Complex deep-sea expeditions try to size up seabed mining impacts

In April 2021 in San Diego, 23 researchers from eight institutions across Europe boarded the MV Island Pride, a Norwegian construction vessel sporting a massive crane, for a 42-day voyage to the central Pacific Ocean. The scientists were seizing the chance to be the first to monitor the environmental impacts of deep-sea mining in real time by observing the inaugural large-scale test of a 25-ton machine belonging to Belgian mining company DEME. The researchers’ mission: collect data before, during, and after the giant harvester started scooping up potato-sized polymetallic nodules rich in copper, manganese, and nickel from the sea floor some 4,500 meters below the ocean surface.

Crustaceans called copepods, seen here in confocal microscopy images from seabed samples collected during the 2021 expedition of the Island Pride, are among those deep-sea creatures that could suffer impacts from deep-sea mining. Image credit: Katja Uhlenkott and Sven Rossel (Senckenberg am Meer, Wilhelmshaven, Germany).

Proponents of mining say nations need these million-year-old nodules nested on the seabed to boost production of technologies such as electric-vehicle batteries and wind turbines that will help the world make the transition to a low-carbon economy (1, 2). But researchers and conservation groups are concerned that mining could irrevocably damage the deep-sea ecosystem—the least explored biome on Earth (and that it could impact midwater ecosystems as well: https://www.pnas.org/doi/10.1073/pnas.2011914117). Little is known about what organisms live in the abyssal depths where the nodules lie or about deep-sea ecosystem function, including how nutrients cycle through food webs.

So researchers are effectively starting from scratch, trying to answer difficult questions about how mining will affect an alien ecosystem. And they are doing so against the clock. Next year, several countries aim to agree on international regulations for large-scale commercial mining in international waters—currently, mining is only permitted for research purposes. But a legal loophole means that commercial harvesting could begin at any time. Nauru Ocean Resources Inc., a subsidiary of The Metals Company, a mining business based in Vancouver, Canada, says it plans to apply for an exploitation contract in July this year. Hence, scientists are racing to figure out how best to protect deep-sea communities from the worst impacts of mining before it’s too late. “If you don't know how an ecosystem works, or which species you have there, there's no way to protect it,” says Patricia Esquete, a deep-sea ecologist at the University of Aveiro in Portugal.

By sampling and identifying benthic fauna and testing the toxicity of metals released when nodules are extracted, researchers are learning how mining could change deep-sea life. But the deep ocean’s unique and uncharted territory presents myriad obstacles. For example, many of the organisms are delicate and can’t be taken to the surface for examination, so tests must be done in special chambers down near the seabed. And researchers are discovering that the diversity of deep-sea life is so vast, it’s unclear whether the experimental outcomes in one area can be applied to other areas, even in the same mining zone.

Deep-sea expeditions also have enormous equipment requirements, making fieldwork expensive; research trips are few and far between, and time at sea is limited. That has scientists prioritizing the kinds of data that will allow them to argue for safeguards—to at least protect the most vulnerable deep-sea life forms, including those yet to be discovered.

Nodules can be seen on the surface of the seabed prior to testing a nodule collector from Belgian mining company DEME (Left). Researchers are concerned that sediment displaced due to mining will blanket areas where nodules are found, harming the organisms living there (Right). Image credit: Annemiek Vink (Bundesanstalt für Geowissenschaften und Rohstoffe [BGR], Hannover, Germany).

Predicting Plumes

The sense of urgency to understand mining impacts ratcheted up in January, when Norway’s parliament approved deep-sea mining in the country’s territorial waters, becoming the first country to green-light exploration operations (3). In principle, commercial mining in international waters shouldn’t begin before the International Seabed Authority (ISA), an intergovernmental body that controls mining in areas of common heritage to all nations, comes up with rules. In the meantime, countries can explore the depths and test mining equipment, which provides opportunities for scientists to assess the possible environmental impacts of seabed harvesting, especially pollution from the plume of sediment kicked up by mining activities.

Using both remote-operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) fitted with cameras, researchers aboard the Island Pride mapped the seabed in a small section of the Clarion Clipperton Zone (CCZ), a 6-million-square-kilometer, nodule-rich area between Hawaii and Mexico. The team representing MiningImpact, a pan-European research project, deployed around 50 optical, acoustic, and electrochemical sensors—some to the sea floor—to measure current speeds, turbidity, and dissolved oxygen for clues as to where sediment plumes move and how they might impact organisms’ activity. The sensors and other gear, including underwater vehicles and sediment core samplers, along with monitors for watching the submersibles’ feed in real time—in total, nine shipping containers’ worth of equipment—are hauled aboard the vessel, then packed into labs and on deck. Space is often in short supply, says Matthias Haeckel, a marine biogeochemist at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, and a lead scientist on the European expedition. A follow-up expedition in 2022 aboard a German vessel, the RV Sonne, carted 18 shipping containers of equipment. “You have to play Tetris on deck to get the gear in place”, he says.

The plume of sediment that huge nodule collectors churn from the sea floor is expected to pose one of the most serious mining-related ecosystem impacts, so Haeckel and his team wanted to know how that plume behaves in the deep-ocean near the sea bed. How far and in which direction does the plume travel? What’s the concentration of particles that it contains? How does the plume affect organisms when it redeposits sediment on the sea floor?

They placed turbidity sensors on the sea floor and attached them to an AUV, which was also equipped with cameras and flown through the plume. The researchers found that the cloud of sand and silt traveled over 4 kilometers—farther than they had anticipated. This indicates that areas beyond the immediate mining site could be impacted.

They were surprised by how thick with particles the plumes were. Particle concentrations in the plume rose up to 100 times higher than background concentrations. Images show that after the plume passes through the water for several hours, it redeposits, completely covering the nodules and organisms on the seabed. “It looks like a snow-covered landscape,” Haeckel says.

Even at roughly 100 meters from the mining site, around 1 centimeter of sediment covered the ocean floor. More disconcerting was the spike in the mortality of nematodes and other benthic organisms that were buried under half a centimeter or more of sediment. Previous experimental studies didn’t suggest such adverse effects (4). “We had not expected this because they are living in the sediment,” Haeckel says. “It’s not clear why they suffer under a centimeter of sediment.”

Predicting how exactly the plume disperses is a work in progress. Models need to factor in an array of variables, including deep-sea currents, mesoscale eddies moving from the coast to the CCZ and bathymetry—the contours of the underwater terrain. But Haeckel says the observations and measurements from the 2021 Island Pride expedition and the 2022 follow-up trip will improve existing models and allow researchers to make better recommendations that could help mitigate mining’s effects. For example, by better understanding how far the plume travels, researchers could suggest where mining sites should be in relation to areas of ecological interest (5).

High Diversity, Slow Recovery

The MiningImpact teams are still analyzing data from their 2021 and 2022 expeditions, but Esquete says they saw little evidence of ecosystem recovery one year after the 2021 equipment test. In particular, larger fauna, including echinoderms, like sea urchins and sea cumbers, and macrofauna, like nematodes and gastropods, suffered large losses immediately after the mining, which likely changed the makeup of the community. These changes could affect the food web and other ecosystem functions, she says. But Esquete notes that it’s hard to pin down the impacts without knowing more about what lives in the deep sea and how communities change naturally over time. “We know there are temporal and seasonal variations in the number of species and community compositions in the deep ocean,” Esquete says. “But we don't know the patterns. So, it’s very difficult to assess any impact.”

Relative to shallower waters, populations in the cold, dark depths are sparse, but their huge diversity presents researchers with another challenge. “The biomass is not high, but the biodiversity is completely mind-blowing,” Esquete says. The first census of metazoan life on the CCZ seabed, published in 2023 by Muriel Rabone, a data scientist at the Natural History Museum in London, and colleagues, found more than 5,500 species in the region, of which 92% were new to science, including many worms and arthropods (6).

Typically, scientists only find a few specimens per species, making it difficult to learn much about them. And their relative rarity raises the risk that mining operations could lead to extinctions, Esquete says. Plus, the assortment of species found in one mining area of the CCZ is often very different from that found in another part, making it hard to fashion recommendations that apply to both (7). This recent, growing understanding of the area’s huge biodiversity means that existing ISA plans for protecting sensitive regions of the CCZ could be ineffective, Esquete adds. In 2012, the ISA adopted a plan to manage the ecosystem in the areas of interest for mining in the CCZ (8). The plan includes 13 areas of particular ecological interest, where mining is not permitted. These areas were chosen prior to much of the research showing the extent of the area’s biodiversity. Instead, the assessment used crude proxies, such as the amount of organic carbon that rains down from the surface, to indicate biodiversity and areas of environmental importance. The protected areas might not be situated in spots with the most diversity, Esquete says.

And it’s not just organisms on the sea floor that are at risk. Researchers warn that the deep midwater ecosystems are also rich in marine life that could suffer harms from the sediments plume (9). In the first study of mining impacts on animals living in the water column, published in November 2023, Esquete and her colleagues found that sediment plumes trigger harmful stress responses in jellyfish (10).

Investigating mining impacts as they happen gives researchers crucial information about the immediate effects. But to ascertain whether the ecosystem could recover and over what time scales, they also need to gauge impacts over several years. Jason Chaytor, a marine geologist with the US Geological Survey, and colleagues attempted to do so by scrutinizing the consequences of a test of deep-sea mining equipment more than half a century ago (11).

“The moratorium only makes sense if the scientific research to fill the knowledge gaps continues. Otherwise, we’ll be back in 10 years or so and still can’t answer these questions.”

—Matthias Haeckel

In 1969–70, Deepsea Ventures, Inc., a Delaware-based mining corporation that is no longer operating, tested equipment to mine manganese nodules from the Blake Plateau in US Atlantic waters. Over a period of eight days in 2022, Chaytor and his colleagues battled the aggressive currents of the Gulf Stream to survey that test site using an AUV fitted with sonar sensors to map the seabed in high resolution; cameras provided images. They found tens of kilometers of drag marks a few centimeters high caused by the machinery used in the 1970s that were still visible. “I was surprised to see that there was still so much there 53 years later,” Chaytor says. The research team is still analyzing their data, but they hope to gain an understanding of whether, years later, the community of benthic organisms around the track marks differs from that in nearby undisturbed areas.

Another study suggests they might. In 2015, a research team co-led by Erik Simon-Lledó at the National Oceanography Centre in Southampton in the United Kingdom examined the long-term impacts of a 1989 seabed disturbance experiment, meant to mimic the effects of mining, in the Peru Basin in the Pacific Ocean. The researchers imaged 11 hectares of impacted and undisturbed seabed to understand how mining activity affected the faunal community. They found that after 26 years, populations of suspension-feeders, including sea anemones and sponges, were 40% lower in the disturbed areas—which were also still visible—compared to undisturbed areas (12). In a separate study of the area, sediment samples showed that the amount of carbon cycling through the benthic food web was 16% lower in communities found living on plow marks as well (13). The results suggest that key ecosystem function didn’t recover decades after the disturbance experiment. Based on their results, nodule mining impacts could, the authors caution, “be greater than expected,” and could lead to “an irreversible loss of some ecosystem functions, especially in directly disturbed areas” (12).

Researchers want to better understand how nodule collectors like this one, dubbed Patania II by Belgian company DEME, will churn seafloor sediment, stir up plumes, and potentially exert big impacts on ocean ecosystems. Image credit: Global Sea Mineral Resources (GSR).

Precautionary Pause

The ISA, made up of 168 member states and the European Union (but excluding the United States), is based in Kingston, Jamaica. Its council met in late March to continue hashing out draft regulations for commercial deep-sea mining, including how to monitor mining activities and how to hold mining companies responsible for their activities. The last meeting, in July 2023, ended without an agreement (14). Scientists tasked with answering the many outstanding questions about the impacts of mining—for instance, how much noise or light pollution the ecosystem could withstand without irreversible harm—say existing data fall well short (15).

Companies and government entities that have been allowed to explore the seabed for exploitation potential are required to collect data, such as on the species they encounter, and chemicals present in the water. Rabone’s team was able to tap this database for their census. This data bounty could help fill knowledge gaps, Rabone says, but can be of poor quality—for example, data are duplicated or mislabeled, she notes in her analysis (16). And the rare research expeditions that gather fresh data generate huge amounts of it, which require time to analyze.

These constraints slow down attempts to draw up recommendations for protecting the ecosystem from mining. Without more and better data, researchers fear that commercial harvesting will kick off without proper safeguards in place. “The goal is to be able to answer questions about what could happen, before it happens,” Chaytor says.

Some nations are already proceeding more cautiously than Norway. A group of 24 countries has called for either a moratorium or a “pause” on commercial harvesting of nodules until more is known about possible environmental harm and how best to govern the industry (17). But if commercial mining does pause, the research must continue, Haeckel warns.

“The moratorium only makes sense if the scientific research to fill the knowledge gaps continues”, he says. “Otherwise, we'll be back in 10 years or so and still can't answer these questions”.