Before the Great Oxidation Event (GOE) 2.4 billion years ago, the Earth’s atmosphere had almost no oxygen. During the GOE, photosynthetic bacteria known as cyanobacteria produced oxygen through photosynthesis, releasing it into the atmosphere. When oxygen was found at a depth of 4,000 meters below the surface of the Pacific Ocean, the researchers thought it was a data error. Researchers have now revealed plans to investigate the source of ‘dark oxygen’ on the sea floor at the Clarion-Clipperton Zone (CCZ) in the Pacific Ocean.
At a press conference in London, the researchers revealed an array of instruments and equipment designed to study oxygen production, either on the sea floor or in laboratory experiments that mimic deep-sea conditions, such as 400 atmospheres of pressure. The Nippon Foundation, a charity based in Tokyo, is funding follow-up studies with a $5.2 million grant.
By May, project scientists will travel to the CCZ— the region between Hawaii and Mexico, where the ‘dark oxygen’ was first found on the Nautilus research vessel. Speaking at the event, team leader Andrew Sweetman, a sea-floor ecologist at the Scottish Association for Marine Science in Oban, UK, discussed two probes—each with different capabilities—equipped with technology to land on the sea floor and take measurements.
“We will be taking landers that are specifically built to look at dark-oxygen production,” he says. The probes will measure proton concentration in seawater using pH sensors. The data will reveal whether water molecules are splitting, which implies that molecular oxygen is being formed.
The original study found dark oxygen in a region containing ancient nuggets of valuable metals such as manganese, nickel, and cobalt, known as polymetallic nodules—these form on ocean floors over millions of years. The researchers hypothesize that these nodules, which resemble large black truffles, may serve as catalysts for water splitting, analogous to those used to produce hydrogen gas in electrochemical cells. However, scientists aren’t limiting their theories to just electrochemistry; they also suggest that microbes could play a role.
The new set of experiments is designed to confirm the team’s original discovery and also find the source of dark oxygen. Electrochemistry and biology might be at play, and these phenomena can be in tandem. Building microscale maps of microbes, minerals, and metabolic activity will paint a better picture.
Chemist Franz Geiger at Northwestern University in Evanston, Illinois, plans to conduct pressure-chamber experiments on polymetallic nodules retrieved from the sea floor to study the rock’s electrochemistry and examine their surfaces using a special transmission electron microscope that can work in liquid cells, which willbe able to map the chemical states of metals on the surface in seawater.
Custom-built electrodes will measure voltage differences between various points across a nodule to see if it catalyzes water splitting.
Sweetman’s team discovered the oxygen during a study that they conducted on behalf of The Metals Company, a sea-bed mining company in Vancouver, Canada, to measure the effect of deep-sea mining of polymetallic nodules on biological ecosystem in the abyss.
The findings churned out controversy, and a team that included researchers at The Metal Comapny announced that they were submitting a list of concerns about the research to Nature Geoscience. Sweetman proposes that in case mining proceeds, his team can suggest practice to limit the damage.
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