Is Deep-Sea Mining Bad for the Environment?

A new generation of prospectors is eager to explore the ocean floor. Will deep-sea digging damage one of the earth’s most valuable ecosystems?

Having ventured to Australia to buy a coal company for $3.1 billion, to Guinea to lock up access to aluminum and diamonds and gold, and to Iraq to insure a big share of that country’s expected postwar oil production—all last year—Chinese companies and government-supported funds have shown that they will go to the ends of the earth to acquire the resources needed to stoke their country’s industrial growth. Now China is angling to be first to exploit a source of minerals that has tempted and frustrated dreamers for almost 150 years: the floor of the deep sea.

In May an arm of the Chinese government submitted plans to explore the seafloor around an underwater ridge in the Indian Ocean near Madagascar, where hot springs in the ocean bottom called hydrothermal vents have created deposits containing gold, silver, copper, nickel, cobalt, and tellurium (used in computers, CDs, and DVDs). The filing came on the first day that the International Seabed Authority, the United Nations agency set up to manage seafloor mining in international waters, accepted exploration plans; as land-based sources of precious metals run dry, China will surely have company. It is no small irony that the first would-be undersea ’49ers made their move in the midst of BP’s Gulf of Mexico disaster, but not for the reason one might think. Just as the reality of the BP spill has, so far, fallen short of the marine Armageddon some green groups predicted, so the actual environmental damage from mining the seafloor looks as though it might, too. If so, nothing is likely to stand in China’s way as it stakes its undersea claims.

The environmental concerns arise from one of those coincidences that makes you wonder about nature’s sense of mischief. The richest lodes of undersea minerals are located at hydrothermal vents. Here, volcanic activity beneath the earth’s crust sends sulfur-rich plumes spewing up from gashes in the seafloor into the ocean, where the plumes support unique ecosystems of animals and microbes. Discovered in 1977, these communities aren’t directly based on sunlight and photosynthesis like every other ecosystem on earth, but on the chemicals in the plume. Microbes turn the chemicals into energy and biomass, larger creatures eat the microbes, and the result is exotic animals like red-tipped tubeworms that have neither mouth nor stomach, as well as anemones, giant red-fleshed clams, jellyfish that resemble dandelions, shrimp, snails, lobsters, and blind white crabs—different combinations of species at each vent.

Since 1977 more than 1,300 species previously unknown to science have been discovered at the vents. “We go back to a site dozens of times and find new species routinely,” says marine biologist Cindy Lee Van Dover of Duke University. The vents may also be where chemistry first became biology—that is, where life on earth began—and thus be scientifically priceless.

In 1979 scientists discovered that the same plumbing that supports the bizarre menageries also creates the mineral deposits that China is eyeing. Magma under the ocean floor heats seawater circulating through rocks above it; the heat causes gold, silver, copper, nickel, zinc, and other metals in the rock to leach into seawater that has percolated miles down through the seafloor crust, explains marine geologist Peter Rona of Rutgers University. The heat then propels the seawater (now as hot as 750 degrees Fahrenheit and full of dissolved metal sulfides) back up through the crust, where it meets colder water. The shock of the cold makes the metal sulfides crystallize. The result: “seafloor massive sulfide deposits” that are rich in valuable metals.

“Massive” is an understatement. One deposit of copper, iron, zinc, gold, and silver sulfides in the Atlantic is, at 600 feet across and 120 feet high, as big as the old Houston Astrodome. In 2009 the Canadian firm Nautilus Minerals, the leading seafloor-mining company, estimated that there are thousands of sulfide systems under the sea, with the potential to yield “several billion tons of copper” alone each year.

The specter of China vacuuming up whatever it can from the seafloor has alarmed many scientists and environmentalists: a 2004 science meeting on seafloor mining produced a long list of possible environmental impacts, including extinctions and decimating the base of food chains. Of particular concern is that sediment stirred up by mining could kill organisms that feed by filtering seawater. If the sediments form clouds in the water, says Lisa Speer, Beijing-based director of the International Oceans Program at the Natural Resources Defense Council, “it can create problems for the [vent] organisms, smothering them.”

That is especially worrisome given that many of those creatures live nowhere else on earth, are largely unknown to science, and have economic value that rivals the minerals’, says Rona. For instance, the microbes are sources of enzymes used in DNA fingerprinting, in detergents, to enhance the flow of oil from old wells, and to produce bioactive compounds that could prove effective against cancer or other diseases. “It would be a great loss to society if we destroyed for commercial benefit what society has not yet discovered,” says Sari Tolvanen, an oceans campaigner for Greenpeace. “It would be like going to a brand-new continent and mining the most valuable rainforests without first studying them.”

‘To the surprise of many scientists, however, the risk mining poses to the vent communities may be smaller than originally feared. For one thing, seafloor deposits are much more concentrated than those on land: at a site 3,000 feet down off Papua New Guinea called Solwara 1, where Nautilus expects to begin mining in 2012, deposits contain 6.7 percent copper. That compares with 0.46 percent for typical deposits on land. Pound for pound, seafloor ore also has more gold, zinc, and silver than land deposits do. That’s why seafloor mining should make economic sense in the first place. It’s also why, to extract a given quantity of metal, less material needs to be processed, which is the most environmentally destructive part of mining. (Processing requires toxic compounds and leaves vast piles of waste.) Seafloor mining might therefore be less destructive than mining on land, which brings such not-exactly-benign consequences as mountaintop removal, mercury pollution, and destruction of watersheds.

In addition, the “cutter suction” technology pioneered by Nautilus—some version of which China presumably would adopt—minimizes how much sediment is stirred up, says Samantha Smith, Nautilus’s environmental manager. Remote-controlled machines smash the sulfide deposits, which are then hoovered up through a riser pipe to a vessel on the surface. Although the process destroys the chimneys that encase the sulfide-rich plumes, the vents themselves survive. The challenge, says Duke’s Van Dover, “is to ensure that cumulative effects of mining activities do not exceed the rate of recovery of the organisms that rely on these habitats for survival.”

Another reason for optimism is that the vents can withstand disasters such as undersea volcanoes. A huge one near the East Pacific Rise erupted in 1991, releasing molten lava that basically paved the seafloor and choked off the geyser, obliterating the vent creatures. Yet microorganisms and larger animals recolonized the vent within two years, as larvae from neighboring vents arrived and set up housekeeping. (Of course, if larvae from a species different from the one wiped out arrive first, the new colony will differ from the original, with unknown consequences for deep-sea biodiversity.) That suggests a resilience that bodes well for recolonization after the mining operation moves on, too, though only for vents on tectonically active sites such as that where the eruption occurred. Vents such as those on the Mid-Atlantic Ridge, for example, are not likely to be frequently overrun by lava and are relatively far apart, suggesting they may be less resilient. Still, “vent organisms seem to be adapted to withstand relatively frequent natural and severe disasters,” says Van Dover. “Seafloor mining might be no worse than what nature delivers, though the effects of mining come on top of what nature does.”

The surest way to spare the vent creatures would be to mine only inactive vents, where the geysers have stopped and the ecosystem has died. Nautilus has not agreed to that, but says it will take steps to preserve vents. “We’ve put in place a number of measures to ensure that ecosystems and biodiversity are maintained,” says Smith. It plans to use undersea robots to move some vent animals away from the area being mined, establish refuges from which vent creatures can seed ecosystems recovering from mining, and allow one vent community to recover from mining before the company tackles adjacent sites.

China has not revealed whether it will take any vent-protecting steps. “[We are] not at the mining stage yet,” says Jin Jiancai, secretary-general of China Ocean Mineral Resources R&D Association, a government group. “We are currently in the prospecting research period, taking samples from the seabed [and doing] environmental assessments.” Doing years of top-secret engineering, too. Last month China unveiled a deep-sea submersible named Jiaolong, named for a mythical sea dragon, that can reach greater depths—23,000 feet—than any other. Last month the Jiaolong planted China’s flag on the floor of the South China Sea. Although the sub would probably not be used for mining—Nautilus’s crunch-and-suck method makes more sense—it is another sign of how serious China is about exploiting the last frontier.

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