Rocks that produce oxygen? A new discovery could revolutionize our understanding of deep-sea ecosystems

The deep ocean is often described as Earth’s last great frontier. Its overwhelming vastness and extreme environments have limited our scientific understanding of this still largely uncharted wilderness. As advances in technology and increased investment in deep ocean exploration are enabling us to learn more about this mysterious world, they are also revealing just how much we don’t know – including phenomena so surprising that when we do stumble across them, they almost defy belief.

An astonishing piece of research published last month describes just such a discovery – one with implications for everything from the clean energy transition to our understanding of the origin of life itself.

Parts of the ocean floor, including the seabed underneath the central Pacific Ocean, contain fields of rocky mineral deposits known as “polymetallic nodules” or “ferromanganese nodules.” These potato-sized rocks, formed over millions of years, are rich in cobalt, nickel and other so-called “critical minerals,” and have for that reason been attracting intense interest from mining companies seeking to mine these nodule fields to extract the valuable minerals they contain.

Polymetallic nodules also provide a critical habitat for species that science has only very recently begun to understand. (Our recent report “We Don’t Need Deep-sea Mining” describes many of these amazing species – and the risks that deep-sea mining could pose to their survival.)

A new study, however, published in the journal Nature Geoscience, suggests there may be something else going on with these nodules – something that could revolutionize our understanding of life in the deep sea: they produce oxygen.

The absence of light in the deepest areas of the ocean means that there are no photosynthetic organisms at those depths releasing oxygen into the water. Seafloor ecosystems are currently assumed to rely exclusively on oxygen produced by organisms in shallower waters and carried down by ocean currents. That being the case, cutting off the supply of that oxygen to a given area of seafloor should lead to a gradual decrease in the oxygen concentration in the water in that area as the organisms living there consume that oxygen.

But researchers working in a nodule-rich area of the Pacific Ocean known as the Clarion-Clipperton Zone (CCZ) recently noticed a strange phenomenon: using specialized instruments to artificially seal off small sections of the ocean floor, they found that in areas with a particular abundance of nodules, oxygen concentrations increased over time.

The only notable difference between the CCZ and other areas of ocean where similar experiments have been conducted was the presence of polymetallic nodules. This led the researchers to hypothesize that the production of this “dark oxygen” must have something to do with these rocks.

The exact mechanism by which this occurs is still yet to be fully understood, but the team posited that the nodules were somehow acting as catalysts enabling the splitting of seawater molecules and thereby releasing oxygen into the water. Subsequent laboratory tests seemed to confirm this as a possibility. Experiments showed that voltages on the surface of each nodule are roughly equivalent to that of a standard AA battery, meaning that while a single nodule may not have enough voltage to be able to split water molecules, multiple nodules sitting on the seafloor in contact with one another potentially could. In other words, in their natural state, these rocks – increasingly sought after for use in EV batteries and other new technologies – may essentially be acting like batteries themselves.

It is difficult to overstate the potential magnitude of this discovery. If correct, it means there is a whole new source of oxygen on this planet hitherto completely unknown to science. Not only would this revolutionize our understanding of how deep-sea ecosystems work, but it could also be a major milestone in the evolution of our understanding of the origins of life itself. And perhaps not just life on this planet – if oxygen can be produced in this way, with no need for photosynthesis, then it could well be happening elsewhere in the universe in worlds other than our own.

In the short term, this study also has major implications for deep-sea mining. We already know that ripping up the nodules threatens wildlife habitats, both on the nodules themselves and across the wider ocean via the spread of sediment plumes kicked up by mining activities. This new discovery, however, means that we could also be removing a source of oxygen potentially vital for sustaining life in the deep sea – again, both directly, by removing the rocks themselves, and also by spreading sediment across potentially hundreds of square miles of seafloor beyond the mining sites themselves. (Oxygen production from the nodules, the researchers hypothesized, may fluctuate with different amounts of sediment coverage, “inviting the urgent question of how sediment remobilization and distribution over large areas during deep-sea mining may influence [oxygen production].”)

For now, the team involved in the study has been keen to stress that their discovery poses more questions than answers, and their findings have already received pushback from mining advocates. The Metals Company – the Canadian firm spearheading the push for deep-sea mining – has already been quick to denounce the study (which, ironically, they themselves funded). But while there is no doubt that there are currently more questions than answers, this makes it all the more vital – particularly in light of the current race to strip the seafloor of these minerals – that science is given time and space to explore these questions and find answers.

While global leaders debate the fate of the seafloor, this research bears out something important that we emphasized in our recent report, which is that we shouldn’t be interfering with the deep ocean until we have a clear idea of exactly what we’re dealing with – which, as this new research demonstrates, we currently don’t.

Indeed, one of the most striking things about this study is that it illustrates not just how much we don’t yet know about the deep ocean, but how much we don’t even know we don’t know. This new discovery is so far outside our previous understanding that the researchers, who first noticed their peculiar readings back in 2013, initially refused to believe that they could be to do with the nodules, and for a long time attributed them simply to equipment malfunctions. (Since the publication of the study, other researchers have come forward with similar data that they, too, had discounted.) Given how much of the ocean is still unexplored, and given how frequently our explorations reveal new and unexpected surprises, how sure can we be that launching a brand-new extractive industry on the ocean floor won’t cause damage that we will later come to regret – and never be able to repair?