Scientists explore ‘dark oxygen’ in deep-sea mining zones

Scientists will launch instruments to the seafloor to find out how metal knots generate oxygen in the depths of the Pacific Ocean, an unexpected phenomenon that has fueled controversy over deep-sea mining.

To their surprise, scientists discovered in 2024 that potato-sized nodules in the darkness of the Pacific and Indian oceans, including the Pacific Clarion-Clipperton Zone, were the source of oxygen, even though it was thought that sunlight and photosynthesis were needed to produce the element on a large scale.

This so-called dark oxygen could support life in the dark at depths of thousands of meters, including microbes, sea cucumbers and carnivorous anemones. His discovery raised questions about proposals by deep-sea mining companies to suck up nodules from the seabed and smelt them for cobalt, nickel and manganese. The find was controversial deep-sea mining companies and other scientists have also demanded more evidence.

Now, the scientists who discovered dark oxygen are returning to the Clarion-Clipperton Zone, the most promising area for deep-sea mining, to try to confirm the existence of this dark oxygen and understand how it is produced.

“Where does the oxygen come from for these diverse animal communities to thrive?” Andrew Sweetman at the Scottish Association for Marine Science, which is leading the expedition, told a news conference. “It can be quite a significant process, and that’s what we’re trying to figure out.”

The team hypothesized that the layers of metals in the nodes generate an electric current that can split seawater into hydrogen and oxygen. They measured up to 0.95 volts of electricity on the surface of the nodes, which is slightly less than an AA battery.

This is less than the 1.23 volts that would normally be required for this electrolysis, but the researchers believe that some individual nodes or several nodes grouped together could generate a higher voltage.

The team will deploy landers — essentially metal frames with instruments inside — at depths of up to 10,000 meters to measure oxygen fluxes as well as pH, as electrolysis would eject protons that make the water more acidic.

The landers will also retrieve sediment cores and nodules for analysis later in the lab, as microscopic organisms may also play a role. Each nodule contains up to 100 million microbes, and scientists will try to identify the microbes using DNA and RNA sequencing and fluorescence microscopy.

“The enormous diversity of microbes remains a moving target. We are still discovering new species,” said a team member Jeff Marlow at Boston University. “Are they active? Are they shaping their environment in interesting and important ways?”

They will also recreate deep-sea conditions in a high-pressure reactor and perform electrolysis in it, as electrolysis has not usually been observed under intense pressures on the sea floor.

“Four hundred atmospheres of pressure, that’s the pressure at which the Titan sub imploded,” he said Franz Geiger at Northwestern University in Illinois, another team member. “We are interested in how water splitting may or may not be efficient at high pressure.”

The ultimate goal is to try to perform an electrochemical reaction under an electron microscope with the microbes and bacteria present, all without killing the microscopic organisms, he added.

While the United Nations’ International Seabed Authority has not decided whether deep-sea mining should be allowed in international waters, US President Donald Trump has pushed for drilling to begin. The Canadian firm The Metals Company has applied to the US government for permission to start deep mining.

ON paper published by scientists at The Metals Company claimed that Sweetman and his colleagues did not find enough energy to power the electrolysis of seawater in 2024, and that the oxygen they observed was likely carried from the surface by the landers they deployed.

Sweetman says that all the surface air bubbles float up as the landers descend, and when deployed in other areas of the ocean, such as the Arctic seafloor, they didn’t measure oxygen at 4,000 meters. Of the 65 experiments conducted at the Clarion-Clipperton Zone, 10 percent detected oxygen consumption and the rest detected oxygen production, according to Sweetman.

He and his colleagues also discovered that part of the water oxidation electrolysis process can occur at the lower voltages found at the nodes. A rebuttal containing this information has been submitted Natural geosciences and is currently undergoing peer review.

“As a commercial interest, there’s certainly an interest in trying to silence this area of ​​work,” Sweetman said of The Metals Company’s objections to his findings.

“Regardless of the source and motivation of the comments, they need to be addressed,” Marlow said. “That’s what we’re in for. [the] process of doing.”

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