As Interest in Deep-Sea Mining Grows, Scientists Raise Alarms About the Possible Ecological Consequences

Gathering minerals such as nickel, cobalt, manganese and lithium from the seabed could affect everything from sponges to whales. The long-term effects of these extractions remain uncertain

Amber X. Chen

– AAAS Mass Media Fellow

July 18, 2025

The deep sea is an extreme environment featuring crushing pressure, near-freezing temperatures and total darkness. It can be hard for humans to imagine anything capable of withstanding such conditions. And yet, life persists.

In rare trips to the deep sea, scientists have uncovered sea cucumbers with purple-magenta ombre coloring; yeti crabs with hairy, feather-like claws; octopuses with ears like the Disney character Dumbo; iridescent mollusks; and phantasmic jellyfish.

This life is all but a fraction of what scientists suspect exists on the deep seafloor. But just as researchers are beginning to discover the multitude of species that call the ocean floor home, countries around the world are already making plans to mine it. Minerals on the deep seafloor were discovered in most oceans in the 1870s during the Challenger expeditions. However, interest in mining these minerals was not popularized until the mid-20th century, when American geologist John L. Mero, known as the “father of ocean mining,” promoted the practice in his 1965 book The Mineral Resources of the Sea.

Global demand for critical minerals found in seabed areas—like nickel, cobalt, manganese and lithium—are on the rise. Currently, these minerals are most commonly mined in Indonesia, the Democratic Republic of Congo, South Africa and Australia, respectively. Many of these sites have been accused in recent years of committing a variety of human rights and labor abuses. Concerns about the longtime viability of such mines are also leading companies to look for minerals elsewhere.

These minerals are used in defense technology, smartphones, electric vehicles and even medical devices. The International Energy Agency predicts that by 2040, demand for these minerals from clean energy technologies will at least double under one scenario.

So now, the prospectors are turning to the depths of the ocean. The International Seabed Authority, the body in charge of approving exploration and development of deep-sea mining projects in international waters, has currently issued 31 mineral exploration contracts, but it has not yet approved any commercial mining operations, as the regulations for such activities are still under review. Meanwhile, 37 countries have so far taken positions against deep-sea mining on international waters, citing potential environmental harms.

Last month, the Trump administration announced that the Bureau of Ocean Energy Management would begin to fast-track the development of deep-sea mining projects. The move follows an executive order President Donald Trump released in late April calling for the expedition of domestic and international deep-sea mining projects as a means of “strengthening our economy, securing our energy future and reducing dependence on foreign suppliers for critical minerals.”

The debate surrounding deep-sea mining represents an interesting tension, as the minerals it produces help power many of the technologies that countries need to achieve sustainability goals such as reducing reliance on fossil fuels. Yet, many environmental scientists are wary of how the process might harm the deep-sea ecosystem, an area of the world that we still know very little about. Current estimates say that less than 0.001 percent of Earth’s deep seafloor has been explored. In an effort to understand how the deep-sea environment might be affected by mining, we contacted five experts and asked them several key questions.

How does deep-sea mining work?

As of now, geologists are considering three different methods to mine the floor of the deep sea. Though some effects and processes overlap, each type employs different technology that picks up distinct mineral deposits, and their environmental impacts vary.

The first of these methods targets sulfide deposits by crushing ore on hydrothermal vent systems near the sites of volcanic activity, at depths between around 3,000 and 13,000 feet. The second looks to obtain cobalt-rich crusts that have accumulated over millions of years on the tops of seamounts between depths of approximately 3,000 and 8,000 feet, by peeling these crusts off from the bedrock. The third targets polymetallic nodules, potato-shaped mineral bits about the size of a fist that contain manganese, iron, copper and nickel. These nodules are found at the deepest parts of the ocean at depths surpassing 13,000 feet. Polymetallic nodules are mined using a “subsea collector”— imagine an undersea Roomba about the size of a small house tracking over the seafloor and scooping up what’s there. Hydrothermal vent mining and cobalt crust mining also employ mining vehicles on the seafloor in order to collect sulfide deposits and cobalt crusts after they are broken off and removed.

Each mining method involves transporting a slurry of mined minerals to a surface vessel, where valuable minerals are then separated from useless residue.

Visualizing Deep-sea Mining

Polymetallic nodule mining has drawn the most interest: 19 of the International Seabed Authority’s 31 exploration contracts are for identifying potential sites for mining these nodules, the largest of which is the Pacific Ocean’s Clarion-Clipperton Zone (CCZ). This section of the eastern Pacific spans 1.7 million square miles off the western coast of Mexico.

How would deep-sea mining affect deep-sea wildlife?

Scientists are still unsure about deep-sea mining’s potential impacts on creatures that call the seafloor home. But from what they have been able to uncover, many predict that mining will have an incredibly negative—if not irreversible—effect on this unique ecosystem.

According to Muriel Rabone, a researcher in the deep-sea ecology and systematics group at London’s Natural History Museum, though the CCZ has been under the most exploration to identify sites for nodule mining, the area is essentially a scientific black hole.

“There’s such extensive knowledge gaps in a lot of deep-sea habitats,” Rabone says.

Rabone was a co-author of a 2023 study examining biodiversity in the CCZ, based on existing data on the area’s species. Her team found that approximately 90 percent of species in the area are undescribed. Of the few species that have been characterized so far, scientists have uncovered arthropods and worms to be the most common creatures on the floor of the CCZ.

“Wherever you’re going to be mining in the deep sea, you’re going to be disturbing very slow-growing types of habitats,” says Kathryn Miller, an environmental scientist at Lancaster University in England. “[There’s also] a high degree of endemism, which just means that the organisms are really highly specific to live in that particular area.”

According to Miller, because everything evolved to live in an extremely dark, cold and high-pressure environment, species on the seafloor are highly specialized. She adds that any sort of ecosystem recovery will likely be extremely slow, or simply won’t happen at all, because the deep sea’s unique habitat conditions would be so disrupted.

How would deep-sea mining affect other ocean animals?

Environmental concerns associated with each form of deep-sea mining are not limited to its effects on species that live in the deepest abysses of the ocean. Species that live higher up in the water column may also be affected by the mining as it dredges up sediment plumes that then rise toward shallower areas.

According to Miller, modeling of the proposed mining plans suggests that sediment plumes could drift for several miles throughout the water column.

Though Miller acknowledges that it’s difficult to predict exactly how far this sediment plume would travel, scientists are worried about its potential risk to filter feeders: organisms like baleen whales, certain fish and sponges that feed through filtering water. “They’re going to be filtering sediment, which could clog up their gills and cause them all sorts of problems,” she says.

Moreover, the noise pollution associated with deep-sea mining technologies also has the potential to harm cetaceans, species like dolphins and whales that use echolocation to communicate, even though these creatures largely inhabit waters miles above where the direct impact of mining would be. 

“The thing with sound is it travels very, very well in water,” says Kirsten Young, a population biologist at England’s University of Exeter. According to Young, because of the ocean’s unique physics, certain frequencies can travel more than 300 miles through different ocean basins.

“[Cetaceans] use sound to communicate all the time, so if there’s something that’s a really loud noise—and it could be a loud, constant noise, or it could be a sharp bang, and it depends on where it is and at what frequency that noise is—it can mask the communication that they have between each other,” adds Young.

For example, the noises produced by deep-sea mining technologies could startle deep-diving beaked whales, causing the animals to rise to the surface much faster than is safe due to the pressure change. A mass stranding of beaked whales in 2018, possibly due to an unknown source of seismic activity, offers a bleak look into how noise pollution might harm these animals. 

What would be the long-term effects of deep-sea mining?

A study published this March in Nature confirms many scientists’ fears that deep-sea mining would damage the seafloor ecosystem. 

Researchers compared a 1979 site of a deep-sea mining test in the CCZ with neighboring undisturbed areas and found that the site still had lower levels of biodiversity, nearly 44 years later in 2023. Moreover, the study found that the physical signs of the test were still visible: Scientists could still see a clear zone that had been stripped of polymetallic nodules and track marks from the vehicle used to collect them.

The original 1979 test employed a roughly 45-foot-long experimental mining machine that mined an unknown quantity of nodules over four days.

Daniel Jones, co-author of the study and research leader at the United Kingdom’s National Oceanography Center, said that the long-term impacts of the mining disturbance are still clear when observing wildlife such as sponges, corals and sea anemones that spend their lives largely immobile on the seafloor. According to Jones, although some of the more mobile creatures had begun to repopulate to similar numbers seen in undisturbed parts of the ocean, the diversity of life may take centuries or more to return.

Although Jones acknowledges that modern mining vehicles may have the technology to create less of a disturbance than the 1979 test vehicle, he emphasizes that the extent of that old test was incredibly small—yet still left a long-lasting mark. Modern mining sites, he notes, will likely be the size of a small town or larger.

“The current proposed method of mining is still to have a vehicle on the seabed floor so the mining vessel will be on the seafloor,” Miller adds. “I don’t see how with the weight of that vessel, it’s going to not cause the same amount of environmental damage.”

Could mining affect other environmental elements on the seafloor?

Andrew Sweetman, a seafloor ecologist and biogeochemist at the Scottish Association for Marine Science, had been doing experiments with benthic landers, large devices used to observe the ocean floor, when he and his colleagues noticed something strange.

“They were showing that the oxygen—instead of going down, instead of it being consumed—was going up,” Sweetman says. A few more tests later, and Sweetman’s team confirmed that oxygen was being produced by manganese oxide particles on the seafloor, most commonly found in polymetallic nodules. Sweetman and his team coined the term “dark oxygen” to refer to this discovery: oxygen production that does not depend on traditional photosynthesis processes, which require light.

Scientists are still unsure of what purpose the dark oxygen serves in the ocean floor ecosystem. It’s even possible that the substance was triggered by researchers’ instruments disturbing the nodules.

“Is it a microbial process linked to the manganese oxides? Is it an electrochemical process linked to the manganese oxides? Is it something completely different that we haven’t thought about?” Sweetman says. “Once we figure that out, we should be in a better position to figure out what is the ecological role, if any, of the process in the ecosystem.”

Sweetman’s findings are evidence that scientists simply don’t know much about the deep ocean ecosystem at all. The worry is that if the nodules are indeed naturally producing oxygen, then the removal of those nodules could have grave consequences for the local ecosystem.

What are the key takeaways about the environmental impacts of deep-sea mining?

Mining companies have lauded the lower environmental effects of deep-sea projects, compared with land-based mining, while also emphasizing that the retrieved minerals will be used in green technologies.

“[The polymetallic nodules] literally sit there like golf balls on a driving range,” Gerard Barron, CEO of the Metals Company, which is looking to be the first to commercially mine the ocean floor, told NPR. “We can pick those nodules up and turn them into metals at a fraction of the environmental and human impacts compared to mining on land.”

Proponents say that the demand for these minerals will keep rising and that the deep sea offers a valuable alternative source for them. The Energy Transitions Commission think thank reports that under a baseline scenario—where we deploy more clean energy technologies and maintain the same recycling trends—our demand for nickel, lithium, cobalt and copper will be higher than supply by 2030.  

However, other groups have pushed back against this prediction: In an October 2024 report, the International Council on Clean Transportation think tank wrote that concerns over a supposed mineral deficiency were “overblown.”

Many scientists have doubts about deep-sea mining’s claim to sustainability. Besides preliminary research on mining’s impacts on the ocean ecosystem and still-unanswered questions on its potential effects on the ocean’s oxygen production and carbon storage, scientists also say that the deep sea is a near-impossible place to regulate. While terrestrial mining can be monitored, says Young, the CCZ, for example, is a particularly difficult place to oversee, and it would require a serious financial investment to fully understand the impacts of mining there. Young’s worry is that commercial deep-sea mining will go something like commercial fishing, which historically has not been well regulated.

“The ocean is a bit of a black box, and I don’t think we know enough about it to be embarking upon an industry which is going to change it irrevocably,” Young adds. “I’m not convinced that we can’t find the minerals in other ways, and we can’t be more responsible with the minerals that we have in use already.”

Sweetman emphasizes that scientists need more time to do research and to be more vocal with their concerns. “We’re going to need to eventually, you know, be brave and say, ‘OK, we know we don’t know everything, but we know enough to make a few decisions now,’” he says.