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<\/div>A nodule from the seabed being tested in a lab<\/p>\n
Camille Bridgewater (2024)<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
Metallic nodules scattered across the seabed in the Indian and Pacific oceans are a source of oxygen for nearby marine life \u2013 a finding that could upend our understanding of the deep ocean.<\/p>\n
Abyssal plains in some regions are scattered with potato-sized nodules packed with valuable cobalt, manganese and nickel, a target for deep-sea mining activity<\/a>.<\/p>\n Andrew Sweetman<\/a> at the Scottish Association for Marine Science in Oban, UK, first noticed something strange about these ocean areas back in 2013, while conducting research in the Clarion-Clipperton Zone, a nodule-rich part of the Pacific Ocean.<\/p>\n Sweetman and his colleagues were sending machines down to the ocean floor to seal off a 22 centimetre square patch of seabed and measure its oxygen flux. Instead of oxygen content decreasing in the monitored sections, the data suggested it was increasing.<\/p>\n But without any noticeable plant life, that didn\u2019t make sense, says Sweetman. \u201cI\u2019ve been taught from a very young age that oxygenated ecosystems are only possible through photosynthesis,\u201d he says. His conclusion was that the machinery he was using was faulty. \u201cI literally ignored the data,\u201d he says.<\/p>\n Then, in 2021, Sweetman was on another research cruise in the Pacific and machines returned the same finding \u2013 increasing oxygen levels on the seabed. Using a different measurement approach yielded the same result.<\/p>\n <\/p>\n \u201cWe were seeing the same oxygen production in these two different datasets,\u201d says Sweetman. \u201cAnd suddenly I realised that for the last eight or nine years I had been ignoring this hugely groundbreaking process.\u201d<\/p>\n He and his colleagues deduced that the metallic nodules must be playing a role in raising the oxygen levels in the deep sea. Lab testing, which involved poisoning the sediment and nodules, ruled out the presence of oxygen-producing microbes.<\/p>\n Instead, Sweetman says the materials in the nodules are acting as a \u201cgeobattery\u201d, generating an electric current that splits seawater into hydrogen and oxygen. \u201cThese nodules are being mined because there\u2019s everything there that you need to make an electric car battery<\/a>,\u201d he says. \u201cWhat if they are acting as natural geobatteries, by themselves?\u201d<\/p>\n Each nodule can produce up to 1 volt of electric potential, the team discovered by probing the rocks. If the rocks were clustered together to join forces, there would be enough voltage to split seawater into hydrogen and oxygen via electrolysis, explaining the elevated oxygen levels.<\/p>\n \u201cPotentially we have discovered a new natural source of oxygen,\u201d says Sweetman. \u201cHow pervasive that is in time and space, I don\u2019t know. But it\u2019s something that\u2019s very, very interesting.\u201d<\/p>\n There are many outstanding questions. For example, the source of energy generating the electric current remains a mystery. It is also unclear whether the reaction happens continuously, under what conditions and the contribution this oxygen plays in sustaining surrounding ecosystems. \u201cWe don\u2019t have all of the information yet, but we know it\u2019s happening,\u201d says Sweetman.<\/p>\n In deep-sea environments devoid of sunlight and plants, some life forms get their energy from chemicals that erupt from the sea floor at hydrothermal vents<\/a>. Some scientists think life on Earth first appeared at these vents, but these early organisms would have needed a source of oxygen to make food from inorganic compounds. The findings raise the possibility that nodules could have been the source of that oxygen to help life get started, says Sweetman.<\/p>\n That interpretation might be a stretch, says Donald Canfield<\/a> at the University of Southern Denmark. Oxygen is needed to produce the manganese oxide contained in the nodules, he points out. \u201cOxygenic photosynthesis is a prerequisite for their production,\u201d he says. \u201cFor this reason, oxygen production by the nodules does not represent an alternative type of oxygen production to be equated with oxygenic photosynthesis. It is very unlikely that they have played a role in the oxygenation of the planet.\u201d<\/p>\n However, Ruth Blake<\/a> at Yale University says the idea of oxygen production in the deep ocean is still \u201cexciting\u201d and warrants more research into the phenomenon and its potential impact on deep-ocean ecosystems.<\/p>\n Sweetman\u2019s study was part-funded by The Metals Company (TMC), a deep-sea mining company looking to harvest metallic nodules in the Clarion Clipperton Zone. In response to the study, Patrick Downes<\/a> at TMC said he has \u201cserious reservations\u201d about the findings, adding that its own analysis suggests Sweetman\u2019s results are due to oxygen contamination from external sources. \u201cWe will be writing a rebuttal article,\u201d Downes said in a statement to New Scientist<\/em>.<\/p>\n However, the findings are likely to strengthen calls for a ban on deep-sea mining, a position backed by many oceanographers who say our understanding of such areas is still developing. Paul Dando<\/a> at the UK\u2019s Marine Biological Association says the paper reinforces the view of deep-sea scientists \u201cthat no mining should take place until we understand the ecology of these nodule fields\u201d.<\/p>\n Sweetman says his findings aren\u2019t necessarily \u201cthe nail in the coffin\u201d for deep-sea mining, but it might restrict extraction to locations where oxygen production is low. More research is also needed to investigate the impact of sediment stirred up by the mining process on the oxygen production, he says.<\/p>\n Topics:<\/p>\n<\/section><\/div>\n