Scientists have discovered that deep-sea minerals can produce oxygen even in a completely dark environment, indicating the existence of another source of oxygen besides photosynthesis. This finding challenges human understanding. So, how does oxygen get produced in the deep sea without light and the ability to carry out photosynthesis?
According to information on the United Nations website, the ocean provides half of the oxygen needed for human respiration and absorbs one-third of the carbon dioxide produced by humans. Before scientists announced this new discovery, it was widely believed that oxygen produced in the ocean was generated through photosynthesis by marine plants, requiring sunlight.
Drawing from an article published by Northwestern University on the science website SciTechDaily, along with reports from CNN and BBC, an international research group including chemists from Northwestern University found oxygen being produced at depths of 13,000 feet (about 4,000 meters) below the ocean surface where light cannot penetrate.
The study was published on Monday, July 22nd, in the journal “Nature Geoscience.”
This remarkable discovery challenges the long-standing assumption that only photosynthetic organisms like plants and algae can produce oxygen using sunlight. The research revealed that in the light-absent depths of the deep sea floor, oxygen appears to be generated by metal nodules that electrolyze seawater into hydrogen and oxygen.
When dissolved metals in the seawater accumulate on shell fragments or other debris, nodules are formed, a process that takes millions of years. Since these nodules contain metals like lithium, cobalt, and copper – all essential for battery production – many mining companies are now developing ways to collect these nodules.
In 2013, marine scientist Andrew Sweetman of the Scottish Association for Marine Science (SAMS) discovered this “dark oxygen” in the Clarion-Clipperton Zone of the Pacific Ocean while sampling the seabed. His team detected oxygen at a depth where photosynthesis-generated oxygen was deemed impossible. At the time, Sweetman thought the sensors must be faulty for registering oxygen readings and sent them back to the manufacturer for testing, but each time, they confirmed that the sensors were functioning correctly.
“When we first got this data, we thought the sensors were wrong because every study in the deep sea only found oxygen being consumed, not produced,” Sweetman said. “We recalibrated the sensors when we returned home, but over the course of ten years, these strange oxygen readings kept appearing.”
“We decided to use an alternative method, which works differently from the photodiode sensors we were using. When both methods yielded the same results, we knew we were onto something groundbreaking and unprecedented,” he said. “For there to be aerobic life on Earth, there must be oxygen, and our understanding was that the oxygen supply on Earth began with photosynthetic organisms. But now we know that oxygen can also be produced in the deep sea without light.”
In the summer of 2023, Sweetman contacted electrochemist Franz Geiger from Northwestern University to discuss possible explanations for the source of oxygen. In his previous research, Geiger found that the reaction of rust and saltwater can generate electricity. Researchers wondered if the polymetallic nodules in the deep sea could produce enough power to generate oxygen. This chemical reaction is part of the process of electrolyzing seawater to extract electrons from oxygen atoms in the water.
To investigate this hypothesis, Sweetman transported several pounds of polymetallic nodules collected from the seabed to Geiger’s lab at Northwestern University. In December 2023, Sweetman visited Northwestern University and spent a week in Geiger’s lab.
A voltage of only 1.5 volts (equivalent to a standard AA battery) is enough to electrolyze seawater. Surprisingly, the research team recorded a voltage of 0.95 volts on the surface of a single nodule. When multiple nodules are clustered together, the voltage increases, similar to batteries being connected in series.
“It appears that we have discovered a natural ‘geobattery.’ These ‘geobatteries’ could serve as a possible explanation for the creation of dark oxygen in the ocean,” Geiger said.