On March 4, after more than a decade of negotiations, states at the United Nations in New York agreed on a wide-ranging treaty focusing on high seas conservation. While this instrument is still to be approved by the General Assembly and will likely take years to come into force, it’s the most consequential development in the law of the sea in many years. The 54-page text creates new rules for establishing marine protected areas, conducting environmental impact assessments, and managing rights related to marine genetic resources.

A last-minute addition pushed by China—seemingly to protect its interests in the South China Sea—has important implications for the instrument’s application to the Southern Ocean.

The draft agreement on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction (the ‘BBNJ Treaty’) is designed to be compatible with the UN Convention on the Law of the Sea (UNCLOS), but covers in detail many topics either not included or barely covered in UNCLOS. It responds to current concerns related to overfishing and other human impacts on the ocean by providing mechanisms to create new marine protected areas (MPAs) where existing regional mechanisms either don’t exist or aren’t up to the task. In this sense, the agreement acts as a major spur to achieving the widely supported 30x30 target set at the 2022 UN biodiversity conference to protect 30% of land and marine areas by 2030.

The treaty applies only to the high seas, and thus not to areas within the jurisdiction of any nation. Hence any marine area where a coastal state has an exclusive economic zone would not be covered.

To achieve 30x30, the Southern Ocean plays a key role. These waters surrounding Antarctica are some of the best candidates for high seas MPAs, and currently include the world’s largest MPA, created by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) in the Ross Sea in 2016. Despite overwhelming support in recent years for additional Antarctic MPAs, CCAMLR, which operates by consensus, has been deadlocked due to opposition by China and Russia. The advent of a UN treaty that would include a conference of the parties (COP) that could push for establishment of MPAs anywhere on the high seas where local bodies with jurisdiction for whatever reason were not able to act was one of the major objectives of environmental campaigners.

The BBNJ Treaty will indeed create a conference of the parties with significant authority. Although the COP procedures under which protected areas are established are relatively complex, the COP can recommend establishing MPAs (in the vernacular of the agreement ‘area-based management tools’) on the high seas that are compatible with those adopted by organisations like CCAMLR. In doing so, they must respect the competences of such bodies and not undermine them. Exactly what steps would ‘undermine’ a body like CCAMLR could be a matter of significant debate, and the lack of definition in the treaty for this crucial concept may result in considerable discussion and even confusion. But at least it’s possible for the COP to act where to do so doesn’t undermine an existing organisation. The COP takes a decision as a general rule by consensus, but ultimately can vote by three-quarters majority to establish an MPA.

A decision that seeks to influence an existing body like CCAMLR which has proven unable to make progress on MPAs follows a long hard road involving development of a proposal, scientific review, coordination with the regional body, overcoming a relatively undefined principle of ‘not undermining’ and ultimately achieving a vote of three-quarters of the member states of the instrument represented in the COP.

But action in the Southern Ocean may have an additional barrier to overcome. The final text contains provisions, purportedly insisted on by China, that may be interpreted as rendering the treaty inoperable when it is applied to the South China Sea. The provisions at issue concern claims to sovereignty and related disputes, ensuring that COP decisions or establishment of protected areas ‘shall not be relied upon as a basis for asserting or denying any claims to sovereignty, sovereign rights, or jurisdiction including in respect of any disputes relating thereto’. The language is particularly opaque, but given the importance reportedly placed by China in securing these words in the final hours of the negotiations, it seems reasonable to conclude that China (and possibly other states) believe that the treaty cannot create MPAs or cover marine genetic resources in areas such as the South China Sea that are subject to marine disputes.

States may argue over what these provisions mean and how to implement them. However, if China decides to become a party to this treaty, it might press for wide recognition of an interpretation that requires exclusion of disputed areas from the treaty’s coverage. In that event many countries which would wish to see China join the treaty—which could include many developing countries for a variety of reasons—might be willing to support that interpretation.

Which gets us to the Southern Ocean. Large parts of the marine spaces in the Southern Ocean—namely areas extending 200 nautical miles from the continent—are subject to disputes over sovereignty. Seven countries, Argentina, Australia, Chile, France, New Zealand Norway, and the UK, claim territory in Antarctica. The claims of Argentina, Chile and the UK substantially overlap in the Antarctic Peninsula. The Australian Antarctic maritime claim covers large areas surrounding the continent. Under the law of the sea, maritime claims depend on land territory and coastal state rights extend from baselines on shore. Most countries, including the US and Russia, and presumably China, do not recognise the Antarctic territorial claims and likely wouldn’t accept the maritime claims either. These disagreements over sovereignty do not matter in the context of CCAMLR, as Article IV of the Antarctic Treaty and its CAMLR Convention counterpart allow the CCAMLR parties to cooperate while maintaining their legal positions.

Given the vibrant biodiversity close to land and ice shelves in the Antarctic, the most important parts of many MPA proposals will be found within waters subject to sovereignty disputes. Thus, the additional BBNJ Treaty clauses insisted on by China could create a formidable barrier to applying the treaty to those areas in Antarctica, including to areas already under consideration in existing MPA proposals in East Antarctica, the Weddell Sea, and the Antarctic Peninsula.

The Chinese initiative to carve out the South China Sea may have the effect—perhaps unintended by Beijing—of heading off a debate between Antarctic territorial claimants and non-claimants about what parts of the Southern Ocean are subject to the BBNJ Treaty. That debate could lead to difficult discussions between a small group of states influential in Antarctica and a wide variety of other states including developing countries that would want to see the treaty apply to the full breadth of the Southern Ocean.

It appears that the BBNJ Treaty has been drafted in a way that will leave the matter of Antarctic MPAs largely to CCAMLR. Nevertheless, this new, large-scale multilateral agreement still has political heft that may prove important in persuading CCAMLR to move forward. The successful completion of the treaty shows that the international community wants progress on MPAs and towards 30x30. Members of the CAMLR Commission, including China and Russia, will find it hard to ignore that reality.