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Scientists Uncover ‘Dark Oxygen’ Production in Deep-Sea Mining Zones

It can be termed the most mind-blowing breakthrough of all: oxygen production above 13,000 feet below the surface of the ocean, independent of sunlight. The sweeping implications this discovery initially held for deep-sea ecosystems and possible mining of the seafloor effects changed everything when first realized in 2013.

Andrew Sweetman, a professor at the Scottish Association for Marine Science, had first ignored sensor readings that registered oxygen production on the seafloor at such extreme depths. “I basically told my students, just put the sensors back in the box. We’ll ship them back to the manufacturer and get them tested because they’re just giving us gibberish,” Sweetman said. However, repeated observations and further validation showed the sensors were telling the truth.

In a paper published in Nature Geoscience, Sweetman reports a challenge to the long-standing theory that oxygen in the deep sea is not created, only consumed. According to his findings, the polymetallic nodules, which take millions of years to form and contain metals like cobalt, nickel, and manganese, could be acting like natural “geobatteries,” producing oxygen by some process similar to seawater electrolysis whereby an electric current is used to split water into oxygen and hydrogen.

Sweetman and colleagues used an instrument called a deep-ocean lander, which girded small areas of the seafloor for their experiments. After their results yielded oxygen levels increasing over time, a result opposite of what was expected,  Sweetman thought that the nodules themselves were producing oxygen. Working with Franz Geiger, an electrochemist at Northwestern University, Sweetman measured voltages from the nodules and returned readings that answered the geobattery hypothesis.

“This is an absolutely amazing, totally unexpected finding,” said Daniel Jones, a professor at the National Oceanography Centre in Southampton, England. There are more than scientific implications in these findings, since deep-sea mining is thought to be extremely harmful to the environment. These nodules carpet a vast area of the ocean floor known as the Clarion-Clipperton Zone, which has emerged as one of the key targets for mining companies in their search for metals that can be used in the construction of green technologies such as solar panels and electric car batteries.

Some critics worry, however, that the practice could have irreparable impacts on marine ecosystems. “In 2016 and 2017, marine biologists visited sites that were mined in the 1980s and found that not even bacteria had recovered in mined areas,” said Geiger. Also very near the top of their list of concerns were potential disruptions to carbon storage, along with the creation of “dead zones” in which marine life is unable to survive.

This is an area regulated by the International Seabed Authority under the UN Convention on the Law of the Sea, where discussions have been made to decide new extraction rules. Deep-sea mining has raised outcry, with calls from countries like the United Kingdom and France for a moratorium so that measures to ensure marine biodiversity can be enacted.

There needs to be scientific oversight in deep-sea mining, said Sweetman. But the discovery of how dark oxygen is created and its function in the deep-sea ecosystem could also answer questions about the emergence of life on Earth. “I think that there’s more science that needs to be done, especially around this process and the importance of it,” said Sweetman. “I hope it’s the start of something amazing.”

It is a discovery that challenges the paradigms but also underscores the importance of cautious and informed approaches in exploiting the ocean’s resources.

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