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Pacific Coastal & Marine Science Center

Law of the Sea - Outer Limits of the US Continental Margins


Sunrise on the Arctic Ocean, August 6, 2010, by Helen Gibbons, USGS.The Convention on the Law of the Sea (LOS) sets forth a process by which a coastal nation (hereafter called State) may establish the outer limits of its extended continental shelf (ECS), i.e., that portion of the seafloor and sub-seafloor of the continental margin that extends beyond 200 nautical miles (nm). Defining the extended continental shelf is likely to be the most important land expansion of the United States in the 21st century, with the potential to add at least one million square kilometers of seafloor for U.S. sovereign rights. It rivals the addition of the Exclusive Economic Zone in terms of its importance to governance and sovereign land rights.

Resources in the ECS are estimated to be worth about $1.2 trillion. While the United States is not party to LOS, accession to LOS is a stated priority for the Clinton, Bush, and now Obama administrations. Under LOS, States have ten years from the date of entry into force of LOS for that State to submit data and other information to the Commission defining its ECS. It is in the U.S. national interest to collect accurate and precise data on the outer limits of its continental shelf in preparation for an eventual submission to the Commission.

Article 76 of LOS specifies the information needed to define the extended continental shelf: physiography, sediment thickness, and geology. USGS, with its national knowledge and expertise of the U.S. continental margins, has a role to play in developing a database of sediment thickness and continental margin geology, as well as assessing existing data for their relevance to making a submission to the Commission on the Limits of the Continental Shelf (CLCS). The LOS project will conduct geoscientific assessments of potential US limits of the juridical continental shelf beyond 200 nm. This work will be done taking into account the guidelines established by the CLCS(CLCS, 1999) as provided under Article 76 of the UNCLOS. To provide these assessments, the project will review, compile, collect (if warranted and authorized) and synthesize geologic and geophysical data from offshore seabed areas beyond 200 nm. These assessments will begin in the regions where geology is the key criterion for making a submission, as identified in Mayer and others (2002).

USGS map of survey tracklinesArctic Ocean; click for larger view.The project will collaborate with other U.S. Federal agencies and academic institutions as needed to achieve these objectives, as well as with neighboring countries where collaboration will benefit data acquisition efforts. Under this project, USGS will lead and/or participate in field programs to collect new data that are required to define the extended continental shelf. This involves planning, budgeting, coordinating, and ultimately conducting complex and sometimes lengthly field experiments in the regions beyond 200 nautical miles, as well as ensuring that the criteria of Article 76 are met for defining these ECS limits. Part of the USGS responsibilities for these field programs is to also publish the significant findings from the surveys.

Finally, this project also provides a mechanism for USGS to research and advise the Department of State about the geologic criteria used in submissions to UNCLOS made by other States and the recommnedations regarding these submissions. Generally only the executive summary of the submission is available, so this advisory role means USGS must identify and become familiar with the public literature on the particular continental margin and then apply LOS Article 76 criteria to assess how reasonable the limits are. Understanding these limits can help the U.S. in developing its case for what constitutes the U.S. extended continental shelf.

Start/End Dates

10/1/2001 - 9/30/2015




The Interagency Task Force Project Plan (2009), which updates the report to Congress completed by Mayer and others (2002), identifies 5 general areas around the United States and its territories where the sediment thickness formula might be the deciding formula in making a submission:

A sixth likely region of extended continental shelf will use the bathymetry formula (western Gulf of Mexico). An additional 9 areas need further study to determine whether the sediment thickness or bathymetry formula will be most beneficial.

With these regions as priorities, the objectives of this project are:

  1. Evaluate the adequacy of existing data for making a submission using the sedimentary thickness formula.
  2. Develop the geological, morphological, and other bases that will determine whether a feature is a natural prolongation of the land territory.
  3. Generate the sediment thickness maps together with supporting documentation about data quality and quantity that can be used in making a submission.
  4. Plan and participate in regional workshops to bring academic, industry, and government researchers together to understand the geological and morphological challenges in each of the identified field areas where there might be an extended continental shelf.
  5. Understand the potential natural resources on and within the seabed of the areas of investigation.
  6. Develop a strategy for acquiring and integrating additional new data into existing data in order to satisfy the requirements for making a scientifically sound submission. This depends on the results of (1), (2), and (3).
  7. Initiate and participate in the acquisition, processing, and interpretation of new geological data.
  8. Utilize all data (in concert with other agencies and groups) toward developing the submission to be made to the Commission on Limits of the Continental Shelf.
  9. Respond to submissions by other States, as requested by DOS.

Note: These objectives are achieved through collaboration and coordination with the other agencies (DOS, NOAA, MMS, Navy, DOE, etc.) as well as neighboring coastal States (e.g., Canada) involved in mapping the limits of the extended continental shelf.



  1. Characterize the types, locations, and quality of existing geologic and geophysical data available in the public and proprietary domains for the areas currently identified: northeast US Atlantic (NEA; Georges Bank), southeast US Atlantic (SEA; Blake Plateau), Gulf of Mexico (GOM), eastern Gulf of Alaska (EGA), Aleutian Basin/Bering Sea (ABS), Arctic/Chukchi Sea (ACS), and the islands comprising western Pacific trust territories (WPI). This approach will be met by mining USGS archives and other databases for relevant geophysical and geological information, and by working with the World Data Center to locate geological and geophysical information from other academic and federal agencies. This approach is consistent with procedures documented by Cook and Carleton (2000), and with the eight locations pertinent to the sediment thickness formula identified by Mayer and others (2002).
  2. Identify areas of data deficiencies, establish new data requirements, initiate plans for appropriate field programs, and conduct the field programs. The objective of this strategy wil be addressed by comparing data-coverage requirements established by the CLCS with existing useable-data locations. Where new data are needed, the project will coordinate with other agencies (e.g. NOAA, NSF, MMS, DoD) in planning field programs.
  3. As needed, compile, synthesize, and interpret existing geological and geophysical data that will be required for making submissions to the CLCS. The objectives of this strategy will be met by producing the necessary maps (e.g., sediment thickness, geologic framework, crustal structure) from available seismic-reflection, refraction, and geologic evidence. Included in this strategy is thorough documentation of appropriate data quality and uncertainty.
  4. Provide scientific advice as needed to other Federal agencies (particularly DOS) that are working on similar UNCLOS issues in areas of interest to the U.S. This strategy will be accomplished via meetings and discussions as opportunities and requests arise.
  5. Document all results in presentations and peer-reviewed publications, as well as data reports.




Tasks and SubTasks


USGS Publication, Open-File Report 2010-1117: “Environmental Assessment for a Marine Geophysical Survey of Parts of the Arctic Ocean, August-September 2010”

Cover of the publication.

According to the United Nations Convention on the Law of the Sea (UNCLOS), individual nations' sovereign rights extend to 200 nautical miles (n.mi.) (370 km) offshore in an area called the continental shelf. These rights include jurisdiction over all resources in the water column and on and beneath the seabed. Article 76 of UNCLOS also establishes the criteria to determine areas beyond the 200 n.mi. (370 km) limit that could be defined as "extended continental shelf," where a nation could extend its sovereign rights over the seafloor and sub-seafloor. This jurisdiction provided in Article 76 includes resources on and below the seafloor but not in the water column. The United States has been acquiring data to determine the outer limits of its extended continental shelf (ECS) in the Arctic and has a vested interest in declaring and receiving international recognition of the reach of its extended continental shelf.



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