The polymetallic nodules that mining companies hope to harvest from the deep sea floor could provide a source of oxygen for the animals, plants and bacteria that live there, researchers say.
The discovery of this “dark oxygen” could shake up negotiations taking place this month in Jamaica, where a global regulatory body, the International Seabed Authority, is meeting to decide the future of deep-sea mining.
The work was recently published in the journal Nature Geoscience.
“This study is a great example of how limited our knowledge of the deep ocean currently is and how much we can still benefit from further scientific research,” said Diva Amon, a Trinidadian marine biologist and postdoctoral researcher with UC Santa Barbara’s Benioff Ocean Initiative.
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The excitement is focused on the potato-sized rocks — or polymetallic nodules — that litter the ocean floor. These nodules contain minerals, such as cobalt and nickel, that green-energy batteries and technologies need.
Companies like Canada’s The Metals Co. have been trying for years to convince international regulators to approve their plans to mine these metal nodules in the Clarion Clipper Zone in the Pacific Ocean, a 7,200-kilometer-long stretch of sea between Hawaii and Mexico.
The company has argued that the metals are essential for construction technologies that do not rely on fossil fuels. They say that the impact mining will have on the ocean floor is not only minimal, but also incomparable to the destruction of rainforests and human communities that land mining causes.
But environmentalists, oceanographers and others say driving large harvesters across the pristine, little-known ocean floor — on top of and along sediment areas three and four miles below the surface — could have unforeseen and disastrous consequences. They are urging lawmakers to delay or ban the industry from digging up one of the planet’s last “pristine” ecosystems.
This new research, funded by TMC, suggests that the toll of mining in the area could be greater than anyone imagined.
That’s because a team of international scientists has discovered that the precious nodules produce oxygen, and may be responsible for enriching this dark, remote ecosystem with one of life’s most important elements.
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Jeffrey Marlow, an assistant professor of biology at Boston University and one of the paper’s authors, said he and his team received funding from TMC to conduct basic environmental studies, including sending a so-called benthic chamber to the ocean floor.
These structures, which he described as about 3 meters tall — “imagine it’s like an overturned box or something you stick in the seabed,” Marlow said — are watertight and gas-tight, and contain instruments designed to take measurements of the chemistry and composition of the sediment.
The sampling method is fairly standard, he said. Scientists measure the amount of oxygen lost, or diminished, over a 48-hour period while the chamber sits on the ocean floor. The decline serves as a proxy for the amount of life down there — as animals breathe, they consume oxygen.
But when they sent the rooms down for this analysis, they saw that the oxygen levels went up, not down.
Marlow said they were sure the machine was defective. They tried again and saw the same results.
“These benthic chamber experiments have been done all over the world for decades,” he said. “So the technology and everything is pretty well established.”
He said they spent days and then weeks trying to solve the problem.
“We had a few redundant ways of measuring it, so we knew none of them were failing. Ultimately, we had to conclude” that oxygen was being produced.
According to the researchers, the nodules – and the metals within them – act like a kind of battery, at a chemical level.
“These rocks are made up of minerals with metals that are … distributed throughout the rocks in heterogeneous ways,” he said. “Each of these metals and minerals can hold an electrical charge in a slightly different way. So essentially, just the natural variation means that there is charge separation … in the same way that you would in a battery.”
This means that there is enough voltage to split water into hydrogen and oxygen.
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But not everyone is convinced by the study’s conclusion, or is happy with it.
TMC, the study’s sponsor, sent The Times a critique of the article, saying the study had been rejected by four scientific publications until it found a home at Nature, which the company described as “a journal fiercely opposed to deep-sea mineral extraction.”
The journal’s communications team did not respond to a request for comment, but the journal is generally considered one of the most prestigious and selective publications among scientists.
TMC also said the methodology was flawed, saying the team’s findings contradicted other work done in the Clarion Clipper Zone that used a different methodology.
“This inability to reproduce the findings with either method suggests that elevated oxygen levels are in fact an artifact in the data,” the company said in a statement, noting that it was “currently preparing a peer-reviewed rebuttal paper.”
Bo Barker Jørgensen, a microbiologist at Denmark’s Aarhus University who was not involved in the research and was not on TMC’s payroll, said the work raised more questions than it answered.
He said he does not think “this discovery is important for our understanding of the ocean in general or for deep-sea mining” and described the research as a “novel and very enigmatic process whose mechanism is still not clear.”
The study authors rejected the criticism, saying that they too were surprised by the findings but that they had been rigorous in ruling out all other possible scenarios.
“We were the harshest critics of this paper for a long time,” said Andrew Sweetman, leader of the Seafloor Ecology and Biogeochemistry research group at the Scottish Assn. for Marine Science and lead author of the paper. “For eight years I ignored the oxygen production data because I thought my sensors were faulty. When we realised there was something going on we tried to debunk it, but in the end we just couldn’t.”
He said he welcomed more research into the topic and urged other scientists to do so as well.
“After the publication of this paper, other researchers came to me with similar datasets, which also provided evidence for the production of dark oxygen. They discarded these datasets because they thought the equipment was faulty,” he said.
This story originally appeared in the Los Angeles Times.