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Client Alert: Recent seabed claims by the United States highlight its absence from major UN oceans treaty

On 19 December 2023, the United States (“US”) announced the outer limits of its extended continental shelf.  In doing so, the US cited the inherent interest in clarifying the seabed areas in which the US is entitled to exercise sovereign rights.  Its announcement has not been without controversy, prompting recent diplomatic reactions from the Russian Federation (“Russia”) and the People’s Republic of China (“China”) in March and April 2024.

What is the extended continental shelf?

The continental shelf is the area of seabed reflecting the natural extension of land territory under the sea.  The “extended continental shelf” refers to the portion of the continental shelf located beyond 200 nautical miles offshore, up to the outer edge of the continental margin.  This threshold reflects the provisions of the United Nations’ major oceans treaty, the 1982 UN Convention on the Law of the Sea (“UNCLOS”).  Often referred to as the “constitution of the oceans”, UNCLOS enjoys near-universal membership of some 169 Parties – with the noticeable exception of the United States.  Under UNCLOS, all coastal State parties are entitled to exercise sovereign rights in subsea areas extending up to 200 nautical miles offshore (even where the outer edge of the continental margin does not extend to that distance).  Beyond the 200 nautical miles, UNCLOS provides that a State may also claim an extended continental shelf up to the outer edge of the continental margin, following specific rules and submissions to the Commission on the Limits of the Continental Shelf (“CLCS”), a specialist body established under UNCLOS.

The US seabed claim and recent reactions to it

As set out in official statements by the US, the newly announced outer limits of its extended continental shelf cover areas of approximately one million square kilometres.  They extend across seven ocean regions:  the Arctic, the Atlantic (east coast), the Bering Sea, the Pacific (west coast), the Mariana Islands, and two areas in the Gulf of Mexico.  Its seabed claim followed long-running offshore mapping and data collection since 2003 by the US’s key governmental agencies, the National Oceanic and Atmospheric Administration and United States Geological Survey, to determine the depth, shape and geophysical characteristics of the seabed and subsoil.  In its announcement, the US confirmed that it had determined its extended continental shelf limits in accordance with customary international law, as reflected in the relevant provisions of UNCLOS and the official Technical Guidelines published by the CLCS.

In March 2024, Russia criticised the recent US seabed claims at the official meetings in Kingston, Jamaica of the International Seabed Authority (the “ISA”).  The ISA is the international organisation established under UNCLOS through which States Parties organise and control, for the benefit of humankind as a whole, mineral resources activities in the areas of the deep seabed beyond national jurisdiction.  Russia criticised the US seabed claims as at odds with UNCLOS and its common heritage regime.  It urged the US to ratify UNCLOS, asserting that the only internationally recognised procedure for establishing the outer limits of a continental shelf was the process set out under UNCLOS Article 76 and the recommendations of the CLCS.  In response, the US (an observer State of the ISA) indicated that its process was in accordance with the relevant UNCLOS provisions and CLCS advice.  The Chinese foreign ministry echoed similar criticisms at an official press conference in April 2024, asserting that the US claims encroached on the areas of international seabed which constitute the common heritage of mankind.


The announcement by the US of the outer limits of its extended continental shelf highlights the growing importance of the seabed as a zone of mineral resource activity, as well as concerns arising from the status of the US as a non-party to UNCLOS.  The rapidly developing industry of deep sea mining is increasingly the focus of both governments and private actors, given its significant potential to deliver critical minerals for the clean energy transition.  States including Belgium, China, France, Germany, Japan, Nauru, Russia, Singapore and the United Kingdom – all parties to the UNCLOS regime – have sponsored contractors for deep seabed mining exploration contracts awarded by the ISA.

As part of its official press release regarding the outer limits of the continental shelf, the US Department of State confirmed that the current Administration continued to support the US becoming an UNCLOS member State.  Although UNCLOS ratification has long enjoyed bipartisan support in the US, efforts to ratify the treaty stalled in 2012, when it became clear that UNCLOS ratification would fail to gain the necessary two-thirds majority vote in the Senate.  In March 2024, a group of nearly 350 former US security, military and foreign policy officials renewed calls for the US to ratify UNCLOS.  It remains to be seen whether and when any US ratification may occur.

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