This story was originally Published in WIRED Italia and translated from Italian.
For more than a decade, Andrew Sweetman and his colleagues have studied the seafloor and its ecosystems, particularly in the Pacific Ocean’s Clarion-Clipperton Belt, an area dotted with polymetallic nodules. These potato-sized rocks contain valuable metals used in making batteries, including lithium, copper, cobalt, manganese, and nickel. They’re an attractive treasure for deep-sea mining companies, which are developing the technology to bring them to the surface.
While nodules might be a promising source of raw materials for batteries, Sweetman thinks they might already be producing something else entirely: oxygen. Oxygen is normally produced by organisms during photosynthesis, but light doesn’t reach 4,000 meters below the ocean’s surface. Instead, as Sweetman and his team from the Scottish Institute for Marine Science suggest in a new paper, the nodules might be triggering reactions that produce this “dark” oxygen from seawater.
Sweetman first noticed something odd in 2013. He and his team were working on measuring oxygen flow in a confined area of the ocean floor that was rich in nodules. The flow of oxygen seemed to increase on the seafloor, even though there were no photosynthetic organisms nearby, so the researchers thought it was an equipment anomaly.
However, the same discovery was repeated in 2021, albeit with a different measurement approach. The scientists were evaluating changes in oxygen levels in a benthic chamber, a device that collects sediment and seawater to create a sealed sample of the seafloor environment. This device allowed them to analyze, among other things, how the microorganisms in the sample environment were consuming oxygen. The oxygen trapped in the chamber should have decreased over time, as organisms in the water and sediments consume it, but the opposite happened: oxygen levels in the benthic chamber increased, despite the dark conditions hindering photosynthetic reactions.
The problem required investigation. First, the team determined conclusively that there were no microbes capable of producing oxygen. Once that was certain, the scientists hypothesized that polymetallic nodules captured in chambers on the ocean floor might be involved. After some lab tests, Sweetman says, it was discovered that the nodules acted like a geobattery: They generate a small electric current (about 1 volt each), which splits water molecules into their two components, hydrogen and oxygen, in a process called electrolysis.
But it’s not entirely clear how the nodes produce oxygen: what generates the current, whether the reaction is continuous, and, most importantly, whether the production of oxygen is enough to sustain an ecosystem.
And there’s an even bigger question: What if electrolysis caused by polymetallic nodules was the catalyst that started life on Earth? Sweetman says this is an intriguing hypothesis that deserves further investigation. It could also happen on other planets, making them potential sources of extraterrestrial life.
These possibilities add weight to the argument that the deep sea floor is a sensitive environment that needs to be protected from industrial development. (A petition has already been signed by more than 800 marine scientists from 44 countries highlighting the broader environmental risks of deep-sea mining and calling for a moratorium on its development.)
But with so many questions still unanswered, some have cast doubt on the findings. The biggest criticism has come from the seafloor mining industry. Patrick Downs of the Metals Company, a deep-sea mining company that mines in the same area Sweetman studied and helped fund some of his research, said the results were due to extraneous oxygen contamination, and that the company plans to publish a paper soon refuting the paper submitted by Sweetman’s group.
