The Sully hydrothermal vent in the northeastern Pacific Ocean is home to tubeworms, a form of life found only in these vents on the seafloor.

Credit: NOAA PMEL EOI Program

Another gold rush is on the way. It’s not in California, a developing country or even on asteroids.

It’s under the sea.

There’s a lot of gold there. So much gold, in fact, that every person on Earth could get 9 pounds of it. That’s the equivalent of about $150 trillion in today’s prices, or about $21,000 a person. Along with the gold, there’s manganese, copper and rare earth metals – those precious substances that power our smartphones and computers.

So why hasn’t this sunken treasure surfaced yet? Deep-sea mining is extremely expensive and extremely difficult. But higher prices for metals and advances in oil and gas drilling are paving the way. The first deep-sea mine could begin operations as soon as 2017.

The potential for profit is great, but so are the environmental risks. The deep ocean is one of the least-understood ecosystems on earth. So how can we accurately predict (and mitigate) the risks of deep-sea mining?

Here’s a look at the big questions facing the next gold rush.

How does deep-sea mining work?

There are three main ways to get minerals from deep-sea mines:

Vacuuming up manganese clusters: Rocky clumps containing manganese and iron – called “nodules” – litter the ocean floor beneath a blanket of silt. Remote-controlled vacuums can suction them up and deliver them to the surface.

Breaking up seafloor crust: Underwater ridges and mountains are rich with minerals and metals, especially cobalt. They’re also home to ancient and slow-growing coral. To get the cobalt, remote-controlled robots drive along the ocean floor and grind up the crust. The robots deliver the mixture to a lift system, which pipes it up to a ship on the surface.

Collecting deposits near hydrothermal vents: When hot water spewing from hydrothermal vents hits the surrounding cold water, minerals and metals dissolved in the hot water condense and fall to the seafloor. Remote-controlled vehicles collect these deposits (usually copper, gold and silver) and pipe them up to the surface. Vents are home to creatures found nowhere else on Earth, like giant tubeworms and bacteria, that survive by converting carbon dioxide into energy for survival.

What are the risks?

No one really knows, and that’s the biggest problem. Deep-sea mining on a commercial scale has never been done before. Scientists don’t know much about the deep sea to begin with. Without that understanding, it’s hard to know how mining would affect the seafloor ecosystem. How many species of flora and fauna are there? How are they interconnected? How resilient are they?

“This mining, when it occurs, is going to be just massive in scale,” Craig Smith, a University of Hawaii oceanographer, told Honolulu Civil Beat. “It probably will have the largest footprint of any single human activity on the planet.”

Deep-sea mining could have environmental effects ranging from the air above the ocean down to the floor of the sea:

Surface: Ships make a lot of noise and their mining equipment will cause of a lot of vibration. Plus, there’s always the potential for fuel leakage and added air pollution.

Shallow waters: Tubes ferry crushed rock and water from the seafloor to the surface, where equipment on a ship removes the water and dumps it back into the ocean. That water, though, is a different temperature and composition from the rest of the surface water.

That dumped water can create clouding. Cloudy surface water is a big deal because phytoplankton would lose their access to the sun. As the basis of the entire marine food chain, phytoplankton use the sun to make their own food. If something happens to them, it would throw the entire food chain for a devastating loop.

Seafloor habitats: Plants and animals on the ocean floor live in perpetual darkness. Mining will shine a light on them for the first time. Robots also will bring new sounds and vibrations. We don’t know how the organisms will react to these unfamiliar stimuli. Crusher robots will sweep up at least some plants and animals into their rock grinders, and robots vacuuming nodules will certainly disturb layers of silt. That can create plumes of sediment, which could choke seafloor creatures that feed by filtering food particles out of the water.

What’s happening right now?

Companies have managed to successfully mine shallow parts of the ocean for several decades. For example, De Beers has gotten some of its diamonds from the shallow waters off the coast of southwest Africa since the 1960s.

But earlier this year, Papua New Guinea and Canada’s Nautilus Minerals Inc. reached the first-ever commercial agreement for deep-sea mining in Papua New Guinea’s national waters, to much criticism. The company is on track to begin operations by 2017.

Seabeds under international waters also are up for grabs. There’s even an International Seabed Authority, established by the United Nations in 1982 to oversee the ocean floor. It granted the first mine exploration licenses in the early 2000s. This year alone, it granted seven new licenses. A total of 26 private and state-owned companies now hold exploration licenses that cover more than 1.2 million square kilometers of international waters. The bulk of the licenses are for a zone in the Pacific Ocean the size of the United States. Other licenses cover areas in the Atlantic and Indian oceans.

The seabed authority has developed regulations for exploration but it hasn’t yet solidified regulations for actual mining. While governments and private companies scramble for a piece of the ocean floor, others are making a renewed push for expanded ocean sanctuaries, free from deep-sea mining and commercial fishing. President Barack Obama created the world’s largest marine reserve in the Pacific Ocean in September.

Regardless, the deep-sea gold rush is on: An analysis from the Massachusetts Institute of Technology predicts deep-sea mining will be widespread by 2040.

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This story was edited by Andrew Donohue and copy edited by Sheela Kamath.

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Rachael Bale is a reporter and researcher for The Center for Investigative Reporting. Previously, she worked at KQED in San Francisco and The Center for Public Integrity, an investigative journalism nonprofit in Washington, D.C., where she covered campaign finance in the 2012 election. A California native, she has a bachelor's degree in political science from Reed College and a master's degree in journalism from American University.