A Review of Scientific Literature

Deep sea mining (DSM) in the Pacific is of growing interest to frontier investors, mining companies and some island economies. To date, no commercial operations have been established, but much seabed mineral exploration is occurring. The focus is on polymetallic nodules in the Clarion Clipperton Zone (CCZ) in the north-eastern equatorial Pacific, and in the exclusive economic zones (EEZs) of several nations.

Some stakeholders promote DSM as essential to supply the metals required for a global transition to renewable energy. However, existing terrestrial mineral stocks, progress towards mining of electronic waste, advances towards the development of circular economies, and alternative sources of metals, challenge assertions that the seabed must be mined.

Some companies and governments maintain that future DSM within EEZs will support national prosperity and the development goals of Pacific island economies with little or no negative impact. At the same time, many Pacific islanders express concern about the social, economic and environmental impacts they anticipate deep sea mining would have on their lives. The body of knowledge validating these concerns is slowly growing.

The feasibility and economic benefits of DSM are unsubstantiated. The world’s first licenced deep sea mining project, Solwara 1 in Papua New Guinea (PNG), has had a significant negative economic outcome for that nation. When Nautilus Inc declared bankruptcy, PNG was left burdened by debt, having been persuaded by that company to invest in its failed project. Civil society there and across the Pacific are vocal in their opposition to DSM with calls for a ban in PNG and a moratorium elsewhere in the region.

In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) reported on the unparalleled rate of extinction of the world’s biodiversity, with implications for human health, prosperity and long-term survival. The Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate has since described the precarious state of marine ecosystems. Yet neither report takes into account the predicted impacts and risks of DSM.

Deep sea habitats are rich in biodiversity of which only a fraction is known to science. In the Pacific, the little information available on deep seabed habitats relates to the CCZ. Almost nothing is known about the species and diversity of deep sea environments across the rest of the region.

This review represents an analysis of literature addressing the predicted and potential impacts of mining deep sea nodules in the Southwest, Central, and Northeast Pacific. More than 250 scientific and other articles were examined to explore what is known — and what remains unknown — about the risks of nodule mining to Pacific Ocean habitats, species, ecosystems and the people who rely on them. The report details scientifically established risks, including those related to the lack of knowledge surrounding this emerging industry.

The accumulated scientific evidence indicates that the impacts of nodule mining in the Pacific Ocean would be extensive, severe and last for generations, causing essentially irreversible damage. Expectations that nodule mining would generate social and economic gains for Pacific island economies are based on conjecture. The impacts of mining on communities and people’s health are uncertain and require rigorous independent studies.


    Many deep sea habitats are highly diverse with very little known about the biology and ecology of the wide range of species they support. Recently discovered deep sea species are typically highly specialised, relatively slow growing, and long lived. These traits make them particularly vulnerable to environmental change.

    Small-scale experiments and trials of remotely operated vehicles (ROVs)1 have shown that nodule mining would alter the composition of deep sea communities for millennia. The hard surface habitats provided by nodules would be removed along with the organisms that grow on them. Because nodules take millions of years to form, the loss of such habitats would essentially be permanent: thus animals that live or rely on them — like deep sea octopus and many immobile species — would be lost. Scientists have stated that species losses would be unavoidable if deep sea mining proceeds and most of these species have not yet been studied.

    DSM exploration leaseholds already cover millions of square kilometres of ocean floor. If only a small portion of exploration areas are fully exploited, mining would cover tens of thousands of square kilometres, with the impacts of these operations extending even further. The impact of a single mine, let alone the cumulative impacts of many mines, is unknown.

    Mining companies have not disclosed details of their proposed operating systems or waste management processes — both being key determinants of the scale and range of potential impacts. Companies indicate that various depths are under consideration for discharge of mine waste back into the sea, after initial processing on board surface support vessels.

    There is little understanding about the characteristics of the waste plumes that would result — how far such plumes would travel vertically and horizontally, what metals and processing agents they would contain, how toxic these would be, and the effects of sedimentation on little-studied deep sea habitats and species when plumes settle. A range of animals including whales, turtles and tuna are known to routinely make extended deep dives to 1,000 metres below the surface and deeper. Such species could be exposed to mine waste discharged at any point in the water column.

    The limited information available on plume behaviour focuses on near-surface waters. There are no empirical studies of the impacts of waste disposal in deeper waters. Studies indicate that plumes resulting from waste discharged near the surface, whether deliberately or accidentally, may be toxic to species living there. Near-surface plumes may also cause plankton blooms.

    These could cause bioaccumulation of toxic metals in marine food webs and affect the movement and migration of species that feed on plankton and fishes, such as birds, sharks and cetaceans. Near-surface plumes could also affect small pelagic fishes, shrimps and squids that make vertical migrations from deep waters to the surface, and are important sources of food for many species including tuna. Mine waste could also trigger blooms of cyanobacteria.

    If mine waste was discharged in mid or deep waters, it is possible that upwelling could result in plumes at higher levels of the water column with similar impacts. Detailed oceanographic assessments of each proposed mine site are required to determine the degree of such risks. Studies are yet to be conducted on mine waste toxicity to deep sea species. Surface support vessels, DSM equipment and infrastructure would meanwhile create noise and light pollution at the surface, seabed and — depending on the operating system — possibly at mid-water depths. Such pollution would affect a wide range of species.

    While the range and scale of predicted and potential environmental impacts would be significant, scientists have concluded that it is highly unlikely that remediation of impacts would be possible. Compensation for impacts by biodiversity offsetting is likewise viewed as unrealistic.

    Pacific peoples have deep cultural and spiritual connections to their ocean born from sailing, fishing and trading over hundreds of generations. As societies and individuals, their identities are intertwined with the ocean including sites that are deep under water and far from human habitation. Studies are yet to explore the full scope of socio-cultural effects of nodule mining.

    The most severe economic impacts of DSM are likely in fisheries. Many Pacific island economies depend on fisheries for national wealth and employment, local livelihoods, cultural practices, and food security. In 2018, the Pacific tuna fishery was worth more than more than USD 6 billion and accounted for a significant share of the GDP of many economies.

    A single DSM risk assessment for fisheries has been carried out. It focused on tuna and suggested the risk might be low due to depth separation between mining activities and tuna habitats. However, it highlighted numerous knowledge gaps, stating that extensive site specific studies would be needed to determine the risks. In addition, mining and waste discharge methods are unknowns that would greatly influence the scale and scope of impacts on fisheries.

    Risks to tuna fisheries and other open-ocean species would be greatly increased by mine waste released in surface layers as well as noise and light pollution from DSM infrastructure. Yellowfin and bigeye tuna would be exposed to waste discharges at depths of up to 1,000 metres or more, as these species make extended deep dives. Climate change research predicts that tropical tuna stocks will move eastwards in future years, shifting their populations into habitats where nodule deposits occur. If plumes from nodule mining affected seamounts, deep sea snapper fisheries would be at risk.

    The contiguous and interconnected nature of ocean ecosystems means that mining impacts would not be contained to any one area or jurisdiction (i.e. they would be transboundary). Cumulative impacts from multiple operations are particularly important considerations. It is not possible at this point to predict the reach and scope of impacts of any individual project let alone the cumulative impacts of the many projects proposed throughout the Pacific.

    Cumulative and transboundary impacts are especially important given the economic value and migratory nature of tuna and other fish stocks that straddle maritime jurisdictions. Recent evidence suggests that deep sea fishes also migrate. Even before any commercial operations have been established, DSM is causing deep social divisions. Many Pacific islanders prioritize preserving habitats, their way of life, livelihoods and food security over the unconfirmed benefits that DSM may bring. They are aware of the destruction caused by many land-based mines and other terrestrial natural resource projects — and the lack of lasting benefits for affected communities that have accrued from these.

    While some governments and community members support deep sea mining for economic development, many Pacific island economies remain underdeveloped after decades of resource extraction. Even if commercially successful, DSM may not provide sufficient revenues to be an economic panacea for Pacific islanders, or to offset predicted and potential losses in current uses of the ocean (e.g. fisheries).

    From a global perspective, concerns have been raised about the damage DSM would do to species and habitats that are part of common human heritage.

    The potential impacts of mining deep sea nodules are poorly understood. As a result it is not possible to adequately assess and manage the risks. In particular:
    • Studies of deep sea biodiversity and habitats in nodule grounds are few. The available information is dominated by research in the CCZ with very little publicly available scientific information about the diversity, biology, ecology, and population dynamics of deep sea species and habitats in the wider Pacific, their ecological roles, and their ability to withstand or recover from deep sea nodule mining.
    • Most of the nodule mining technology and methods is proprietary information, or has yet to be developed. The scale and period of proposed operations are not clear. Thus, it is not possible to predict the extent of physical damage to seafloor habitats and biota, plumes generated and their spread, or sedimentation.
    • Also unknown are the impacts on surface, mid-water and deep sea species of noise and light pollution.
    • Nodule mining will create cumulative pressures on species, habitats, and ecosystems including species in shallower waters that may be exposed to waste. Global oceans are already experiencing stress from numerous sources including acidification, land-based pollutants such as plastics, and climate change. DSM’s contribution to the cumulative impacts of multiple stressors is unknown.
    • The extent of impacts across jurisdictional boundaries is also unknown. The migratory nature of many marine organisms and the interconnected nature of oceans means that DSM at one site would affect marine life and fish stocks at another. Migrations of deep sea fishes have been demonstrated in the Atlantic Ocean and could occur in Pacific. Transboundary impacts of nodule mining may become a source of conflict.
    • Social and economic costs and benefits for Pacific island economies are unknown. The economic feasibility of nodule mining, distribution of earnings, duration of benefits, liabilities for companies and governments, and social impacts are yet to be independently examined. In PNG, the distribution of wealth from resource extraction projects has been at the heart of several armed conflicts, notably the Bougainville Civil War (leading to a referendum on independence in 2019) and recent conflicts over royalties from natural gas in the highlands.
    • No information exists in the public domain on the potential impacts on human health through bioaccumulation of metals that would be contained in plumes generated by nodule mining. This is a highly significant knowledge gap as seafood forms a major component of the diet of Pacific islanders, and commercial fisheries are major contributors to the GDP of many Pacific economies.
    • No studies are available on the full scope of social, cultural and economic effects.
    • There is no evidence that it is possible to develop spatial management arrangements to ensure the protection of deep sea species and ecosystems, especially in view of the transboundary and cumulative nature of DSM related impacts. It is also unclear whether such arrangements could protect species moving through waters above the seabed.
    • The carbon sequestration functions of deep sea ecosystems are recognised but poorly understood. How these and global carbon balance might be affected by nodule mining is unknown.

This review concludes that mining deep sea polymetallic nodules in the Pacific will have severe and long-lasting impacts on the seabeds mined and the species they support and may pose significant risks to marine ecosystems more broadly. The potential impacts on fisheries, communities and human health are largely unknown and thus pose risks.

The review finds that the relationship of Pacific islanders to the ocean is not well integrated into discussions about nodule mining and that social and cultural impacts are yet to be meaningfully explored.

Lastly, the social and economic benefits are questionable. We conclude that a precautionary approach to nodule mining is warranted and a moratorium on deep sea mining in the Pacific is the only responsible way forward.