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USGS oceanographer Amy Gartman and team seek to understand how and where mineral-rich deposits form in the ocean, and what effects mining them could have on the deep-sea environment.

This article is part of the April-May 2018 issue of the Sound Waves newsletter.  

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 Marine 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.

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.

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.”

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.”

Very crusty rock with tan outer layer, gray core, and bright yellow center. Man's booted foot is in background.
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.

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.

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.”

Collage of black nodules or rocks of varying sizes and shapes arranged next to one-inch scales, from one inch wide to 7 or so.
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 article in Ore Geology Reviews by James Hein and others, 2015.

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.

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.”

Container of mud from the Clarion-Clipperton Zone
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.

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.

“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.

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.”

sphalerite, cubes of pyrite, and covellite
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.
Amy Gartman waits for an X-ray diffractometer
Amy Gartman waits for an X-ray diffractometer to analyze samples of hydrothermal sulfide minerals. 
 Locations of Clarion-Clipperton Zone
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.

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