Deep-sea mining could soon be approved — how bad is it?

Commercial mining of the sea floor could soon get the green light. The International Seabed Authority (ISA), a body associated with the United Nations that oversees deep-sea mining in international waters, is now meeting in Kingston, Jamaica, where it could decide whether companies can begin excavating the sea floor for minerals and metals such as cobalt, nickel and sulfides.

Proponents say that this move could help with meeting the growing demand for rare-earth metals used in batteries both for electric cars and for storing renewable energy, aiding the shift to a low-carbon economy. However, research hints that the potential ecological impacts of deep-sea mining are larger than previously thought. Nature explores just how bad deep-sea mining could be.

What’s the evidence for the effects of deep-sea mining on marine life?

Scientists say that very little is known¹ about deep-sea ecosystems, making it difficult to assess how they will be affected by mining. However, a few new studies are providing clues to the damage that large-scale mining might cause.

A study² published today in Current Biology is the first to examine the environmental effects of mining cobalt-rich crusts. These rock-hard, metallic layers, which form on the side of underwater mountains called seamounts, are among three deep-sea resources that have been proposed to the ISA as a target for mining. In 2020, a two-hour operation funded by the Japanese government excavated a roughly 120-metre-long strip of cobalt-rich crust on a seamount in the northwest Pacific Ocean, as a test run for mining activities.

To investigate the operation’s effects, scientists reviewed video footage collected by a remotely operated vehicle. They found that, in the year after the excavation, the density of active swimming animals, such as fish and shrimp, dropped by 43% in areas directly affected by sediment kicked up by mining, and by 56% in adjacent areas.

Travis Washburn, a benthic ecologist and co-author of the study who at the time was at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, says that he didn’t expect to see any ecological impacts from such a small mining operation. He suggests that the fish and shrimp swam away from the area because the mining and sediment pollution might have affected their food supply. The results show that effects are felt beyond the mining areas “by a pretty substantial amount”, he says.

A study³ published last week suggests that tuna near the ocean surface could gravitate to areas likely to be affected by mining. Writing in npj Ocean Sustainability, scientists project that climate change will drive large numbers of the fish into the Clarion–Clipperton Zone (CCZ), a 4.5-million-square-kilometre area in the eastern Pacific Ocean between Hawaii and Mexico where much of the mining interest is focused. The study predicts that by middle of the century, the zone’s total biomass of skipjack (Katsuwonus pelamis) will rise by around 31% and yellowfin (Thunnus albacares) by 23%.

Tuna catch rates soared after creation of no-fishing zone in Hawaii

Data about deep-sea mining’s effects on animals in the upper layers of the sea are scare. But co-author Diva Amon, a marine biologist and a scientific adviser to the Benioff Ocean Science Laboratory at the University of California, Santa Barbara, says that deep-sea mining could harm tuna and other organisms, such as Pacific leatherback turtles (Dermochelys coriacea).

Plumes of sediment stirred up by mining could contaminate sea water and damage fishes’ gills and filter-feeding apparatus, says Amon. The same problems could occur when mining waste is thrown back into the water. Furthermore, noise from the mining operations could alter the tunas’ feeding and reproductive behavior, she adds.

“Deep-sea mining will potentially have impacts from the sea surface right down to the sea floor,” says Amon.

Is deep-sea mining more damaging than mining for these minerals on land?

Proponents of deep-sea mining, such as The Metals Company, a mining start-up based in Vancouver, Canada, that is seeking permission to harvest metals on the sea floor, argue that deep-sea mining will benefit the environment by helping the shift to a green economy. They also argue that sediment plumes’ effects can be minimized and that mining contractors don’t currently propose to release waste from exploiting mineral-rich sea floor deposits called polymetallic nodules.

Amon says that deep-sea mining is unlikely to replace terrestrial mining, so comparing one with the other is not helpful. “Both will proceed, and we’ll see double destruction in two different parts of the planet,” she says.

Washburn says that deep-sea mining might cause less direct damage to people than does terrestrial mining. But by spoiling huge swathes of the sea floor, it could disrupt marine processes such as carbon sequestration, which helps to offset humans’ greenhouse gas emissions.“I don’t think anybody has enough information to say which one is better or worse,” he says.

What are the key questions that still need to be answered?

Scientists first need to know more about what lives in the deep ocean, says Amon. Then they can begin to investigate how extensive mining can be before it causes serious harm to key ecosystem functions, such as the ocean’s ability to sequester carbon. The challenge, she says, is that deep-ocean science is slow and expensive, and scientists need more time and money to understand mining’s consequences.

Electric cars and batteries: how will the world produce enough?

Matthew Gianni, co-founder of the Deep-Sea Conservation Coalition, a conservation group based in Amsterdam, says that deep-sea mining could become unnecessary thanks to advances in recycling and the advent of batteries that use iron and phosphate instead of nickel and cobalt. Furthermore, improvements in environmental standards for terrestrial mining will lessen the industry’s ecological damage.

Washburn, who started his career studying ecological disasters such as 2010’s Deepwater Horizon oil spill, is buoyed by the efforts to assess potential impacts before the mining operations begin. Historically, humanity tends to act first and consider the consequences later, he says.

“We’re actually trying to figure it out beforehand so that’s a pretty good place to be,” he says.