The discovery that oxygen is not only being stored but created in the unlit depths of Earth’s oceans has been described as “one of the most exciting findings in ocean science in recent times” by Prof Nicholas Owens, director of the Scottish Association for Marine Science (SAMS).
A SAMS-led team’s identification of what they term “dark oxygen” 4km beneath the surface of the Pacific, reported in a study out this week, challenges the previous scientific consensus that oxygen can be created only by plants and algae converting energy from sunlight.
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The finding has even called into question how life on Earth originated – and is likely to provide another argument against deep-sea mining.
Prof Andrew Sweetman of Oban-based SAMS and an international scientific team identified dark oxygen while engaged on ship-based fieldwork to assess the potential effects of deep-sea mining in the Pacific’s Clarion-Clipperton Zone (CCZ) between Hawaii and Mexico.
“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,” says Prof Sweetman. “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?”
’Batteries in a rock’
Deep-sea mining companies are looking to extract the polymetallic nodules that lie all over the seabed in the CCZ. These contain metals such as manganese, nickel and cobalt used to produce lithium-ion batteries.
Prof Sweetman’s team found that these nodules carry a very high electric charge that could result in “seawater electrolysis” – the natural splitting of salt water into hydrogen and oxygen. The process requires only the equivalent voltage of an AA battery, about 1.5V.
Analysing multiple nodules, the team recorded readings of up to 0.95 volts on their surfaces, and deduced that significantly higher voltages could occur when the nodules were clustered together, resulting in the production of dark oxygen.
“Through this discovery, we have generated many unanswered questions and I think we have a lot to think about in terms of how we mine these nodules, which are effectively batteries in a rock,” said Prof Sweetman.
“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. We would come home and recalibrate the sensors but, over the course of 10 years, these strange oxygen readings kept showing up.
“We decided to take a back-up method that worked differently to the optode 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.”
Rethink on evolution
Prof Sweetman has previously been involved in identifying Marine Protected Areas (MPAs) around the Clarion-Clipperton Zone, assessing the biodiversity in certain areas where it is thought that potential deep-sea mining should be avoided. He now thinks the assessment might need to be reviewed in the light of the new evidence.
“The discovery of oxygen production by a non-photosynthetic process requires us to rethink how the evolution of complex life on the planet might have originated,” commented Prof Owens.
“The conventional view is that oxygen was first produced around three billion years ago by ancient microbes called cyanobacteria and there was a gradual development of complex life thereafter. The potential that there was an alternative source requires us to have a radical rethink.” The study is published this week in Nature Geoscience.
Also on Divernet: HOW DO SHIFTING O2 LEVELS AFFECT MARINE LIFE?, RISE IN DEAD ZONES CAUSES CONCERN, WHALING NATION FIRST TO ENABLE DEEP-SEA MINING, MOST LIFE IN DEEP-MINERS’ TARGET ZONE NEW TO SCIENCE
