Defining the Limits of the U.S. Continental Shelf

Since 2001, the United States has been engaged in gathering and analyzing data to determine the outer limits of its extended continental shelf (ECS). Under the Convention on the Law of the Sea, every coastal State has a continental shelf out to 200 nautical miles from its coastal baselines (or out to a maritime boundary with another coastal State), and beyond that distance if certain criteria are met. Article 76 of the Convention sets forth the criteria upon which a coastal State may determine a continental shelf that extends beyond 200 nautical miles. The ECS is that portion of the continental shelf that lies beyond this 200 nautical mile limit. Beginning in 2007 the effort to delimit the U.S. ECS became the Extended Continental Shelf Project, directed by an interagency task force.

Defining the U.S. Extended Continental Shelf
The process to determine the outer limits of a State’s ECS requires the collection and analysis of data that describe the depth, shape, and geophysical characteristics of the seabed and sub-sea floor. Particularly important is bathymetric and sediment thickness data.

The U.S. Extended Continental Shelf Task Force, an interagency body headed by the U.S. Department of State, coordinates the work to define the limits of the U.S. continental shelf. Participants in this Task Force include: State Department, NOAA (National Oceanic and Atmospheric Administration), the U.S. Geological Survey, the Executive Office of the President, the Joint Chiefs of Staff, the U.S. Navy, the U.S. Coast Guard, the Department of Energy, the National Science Foundation, the Environmental Protection Agency, the Minerals Management Service, and the Arctic Research Commission.

Why define the U.S. extended continental shelf?
A coastal State can exercise certain sovereign rights over its continental shelf, including: exploration, exploitation, conservation, and management of non-living resources of the seabed and subsoil of the continental shelf, such as ferromanganese crusts, ferromanganese nodules, gas hydrate deposits, and petroleum; and exploration, exploitation, conservation, and management of living, "sedentary" resources, such as clams, crabs, scallops, sponges, and mollusks.

While a continental shelf is coincident with the exclusive economic zone (EEZ) out to 200 nautical miles, the ECS is not an extension of the EEZ. Sovereign rights that apply to the EEZ, especially rights to the resources of the water column (e.g., pelagic fisheries) do not apply to the ECS.

Establishing ECS limits will define the U.S. continental shelf in concrete geographical terms. Moreover, the United States has an inherent national interest in knowing, and declaring to others with specificity and certainty, the extent of sovereign rights with regard to the U.S. continental shelf beyond 200 nautical miles. Such certainty and international recognition is important to establishing the stability necessary for development and conservation of these potentially resource-rich areas.

The collection and analysis of the data necessary to support the establishment of the U.S. ECS will, in itself, serve a range of other environmental, geologic, engineering, and resource management needs. The data will provide a better scientific understanding of formation and transformation processes of our continental margins. The United States will gain specific insights related to such areas as climate variability, marine ecosystems, undiscovered or unconventional energy, mineral resources, and hazards resulting from extreme events, such as earthquakes and tsunamis. Finally, exploration of little known areas, particularly in the ice-covered Arctic, will advance our operational capabilities and open new windows on this remote and inaccessible environment.

Data Collection and Analysis
In late 2001, Congress directed the University of New Hampshire’s Joint Hydrographic Center (JHC) -- a partnership with NOAA -- to conduct a study that evaluated current data holdings relevant to establishing the U.S. ECS, and to recommend what additional data would be needed. This study identified a number of areas where the United States may have extended continental shelf: the Atlantic East Coast, the Gulf of Mexico, the Gulf of Alaska, the Bering Sea, the Arctic Ocean, Kingman Reef/Palmyra Atoll, and the Mariana Islands/Guam.

This amounts to about one million square kilometers or approximately twice the size of California. Roughly half of that area is likely to exist off Alaska. Additional analyses and data collection suggest an even larger ECS, in these and possibly other areas. As additional data are collected and existing data analyzed, we will begin to come to a more definitive conclusion as to the extent of the U.S. ECS.

Since 2002, the JHC has continued to receive grants from NOAA as directed by Congress to collect the bathymetric data specified in the study. The JHC has collected more than one million square kilometers of bathymetric data from eleven cruises: Arctic Ocean (2003, 2004, 2007), Gulf of Alaska (2005), Gulf of Mexico (2007), Atlantic Ocean (2004, 2005, 2008), Northern Mariana Islands and Guam (2006, 2007), and Bering Sea (2003). A cruise is planned for an area off Kingman Reef and Palmyra Atoll in 2008 or early 2009.

All data collected thus far by the United States in support of defining its continental shelf have been released to the public. The bathymetric data is available from the National Geophysical Data Center and the Joint Hydrographic Center.

Useful Links

 National Geophysical Data Center (NGDC)

Joint Hydrographic Center at the University of New Hampshire

For Additional Information
Matt Cassetta – Public Affairs Officer at the U.S. Department of State