The Mysterious Discovery of ‘Dark Oxygen’ on the Ocean Floor

Researchers believe they have discovered oxygen being produced 4,000 meters below the sea surface, and think polymetallic nodules—the sought-after bounty of deep-sea miners—could be the source.

For more than 10 years, Andrew Sweetman and his colleagues have been studying the ocean floor and its ecosystems, particularly in the Pacific’s Clarion-Clipperton Zone, an area littered with polymetallic nodules. As big as potatoes, these rocks contain valuable metals—lithium, copper, cobalt, manganese, and nickel—that are used to make batteries. They are a tempting bounty for deep-sea mining companies, which are developing technologies to bring them to the surface.

The nodules may be a prospective source of battery ingredients, but Sweetman believes they could already be producing something quite different: oxygen. Typically, the element is generated when organisms photosynthesize, but light doesn’t reach 4,000 meters below the ocean’s surface. Rather, as Sweetman and his team at the Scottish Association for Marine Science suggest in a new paper, the nodules could be driving a reaction that produces this “dark” oxygen from seawater.

Sweetman first noticed something strange in 2013. With his team, he’d been working to measure oxygen flow in confined areas within nodule-rich areas of the seabed. The flow of oxygen seemed to increase at the seafloor, despite the fact that there were no photosynthesizing organisms nearby, so much so that the researchers thought it was an instrumental anomaly.

The same finding, however, was repeated in 2021, albeit using a different measurement approach. The scientists were assessing changes in oxygen levels inside a benthic chamber, an instrument that collects sediment and seawater to create enclosed samples of the seabed environment. The instrument allowed them to analyze, among other things, how oxygen was being consumed by microorganisms within the sample environment.

read more at wired.com.