Saleem Ali, an environmental systems scientist at the University of Delaware who also provides research and advice on critical metals to the United Nations, says that deep-sea mining should be part of discussions on the green transition. He coauthored a 2022 analysis, funded by The Metals Company, that compared mining waste from terrestrial deposits to that of seabed resources. (Ali says he has never received direct funding from The Metals Company.) For example, the analysis looked at the impact of terrestrial mine tailings on water pollution and local biodiversity, and at the anticipated pollution from nodule mining, such as seabed sediment kicked into the water column by harvesting machines. It suggests that both types of mining will have effects on biodiversity, but deep-sea mining could result in less waste and fewer risks for communities than terrestrial mining. The study cautions, however, that its conclusions are limited by “substantial uncertainty” regarding impacts of sediment plumes.
Ali adds that the International Seabed Authority has been collecting data for at least 30 years, which should be sufficient to develop rules and regulations to govern seabed mining even if it’s unclear what the long-term impacts are, and whether the environmental impacts are likely to be better or worse than mining on land.
“I’m not saying that we should go ahead with it. I’m saying that it deserves to be considered in this broad context of very difficult choices we have to make,” he says.
But opponents calling for moratoriums or bans note that the same study that The Metals Company refers to as evidence of quick recovery eventually reached more pessimistic conclusions from its data as a whole. “The effects of polymetallic nodule mining are likely to be long term,” the authors wrote, and the analyses “show considerable negative biological effects of seafloor nodule mining, even at the small scale of test mining experiments.” Scientists are concerned that deep-sea organisms, which are adapted to living in a dark, quiet, and sparsely populated environment, will not cope well with the noise and light disturbances from mining. The organisms will also be exposed to toxic metals and plumes of sediment that can interfere with feeding and breathing. The Metals Company did not respond to several requests for comment.
Credit:
ROV TEAM / GEOMAR (CC-BY 4.0)
The seafloor of Clarion-Clipperton Zone is home to many creatures, some of which are shown here: anemone (top left), sea cucumber, Psychropotes longicauda (top right), sea urchin Plesiodiadema sp. (bottom right), and starfish (bottom left). The biology and ecology of these depths remain poorly understood, making it hard to know what the ecological impacts of deep-sea mining would be.
Credit:
ROV TEAM / GEOMAR (CC-BY 4.0)
Because of these unknowns, the mining rules shouldn’t be rushed, says Anna Metaxas, a deep-sea ecologist at Dalhousie University in Canada who coauthored a 2025 overview of the potential impacts of mining on the deep-ocean ecosystem in the Annual Review of Environment and Resources. Metaxas participates in the Deep-Ocean Stewardship Initiative, a nonprofit international network of experts to inform deep-sea policy and governance. She says that she earlier led a project with experts in land and deep-sea mining to develop a framework for environmental comparisons of mining on land and the seabed. But in 2024, she and her coauthors concluded that data are at present too scarce to do so.
“Our knowledge gaps are really large,” agrees Matthias Haeckel, a marine biogeochemist at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany. He is part of a group of 30 researchers and technical experts tasked by the International Seabed Authority in 2024 to develop values needed for monitoring and assessing mining impacts. The group looked at toxicity, such as that from heavy metals, turbidity from sediment kicked up by harvesting machines, and underwater noise and light pollution. They are expected to submit a first draft of standards and guidelines at some point later this year.
Seeking 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, and perhaps adopt, mining regulations. The Metals Company is still waiting for a nod from the United States to start commercial mining in the Clarion-Clipperton Zone. But it says it expects to have a permit by the end of this year and to start mining shortly after.
Meanwhile, scientists like Haeckel are scrambling to launch additional research cruises to provide critical data that will inform decisions about the future of seabed mining and the mining code. Haeckel is leading a European project called MiningImpact that will return later this year to research sites where, in 2021, it monitored part of the mining tests by Global Sea Mineral Resources, a subsidiary of the Belgian company DEME. The third phase of MiningImpact aims to see how the ecosystem has fared five years on, and to promote further understanding of the ecology of life in the abyssal depths.
“The Clarion-Clipperton Zone is a large area, and there are still many, many open questions,” Haeckel says. He wonders how mining in the area could be properly regulated when scientists hardly know yet what creatures live down there, or how they interact.