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Among metal-rich nodules of the Clarion-Clipperton Zone, a sea anemone–like cnidarian trails 2-meter tentacles.


Bus-size robot set to vacuum up valuable metals from the deep sea

Sometimes the sailors' myths aren't far off: The deep ocean really is filled with treasure and creatures most strange. For decades, one treasure—potato-size nodules rich in valuable metals that sit on the dark abyssal floor—has lured big-thinking entrepreneurs, while defying their engineers. But that could change next month with the first deep-sea test of a bus-size machine designed to vacuum up these nodules.

The trial, run by Global Sea Mineral Resources (GSR), a subsidiary of the Belgian dredging giant DEME Group, will take place in the international waters of the Clarion-Clipperton Zone (CCZ), a nodule-rich area the width of the continental United States between Mexico and Hawaii. The Patania II collector, tethered to a ship more than 4 kilometers overhead, will attempt to suck up these nodules through four vacuums as it mows back and forth along a 400-meter-long strip.

Ecologists worried about the effect of the treasure hunt on the fragile deep-sea organisms living among and beyond the nodules should get some answers, too. An independent group of scientists on the German R/V Sonne will accompany GSR's vessel to monitor the effect of the Patania II's traverses. The European-funded effort, called MiningImpact2, will inform regulations under development for seafloor mining, says James Hein, a marine geologist at the U.S. Geological Survey in Santa Cruz, California. "That work is critical."

Since the 1970s, interest in deep-sea mining has waxed and waned with commodity prices. A decade ago, companies were focused on sulfides, copper-rich deposits that form from the mineral-laden hot water gushing from hydrothermal vents. But a plan to mine deposits off Papua New Guinea has met with opposition because the vents are scarce and fragile, and they host unusual life forms. "They are such weird, unique ecosystems," says Andrew Thaler, a deep-sea ecologist who tracks the industry at Blackbeard Biologic, a consultancy in St. Michaels, Maryland. As a result, he says, "It's politically harder to get more mining licenses."

The nodules, however, are abundant, and they are rich in cobalt, a costly metal important for many electronics that is now mined in the forests of the Democratic Republic of the Congo, a conflict zone. If Earth had never been mined and you had to choose between the rainforest or seabed, "you'd absolutely go to the sea floor," Thaler says. "No brainer." The nodules form on deep abyssal plains where sedimentation rates are low, allowing metal compounds dissolved in seawater to encrust a nucleus, like a shark tooth or a rock, over millions of years. Microbes aid the process, especially where they are nourished by nutrients drifting down from life-rich surface waters, says Beth Orcutt, a geomicrobiologist at the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine.

Ideal for nodule formation, the CCZ is estimated to contain some 27 billion metric tons of the ore. But its abyssal plain is also a garden of exotic life forms. Craig Smith, a benthic ecologist at the University of Hawaii in Honolulu, has helped lead biological surveys in the CCZ that, in one case, revealed 330 species living in just 30 square kilometers, more than two-thirds of them new to science. The CCZ's inhabitants include a giant squid worm, predatory sponges resembling ornamented Christmas trees, green-yellow sea cucumbers that researchers called "gummy squirrels," and a greater variety of bristle worms than ever reported before. "I didn't expect any part of the CCZ to have among the highest diversities of any deep-sea habitat," Smith says. "That caught me by surprise."

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Mining could leave a lasting imprint on these ecosystems. In 2015, MiningImpact scientists visited the site of a 1980s experiment off Peru in which a small sledge was pulled along the bottom to simulate nodule harvesting. Three decades later, "It looked like the disturbance had taken place yesterday," says Andrea Koschinsky, a geochemist at Jacobs University in Bremen, Germany, who is working on MiningImpact2. A similar pattern has been seen at small dredging sites in the CCZ. Life in the path of a collector will be lost, says Jens Greinert, a marine geologist at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, who notes that many filter feeders, such as corals and sponges, live right on the nodules. "They will be sucked up and are gone. You can't go back."

Such concerns make many environmentalists wary of opening any of the deep sea to mining. Some, including United Nations Special Envoy for the Ocean Peter Thomson, are floating the idea of a 10-year "precautionary pause." "It seems like you have these two opposed agendas," says Kirsten Thompson, a marine ecologist at the University of Exeter in the United Kingdom.

GSR declined to comment until after the trial, but other factors are likely to delay commercial operations in the CCZ until late next decade. For one thing, the legal framework for mining in international waters is uncertain. Although the United Nations's International Seabed Authority has granted contracts for exploration, it is still drafting rules that will govern commercial operations and set limits for environmental damage. The rules are unlikely to be final before 2021. For another, the collector, the most advanced mining equipment ever tested at depth, may not work as planned. "When you throw a new piece of technology into the ocean, the ocean tends to throw it right back at you," Thaler says.

To gauge the risk to ecosystems, scientists aboard the Sonne are already patrolling the CCZ, collecting baseline data. Next month, the Sonne will rendezvous with GSR's ship, and over several weeks the two ships, working some 400 meters apart, will conduct the tests in two areas where GSR has exploration contracts from the United Nations. Before each test, the Sonne will spend nearly 3 days sending more than 60 sensors, including radar, sonar, and cameras, down a lift to the sea floor, using a remotely operated vehicle (ROV) to place them. "It's a little bit like playing Tetris," Greinert says.

These sensors will focus on the plume of sediment the collector kicks up. The waters of the CCZ are some of the clearest in the world, and scientists have long feared that mining could spread a vast blanket of silt, hurting life far outside the mining area. Recent experiments, however, suggest most of the silt particles will clump together and fall out within a kilometer or two, Koschinsky says. But a film of finer nanoparticles might spread farther.

As the collector trundles along, the ROV and an autonomous deep-sea robot will follow, capturing close and distant views. At the end of the 400-meter swath, the collector will drop the nodules it harvested in a pile. (This "preprototype" has no system for delivering them to the surface.) The sensors will continue to monitor the plume for 4 days after the work is done.

Although environmentalists might be tempted to condemn any deep-sea mining, even such a small test, GSR should be commended for its willingness to cooperate with the scientists, says Cindy Van Dover, a deep-sea biologist at Duke University in Durham, North Carolina. "I say bravo. We can't get answers until we start doing stuff." Yet given the test's limited scope and the unknowns of deep-sea life, she doubts it will solve what is, to her, the most pressing question: "How will we know we screwed it up?"