New studies say: Deep-ocean floor produces its own ‘dark oxygen’

Recent studies have revealed a fascinating discovery about the deep-ocean floor - it produces its own 'dark oxygen'. This phenomenon challenges our understanding of oceanic ecosystems and has significant implications for climate change research. The findings, published in the journal Nature Geoscience, shed light on a previously unknown process that occurs in the depths of the ocean.

The traditional view was that oxygen in the deep ocean was solely derived from photosynthesis at the surface. However, researchers have now found evidence of a new source of oxygen production occurring on the ocean floor. This 'dark oxygen' is generated through chemical reactions involving organic matter and minerals in deep-sea sediments. The implications of this discovery are far-reaching, as it suggests that deep-sea ecosystems may be more complex and self-sustaining than previously thought.

Andrew Sweetman, of the Scottish Association for Marine Science (SAMS), made the “dark oxygen” discovery while conducting ship-based fieldwork in the Pacific Ocean. Northwestern’s Franz Geiger led the electrochemistry experiments, which potentially explain the finding.

“For aerobic life to begin on the planet, there had to be oxygen, and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” said Sweetman, who leads the Seafloor Ecology and Biogeochemistry research group at SAMS. “But we now know that there is oxygen produced in the deep sea, where there is no light. I think we, therefore, need to revisit questions like: Where could aerobic life have begun?”

Scientists made the discovery while sampling the seabed in the Clarion-Clipperton Zone, a ridge extending 4,500 miles across the eastern Pacific. When they discovered oxygen 13,000 feet underwater, in areas so dark that photosynthesis would be impossible, they initially thought their equipment had malfunctioned. Eventually, they came to suspect the polymetallic nodules were a source of this “dark” oxygen.

When combined with saltwater, rust can generate electricity, enough to liberate the oxygen atom from a molecule of water. Researchers thought nodules may serve the same function, and so they tested them in a lab. One nodule, they found, could produce close to 1 volt of electricity. When clustered together, nodules could generate enough electricity to split seawater.

This means, they say, that the nodules sitting on the seabed could generate electric currents large enough to split, or electrolyse, molecules of seawater.

The researchers think the same process - battery-powered oxygen production that requires no light and no biological process - could be happening on other moons and planets, creating oxygen-rich environments where life could thrive.

"In 2016 and 2017, marine biologists visited sites that were mined in the 1980s and found not even bacteria had recovered in mined areas," Geiger said. "In unmined regions, however, marine life flourished. Why such 'dead zones' persist for decades is still unknown. However, this puts a major asterisk onto strategies for sea-floor mining as ocean-floor faunal diversity in nodule-rich areas is higher than in the most diverse tropical rainforests."

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Sarah H

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