Altimetry and the law of the sea definition of the continental shelf
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Altimetry and the Law of the Sea definition of the Continental Shelf. Dave Monahan Canadian Hydrographic Service and Ocean Mapping Group, University of New Brunswick Global Bathymetry for Oceanography, Geophysics, and Climatology. The United Nations Convention on the Law of the Sea (UNCLOS).

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Altimetry and the law of the sea definition of the continental shelf
Altimetry and the Law of the Sea definition of the Continental Shelf

  • Dave Monahan

  • Canadian Hydrographic Service and

  • Ocean Mapping Group, University of New Brunswick

  • Global Bathymetry for Oceanography, Geophysics, and Climatology

Altimetry and UNCLOS


The united nations convention on the law of the sea unclos
The United Nations Convention on the Law of the Sea (UNCLOS) Continental Shelf

  • The biggest single boundary-making event in human history.

  • Within a short period of time, two-thirds of the earth’s surface will be divided into zones fringing the coasts and over which individual Coastal States exercise varying degrees of sovereignty, with the residual “Area” being administered by the UN.

  • Reasonably straightforward measurements of 12, 24 and 200 M establish the Territorial Sea, the Contiguous Zone and the Exclusive Economic Zone

  • The Outer Limit of a Coastal State’s Continental Shelf, or its Exclusive Economic Zone where there is no Shelf, forms the boundary of the “Area”.

  • A Coastal State must establishing the existence of, and delineate the limits to, a juridical Continental Shelf, as part of a claiming process

Altimetry and UNCLOS


The idea behind the definition in article 76
The idea behind the definition in Article 76 Continental Shelf

  • Broad-margin states wanted the definition to permit an extensive shelf, in opposition to those with no physiographic shelves who would benefit from the Area being as large as possible.

  • Eventually settled on a principal that would see “the natural prolongation” of the continent available to the Coastal State, with the true oceanic ocean floors being included in the Area.

  • According to prevalent knowledge, this granted hydrocarbons to the Coastal State and minerals like “manganese nodules” to the International Seabed Authority.

Altimetry and UNCLOS


The model that influenced the wording of article 76
The model that influenced the wording of Article 76 Continental Shelf

  • Foot of the Slope was a sea floor feature that was seized on to mark the division between continental and oceanic crust.

  • Article 76 definition: ‘In the absence of evidence to the contrary, the foot of the continental slope shall be determined as the point ofmaximum change in the gradient at its base.’

Altimetry and UNCLOS


The foot of the slope and beyond
The Foot of the Slope and Beyond Continental Shelf

  • Since the Continental Rise is composed of sediment, and hydrocarbons occur only in sediment, it was argued that the shelf should include portions of the Rise.

  • Options: either a measurement of 60 M seawards or the point where the thickness of sedimentary rocks is at least 1 per cent of the shortest distance to the Foot of the Slope.

Altimetry and UNCLOS


Constraints to unbounded expansion
Constraints to unbounded expansion Continental Shelf

  • The disadvantaged states forced the inclusion of a finite Outer Constraint

  • Continental Shelf can not extend beyond the most seaward of a line 350 M from Baselines, or a line 100 M seaward of the 2500 m isobath.

  • Outer Constraint restricted to 350 M over “submarine ridges”

Altimetry and UNCLOS


Where are the juridical continental shelves likely to be
Where are the Juridical Continental Shelves likely to be? Continental Shelf

Altimetry and UNCLOS


The first claim russia december 2001
The first claim, Russia, December 2001 Continental Shelf

  • Wakey, Wakey!

Altimetry and UNCLOS


The boundary making process
The Boundary Making Process Continental Shelf

  • 1. Boundary is defined through words of the Convention (Treaty)

  • 2. Boundary is delineated on maps and diagrams

  • 3. Boundary is demarcated - on land by constructing markers, at sea by depositing coordinates with the Secretary-General of the UN.

  • Continental Shelf boundaries must be submitted to the Commission on the Limits of the Continental Shelf (CLCS) for review as part of Step 2

  • The CLCS has issued Guidelines on the quantity and type of data they consider acceptable for delineation, (but in places may overstepped their mandate and entered the realm of definition)

  • Coastal States have to steer a course between the Convention and the Guidelines

Altimetry and UNCLOS


Elements of the delineation process that altimetry might contribute to
Elements of the delineation process that altimetry might contribute to

  • Determining the 2500 m isobath for use in the 2500 m plus 100 nm outer constraint constraint

  • Locating the “Foot of the Slope” if it exists as a physiographic feature, or, where it does not, locating the continent/ocean boundary

  • Determining the geological nature of submarine “ridges”

Altimetry and UNCLOS


World excluding polar regions 2500 m contour extracted from gebco digital atlas
World ( contribute toexcluding Polar Regions) 2500 m contour. Extracted from GEBCO Digital Atlas

Altimetry and UNCLOS


How well are continental slopes mapped worldwide
How well are continental slopes mapped worldwide? contribute to

  • Relatively fewer investigations concentrated on continental slopes

  • Much of the data over them was not collected by systematic surveys but by transit tracks.

  • Water properties over Slopes often complicated and poorly known, leading to higher uncertainty in acoustic measurements

Altimetry and UNCLOS


Sources of data
Sources of data contribute to

  • Instruments

    • Single beam echo sounder, variable sounding line spacing

    • Sidescan, most notably GLORIA.

    • Multibeam coverage is only increasing at a slow rate.

  • Data bases and maps

    • Contour maps, grids and raw sounding data bases exist, based on the sporadic acoustic data.

  • Limitation to acoustic methods

    • Vessel speed and availability. GoMAP project estimates 200 ship years to survey the world ocean (excluding the Arctic) from the 500 m contour out

Altimetry and UNCLOS


2500 m isobath specified by the convention
2500 m isobath specified by the Convention contribute to

  • Definition “the 2,500 metre isobath, which is a line connecting the depth of 2,500 metres.”

  • Implies an absolute 2500m isobathwithout specifying surface that depth is measured from

  • Refers to “the 2500 m isobath” as if there were only one fringing a Continental Shelf, while allowing for “submarine elevations that are natural components of the continental margin” which might mean that there is more than one 2500 m isobath off a margin

Altimetry and UNCLOS


Requirements specified by guidelines
Requirements specified by Guidelines contribute to

  • Uncertainty assessment based on International Hydrographic Organization standard S44

  • “ no need to submit ... a full 2,500 m isobath…” but “the full bathymetric database will be regarded as an essential component of the supporting scientific and technical data.”

  • Want to use the most landward 2500 m isobath where multiple isobaths exist

  • Want to judge whether submarine elevations are part of the continental margin on a “case-by-case basis”.

Altimetry and UNCLOS


Which 2500 m isobath to use
Which 2500 m isobath to use contribute to

  • a) where 2500m contours surround “submarine elevations”

  • b) where the 2500m contour doubles back on itself

  • c) whether the contour is on a “ridge”

Altimetry and UNCLOS


Vertical uncertainty at 2500 m from iho s44
Vertical uncertainty at 2500 m from IHO S44 contribute to

  • Combines fixed (constant) and variable ( with depth) errors as Root Sum of Squares.

  • Provides multipliers and constants for depth measurement and isobath

Altimetry and UNCLOS


Horizontal uncertainty at 2500 m from iho s44
Horizontal uncertainty at 2500 m from IHO S44 contribute to

Altimetry and UNCLOS


Comparison of four different 2500 m isobaths
Comparison of four different 2500 m isobaths contribute to

  • Off New Jersey, plotted the 2500m contour from

    • ETOPO-5 data

    • GEBCO-97 Digital Atlas CD

    • NGDC’s Coastal Relief Model CD’s

    • Predicted Topography Smith and Sandwell (1997 )

Altimetry and UNCLOS


mbes contribute to

Altimetry and UNCLOS


Horizontal differences between 2500m contours from ETOPO5, Predicted, GEBCO and multibeam. Multibeam is assigned the value of zero.

Altimetry and UNCLOS


Histogram of horizontal differences between 2500m contours from ETOPO5, Predicted, GEBCO and multibeam survey.Multibeam is considered true and the displacement of the other three measured seawards (+) or landward (-).

Altimetry and UNCLOS


Histogram of horizontal differences between 2500m contours from ETOPO5, Predicted, GEBCO and multibeam survey.Multibeam is considered true and the displacement of the other three measured seawards (+) or landward (-).

S44 Uncertainty

Altimetry and UNCLOS


Findings for 2500 m isobath
Findings for 2500 m isobath from ETOPO5, Predicted, GEBCO and multibeam survey.

  • Over the sample area, the 2500 m isobath based on altimetric data

    • a) is as accurate as those from other world-scale maps and

    • b) meets the IHO spec S44.

Altimetry and UNCLOS


Maximization of area claimed
Maximization of area claimed from ETOPO5, Predicted, GEBCO and multibeam survey.

  • Outer Limit can be delineated by straight lines not exceeding 60 nautical miles in length, connecting fixed points.

  • To maximise area must select the fixed points carefully

Altimetry and UNCLOS


Optimal selection of points
Optimal selection of points from ETOPO5, Predicted, GEBCO and multibeam survey.

  • Long wavelength contours may miss localised seaward protrusions

  • Strategy conduct large scale, short wavelength MBES surveys along the altimetric based 2500 m isobath

  • Select most seawards points on which to base 100 nm arcs

Altimetry and UNCLOS


Roles for predicted bathymetry in continental shelf delineation
Roles for predicted bathymetry in Continental Shelf delineation

  • “desk –top study” to determine the likely area to be included within a juridical Continental Shelf

  • Quality control device to assess the accuracy of existing sounding data

  • In developing a plan for building the case data to substantiate it.

  • Infer morphologic trends between existing sounding lines

  • Plan the orientation of any new sounding lines.

Altimetry and UNCLOS


Such use of altimetric data is consistent with the view expressed by the Commission on the Limits of the Continental Shelf

  • “4.2.6. Other sources of evidence, such as satellite altimetry-derived bathymetric data or imaging side-scan sonar information, will not be regarded as admissible for the purpose of delineating the 2,500 m isobath. This information, however, might be useful as additional qualitative information in support of other parts of a submission but will not be considered during the determination of this or any other isobaths. However, this data will be considered admissible as supporting information in a submission.”

Altimetry and UNCLOS


Roles for predicted bathymetry in continental shelf delineation1
Roles for predicted bathymetry in Continental Shelf delineation

  • “desk –top study” to determine the likely area to be included within a juridical Continental Shelf

  • Quality control device to assess the accuracy of existing sounding data

  • In developing a plan for building the case data to substantiate it.

  • Infer morphologic trends between existing sounding lines

  • Plan the orientation of any new sounding lines.

  • That’s what I thought before yesterday’s presentations!

Altimetry and UNCLOS


Locating the “Foot of the Slope” if it exists as a physiographic feature, or, where it does not, locating the continent/ocean boundary

  • Presence/absence of sediment

  • Slope/Rise junction

Altimetry and UNCLOS


Determining the geological nature of submarine ridges
Determining the geological nature of submarine “ridges” physiographic feature, or, where it does not, locating the continent/ocean boundary

  • Outer Constraint at 350 nm along “ridges”

  • Article 76 “...on submarine ridges, the outer limit of the continental shelf shall not exceed 350 nautical miles... This paragraph does not apply to submarine elevations that are natural components of the continental margin...”

  • CLCS Guidelines 7.2.11. “As it is difficult to define the details concerning various conditions, the Commission feels it appropriate that the issue of ridges be examined on a case-by-case basis.”

Altimetry and UNCLOS


Example from the arctic
Example from the Arctic physiographic feature, or, where it does not, locating the continent/ocean boundary

  • Maximum area would terminate at 350 nautical miles if Alpha Ridge is ruled to be oceanic ie not a natural prolongation of land

Altimetry and UNCLOS


Example from the arctic 2
Example from the Arctic 2 physiographic feature, or, where it does not, locating the continent/ocean boundary

  • Yellow line is median

  • Maximum area would terminate at median if Alpha Ridge is ruled to be continental ie a natural prolongation of land

Altimetry and UNCLOS


Take home message
Take Home Message physiographic feature, or, where it does not, locating the continent/ocean boundary

  • Delineating a juridical Continental Shelf under Article 76 of UNCLOS is complicated and contains many judgmental elements

  • Altimetry can contribute to:

    • 2500 m isobath

    • Foot of the Slope or evidence to the contrary

    • nature of ridges

Altimetry and UNCLOS


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