Can metallic nodules found in the most profound, obscure parts of the sea produce oxygen without receiving sunlight?

While some researchers believe this theory, others dispute the assertion that what’s known as “dark oxygen” is generated within the sunless depths of the ocean floor.

The findings — outlined in detail in the July issue of Nature Geoscience — challenged previously accepted beliefs regarding the beginnings of life on our planet and ignited significant scientific discussion.

The discoveries had significant implications for mining firms keen on extracting the valuable metals found inside these polymetallic nodules.

Scientists have indicated that potato-sized nodules might generate sufficient electrical currents to divide seawater into hydrogen and oxygen through a process called electrolysis.

This raised questions about the widely accepted belief that life became feasible only when creatures began generating oxygen through photosynthesis, a process dependent on sunlight, around 2.7 billion years ago.

“The deep-sea find challenges our understanding of how life began,” stated the Scottish Association for Marine Science in a press release released alongside the research paper.

Delicate ecosystem

Environmentalists argued that the discovery of dark oxygen highlighted our limited understanding of life in such extreme environments, thereby strengthening their position that deep-sea mining entails significant environmental hazards.

The environmental organization stated that Greenpeace has been advocating for years against the commencement of deep-sea mining in the Pacific because of the potential harm it might cause to fragile deep-sea ecosystems.

This remarkable finding highlights the critical nature of that appeal.

The finding occurred in the Clarion-Clipperton Zone, an extensive undersea area within the Pacific Ocean located between Mexico and Hawaii, which has become increasingly appealing to mining corporations.

Spread across the ocean floor at a depth of four kilometers (2.5 miles), these polymetallic nodules hold manganese, nickel, and cobalt—metals essential for manufacturing electric vehicle batteries and various low-carbon technologies.

The study leading to the dark oxygen revelation received partial funding from The Metals Company, a Canadian enterprise involved in deep-sea mining, which aimed to evaluate the environmental effects of such activities.

It has strongly condemned the research conducted by marine ecologist Andrew Sweetman and his team, citing “methodological flaws” as the primary issue.

Michael Clarke, an environmental manager at The Metals Company, informed AFP that these findings can be better attributed to inadequate scientific methods and subpar research rather than some unprecedented occurrence.

Scientific doubts

Sweetman’s discoveries were met with significant controversy, as numerous members of the scientific community either voiced doubts or outright dismissed his conclusions.

Since July, five scholarly research papers challenging Sweetman’s conclusions have been sent for evaluation and potential publication.

“As he failed to provide concrete evidence for his observations and hypotheses,” stated Matthias Haeckel, a biogeochemist from the GEOMAR Helmholtz Centre for Ocean Research located in Kiel, Germany.

A multitude of queries persist following the release of this work. Consequently, the scientific community must undertake comparable experiments and so verify or refute these findings.

Olivier Rouxel, a geochemist from Ifremer—the French national institute for ocean research and technology—stated to AFP that there was “no agreement whatsoever regarding these findings.”

He mentioned that deep-sea sampling poses constant challenges,” noting it was plausible that the observed oxygen could be attributed to “air bubbles trapped within the equipment.

He doubted that deep-sea nodules, which are several million years old, could continue generating sufficient electric currents once their “power sources deplete rapidly.”

He questioned how it could be possible to sustain the ability to produce an electric current within a nodule that develops at an exceedingly sluggish rate.

When reached out to by AFP, Sweetman mentioned that he was working on providing an official reply.

“Such exchanges are quite typical for scientific articles and they advance the field,” he stated.