![\"Getty](\"https:\/\/ichef.bbci.co.uk\/news\/480\/cpsprodpb\/9eef\/live\/e4ae0c60-482b-11ef-93c3-ffc52948adf5.jpg.webp\")
Getty Images<\/span><\/div>\n<\/div>\nScientists have discovered \u201cdark oxygen\u201d being produced in the deep ocean, apparently by lumps of metal on the seafloor.<\/p>\n About half the oxygen we breathe comes from the ocean. But, before this discovery, it was understood that it was made by marine plants photosynthesising – something that requires sunlight. <\/p>\n Here, at depths of 5km, where no sunlight can penetrate, the oxygen appears to be produced by naturally occurring metallic \u201cnodules\u201d which split seawater – H2O – into hydrogen and oxygen. <\/p>\n Several mining companies have plans to collect these nodules, which marine scientists fear could disrupt the newly discovered process – and damage any marine life that depends on the oxygen they make.<\/p>\n<\/div>\n \u201cI first saw this in 2013 – an enormous amount of oxygen being produced at the seafloor in complete darkness,\u201d explains lead researcher Prof Andrew Sweetman from the Scottish Association for Marine Science. \u201cI just ignored it, because I\u2019d been taught – you only get oxygen through photosynthesis.<\/p>\n \u201cEventually, I realised that for years I\u2019d been ignoring this potentially huge discovery,\u201d he told BBC News.<\/p>\n He and his colleagues carried out their research in an area of the deep sea between Hawaii and Mexico – part of a vast swathe of seafloor that is covered with these metal nodules. The nodules form when dissolved metals in seawater collect on fragments of shell – or other debris. It’s a process that takes millions of years. <\/p>\n And because these nodules contain metals like lithium, cobalt and copper – all of which are needed to make batteries – many mining companies are developing technology to collect them and bring them to the surface. <\/p>\n But Prof Sweetman says the dark oxygen they make could also support life on the seafloor. And his discovery, published in the journal Nature Geoscience, raises new concerns about the risks of proposed deep-sea mining ventures.<\/p>\n<\/div>\n The scientists worked out that the metal nodules are able to make oxygen precisely because they act like batteries.<\/p>\n \u201cIf you put a battery into seawater, it starts fizzing,\u201d explained Prof Sweetman. \u201cThat\u2019s because the electric current is actually splitting seawater into oxygen and hydrogen [which are the bubbles]. We think that\u2019s happening with these nodules in their natural state.\u201d<\/p>\n \u201cIt’s like a battery in a torch,\u201d he added. \u201cYou put one battery in, it doesn’t light up. You put two in and you’ve got enough voltage to light up the torch. So when the nodules are sitting at the seafloor in contact with one another, they\u2019re working in unison – like multiple batteries.\u201d<\/p>\n The researchers put this theory to the test in the lab, collecting and studying the potato-sized metal nodules. Their experiments measured the voltages on the surface of each metallic lump – essentially the strength of the electric current. They found it to be almost equal to the voltage in a typical AA-sized battery. <\/p>\n This means, they say, that the nodules sitting on the seabed could generate electric currents large enough to split, or electrolyse, molecules of seawater.<\/p>\n The researchers think the same process – battery-powered oxygen production that requires no light and no biological process – could be happening on other moons and planets, creating oxygen-rich environments where life could thrive.<\/p>\n<\/div>\n The Clarion-Clipperton Zone, where the discovery was made, is a site already being explored by a number of seabed mining companies, which are developing technology to collect the nodules and bring them to a ship at the surface.<\/p>\n The US National Oceanic and Atmospheric Administration (NOAA) has warned that this seabed mining could \u201cresult in the destruction of life and the seabed habitat in the mined areas\u201d. <\/p>\n![](\"https:\/\/www.bbc.com\/bbcx\/grey-placeholder.png\")
![\"NOC\/NHM\/NERC](\"https:\/\/ichef.bbci.co.uk\/news\/480\/cpsprodpb\/39ef\/live\/932a1750-481f-11ef-96a8-e710c6bfc866.jpg.webp\")
NOC\/NHM\/NERC SMARTEX <\/span><\/div>\n<\/div>\n![\"Science](\"https:\/\/ichef.bbci.co.uk\/news\/480\/cpsprodpb\/5a53\/live\/86bebee0-483c-11ef-b3e5-5dba2a08343d.jpg.webp\")
Science Photo Library\/NOAA<\/span><\/div>\n<\/div>\n<\/figure>\n![\"Camille](\"https:\/\/ichef.bbci.co.uk\/news\/480\/cpsprodpb\/4d3c\/live\/2a7ea170-4820-11ef-95ce-0dd81a19f969.jpg.webp\")
Camille Bridgewater<\/span><\/div>\n<\/div>\n