Production of 'dark' oxygen deep in the ocean comes to light

Deep in the ocean, scientists discovered the presence of "dark" oxygen, which is oxygen produced without photosynthesis. Oxygen was previously thought to require light to be produced; the new finding calls that notion into question. The implications of this discovery could affect future deep-sea mining prospects.

Oxygen in the ocean

A new study published in the journal Nature Geoscience found evidence of oxygen production near polymetallic nodules located deep in the ocean. Called dark oxygen, this oxygen is being produced without light. "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," Nicholas Owens, the director of the Scottish Association for Marine Science, said in a news release. "The potential that there was an alternative source [for oxygen] requires us to have a radical rethink."

Polymetallic nodules comprise several metals including manganese, nickel and cobalt. These metals are culled during deep-sea mining in order to build electric vehicle batteries. However, the metals may have been serving a larger purpose all along. "The regional significance of such [dark oxygen production] cannot really be assessed with the limited nature of this study, but it does suggest a potential unappreciated ecosystem function of manganese nodules at the deep-sea floor," Craig Smith, a professor emeritus of oceanography at the University of Hawaii at Mānoa, said to CNN. 

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Scientists posit that the formation of dark oxygen is an electrochemical process. The polymetallic nodules in the deep sea behave like a geobattery in which they "generate a small electric current (about one volt each) that splits water molecules into their two components, hydrogen and oxygen, in a process called electrolysis," said Wired. Still, "it's not known what generates the electric current, whether the reaction is continuous and, crucially, whether the oxygen production is significant enough to sustain an ecosystem."

An ecosystem disrupted

While much about the production of dark oxygen is unknown, evidence has shown that areas of the sea that have been mined experience a severe loss of marine life. "In unmined regions, however, marine life flourished. Why such 'dead zones' persist for decades is still unknown," Franz Geiger, one of the authors of the study, said to CNN. "However, this puts a major asterisk onto strategies for sea-floor mining as ocean-floor faunal diversity in nodule-rich areas is higher than in the most diverse tropical rainforests."

The dark oxygen findings also raise questions about the origins of life itself. "This discovery implies the possibility that aerobic [oxygen-dependent] life arose before photosynthesis evolved," said The Economist. "That is controversial. But dark oxygen could certainly help aerobic microbes that survive in the deep today — as well as the larger organisms that eat them." 

The ongoing call for more deep-sea mining to glean materials for electric vehicles could potentially damage the ocean's ecosystem. "We need to be really careful," Geiger said to NPR. The deep-sea mining needs to be "done on a level and at a frequency that is not detrimental to life down there."