Continental shelf II: Seafloor highs · submarine ridges, the outer limit of the continental shelf shall not exceed 350 nautical miles from the baselines from which the breadth of

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C o n t i n e n t a l s h e l f I I : S e a f l o o r h i g h s

S c i e n t i f i c i n t r o d u c t i o nW a l t e r R o e s t , I f r e m e r, F r a n c e

M e m b e r o f C L C S ( 2 0 1 2 –2 0 1 7 )

New Knowledge and Changing Circumstances –Reykjavik – 28 and 29 june 2018

Disclaimer

“ The views expressed herein are solely

those of the author and do not necessarily

reflect the views of the Commission on the

Limits of the Continental Shelf “nor those of

any Government

204/07/2018

Introduction

• Seafloor highs are probably the most difficult

features to deal with in Article 76

• Seafloor elevations and ridges have been known

for a long time, but for many their origin,

formation and precise extent was unclear in the

late 70s, when Article 76 was developed (new

knowledge)

• Ridges are mentioned twice in Article 76, limiting

their contribution to the continental margin/shelf:

can there be exceptions ? In other words: Is a

ridge always a ridge?

• Continental margin (paragraph 4) versus

continental shelf (application of constraints) 04/07/2018 3

Article76 - Seafloor HighsParagraphs 3 and 6 mention ridges and elevations:

3. The continental margin comprises the submerged

prolongation of the land mass of the coastal State […]

shelf, the slope and the rise. It does not include the

deep ocean floor with its oceanic ridges or the

subsoil thereof.

6. 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. This paragraph does not apply to

submarine elevations that are natural components of

the continental margin, such as its plateaux, rises,

caps, banks and spurs.04/07/2018 4

Knowledge in 1978

A/CONF.62/C.2/L.98 and Add.1, 18 April 1978

Knowledge in 1978

Kerguelen Plateau



Knowledge in 1978

French Submission to the CLCS

Resolution of satellite derived bathymetry versus multi beam bathymetric data

Shelf Slope Rise Deep Ocean Floor

Excluded from the

Continental MarginContinental Margin

Deep Ocean Floor

is excluded from

the Continental

Margin

UNCLOS Article 76: the continental shelf

Shelf Slope Rise Deep Ocean Floor

Excluded from the

Continental Shelf

CLCS Guidelines - Seafloor Highs

Continental Margin

What about

Oceanic Ridges?

CLCS Guidelines - Seafloor Highs

7.1.2. Article 76 mentions three types of seafloor highs:

- Oceanic ridges of the deep ocean floor (para. 3);

- Submarine ridges (para. 6) ;

- Submarine elevations (para. 6) .

7.1.3. None of these terms is precisely defined ….

Scientific and Technical Guidelines, CLCS/11, Chapter 7

Ridges form by a variety of geological processes

Ridges formed by the sea-floor spreading and associated volcanic magmatic processes;

Ridges formed along transform faults and created as an inherent part of the sea-floor spreading process;

Ridges formed by later tectonic activity resulting in uplift of oceanic crust;

Ridges formed by volcanic activity related to the movement of crust over a hot spot;

Ridges formed by interaction of oceanic crustal plates;

Ridges formed by regional excessive volcanism related to plumes of anomalously hot mantle;

Ridges associated with active plate boundaries and the formation of island arc systems. […];

Ridges formed by rifting (extension and thinning) of continental crust. […]

Scientific and Technical Guidelines, CLCS/11, Chapter 7

Google

Two critical questions

Since Article 76 only mentions 2 types of ridges, Oceanic Ridges (deep ocean floor?) and Submarine Ridges (restricted to 350 M):

• Can an Oceanic Ridge become a submarine ridge?– Yes, if it lies within the continental margin

• Can an Oceanic Ridge become a natural component– Yes, if it lies within the continental margin and

shares significant geological characteristics with the landmass











Example of Iceland

From Summary of Recommendations by the CLCS to Iceland

Geologial

continuity within

a V-

shaped area of

the Reykjanes

Ridge:

Example of

gravity data

Hey et al., 2010

FOS points accepted by Subcommission


Iceland in the

western and

southern parts of

the Reykjanes

Ridge

Example of Iceland• The CLCS treats Ridges on a case by case basis

• The Subcommission recognised that part of the Reykjanes Ridge was a natural component of Iceland’s continental margin (morphologically AND geologically connected)

• Therefore, the prevalent view in the Subcommission was that the depth constraint is the applicable constraint in the western and southern parts of the Reykjanes Ridge.

• The Commission concluded that the data and information contained in the Submission were inconclusive to support the western and southern parts of the Reykjanes Ridge as a natural component of the continental margin of Iceland

FOS points accepted by Subcommission


FOS points 03 to 08 were

accepted unanimously by the

Commission.

While some members of the

Commission accepted the

locations of the FOS points

110, 120, 23, and 145, other

members did not accept the

location of the base of the

continental slope around

them

Conclusion1. The extent and configuration of the continental margin of a

coastal state […] is determined in accordance with Article 76, paragraph 4.

2. Seafloor highs that are not enclosed by the FOS envelope are excluded from contributing to the establishment of the outer edge of the continental margin […]. However, such seafloor highs, or parts thereof, can ultimately lie within the outer edge […].

3. Seafloor highs that lie beyond the outer edge of the continental margin are considered part of the “deep ocean floor with its oceanic ridges” in the sense of Article 76, paragraph 3.

4. Classification of seafloor highs is determined on the basis of the geological characteristics of the features in addition to their already proven morphological continuity with the landmass of the coastal state.

Harald Brekke & Philip Symonds (2011): Ocean Development & International Law

Thank you!

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Continental shelf II: Seafloor highs · submarine ridges, the outer limit of the continental shelf shall not exceed 350 nautical miles from the baselines from which the breadth of