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A surprising discovery made public in July which metallic rocks apparently produced oxygen on the seabed of the Pacific Ocean, where no light can penetrate, was a scientific bomb.
Early research suggested that potato-sized, metal-rich nodules, found primarily 4,000 meters (13,100 feet) below the surface in the Clarion-Clipperton area, released an electrical charge, splitting the seawater into oxygen and hydrogen by electrolysis. This unprecedented natural phenomenon challenges the idea that oxygen can only be produced from sunlight via photosynthesis.
Andrew Sweetman, a professor at the UK’s Scottish Association for Marine Science and the originator of the discovery, is embarking on a three-year project to study the production of ‘dark’ oxygen in more detail. Sweetman and his team use custom-built platforms equipped with sensors that can be deployed to depths of 11,000 meters (36,089 feet). The Nippon Foundation is funding the $2.7 million (£2.2 million) research project, announced on Friday.
The discovery of dark oxygen revealed how little is known about the depths of the ocean, and the Clarion-Clipperton timetableor CCZ, in particular. The region is being explored for deep-sea mining of rare metals contained in rock nodules. These form over millions of years and metals play a key role in new and green technologies.
“Our discovery of dark oxygen was a paradigm shift in our understanding of the deep sea and potentially life on Earth, but it raised more questions than answers,” said Sweetman, head of the ecology group. and biogeochemistry of the seabed from his institution, in a press release. release. “This new research will allow us to explore some of these scientific questions further.”
Sweetman said the initial goal of the new project was to determine whether dark oxygen production was replicated in other areas of the CCZ where the nodules can be found, and then to understand exactly how the oxygen was produced.
Better understanding the phenomenon could also help space scientists discover life beyond Earth, he added.
Oxygen is difficult to produce without continuous energy from sunlight, but other scientists have also discovered unexpected oxygen molecules in remote, light-deprived places. Sweetman said dark oxygen production could be a broader phenomenon that has been overlooked.
Emil Ruff, a microbiologist at the Marine Biological Laboratory in Woods Hole, Massachusetts, oxygen detected in fresh water samples in Alberta, tens or hundreds of meters below the Canadian prairie, a discovery that he and his co-authors from the University of Calgary and the Woods Hole Oceanographic Institution reported in a study published in June 2023. In some cases, dark oxygen had been isolated from the air atmosphere for more than 40,000 years.
If oxygen is not continually added to an environment (by trees and plants, for example), it will eventually disappear.
“After 40,000 or 30,000 years (separated from surface processes), there’s no reason to really think there should be any oxygen left. Because oxygen is such a delicious electron acceptor, it usually oxidizes chemically or microbially,” Ruff said. “So what was he doing there?”
Similar to Sweetman, Ruff said he initially thought atmospheric oxygen had contaminated his samples, taken from 14 underground aquifers. Given the age of the samples, the oxygen would have reacted with other substances long ago and disappeared.
After patiently working in the laboratory and in the field, Ruff finally discovered that microbes in water produced oxygen. The microbes had apparently evolved an obscure but clever trick that allowed them to produce molecules in the absence of light.
Through a series of chemical reactions, the microbes were able to break down soluble compounds called nitrites, molecules made up of one nitrogen atom and two oxygen atoms, to produce molecular oxygen in a process called disproportionation. The microbes also had the ability to use oxygen to consume methane in the water to produce energy.
Additionally, Ruff found that the amount of oxygen produced was sufficient to support other forms of oxygen-dependent microbial life in groundwater.
“Nature never ceases to surprise us,” he says. “There are so many things that people have said, ‘Oh, that’s impossible,’ and then later it turns out that’s not the case.”
To study dark oxygen in more detail, Ruff and his team traveled to a 3-kilometer-deep (9,500-foot-deep) mine in South Africa in August to sample water trapped in the rock for 1, 2 billion years.
Scientists already knew that the mine water contained oxygen molecules, but it is not clear how they formed. Ruff and his colleagues are still studying the samples they took, but they have two hypotheses about how the oxygen molecules might be product, he said.
The site is mined for gold and uranium, a radioactive metal. Radiolysis, the splitting of water molecules by radioactivity, is one possible way to produce oxygen without sunlight. Alternatively, oxygen production could involve microbes in processes similar to those Ruff finds in Canadian groundwater.
Sweetman said Friday that the new project would also seek to understand whether microbial reactions played a role in producing dark oxygen on the seafloor. In particular, the project will examine how hydrogen is released during the production of oxygen by the metal nodules and whether the hydrogen was used as an energy source for the microbe communities detected in parts of the deep ocean.
“I think we haven’t completely put the mechanism in place yet and we will need a lot of time to understand it,” he said.
Ruff said he hopes to collaborate with Sweetman and other scientists involved in dark oxygen research to understand how the chemical signature of oxygen produced by electrolysis of seawater differs from that produced by microbes or radiolysis.
Dark Oxygen and the Search for Extraterrestrial Life
NASA officials are interested in research into dark oxygen production because it could inform scientific understanding of how life might sustain itself on other planets without direct sunlight, Sweetman said.
The space agency wants to conduct experiments to understand how much energy is needed to potentially produce oxygen at higher pressures that occur on Enceladus And Europethe icy moons of Saturn and Jupiter, respectively, he added. These moons are among the targets for studying the possibility of life.
Deep-sea mining companies aim to extract the cobalt, nickel, copper, lithium and manganese contained in the nodules for use in solar panels, electric car batteries and other green technologies. Some companies have challenged Sweetman’s research.
Critics say deep-sea mining could irrevocably damage the pristine underwater environment and could disrupt the way carbon is stored in the ocean, contributing to the climate crisis.
The Metals Co. said it had submitted a rebuttal to Nature Geoscience, the journal that published original research. The submission was undergoing peer review but has not yet been published, the company said.
Sweetman said he was aware of the critical reaction and would respond “through peer-reviewed channels.”
“We are completely convinced that this is a real process going on at the bottom of the sea,” he said.
Sweetman also said it was prudent to suspend exploitation of seabed resources until the ecosystem was better understood.
Amy Gartman, a research oceanographer and global marine minerals project leader at the U.S. Geological Survey’s Pacific Coastal and Marine Science Center in Santa Cruz, Calif., said the USGS has not observed any electrical phenomena in the ferromanganese nodules examined so far. She was not involved in either Sweetman’s or Ruff’s research.
“Researchers are currently trying to replicate the phenomena reported by Sweetman and others,” she said. “Scientific research is a process and it may take some time before a conclusive answer is found. »