Japan's deep-sea venture a test for global ocean governance

Critical-mineral security might justify scientific exploration, but not ecological shortcuts into the deep sea.

On June 29, the Japanese prime minister instructed relevant ministers to accelerate the development and commercialization of rare-earth extraction from seabed mud within its exclusive economic zone around Minamitorishima (Marcus Island).

This follows a February 2026 announcement that Japan had successfully recovered rare-earth-rich sediment from a depth of nearly 6,000 meters in the same area, with a full-scale mining trial expected in 2027.

Tokyo has framed this move as a meaningful accomplishment in strengthening supply-chain resilience and diversifying Japan's sources of rare-earth supply.

Rare earths are essential to clean energy, advanced manufacturing, defense technologies, and digital infrastructure. No country should be denied the right to pursue lawful resource development.

The real question, however, is whether such development can proceed before environmental risks are properly understood, independently assessed, and effectively controlled.

Deep-sea rare-earth mud extraction is an industrial intervention in one of the least-explored and most fragile ecosystems on Earth. Disturbing the seabed may create sediment plumes near the ocean floor.

Any water discharged during dewatering or other processing stages could form additional plumes in the water column, carrying suspended particles and potentially harmful dissolved substances. Ocean currents could carry these materials beyond Japan's EEZ, making the environmental risks potentially transboundary.

Under Article 56 of the United Nations Convention on the Law of the Sea, or UNCLOS, Japan enjoys sovereign rights to explore and exploit natural resources within its EEZ. However, these rights are neither absolute nor unconstrained.

The Convention establishes a clear balance: resource development must be exercised with due regard for the rights of other states and in conformity with the duty to protect and preserve the marine environment.

Article 194 of UNCLOS requires states to take all necessary measures to ensure that activities under their jurisdiction or control do not cause damage by pollution to other states and their environment, and that pollution arising from incidents or activities under their jurisdiction or control does not spread beyond the areas where they exercise sovereign rights.

If sediment plumes, return-water discharge, underwater noise, artificial light, or other contaminants from Japan's deep-sea mining affect adjacent high-seas ecosystems or the waters of other states, Japan could constitute a breach of international obligations, entitling affected states to invoke state responsibility.

The credibility of Japan's environmental impact assessment process is therefore central. Article 206 of UNCLOS obligates states to assess the potential effects of activities likely to cause substantial pollution or significant and harmful changes to the marine environment.

For deep-sea mining, an environmental impact assessment should be science-based, independently reviewed, and publicly accessible, not merely a procedural formality completed after political decisions have been made.

At such depths, ecological recovery after deep-sea mining is uncertain and likely to be slow. Many abyssal species have low growth rates, limited dispersal capacity, and narrow habitat ranges. The precautionary approach is thus a practical requirement of responsible ocean governance. Neighboring countries, Pacific Island states, fisheries stakeholders, and the global scientific community all have legitimate interests in scrutinizing Japan's environmental assessment and monitoring arrangements.

This does not mean deep-sea mining should be permanently prohibited. It may become acceptable if advanced extraction technologies can demonstrably minimize seabed disturbance and ecological harm, supported by high-precision, long-term environmental monitoring.

This reminds one of Japan's earlier unilateral discharge of nuclear-contaminated wastewater from the crippled Fukushima Daiichi Nuclear Power Plant into the Pacific, undermining regional trust in its marine environmental governance. The same pattern must not be repeated in the deep sea: deciding first, consulting later, and shifting ecological uncertainty onto neighboring countries and the wider international community.

Addressing the challenges posed by Japan's deep-sea mining venture requires a multilayered response leveraging legal, scientific, financial, and market-based mechanisms. Independent scientific reviews should rigorously evaluate Japan's baseline data, plume dispersion models, toxicity assessments, and monitoring designs. Simultaneously, governments and international organizations need to press for full disclosure of EIA reports and post-operational monitoring data. Finally, global markets are urged to categorize rare earths obtained from unverified deep-sea extraction as high-risk commodities.

Japan is entitled to pursue supply-chain resilience, but not by externalizing ecological risk to the Pacific Ocean and the global marine environment.

The Minamitorishima project must not become a precedent for premature and unilateral deep-sea extraction. Instead, it should push the international community to build a framework that keeps the door open to future responsible development while closing the door on reckless environmental risk-taking.

The author is an associate professor of the Law School, Ocean University of China.

The views don't necessarily reflect those of China Daily.