sediment thickness criterion; or the “Hedberg formula”, consisting of a line delineated by reference to fixed points not more than 60 nautical miles from the foot of the
continental slope (item “ii”).
The “Irish formula” is essentially based on the thickness of sedimentary rocks and
aims at measuring the sedimentary affinity between mainland and seabed.
40 The
“Hedberg formula”, on the other hand, focuses on the determination of the foot of
continental slope. Intrinsic difficulties in finding the precise base (or foot) of the
continental slope led to the establishment of a “boundary zone”, which was set in
60 nm as the “minimum technically practical width of the boundary zone”.
41
Once the outer edge of the continental margin has been determined, coastal states
rely on Art. 76 (5) UNCLOS to ascertain the fixed points comprising the outer limits
of the continental shelf, where the state will exercise sovereign rights. Here, two
other criteria are available for states, to be used alternatively. The first criterion is
grounded exclusively on distance: the outer limits shall not exceed 350 nm from the
baselines from which the territorial sea is measured. The second criterion is slightly
more complicated, resulting from the combination of distance and depth criteria: the
outer limits shall not exceed 100 nm from the 2500-meter isobath.
42 The resulting
outer limits may extend beyond 350 nm, in case the water depth be relatively
shallow.
43
When demonstrating the sedimentary affinity between landmass and continental
margin, coastal states must take into account rather complex geological and geomorphological features, such as “submarine ridges”, “submarine elevations” and
“oceanic ridges”, “caps”, “banks”, “spurs” etc.
44 The thorny process of defining and
understanding those features has been a learn-by-doing experience, in which coastal
states and the CLCS interact in fixing the feature’s meanings. Submarine elevations
are considered “natural components of the continental margin, such as its plateaus,
rises, caps, banks and spurs”.
45 The full content of paragraph 5 applies to submarine
elevations, i.e. the two criteria: depth [350 nm], and depth plus distance [2500-meter
isobath + 100 nm]. Submarine ridges are not natural components of the continental
margin, but are taken as “natural prolongation” of the land mass. As such, once that
feature is found on the seabed, the outer limit of the continental shelf shall not exceed
350 nm. Oceanic ridges, in line with paragraph 3, are neither a feature of the
continental margin nor the “natural prolongation” of the mainland. Thus, they are
not to be taken into account in the extension of the continental shelf beyond 200 nm.
40 The “Irish formula” was proposed in the 75th Informal Meeting of the Second Committee of
UNCLOS III, in 15 April 1976.
41 See Hedberg (1972).
42 The 2500-meter isobath is a line connecting the depth of 2500 m, as stated in Art. 76, paragraph
5, UNCLOS.
43 When applying the depth criterion, the identification of the relevant coasts becomes “redundant”,
so Kunoy (2013), p. 2.
44 The definition of caps, banks and spurs can be found in the online glossary of the International
Hydrographic Organization (IHO).
45 Art. 76, paragraph 6 UNCLOS.
3.2 Formulae to Precise the Outer Edge of the Continental Margin and the. . .
55
continental slope (item “ii”).
The “Irish formula” is essentially based on the thickness of sedimentary rocks and
aims at measuring the sedimentary affinity between mainland and seabed.
40 The
“Hedberg formula”, on the other hand, focuses on the determination of the foot of
continental slope. Intrinsic difficulties in finding the precise base (or foot) of the
continental slope led to the establishment of a “boundary zone”, which was set in
60 nm as the “minimum technically practical width of the boundary zone”.
41
Once the outer edge of the continental margin has been determined, coastal states
rely on Art. 76 (5) UNCLOS to ascertain the fixed points comprising the outer limits
of the continental shelf, where the state will exercise sovereign rights. Here, two
other criteria are available for states, to be used alternatively. The first criterion is
grounded exclusively on distance: the outer limits shall not exceed 350 nm from the
baselines from which the territorial sea is measured. The second criterion is slightly
more complicated, resulting from the combination of distance and depth criteria: the
outer limits shall not exceed 100 nm from the 2500-meter isobath.
42 The resulting
outer limits may extend beyond 350 nm, in case the water depth be relatively
shallow.
43
When demonstrating the sedimentary affinity between landmass and continental
margin, coastal states must take into account rather complex geological and geomorphological features, such as “submarine ridges”, “submarine elevations” and
“oceanic ridges”, “caps”, “banks”, “spurs” etc.
44 The thorny process of defining and
understanding those features has been a learn-by-doing experience, in which coastal
states and the CLCS interact in fixing the feature’s meanings. Submarine elevations
are considered “natural components of the continental margin, such as its plateaus,
rises, caps, banks and spurs”.
45 The full content of paragraph 5 applies to submarine
elevations, i.e. the two criteria: depth [350 nm], and depth plus distance [2500-meter
isobath + 100 nm]. Submarine ridges are not natural components of the continental
margin, but are taken as “natural prolongation” of the land mass. As such, once that
feature is found on the seabed, the outer limit of the continental shelf shall not exceed
350 nm. Oceanic ridges, in line with paragraph 3, are neither a feature of the
continental margin nor the “natural prolongation” of the mainland. Thus, they are
not to be taken into account in the extension of the continental shelf beyond 200 nm.
40 The “Irish formula” was proposed in the 75th Informal Meeting of the Second Committee of
UNCLOS III, in 15 April 1976.
41 See Hedberg (1972).
42 The 2500-meter isobath is a line connecting the depth of 2500 m, as stated in Art. 76, paragraph
5, UNCLOS.
43 When applying the depth criterion, the identification of the relevant coasts becomes “redundant”,
so Kunoy (2013), p. 2.
44 The definition of caps, banks and spurs can be found in the online glossary of the International
Hydrographic Organization (IHO).
45 Art. 76, paragraph 6 UNCLOS.
3.2 Formulae to Precise the Outer Edge of the Continental Margin and the. . .
55