A spontaneous chemical reaction creates oxygen unnoticed deep beneath Earth’s ocean floor, creating oxygen unnoticed without the involvement of life. The unexpected discovery overturns the long-held idea that photosynthetic organisms produce the oxygen we need to breathe.
Biogeochemist Andrew Sweetman, from the Scottish Association for Marine Sciences (SAMS), and colleagues made a surprising discovery while measuring oxygen levels on the seabed to assess the impact of deep-sea mining.
“The discovery of oxygen production by a non-photosynthetic process forces us to rethink how the evolution of complex life on the planet may have occurred,” says SAMS oceanographer Nicholas Owens, who was not involved in the study.
“I think this is one of the most interesting discoveries in oceanology in recent times.”
Black, round rocks litter the ground in the middle of the Pacific Ocean, where scientists’ measurements have shown that oxygen levels are slowly but surely rising at depths of more than 4,000 meters (13,000 feet).
“When we first got this data, we thought the sensors were faulty because every deep-sea survey looked at oxygen consumption, not production. We would come home and recalibrate the sensors, but for 10 years these strange oxygen readings kept popping up,” Sweetman explains.
“We decided to use a backup method that worked differently than the optical sensors we were using, and when both methods showed the same result, we knew we had something innovative and unexpected in store.”
To investigate this mystery, researchers collected some night rocks to see if they were the source of “dark oxygen” formation in the lab.
These concentrations cover large areas of the ocean floor. They are natural deposits of rare earth metals such as cobalt, manganese, and nickel mixed into a polymetallic mixture. We value these metals for their use in batteries, and it turns out that this is exactly how rocks move spontaneously on the ocean floor.
The researchers found that individual polymetallic assemblies produce voltages of up to 0.95 V. So when grouped together like series batteries, they can easily reach the 1.5 V needed to separate oxygen from water in an electrolysis reaction.
“We seem to have discovered a natural ‘geobattery,'” says Northwestern University chemist Franz Geiger. “These geobatteries form the basis of a possible explanation for dark oxygen production in the ocean.”
While much remains to be discovered, such as the extent of oxygen production by polymetallic nodules, the discovery offers a possible explanation for the mysterious persistence of “dead zones” in the ocean, even decades after deep-sea mining ceased.
“In 2016 and 2017, marine biologists visited areas mined in the 1980s and found that even bacteria had not recovered in the mined areas. But marine life thrived in the unmined areas,” Geiger explains.
“It is still unknown why such ‘dead zones’ persist for decades. However, since the diversity of ocean-floor fauna in nodule-rich areas is higher than in highly diverse rainforests, this puts a big asterisk on seabed mining strategies.”
Beyond these huge implications for deep-sea mining, “dark oxygen” also raises a host of new questions about the origins of oxygen-breathing life on Earth. Ancient microbial cyanobacteria have long been thought to be the first suppliers of oxygen, a waste product of photosynthesis, which converts sunlight into energy, essential for the evolution of complex life billions of years ago.
“We now know that oxygen is produced in the deep sea, where there is no light,” Sweetman says.
“So I think we need to go back to questions like: Where might aerobic life have begun?” This study was published in: Nature Geology.
Source: Port Altele
