What is Deep-Sea Mining Doing to the Planet?

Walking through the docks in Southampton, Britain’s second-largest container port, I felt my sense of scale shifting and bending around me. Cranes stood like headless, metal giraffes against a backdrop of shipping containers neatly stacked like Lego blocks. A cargo ship moored at the eastern dock looked more like a colossal cliff face than a vessel capable of moving. Just across from Berth 44, from which the Titanic sailed, is the National Oceanography Centre, the largest ocean science institution in the United Kingdom.

I went through the glass entrance hall, under the mustachioed knight figurehead from the historic ship HMS Challenger, along the corridors and out into the back lot, where I stepped into a windowless shed. A tang of preserving alcohol hit my nostrils as the strip lights flickered on, revealing a modest-size room packed with shelves and glassware. I had come to see a collection of creatures that once roamed a much wider realm. Crammed on the shelves was a miscellany of animals from the abyss.

My guide was deep-sea biologist Daniel Jones, and together we snooped along the shelving, peering at the preserved creatures floating in jars. I spied five-pointed starfish, coiling snail shells, spiny crabs, and gangly sea spiders with their legs folded to fit in the jar. There were dumbo octopuses and piglet squid, both smaller than I expected, not much more than a handful, floating in their tiny captive ocean. I rummaged through the jars and found large coral polyps resembling flowers made of stone, bamboo corals with finely branching twigs, giant barnacles, plump, pink shrimp that looked fresh from the barbecue, and lots of sea cucumbers. There was Oneirophanta, “the one who appears in dreams,” a sea cucumber with a cloak of long, white tentacles and dozens of stubby tube feet, like nipples, for walking across the seabed. Some sea cucumbers were so big each one occupied its own large Kilner jar, and some preserved together looked like fistfuls of caterpillars.

One species in particular I was curious to behold in the flesh after seeing photographs of its intriguing form in the wild abyss. Nicknamed the gummy squirrel (and officially called Psychropotes longicauda), this six-inch-long sea cucumber has a translucent lemon-yellow body with an unusual appendage sprouting from its rear end that looks like a squirrel’s tail. “I don’t think you’re going to like it,” Jones said, pulling a jar off a shelf and showing me a pallid, shapeless blob. The animal in the jar was certainly no longer beautiful, although still useful; DNA taken from snippets of preserved specimens has helped show there are in fact numerous species that look rather alike but are nevertheless genetically distinct.

Up in Jones’s office, I saw arranged along a bookcase a selection of black lumpy rocks. One was the size and texture of a large head of broccoli; some looked like nuggets of coal, and some were smooth, disk-shaped pebbles. Jones passed me a fist-sized chunk, and for a moment it felt wrong. It was far too heavy for its size, like the rock my grandmother found long ago in her garden that my family has always thought might be a meteorite. Jones’s rocks didn’t fall from space but grew right where they were, lying on the deep seabed.

At the heart of each rock is a tooth dropped by a shark millions of years ago or a chip of whale ear bone or some other small, hard fragment. As eons passed, waterborne minerals and metals settled in thin layers onto the solid nucleus, in the way a pearl forms, and the rocks gradually became bigger and heavier.

I remember being told in high school science classes about these rocky nodules that lie on the abyssal plains and how one day they could be mined for metals inside them. Back then, the image I held in my mind was of a blank flatland of oozy mud and rocks, not a place where marvelous things live and grow, including bright yellow sea cucumbers with tails.

The first time these deep-sea rocks were trawled up from the abyss was in the mid-nineteenth century, by the British scientists on board HMS Challenger as they circled the planet and learned so much about the oceans. The abyssal nodules were put on display to the public and treated like exotic curiosities, as if they had come from outer space. Not until much later did people begin to ponder the weighty metals inside them and wonder whether it might be worth going back to gather more.

As I write this, midway through 2020, no commercial mines are operating on the deep seafloor. But there is a possibility that by the time you read this, the first mines will have opened or at least been given the go-ahead.

In the past few years, mining corporations have been making plans to mine nodules several miles beneath the sea surface and across thousands of square miles of the abyss. What they’re after is the metals that lie inside those rocks. Though composed roughly of 30 percent manganese, a metal that’s not in great demand, the rocks also contain traces of other, more desirable elements, such as nickel, copper, and cobalt.

Besides abyssal nodules, two other targets have come into view for aspiring deep-sea miners. Some operations plan to mine seamounts. In a way similar to the layering of the nodules, metal-rich crusts settle onto the tops and flanks of these underwater mountains. It takes millions of years for a finger-thick layer to form, yet it would probably take only hours for those deposits to be drilled and scraped away by mining machinery and dispatched to the surface. Mining corporations also have plans to knock down and demolish the chimneys of hydrothermal vents. As scorching fluids collide with cold seawater, quickly cooling and precipitating, they deposit a mix of metals, such as iron, lead, zinc, silver, and gold.

The proposed mining ventures bear the hallmarks of extractivism, a centuries-old economic model commonly associated with colonialism and latterly with transnational corporations that extract natural raw materials for export. The goal is to mine a resource on a one-shot basis, then move on elsewhere and repeat. This has traditionally included such practices as gold and gem pit mining, mountain-top removal for coal, and clear-felling of old-growth forests. Central to the model are so-called sacrifice zones, those places that would inevitably be destroyed in the name of economic gain. Huge swaths of the deep sea—hundreds of square miles per mine per year—are in line to become such sacrificial zones.

There are, no doubt, mineral riches to be found in the deep, and many people are in favor of cashing them in now, but numerous peer-reviewed research papers warn of the dangers of doing so. At this point, what the science is saying—loud and clear—is that the deep-sea mining industry would pose dangerous risks to biodiversity and the environment, on timescales and intensities that cannot yet be fully quantified but could be catastrophic and permanent.

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Terrestrial mining regulations often require that biodiversity loss, ideally, should be avoided or minimized; lost populations should somehow be replaced afterward or even replenished elsewhere. In the deep, avoiding the loss of biodiversity would be impossible, for the obvious reason that seabed mines would directly demolish species and habitats. Losses away from the mining sites could perhaps be minimized by controlling where the sediment plumes drift, with some kind of baffle around mining machinery and by designing machines that trample less heavily across the abyss. Impacts could also be reduced by setting aside substantial portions of the abyss as no-mining zones.

Replacing lost species in the deep is near impossible. The theory of remediation suggests that animals and plants can be reintroduced to a mined site once operations have finished to help kick-start the ecosystem’s recovery, for instance by replanting a felled forest with saplings grown elsewhere. The costs of doing something like this in the deep would be astronomical and could well cause more harm than good. It’s difficult to imagine how thousand-year-old corals plucked from healthy seamount ecosystems and fixed to the sides of mined mounts would survive, or how tube worms in their thousands would be glued, one by one, in places where hydrothermal vent fluids still pour through the seabed.

The strategy of offsetting is also problematic in the deep sea. This involves attempting to cancel out the destruction of an ecosystem by protecting and restoring a similar ecosystem somewhere else. As scientists are increasingly discovering, shuffling bargaining chips in this way is not a reliable option for the deep sea. For instance, studies show that no two hydrothermal vent ecosystems are alike; each contains its own unique assemblage of species, depending on the mix of geological and chemical conditions; so, protecting one vent field is no guarantee species will be saved from destruction at another.

Some have proposed that mining the deep could be offset by restoring coral reefs in shallow waters, by way of an ecological apology to the planet. This does, however, assume there is some equivalency of species, an Iridogorgia deep-sea coral traded, for example, for a tropical Acropora. Moreover, this approach to accounting for a net benefit to global biodiversity is so ambiguous as to be scientifically meaningless.

There is also talk of mining only inactive or dormant hydrothermal vents, areas where chimneys have naturally stopped pouring out hot fluids. However, these areas are not empty of life but contain their own ecosystems about which even less is known.

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The apparently unavoidable loss of biodiversity from seabed mines casts serious doubt over whether it is possible to sustainably mine the deep. The stakes soar even higher when we look at the possible impacts on the planet as a whole. Plans for mining the seabed are accelerating, and at the same time our awareness is growing of how the deep sea plays a critical role in regulating the earth’s life-support systems.

Numerous deep-sea experts advise that seabed mining has the potential to worsen the climate crisis. Stores of carbon in the abyss could get disrupted by mining activities that churn up delicate microbial communities that have taken millions of years to evolve. It’s also not clear how vent mining would upset chemosynthetic microbes that mop up methane that bubbles through the seabed. Released to the atmosphere, methane becomes a greenhouse gas 25 times more potent than carbon dioxide. Whether mined vents would burp more methane is another unresolved matter.

With all of this in mind, if the International Seabed Authority (the United Nation’s body charged with overseeing the exploitation and protection of the seabed) gives commercial mines permission to open before the full impacts of mining are well understood, it risks tragically failing in its responsibilities to safeguard life in the abyss—not to mention threatening the rest of the planet.

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Efforts are being made to answer the most pressing questions regarding the impacts of deep-sea mining, some by scientists sponsored by mining corporations to study proposed mining sites. Several relatively small-scale simulated mining experiments have been conducted in the abyss, giving some clues as to the possible outcomes. The most ambitious, which started in 1989, took place in the Peru Basin off the Pacific coast of South America, where a team of German researchers selected a four-square-mile block of an abyssal nodule field (tiny compared to the size of future mines) and dragged a twenty-six-foot-wide plow harrow across it seventy-eight times. The plow didn’t remove the nodules but pushed them aside and buried them in the soft sediment. Scientists have been back at intervals to survey the site, and in 2015 an autonomous submersible photographed the whole area. The resulting photomosaic showed the plow tracks still clearly visible, crisscrossing the seabed, almost three decades later. Even these modest disturbances to the sediments have barely changed in all that time in the calm and still abyss. Mobile animals such as crabs and sea cucumbers had begun to move back in, but the sedentary animals—the corals, sponges, and anemones—were still missing.

Troubles stirred up by scraping over the abyss extend beyond visible animals. Another team of researchers visited the Peru Basin and made some fresh seabed tracks to compare to the decades-old scars. In this part of the abyss, the seabed is covered in a thin layer of sediments that acts like an intricately structured living skin, crawling with microbes. This microscopic community processes the raw organic matter that falls from above as marine snow, incorporating this carbon into the seabed ecosystem. When this delicate skin was experimentally turned over, the microbes were thrown into disarray; immediately half were lost. In the older tracks, thirty years later, the abundance of microbes was still at least 30 percent lower than in undisturbed areas. The study, published in 2020, predicted that microbial life and carbon flux in the seabed would take at least fifty years to return to normal, strengthening concerns over the climate impacts of seabed mining.

A few other mining-simulation studies have been carried out, all with worrying outcomes for biodiversity, but they all share one important shortcoming—they are academic trials, not industrial enterprises. The impacts of full-scale mining would likely be far worse than anything they have shown. In 2022 and 2023 scientists and miners plan to study what happens as prototype mining machines of the designs that would be used in commercial-scale mining are deployed. However, the time frames for exploitation and good science do not necessarily match. Scientists will need time to reach conclusions, and it remains to be seen whether officials at the International Seabed Authority will be patient and wait for the science to properly assess the impacts before deciding whether or not mines should go ahead. There is a tangible sense within the scientific community of the unstoppable momentum of an industry backed by powerful lobbies against which scientists can’t do battle.

“Even if we found unicorns living on the seafloor,” says Daniel Jones, of the British National Oceanography Centre, “I don’t think it would necessarily stop mining.”

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Adapted from The Brilliant Abyss by Helen Scales. Used with the permission of Atlantic Monthly Press. Copyright © 2021 by Helen Scales.