The plume carries no flag: unilateral seabed mining and the pollution duties that bind nonparties to UNCLOS

The USA has begun to license commercial recovery of polymetallic nodules in the Clarion-Clipperton Zone under its own statute, outside the International Seabed Authority, while the Authority’s exploitation regulations remain unadopted. Scholarship has treated this largely as a question of allocation, asking whether a nonparty can acquire good title to nodules in the Area, and has rebuilt what remains as a duty to cooperate. This article asks a different question: which pollution duties bind a nonparty that mines the Area, and on what legal basis. It argues that the environmental obligations of Part XII of the United Nations Convention on the Law of the Sea are severable from the allocative bargain of Part XI. The duties of prevention, due diligence, and prior environmental impact assessment bind the nonparty as customary international law, on evidence that includes its own practice and its obligations under the 1958 Convention on the High Seas. The treaty-specific requirement of Article 209(2) does not bind it, but serves as evidence of what customary due diligence demands in the Area. A State that leaves the referent institution while remaining bound by the rule of reference engages in what the article names referential arbitrage, and the benchmark on which the arbitrage relies proves thinner than claimed but not empty. Sediment and discharge plumes then defeat the geography on which unilateral licensing depends: a licence draws a boundary, and a plume does not observe it. The 1972 London Convention excluded seabed mining discharge on the assumption that a seabed regime would govern it, a carve-out extended on credit that unilateral licensing never redeems. Exit does not remove State responsibility; it concentrates it on the licensing State. The article closes with measures that require no accession, among them an advisory request the Authority’s Council may make on its own motion.