Dark oxygen discovered in the deep sea in groundbreaking study

An international team of scientists has discovered that oxygen is being produced by potato-shaped metallic nodules thousands of feet below the surface of the Pacific Ocean.

The findings, which were published Monday in the Nature Geoscience journal, defy the scientific consensus of how oxygen is produced — and could even force a radical rethink of the origins of complex life on Earth.

Alongside implications for ocean science, the research raises fresh concerns about the risks of deep-sea mining.

A team of scientists led by professor Andrew Sweetman at the U.K.’s Scottish Association for Marine Science found that oxygen is being produced in complete darkness approximately 4,000 meters (13,100 feet) below the ocean’s surface.

It was previously thought that only living organisms such as plants and algae could use energy to create the planet’s oxygen through a process called photosynthesis, which requires sunlight.

“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,” Sweetman said.

“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?”

“Dark oxygen” was discovered while researchers conducted ship-based fieldwork in the Pacific Ocean. The team sampled the seabed of the Clarion-Clipperton Zone, an abyssal plain between Hawaii and Mexico, to assess the possible impacts of deep-sea mining.

Researchers analyzed multiple nodules and found many were carrying a “very high” electric charge, which they said could lead to the splitting of seawater into hydrogen and oxygen through a process called seawater electrolysis.

“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,” Sweetman said.

He added that further research into “dark oxygen” production would be necessary.

The study was partly funded by Canadian deep-sea mining firm The Metals Co., which aims to mine in an area of the Clarion-Clipperton Zone by late 2025.

The controversial practice of deep-sea mining involves using heavy machinery to remove valuable minerals and metals — such as cobalt, nickel, copper and manganese —that can be found in polymetallic nodules on the ocean floor. The end uses of these minerals are wide-ranging and include electric vehicle batteries, wind turbines and solar panels.

Scientists have warned that the full environmental impacts of deep-sea mining are hard to predict.

Environmental campaign groups, meanwhile, say that the practice cannot be done sustainably and will inevitably lead to ecosystem destruction and species extinction.

“The discovery that a process associated with polymetallic nodules is producing oxygen, in an area targeted by the deep-sea mining industry, provides further support on the urgent need for a moratorium,” said Sofia Tsenikli, deep-sea mining global campaign lead for the Deep Sea Conservation Coalition, a nongovernment environmental group.

“This research emphasizes just how much we still have to discover and learn about the deep sea and raises more questions about how deep-sea mining could impact deep-sea life and processes,” Tsenikli said Monday.

Correction: The Clarion-Clipperton Zone is an abyssal plain between Hawaii and Mexico. An earlier version misspelled its name.