Mystery oxygen source discovered on the sea floor — bewildering scientists || A chemical reaction could be producing oxygen by splitting water molecules, but its source of energy remains unknown.

Something is pumping out large amounts of oxygen at the bottom of the Pacific Ocean, at depths where a total lack of sunlight makes photosynthesis impossible.

The phenomenon was discovered in a region strewn with ancient, plum-sized formations called polymetallic nodules, which could play a part in the oxygen production by catalysing the splitting of water molecules, researchers suspect.

“We have another source of oxygen on the planet, other than photosynthesis,” says study co-author Andrew Sweetman, a sea-floor ecologist at the Scottish Association for Marine Science in Oban, UK — although the mechanism behind this oxygen production remains a mystery. The findings could also have implications for understanding how life began, he says, as well as for the possible impact of deep-sea mining in the region.

Sweetman and his collaborators first noticed something amiss during field work in 2013. The researchers were studying sea-floor ecosystems in the Clarion–Clipperton Zone, an area between Hawaii and Mexico that is larger than India and a potential target for the mining of metal-rich nodules.

“I suddenly realized that for eight years I’d been ignoring this potentially amazing new process, 4,000 metres down on the ocean floor,” says Sweetman.