Source: Science Magazine; Vol. 344 no. 6183 p. 463 

If all goes as planned, the world's first commercial deep-sea mine will open for business in 2016, with engineers deploying a trio of robots to claw high-grade copper and gold ore from the sea floor 1500 meters down off Papua New Guinea (PNG). Last week, after years of dickering, PNG's government and Canada-based Nautilus Minerals signed an agreement to move forward with the ambitious project. "We were very happy" to get the deal done, says Nautilus CEO Mike Johnston.

Critics aren't so pleased. Some marine biologists worry the mining will start before researchers can assess how it will affect deep-sea ecosystems. Others argue that national and international regulators aren't ready to ensure that underwater miners protect the environment. "The environmental impacts are unknown [and] the mining system is completely untested," said Effrey Dademo of ACT NOW!, a PNG group opposing the mine, in a statement.

For decades, such debates were largely academic, because mining at depths greater than 1000 meters was considered economically unworkable. But as technology advanced, Nautilus and other companies began prospecting. In some locations, the sea floor is littered with polymetallic nodules—hard, round masses of rock slowly precipitated from seawater and bearing iron, manganese, nickel, and other metals—that miners could scoop up with relative ease. In others, mineral-laden water gushing from hydrothermal vents has created rich outcrops. Although the vents are harder to mine, the payoff can be greater, because the deposits can include both precious metals and rare earth elements critical for computers, cellphones, and other modern technologies.

For its project, Nautilus has targeted a vent site known as Solwara 1, located near seafloor cracks created as two tectonic plates pull apart. Superhot fluids spew from deep in the crust, mixing with the cold seawater to form towers of ore-laden sediment known as "black smokers." Company surveyors say the area, covering about 11 hectares, is particularly rich in copper and gold.

It is also home to many kinds of sea creatures, including tubeworms and bivalves, according to environmental impact studies sponsored by Nautilus. But the company says it can mine without doing much long-lasting damage, in part by taking steps to control sediment plumes and relocate animal communities. The "overall effects [will be] reversible and moderate," says a 2008 company study, which predicts that seafloor populations would rebound within a few years after mining ended.

Opponents are skeptical, with some saying they doubt that the PNG government—which has a 15% stake in the project—has the technical expertise to conduct adequate and independent oversight. Oceanographer Cindy Van Dover of Duke University in Durham, North Carolina, who helped Nautilus conduct some of its preliminary studies, concedes that "there's no way to know what the impact" will be. Doing the studies that some scientists would like to see completed before mining begins would be expensive, she notes, with sustained seafloor research costing $80,000 a day or more. There are no concrete plans for major new environmental impact studies. "I don't know how to get to that happy place where the scientific community will let the mining go on and be confident that we will get the right amount of science," she says.

In the meantime, Nautilus says it plans to move ahead with outfitting a vessel to deploy its mining robots, including a 300-ton behemoth that will chew through the sea floor, and another that will pump a slurry of mineral-rich ore to the surface. It hopes to be operating within 30 months, Johnston says.

Nautilus may soon have company. Other nations, including Fiji, are negotiating seafloor mining rights. And the United Nation's little-known International Seabed Authority, based in Kingston, has already issued 19 permits for prospecting in international waters.