Scientists Discover ‘Dark Oxygen’ on Seafloor, Challenging Ideas on the Origin of Life

Scientists have discovered “dark oxygen” being created on the ocean seafloor by “polymetallic nodules” that potentially support life, new research in the journal Nature Geoscience shows.

Andrew Sweetman, the study’s lead author and member of the Scottish Association for Marine Science (SAMS), believes the nodules create oxygen because they behave like natural batteries. “If you put a battery into seawater, it starts fizzing,” Sweetman told the BBC. “That’s because the electric current is actually splitting seawater into oxygen and hydrogen [which are the bubbles]. We think that’s happening with these nodules in their natural state.”

Scientists dubbed it “dark oxygen” because, as opposed to photosynthesis, which was previously thought to be responsible for the bulk of oxygen creation in the ocean, the production of dark oxygen doesn’t require sunlight. In fact, the nodules that seem to create it are far deeper than light can penetrate.

The discovery calls into question how big of a part dark oxygen truly plays in our oceans, and has the potential to completely reshape our understanding of the origin of life.

Sweetman first felt something was off in 2013 during fieldwork in the Clarion–Clipperton Zone, a mineral-rich area between Hawaii and Mexico, according to Nature. The team sent down a module to create “an enclosed microcosm of the seafloor,” the authors wrote, where they discovered oxygen. 

This by itself wasn’t outside the ordinary: oxygen had been detected this deep in the ocean before, carried down by currents. However, while oxygen levels usually taper off when enclosed, the oxygen levels here had increased.

Sweetman thought it was a sensor malfunction until he had similar results years later. “I suddenly realized that for eight years I’d been ignoring this potentially amazing new process, 4,000 metres down on the ocean floor,” Sweetman told Nature.

Scientists aren’t the only ones interested in these nodules, however. Because they are covered in lithium, copper, nickel and other valuable metals used for goods like batteries and electric vehicles, multiple companies have been researching deep-sea mining to exploit the nodules, including Global Sea Mineral Resources, The Metals Company, Lockheed Martin and others.

Deep-sea mining is a controversial practice, however, because it has been linked with biodiversity loss and destruction of habitats.

Sweetman believes that dark oxygen could be supporting life on the seafloor and opposes deep sea mining near these modules. “If there’s oxygen being produced in large amounts, it’s possibly going to be important for the animals that are living there,” he told Nature.

Sweetman and the other researchers also wonder whether this same process could be happening on other planets or moons, potentially supporting life.

“If the process is happening on our planet, could it be helping to generate oxygenated habitats on other ocean worlds such as Enceladus and Europa and providing the opportunity for life to exist?” Sweetman said to The Guardian.