After a mission into the depths of the Pacific Ocean detected oxygen in an environment believed incapable of supporting photosynthesis, an international research team is in the final preparatory stages of a robotic expedition this Spring to hunt for the aptly named ‘dark’ oxygen.
Funded by the Japanese charitable Nippon Foundation, the mission could reveal a naturally occurring oxygen-generating source, a previously undiscovered biological process, or a hybrid system where biological organisms and natural seafloor formation work together to produce the mysterious O2.
Source of Controversial Dark Oxygen Remains a Mystery
Years ahead of the forthcoming mission, a team led by Andrew Sweetman, a sea-floor ecologist at the Scottish Association for Marine Science in Oban, UK, originally discovered the mysterious oxygen while working for a mining company in Vancouver, Canada. While that mission was designed to measure potential effects the mining of naturally occurring polymetallic nodules might have on the local environment, the landers deployed by Sweetman’s team found an unexpected signal of dark oxygen in the 4,000-meter-deep sunless abyss.
Unfortunately, the sensors used during that mission could not measure pH, limiting their ability to track the source of dark oxygen. Still, finding unexpected oxygen this close to the ancient, mushroom-shaped polymetallic nodules, which contain valuable metals like cobalt and manganese, led Sweetman’s team to suspect that a catalytic reaction similar to those used in hydrogen gas electrochemical cells could be occurring.
Unable to test further to rule out a biological cause, the source of dark oxygen has remained an unexplored mystery. The findings have also been met with skepticism by some other scientists, motivating the team to undertake the new expedition.
The Scientific Tools That Will Hunt for the Source
During a recent press conference, Sweetman’s team revealed the complex suite of instruments it will use to hunt for the source of the dark oxygen. Notably, these same sensors will be used in mirror laboratory experiments designed to simulate the 400 atmospheres of pressure found in the deep-sea environment where the first detection occurred.
“We will be taking landers that are specifically built to look at dark-oxygen production,” Sweetman told conference attendees.
When discussing mission launch, the sea-floor ecologist said his team will hitch a ride aboard the research vessel Nautilus as it travels to the Clarion-Clipperton Zone between Mexico and Hawaii. Once they reach the site of the first dark-oxygen detection, they will deploy two sea-floor landers equipped with a suite of sensitive instruments.
Once they reach the seafloor, the lander’s pH sensors will measure the proton concentrations in the local seawater. If these sensors detect unusually high proton concentrations, it would suggest that water molecules are splitting as they do in abiotic catalytic reactions.
Team member Jeff Marlow, a geobiologist from Boston University, said his team’s deep-sea hunt will include creating microscale mineral and microbial maps that could reveal a natural explanation. The researcher noted that the team would also probe for biological explanations.
“Our primary culprits are electrochemistry and biology,” Marlow told conference attendees. “Perhaps they work separately, perhaps they work in tandem.”
Lab Experiments Will Simulate Deep-Sea Environments
After the expedition returns with samples of the polymetallic nodules, Chemist Franz Geiger at Northwestern University in Evanston, Illinois, will use the simulated deep-sea environment to investigate their electrochemical properties. Geiger will also examine the nodules’ surfaces with a specialized transmission electron microscope designed for liquid cells.
During those experiments, Geiger’s team hopes to map the chemical states of the metals on the surface of the multi-million-year-old nodules when they are exposed to seawater and simulated pressures. The researcher said this process will involve custom-built, sensor-packed arrays designed to monitor voltage differences across hundreds of nodule locations. In theory, these experiments could demonstrate that the nodules catalyze water splitting, yielding an unexpected source of dark oxygen.
When discussing the value of solving the dark oxygen origin mystery, Sweetman said that understanding the complex dynamics of marine ecosystems is critical, especially if mining of the region’s natural resources occurs.
“If mining goes ahead, we can suggest mining practices that limit the damage as much as possible,” he explained.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.