Deep sea mining has a new discovery to contend with.

Deep sea mining has brought many abyssal research theories to light, including the vibrancy and delicacy of the sunless seafloor ecosystem, the amazing accretion of desirable minerals over millions of years into priceless little nodules that have been suggested could nearly eliminate land-based battery mineral mining in its entirety, and a new mystery – dark oxygen – defying previous theories about the origins of life on Earth.

The oxygen, which the researchers theorize is being produced from combinations of metals forming natural batteries, might be playing an unexpected role in the ecosystem of the deep ocean and the origins of organisms that metabolize oxygen.

"For aerobic life to begin on the planet, there had to be oxygen and our understanding has been that Earth's oxygen supply began with photosynthetic organisms," said Andrew Sweetman, a researcher at the Scottish Association for Marine Science, UK. "But we now know that there is oxygen produced in the deep sea, where there is no light. I think we therefore need to revisit questions like: where could aerobic life have begun?"

These polymetallic nodules are essentially concentric layers of iron and manganese, formed by the slow accretion of minerals from seawater with various amounts of nickel, copper and cobalt around a small core of ocean detritus. The combination is tailor-made for battery chemistry needs.

This natural combination of minerals has shown the potential to provide a small amount of charge –enough to make seawater undergo electrolysis, a reaction where water is split into hydrogen and oxygen.

According to the international team's study, published in Nature Geoscience, there are still further questions that need to be answered, and it's not yet clear how widespread this deep-sea oxygen production is.

"When we first got this data, we thought the sensors were faulty, because every study ever done in the deep sea has only seen oxygen being consumed rather than produced," said Sweetman, lead author of the study. "We would come home and recalibrate the sensors but over the course of 10 years, these strange oxygen readings kept showing up."

Funded by The Metals Company, Sweetman's colleagues have been studying what effects potential deep-sea mining might have on the seabed of the North Pacific's Clarion-Clipperton Zone. This zone has been in the news, drawing a lot of interest from deep-sea miners from several countries.

The researchers placed chambers on the sea floor, about 4.2 kilometers (2.6 miles) deep, at locations across more than 4,000 kilometers (2,500 miles) of the zone, inside which oxygen concentration increased steadily over two-day periods.

They then went looking for the mechanism for this oxygen production, since there was no sunlight for photosynthesis.

"We decided to take a back-up method that worked differently to the optode [oxygen] sensors we were using and when both methods came back with the same result we knew we were onto something ground-breaking and unthought-of," Sweetman said.

"It appears that we discovered a natural 'geobattery'," says co-author Professor Franz Geiger, a chemist at Northwestern University, U.S. The individual nodules appeared to have a potential of 0.95V, and multiple nodules together could easily provide sufficient electrical current needed to make oxygen out of seawater. "These geobatteries are the basis for a possible explanation of the ocean's dark oxygen production."

"The polymetallic nodules that produce this oxygen contain metals such as cobalt, nickel, copper, lithium and manganese – which are all critical elements used in batteries," said Geiger. "We need to rethink how to mine these materials, so that we do not deplete the oxygen source for deep-sea life."

Geiger also says that these nodule-rich areas of the ocean floor support more biodiversity than tropical rainforests.

"In 2016 and 2017, marine biologists visited sites that were mined in the 1980s and found not even bacteria had recovered in mined areas," says Geiger. "In unmined regions, however, marine life flourished. Why such 'dead zones' persist for decades is still unknown. However, this puts a major asterisk onto strategies for sea-floor mining."

There are currently two primary deep-sea mining technologies – dredging and hydraulic suction systems. Both remove a layer of seafloor and then eject tailings back into the ocean. These techniques have a host of vocal critics, from environmentalists and scientists to industry leaders, who are reluctant to invest in such contentious methods.

However, not all deep-sea mining harvesters are created equal.

Impossible Metals has devised a unique robotic collection system that plucks individual nodules from the seafloor, using AI to avoid nodule fauna without causing a plume and has no significant impact on sediment structure.

While the abyssal seabed is both a priceless expanse of ecological underpinnings as well as host to what may be a treasure trove of clean energy transition feedstocks, the takeaway may be that the global deep sea mining industry need only reinvent itself in a similar fashion as modern land-based mining has done and bring extraction technologies into the present day with new, more efficient and sustainable methods.