wallaby and Exmouth │
│ │ │laby and E│ontinental shelf. │Plateaus Region: evidence │
│ │ │xmouth Pla│ │presented in respect of th│
│ │ │teaus. │ │e area involving Joey Rise│
│ │ │ │ │ and Williams Ridge was in│
│ │ │ │ │sufficient; the part of th│
│ │ │ │ │e Submission regarding oth│
│ │ │ │ │er areas was adopted; │
│ │ │ │ │(d)Lord Howe Rise Region, │
│ │ │ │ │Naturaliste Plateau Region│
│ │ │ │ │ and South Tasman Rise Reg│
│ │ │ │ │ion: the part of the Submi│
│ │ │ │ │ssion concerning these reg│
│ │ │ │ │ions was adopted after the│
│ │ │ │ │ location of certain foot │