Deep-ocean floor produces its own ‘dark oxygen’

A world group of researchers, together with a Northwestern College chemist, has found that metallic minerals on the deep-ocean flooring produce oxygen — 13,000 toes beneath the floor.

The shocking discovery challenges long-held assumptions that solely photosynthetic organisms, resembling vegetation and algae, generate Earth’s oxygen. However it now seems oxygen additionally may be produced on the seafloor — the place no gentle can penetrate — to help the oxygen-breathing (cardio) sea life residing in full darkness.

Andrew Sweetman, of the Scottish Affiliation for Marine Science (SAMS), made the “darkish oxygen” discovery whereas conducting ship-based fieldwork within the Pacific Ocean. Northwestern’s Franz Geiger led the electrochemistry experiments, which probably clarify the discovering.

“For cardio life to start on the planet, there needed to be oxygen, and our understanding has been that Earth’s oxygen provide started with photosynthetic organisms,” mentioned Sweetman, who leads the Seafloor Ecology and Biogeochemistry analysis group at SAMS. “However we now know that there’s oxygen produced within the deep sea, the place there isn’t a gentle. I feel we, subsequently, have to revisit questions like: The place might cardio life have begun?”

Polymetallic nodules — pure mineral deposits that type on the ocean flooring — sit on the coronary heart of the invention. A mixture of varied minerals, the nodules measure anyplace between tiny particles and a mean potato in measurement.

“The polymetallic nodules that produce this oxygen include metals resembling cobalt, nickel, copper, lithium and manganese — that are all vital parts utilized in batteries,” mentioned Geiger, who co-authored the research, which revealed July 22 in Nature Geoscience. “A number of large-scale mining corporations now intention to extract these treasured parts from the seafloor at depths of 10,000 to twenty,000 toes beneath the floor. We have to rethink methods to mine these supplies, in order that we don’t deplete the oxygen supply for deep-sea life.”

Geiger is the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern’s Weinberg Faculty of Arts and Sciences and member of the Worldwide Institute for Nanotechnology and the Paula M. Trienens Institute for Vitality and Sustainability.

‘One thing ground-breaking and unthought-of’

Sweetman made the invention whereas sampling the seabed of the Clarion-Clipperton Zone, a mountainous submarine ridge alongside the seafloor that extends almost 4,500 miles alongside the north-east quadrant of the Pacific Ocean.

“After we first bought this knowledge, we thought the sensors have been defective as a result of each research ever executed within the deep sea has solely seen oxygen being consumed fairly than produced,” Sweetman mentioned. “We’d come dwelling and recalibrate the sensors, however, over the course of 10 years, these unusual oxygen readings saved exhibiting up.

“We determined to take a back-up technique that labored otherwise to the optode sensors we have been utilizing. When each strategies got here again with the identical end result, we knew we have been onto one thing ground-breaking and unthought-of.”

Hidden ‘geobatteries’ at play

In summer season 2023, Sweetman contacted Geiger to debate doable explanations for the oxygen supply. In his earlier work, Geiger discovered that rust, when mixed with saltwater, can generate electrical energy. The researchers puzzled if the deep-ocean’s polymetallic nodules generated sufficient electrical energy to supply oxygen. This chemical response is a part of a course of known as seawater electrolysis, which pulls electrons out of water’s oxygen atom.

To research this speculation, Sweetman shipped a number of kilos of the polymetallic nodules collected from the ocean flooring to Geiger’s laboratory at Northwestern. Sweetman additionally visited Northwestern final December, spending per week in Geiger’s lab.

Simply 1.5 volts — the identical voltage as a typical AA battery — is sufficient to break up seawater into hydrogen and oxygen. Amazingly, the group recorded voltages of as much as 0.95 volts on the floor of single nodules. And when a number of nodules clustered collectively, the voltage may be way more vital, similar to when batteries are linked in a collection.

“It seems that we found a pure ‘geobattery,’” Geiger mentioned. “These geobatteries are the premise for a doable clarification of the ocean’s darkish oxygen manufacturing.”

A brand new consideration for miners

The researchers agree that the mining business ought to think about this discovery earlier than planning deep-sea mining actions. In line with Geiger, the entire mass of polymetallic nodules within the Clarion-Clipperton Zone alone is sufficient to meet the worldwide demand for vitality for many years. However Geiger seems to be to mining efforts within the Eighties as a cautionary story.

“In 2016 and 2017, marine biologists visited websites that have been mined within the Eighties and located not even micro organism had recovered in mined areas,” Geiger mentioned. “In unmined areas, nonetheless, marine life flourished. Why such ‘useless zones’ persist for many years remains to be unknown. Nonetheless, this places a serious asterisk onto methods for sea-floor mining as ocean-floor faunal variety in nodule-rich areas is larger than in probably the most various tropical rainforests.”