Deep Sea Nodules Uncovered as Surprising Oxygen Source

Metallic nodules scattered across the floor of the Indian and Pacific Oceans provide a source of oxygen for nearby marine life, a discovery that could upend our understanding of the deep ocean.

In some areas, the abyssal plains are dotted with potato-sized nodules rich in valuable cobalt, manganese and nickel that are targets for deep-sea mining activities.

Andrew Sweetman Researchers from the Scottish Institute for Marine Science in Oban, UK, were conducting research in the Clarion-Clipperton Zone of the Pacific Ocean (a region rich in nodules) in 2013 when they first noticed something odd about these waters.

Sweetman and his colleagues sent a machine to the ocean floor, sealed off a 22-square-centimeter section of the seafloor, and measured the flow of oxygen. Far from decreasing, the data suggested that oxygen content was actually increasing in the monitored areas.

But in the absence of any noticeable vegetation, Sweetman says, that didn’t make sense. “I was taught from an early age that oxygen-rich ecosystems were only possible through photosynthesis,” he says. He came to the conclusion that the machine he was using was flawed. “I literally ignored the data,” he says.

Then, in 2021, Sweetman went on another research cruise in the Pacific Ocean, and the machine made the same discovery: elevated oxygen levels at the ocean floor, even using a different measurement method.

“We were seeing the same oxygen production in these two different data sets,” Sweetman says, “and suddenly we realized that we’d been ignoring this incredibly innovative process for the last eight or nine years.”

He and his colleagues speculated that the metal nodules must play a role in boosting oxygen levels in the deep ocean, and laboratory tests of contaminating sediments and nodules ruled out the presence of oxygen-producing microorganisms.

Instead, Sweetman says the material in the nodules acts as a “geo-battery,” generating an electrical current that splits seawater into hydrogen and oxygen. “The reason these nodules are mined is because they contain everything you need to make electric car batteries,” he says. “What if the nodules themselves were acting as natural geo-batteries?”

When the team examined the rocks, they found that each nodule generated an electrical potential of up to 1 volt — when they combined together they could generate enough voltage to electrolyze seawater into hydrogen and oxygen, explaining why oxygen levels rise.

“We may have discovered a new natural source of oxygen,” Sweetman said, “We don’t know how widespread it is in time and space, but it’s very intriguing.”

Many questions remain unanswered. For example, the source of energy that creates the current remains a mystery. It’s also unclear whether the reaction occurs continuously, under what conditions, or how this oxygen contributes to maintaining the surrounding ecosystem. “We don’t have all the information yet, but we know it’s happening,” Sweetman says.

In deep-sea environments without sunlight or vegetation, some life forms get their energy from chemicals spewing from hydrothermal vents on the ocean floor. Some scientists believe life on Earth first emerged at these vents, but these early organisms would have needed a source of oxygen to make food from inorganic compounds. The new discovery suggests that the nodules could have been the oxygen source that helped life begin, Sweetman said.

That interpretation may be unreasonable, Donald Canfield The University of Southern Denmark researcher points out that oxygen is needed to produce the manganese oxides found in nodules. “Oxygenic photosynthesis is a prerequisite for the formation of nodules,” he says. “Therefore, oxygen production by nodules is not an alternative oxygen production equivalent to oxygenic photosynthesis. It is highly unlikely that nodules played a role in oxygenating the Earth.”

but, Ruth Blake The Yale researchers say the idea of ​​producing oxygen in the deep sea remains “exciting” and that further study is needed into the phenomenon and its potential impact on deep-sea ecosystems.

Sweetman’s research was funded in part by The Metals Company (TMC), a deep-sea mining company that is targeting metal nodules in the Clarion-Clipperton field. Patrick Downs TMC’s Downs said he had “serious concerns” about the findings, adding that his company’s analysis suggested Sweetman’s results were due to outside oxygen contamination. “We intend to write a rebuttal,” Downs said in a statement. New Scientist.

But the findings are likely to strengthen calls for a ban on deep-sea mining, backed by many oceanographers who say their understanding of these regions is still evolving. Paul Dando Researchers from the British Marine Biological Society said the paper reinforced the view among deep-sea scientists that “we shouldn’t mine these nodules until we understand their ecology”.

Sweetman said the discovery isn’t necessarily a “say-tale” move for deep-sea mining, but it could limit mining in places where oxygen production is low, and more research is needed to explore how sediments disturbed by the mining process affect oxygen production, he said.