Salim Ali, an environmental systems scientist at the University of Delaware, who also provides research and advice on critical metals to the United Nations, says deep-sea mining should be part of the discussion on the green transition. He co-authored a 2022 analysis, funded by The Metals Company, which compared mining waste from terrestrial deposits to marine resources. (Ali says he has never received direct funding from The Metals Company.) For example, the analysis looked at the effects of terrestrial mine tailings on water pollution and local biodiversity, and anticipated pollution from nodule mining, such as marine sediment released into the water column by harvesting machines. This suggests that both types of mining will impact biodiversity, but deep sea mining may cause less waste and less risk to communities than terrestrial mining. However, the study cautions that its conclusions are limited by “substantial uncertainty” regarding the impacts of sedimentation.
Ali says the International Seabed Authority has been collecting data for at least 30 years, which should be enough to develop rules and regulations to control seabed mining, even if it’s not clear what the long-term effects are, and whether the environmental impacts are likely to be better or worse than mining on land.
He says, “I’m not saying we should go ahead with it. What I’m saying is that it needs to be considered in the broader context of the very difficult choices we have to make.”
But opponents calling for a moratorium or ban say the study, which The Metals Company points to as evidence of a quick recovery, ultimately reached a more pessimistic conclusion than its data suggests overall. “The impacts of polymetallic nodule mining are likely to be long-term,” the authors wrote, and the analysis “shows considerable negative biological impacts of seafloor nodule mining, even in small-scale test mining experiments.” Scientists are concerned that deep-sea creatures, which are adapted to living in dark, cool and sparsely populated environments, will not cope well with the noise and light disturbances caused by mining. The creatures would also be exposed to toxic metals and plumes of sediment that could interfere with feeding and breathing. The metals company did not respond to multiple requests for comment.
The sea floor of the Clarion-Clipperton Zone is home to many creatures, some of which are shown here: anemone (top left), sea cucumber, Psychroptes longicauda (top right), sea urchin Plesiodiadema sp.. (bottom right), and starfish (bottom left). The biology and ecology of these depths are poorly understood, making it difficult to know what the ecological impacts of deep sea mining will be.
Credit: ROV Team / Geomar (CC-BY 4.0)
The sea floor of the Clarion-Clipperton Zone is home to many creatures, some of which are shown here: anemone (top left), sea cucumber, Psychroptes longicauda (top right), sea urchin Plesiodiadema sp.. (bottom right), and starfish (bottom left). The biology and ecology of these depths are poorly understood, making it difficult to know what the ecological impacts of deep sea mining will be.
Credit: ROV Team / Geomar (CC-BY 4.0)
“The gap in our knowledge is really huge,” agrees marine biogeochemist Matthias Heckel of the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany. He is part of a group of 30 researchers and technical experts appointed by the International Seabed Authority in 2024 to develop essential values for monitoring and assessing mining impacts. The group looked at toxicities, such as toxicity from heavy metals, dirt from sediment generated by harvesting machines, and underwater noise and light pollution. They are expected to submit the first draft of standards and guidelines sometime later this year.
Looking for answers—and soon
The International Seabed Authority Council—its executive body—convened in Jamaica in early March and will do so again in July to debate mining rules and perhaps adopt them. The metals company is still awaiting approval from the United States to begin commercial mining in the Clarion-Clipperton Zone. But it says it hopes to get the permit by the end of this year and start mining soon after.
Meanwhile, scientists like Haeckel are scrambling to launch additional research cruises to provide vital data that will inform decisions about the future of marine mining and mining codes. Heckel is leading a European project called MiningImpact that will return to research sites later this year, where in 2021, it monitored part of the mining trials by Global Sea Mineral Resources, a subsidiary of Belgian company DEME. The third phase of MiningImpact aims to look at how the ecosystem has performed over five years, and promote further understanding of the ecology of life in the ocean depths.
“The Clarion-Clipperton Zone is a big area, and there are still many, many open questions,” Heckel says. They wonder how mining in the region can be appropriately regulated, when scientists still hardly know what organisms live there, or how they interact.
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