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Cover Story

How Will Underwater Mining Affect the Deep Ocean? Growing a Research Community to Find Out



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Just a handful of scientists are looking at how deep-sea mining could affect the chemistry of the ocean. USGS oceanographer Amy Gartman wants to change that.

Gartman is a member of the USGS Global Ocean Mineral Resources project, which seeks to understand how and where mineral-rich deposits form in the ocean, and what effects mining them could have on the deep-sea environment.

“Commercial deep-ocean mining will be underway within half a decade,” says the project leader, research geologist James Hein. Last September, Japan announced the successful extraction of ore from deep-water hydrothermal deposits off the coast of Okinawa. These deposits precipitate from mineral-laden water flowing out of deep-sea hot springs, sometimes called “black smokers” for the dark color of the billowing water. The deposits are attractive to nations and mining companies for their concentration of such metals as copper, zinc, gold, and silver. The pilot-scale mine off Okinawa demonstrated that “enough zinc can be recovered annually to meet Japan’s needs,” says Gartman.

Photo of dark clouds of mineral-laden water emerging from a hydrothermal vent on the Niua underwater volcano
Above: Mineral-laden water emerging from a hydrothermal vent on the Niua underwater volcano in the Lau Basin, southwest Pacific Ocean. As the water cools, minerals precipitate to form tower-like “chimneys.” Image taken during 2016 cruise “Virtual Vents.” Photo credit: Schmidt Ocean Institute, ROV ROPOS. [larger version]

Gartman recently succeeded Hein as a member of the U.S. delegation to the International Seabed Authority (ISA). The ISA is charged with implementing the Convention on the Law of the Sea, an international treaty governing the use of the oceans and their resources. The U.S. has not ratified the convention but attends ISA sessions as an observer nation. Hein, an internationally recognized expert in deep-ocean mineral deposits, has gone to yearly ISA meetings since 2000, when he began to teach workshops to ISA members. In 2007, the State Department invited him to become part of the U.S. delegation. In 2016, he brought Gartman along.

“I introduced Amy to numerous people and asked if she could take my place as scientific advisor to the U.S. Delegation to the Seabed Authority. I’m still their advisor on other matters,” says Hein.

Long-distance photo of the International Seabed Authority 24th Council meeting in a large auditorium
Above: Bird’s-eye view of the International Seabed Authority 24th Council, March 2018. Photo courtesy of ISA. [larger version]

Gartman attended her third ISA meeting last March. The member nations are currently developing regulations for exploitation of seabed resources in areas beyond national jurisdictions, called “the Area.” As science advisor, Gartman helps the U.S. delegates understand the nature and locations of different types of mineral deposits, and what environmental protections might be needed if they are mined. She sits with the delegates during ISA meetings, explaining the science of the topics under discussion, and she communicates with them throughout the year.

“For instance,” said Gartman, “in December the President issued an executive order (see “Presidential Executive Order on a Federal Strategy to Ensure Secure and Reliable Supplies of Critical Minerals”) on critical minerals—minerals essential to the Nation’s economy and security—and the delegates wanted to know which of those occur in the Area.”

Photo of a cross section of a hydrothermal vent chimney showing the center tube and layers of minerals surrounding it
Above: Cross section of a hydrothermal vent chimney from East Diamante Caldera in the Mariana volcanic arc, west Pacific Ocean, collected during a 2010 research cruise. Most of the sample is zinc sulfide. Silica lines the conduit through which the water flowed; a trace of iron imparts the yellow color. Photo credit: James Hein, USGS. [larger version]

Gartman does more than provide information to the U.S. delegates; she’s trying to grow the community of scientists studying the potential effects of deep-sea mining.

“There’ve been a lot of people who are trying, before mining commences, to categorize all the animals that live [near hydrothermal deposits], and how resilient they are,” says Gartman. Such animals include giant tube worms and snails, fish, and shrimp. “But there are not many scientists studying, for example, physical oceanography or microbiology in relation to marine mining—I think it’s important to get a broad swath of scientific expertise involved.”

To that end, Gartman has been networking with scientists at ISA and beyond. Just before the March ISA session, she assisted in a research cruise off San Diego run by researchers from Scripps Institution of Oceanography and the Massachusetts Institute of Technology (MIT). “They wanted to figure out how the [manganese] nodule-mining plume will behave in ocean water,” says Gartman.

Manganese nodules are another type of mineral deposit, different from the hydrothermal deposits recently test-mined by the Japanese. Typically, golf-ball to baseball size, nodules sit atop sediment on the abyssal plains of the global ocean. They grow slowly, over millions of years, by the accretion of iron and manganese oxides around a tiny nucleus, such as a large grain of sand, a shark’s tooth, or an older nodule fragment. Nickel, copper, cobalt, lithium, molybdenum, and manganese are among the metals they concentrate from seawater.

Photo of a labeled arrangement of manganese nodules taken from the linked report
Above: Manganese nodules from the deep seafloor off the Cook Islands in the southwest Pacific Ocean. Alternating black-and-white squares are 1 centimeter on a side. From a paper by James Hein and others. [larger version]

The techniques envisioned for harvesting nodules would create plumes of sediment—first as a harvesting machine scoops them up, and, for some operations, later as sediment cleaned from the nodules is released back to mid-waters or the deep seabed. When the sediment particles settle down to the ocean floor, organisms, particularly immobile ones, could be covered and killed. The cruise out of San Diego sought to better understand how the plumes might behave. The team released artificial sediment plumes and then imaged them using 3D sonar techniques to track how they spread and settle.

“I went to help out with fluid sampling,” says Gartman. “If you want to know the effects of the plume, you need to not just model its physical behavior, but understand its chemical behavior.”

Gartman collected seawater samples for Anela Choy, a biological oceanographer with the Monterey Bay Aquarium Research Institute who studies deep-sea food webs. Choy will analyze the samples for carbon and nitrogen isotopes to see how plumes might affect plankton—organisms floating in the water that rely on these nutrients. Impacts on plankton, which form the base of the marine food web, could have wide-reaching effects on ocean life. 

Although the March cruise took place off San Diego, the scientists made some of the artificial plumes with mud from the Clarion-Clipperton Zone, a vast expanse of the deep Pacific seafloor that is likely to be the first area mined for nodules. Gartman obtained a container of the mud, which she plans to study in collaboration with Phoebe Lam, a geochemist at the University of California, Santa Cruz.

Photo of a container of brown, lumpy mud from the Clarion-Clipperton Zone
Above: Container of mud from the Clarion-Clipperton Zone, an expanse of the deep Pacific seafloor rich in manganese nodules. Amy Gartman (USGS) and Phoebe Lam (University of California, Santa Cruz) will study chemical interactions between the mud and metals in seawater. Photo credit:  Amy Gartman, USGS. [larger version]

Gartman and Lam want to determine whether metals from seawater will attach to clay particles in mud stirred up by mining. Such “metal sorption reactions” would take metals out of the surrounding water. “But some nodules are likely to be broken up a bit during mining,” says Gartman, which would release metals. “So, it’s an open question,” she says, “whether nodule mining is more likely to add metals to seawater or remove them.”

The answer matters because metals, such as iron, “are micronutrients,” says Gartman. “You think of the big nutrients that nothing can live without—like nitrogen and carbon and phosphorous. But once those needs are met, just like people get anemic, phytoplankton can’t grow without iron.” Gartman and Lam’s study will shed light on how nodule mining is likely to affect the seawater concentration of these important micronutrients.

Lam is also involved in the International GEOTRACES program, which is mapping the distribution of trace elements and isotopes in the ocean and researching the processes that control their distribution. A GEOTRACES cruise scheduled for September will cross the western edge of the Clarion-Clipperton Zone on a long traverse from Alaska to Tahiti. Gartman notes that the cruise will “collect great trace-metal base-line data in the CCZ before mining starts.”

Graphic map of the Pacific Ocean, showing locations of Clarion-Clipperton Zone (CCZ), the Mariana Arc, Lau Basin, and the Cook Islands
Above: Pacific Ocean, showing locations of Clarion-Clipperton Zone (CCZ), the Mariana Arc, Lau Basin, and the Cook Islands. Planned path of September GEOTRACES cruise (dashed line) passes through the western part of the Clarion-Clipperton Zone. Base from USGS Coastal and Marine Geology Program Interactive Maps. [larger version]

In working to engage other scientists in research on deep-sea mining effects, Gartman is following in the footsteps of a pioneer deep-sea scientist at Duke University. “In 2010, I was at a meeting with Cindy Van Dover, one of the foremost hydrothermal marine biologists, and the only woman to date to have piloted the submersible ALVIN.” Van Dover had been hired by Nautilus Minerals, a company working to develop deep-sea mining capabilities, to do some background biological assessments prior to mining. She could see that the development of a marine mining industry would require scientific input, and she urged other scientists, like Gartman, to get involved.

Photo of Amy Gartman standing in front of an X-ray diffractometer while analyzing samples of hydrothermal sulfide minerals
Above: Amy Gartman waits for an X-ray diffractometer to analyze samples of hydrothermal sulfide minerals. Photo credit: Amy West, USGS contractor. [larger version]

 “My Ph.D. project dealt with the oxidation of sulfide minerals at hydrothermal vents.” Sulfide minerals are crystalline compounds that combine the element sulfur with other elements, most commonly metals. One example is the mineral pyrite, or “fool’s gold,” which combines iron with sulfur (FeS2). “Iron from vents is found mainly in sulfides,” says Gartman, “and our work showed that the rate at which the sulfides oxidize [react with oxygen in the seawater] could act as a time-release, introducing the iron slowly to the oceans.”

 “I realized that my work was directly relevant to deep-sea mining, and nobody else was doing it. If we’re going to think about mining sulfide deposits, we should know the rates at which [iron and other] metals will enter the oceans, and how far these metals will travel and what the effect on life might be.”

Now at the USGS, Gartman is continuing her work on the “seafloor massive sulfide” deposits that form at hydrothermal vents. The technique for mining these deposits involves crushing them and pumping the slurry of particles up to the ship. This crushing will release a new class of particles, different from the natural ones in hydrothermal “black smoke.” Gartman is studying both types of particles, contrasting what the two types are made of and the rates at which they release metals. She is focusing on the minerals covellite, sphalerite, and chalcopyrite, the latter two being among the main minable ores in hydrothermal deposits. She's also looking at trace minerals, like bismuth-telluride and gold, that exist in low concentrations in these systems and may be toxic, technologically important, or useful as clues to how the deposits formed.

Close-up photo of several sulfide minerals that occur at hydrothermal vents
Above: Examples of sulfide minerals that occur at hydrothermal vents and are being studied by Amy Gartman: (left to right) sphalerite, an ore of zinc that often contains iron ([Zn,Fe]S); cubes of pyrite, rich in iron (FeS2); and covellite, containing copper and sulfur (CuS).The pyrite cubes are a little more than half an inch on a side. Photo credit: Helen Gibbons, USGS [larger version]

As Gartman and her colleagues advance their studies of potential deep-sea mining effects, they’ll keep trying to interest other researchers. “I think most scientists want their work to have societal relevance,” she says, “and so they tend to be pretty receptive. We just talk to people and try to engage them.”

Related Sound Waves Stories
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Unusual Mineral Deposits Record the Unique History of the Arctic Ocean
Nov. - Dec. 2017
USGS Science Enriched by Mendenhall Research Fellows
March 2017

Related Websites
Global Ocean Mineral Resources
USGS
Virtual Vents Research Cruise
Schmidt Ocean Institute
International Seabed Authority 24th Council
ISA
Presidential Executive Order on a Federal Strategy to Ensure Secure and Reliable Supplies of Critical Minerals
White House Executive Order
Layered Hydrothermal Barite-Sulfide Mound Field, East Diamante Caldera, Mariana Volcanic Arc
Economic Geology
Scripps-Led Research Team to Study Sediment Plumes at Sea
Scripps Institution of Oceanography
Critical metals in manganese nodules from the Cook Islands EEZ, abundances and distributions
Ore Geology Reviews
Anela Choy
SOEST
Clarion-Clipperton Zone
ISA
Phoebe Lam
UCSC
GEOTRACES program
GEOTRACES
Coastal and Marine Geology Program Interactive Maps
USGS
Cindy Van Dover
Duke University
First Observation of Gold Particles in Hot Hydrothermal Fluids
USGS News

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