This story originally appeared in WIRED Italia and has been translated from Italian.
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 filled with polymetallic nodules. About the size of a potato, these rocks contain valuable metals — lithium, copper, cobalt, manganese and nickel — that are used to make batteries. They are tempting prizes for deep-sea mining companies, which are developing technologies to bring them to the surface.
The nodules could be a potential source of battery components, but Sweetman thinks they could already be producing something very different: oxygen. Normally, the element is generated when organisms carry out photosynthesis, but light does not reach 4,000 metres below the ocean surface. Instead, as Sweetman and his team at the Scottish Association for Marine Science Suggest a new articleThe nodules could be driving a reaction that produces this “dark” oxygen from seawater.
Sweetman first noticed something strange in 2013. With his team, he had been working to measure oxygen flux in confined areas within nodule-rich areas of the seafloor. Oxygen flux seemed to increase on the seafloor, even though there were no photosynthetic organisms nearby — so much so that the researchers thought it was an instrumental anomaly.
However, in 2021 the same finding was repeated, albeit with a different measurement method. The scientists were assessing changes in oxygen levels inside a benthic chamber, an instrument that collects sediment and seawater to create closed samples of the seafloor environment. The instrument allowed them to analyse, among other things, how microorganisms within the sample environment consumed oxygen. The oxygen trapped in the chamber should have decreased over time as organisms in the water and sediment consumed it, but it did the opposite: even though dark conditions prevented any photosynthetic reaction, oxygen levels in the benthic chamber increased.
The problem needed to be investigated. First, the team determined with certainty that there were no microorganisms capable of producing oxygen. Once they were sure, the scientists hypothesized that polymetallic nodules captured in the benthic chamber might be involved. After several lab tests, Sweetman says, they discovered that the nodules act as a geobattery: They generate a small electric current (about 1 volt each) that splits water molecules into their two components, hydrogen and oxygen, in a process called electrolysis.
However, it is not entirely clear how the nodules produce oxygen: it is not known what generates the electrical current, whether the reaction is continuous and, crucially, whether the oxygen production is significant enough to sustain an ecosystem.
And there’s an even more important question: what if electrolysis induced by polymetallic nodules was the spark that gave rise to life on Earth? According to Sweetman, this is an exciting hypothesis that should be studied further. It might even be possible that this could occur on other worlds and be a potential source of extraterrestrial life.
These possibilities reinforce the argument that the seabed is a delicate environment that must be protected from industrial exploitation (there is already a petition, signed by more than 800 marine scientists from 44 different countries, highlighting the wider environmental risks of deep-sea mining and calling for its development to be halted).
But with so many questions still unanswered, some are questioning the results. The biggest criticism has come from the world of deep-sea mining: Patrick Downes of Metals Company, a deep-sea mining company that works in deep waters (the same waters Sweetman studied and partly funded his research),says the results are the result of oxygen contamination from external sources, and that his company will soon publish a paper refuting the thesis presented by Sweetman’s group.
