Researchers say the polymetallic nodules that mining companies hope to harvest from the seafloor could be a source of oxygen for the animals, plants and bacteria that live there.
The discovery of this “black oxygen” could well upend negotiations taking place this month in Jamaica, where a global rule-making 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 is currently and how much more we can gain through further scientific research,” said Diva Amon, a marine biologist from Trinidad and a postdoctoral researcher at UC Santa Barbara’s Benioff Ocean Initiative.
Interest is focused on potato-sized rocks – or polymetallic nodules – that are scattered across the seafloor. These nodules contain minerals, such as cobalt and nickel, needed for batteries and green energy technologies.
For years, companies like Canada’s The Metals Co. have been trying to persuade the international authority to green light their plans to mine the metal nodules in the Pacific Ocean’s Clarion Clipper Zone, a 4,500-mile stretch of sea between Hawaii and Mexico.
The company says the metals are essential for developing technologies that do not rely on fossil fuels. It says the impact of mining on the seabed is not only minimal, but is not comparable to the destruction of rainforests and human communities caused by land-based mining.
But environmentalists, oceanographers and other experts say moving big harvesting machines across the pristine, little-known seabed — above and along sediments three to four miles below the surface — could have unintended 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 consequences of mining in the region could be more severe than anyone could have imagined.
That’s because a team of international scientists has discovered that the precious nodules produce oxygen and could be responsible for enriching this dark, isolated ecosystem with one of the most important elements of life.
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 the TMC to conduct basic environmental studies, which included sending something called a benthic chamber to the ocean floor.
The structures, which he described as about 10 feet tall — “think of it like an upside-down box or something you sink into the seafloor,” Marlow said — are watertight and gas-tight and contain instruments designed to take measurements of sediment chemistry and composition.
The sampling method is pretty standard, he explained. Scientists measure how much oxygen is lost, or declining, over a 48-hour period that the chamber sits on the ocean floor. The decline serves as a measure of how much life is living there: When animals breathe, they consume oxygen.
But when they sent the chambers for this analysis, they noticed that the oxygen levels had increased, not decreased.
Marlow said they were certain the machine was faulty. They tried again and found the same results.
“These benthic chamber experiments have been done around the world for decades,” he said. “So the technology and everything else is pretty well established.”
He said they spent days, then weeks, resolving the problem.
“We had several redundant measurement methods, so we knew none of them were failing. Ultimately, we were forced to conclude” that oxygen was being produced.
Researchers believe the nodules – and the metals they contain – function like a battery, at a chemical level.
“These rocks are made up of minerals containing metals that are heterogeneously distributed throughout the rock,” he explained. “Each of these metals and minerals is able to hold an electrical charge in a slightly different way. So, essentially, just the natural variation means that there is a separation of charge… in the same way that you would find in a battery.”
This means there is enough voltage to take water and “split it into hydrogen and oxygen.”
But not everyone is convinced – or satisfied – by the study’s conclusion.
TMC, which sponsored the research, sent the Times a critique of the paper, saying the research had been rejected by four scientific journals before finding a home in Nature, which the company described as “a journal that has taken a strong stance against deep-sea mineral sourcing.”
A request for comment from the journal’s communications team went unanswered, but the periodical is generally considered one of the most prestigious and selective publications among scientists.
TMC also said the methodology was flawed, arguing that the team’s findings contradicted other work that had been conducted in the Clarion Clipper area but used a different method.
“This failure to reproduce the results with both methods suggests that the elevated oxygen levels are actually an artifact in the data,” the company said in a statement. The company said it is “currently preparing a peer-reviewed paper as a rebuttal.”
Bo Barker Jørgensen, a microbiologist at Aarhus University in Denmark who was not involved in the research or paid by TMC, said the work raised more questions than it answered.
He said he did not think “this discovery is important to our understanding of the ocean in general or to deep-sea mining” and described the research as a “new and very puzzling process for which the mechanism is still unclear.”
The study’s authors pushed back against the criticism, saying they too were intrigued by their findings but had been rigorous in eliminating all other possible scenarios.
“We were the biggest critics of this study for a long time,” said Andrew Sweetman, head of the deep-sea ecology and biogeochemistry research group at the Scottish Association for Marine Science and lead author of the study. “For eight years I dismissed the data showing oxygen production, thinking my sensors were faulty. Once we realised there might be something going on, we tried to disprove it, but in the end we just couldn’t.”
He said he wanted more research to be done on the subject and urged other scientists to conduct further research.
“Following the publication of this paper, other researchers contacted me with similar datasets also showing evidence of dark oxygen production which they dismissed as faulty equipment,” he said.
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