In a groundbreaking study published on July 22 in Nature Geoscience, an international team of researchers revealed that metallic minerals on Earth’s deep-ocean floor are triggering chemical reactions that produce a mysterious form of oxygen, dubbed “dark oxygen.” This discovery challenges the long-standing belief that only photosynthetic organisms, such as plants and algae, can generate oxygen on Earth.
Study details and discoveries
The study, titled “Evidence of Dark Oxygen Production at the Abyssal Seafloor,” suggests that oxygen can also be created in the depths of the ocean, where light cannot penetrate, supporting aerobic marine life that thrives in complete darkness. This finding has profound implications for our understanding of how oxygen is produced and sustained in the Earth’s oceans.
Initial observations and confirmation
Andrew Sweetman, of the Scottish Association for Marine Science (SAMS), first observed the phenomenon during ship-based fieldwork in the Pacific Ocean in 2013. Sweetman and his team noticed unusual oxygen readings while studying seafloor ecosystems in the Clarion–Clipperton Zone, a region known for its metal-rich nodules. Initially, they suspected faulty equipment but repeated measurements consistently showed the presence of oxygen.
“For aerobic life to begin on the planet, there had to be oxygen, and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” Sweetman explained. “But we now know that there is oxygen produced in the deep sea, where there is no light. I think we, therefore, need to revisit questions like: Where could aerobic life have begun?”
Breakthrough experiments
The team conducted further experiments to verify their findings. Franz Geiger of Northwestern University led the electrochemistry experiments, which provided potential explanations for the “dark oxygen” phenomenon. Sweetman and his collaborators confirmed their results using multiple methods, ensuring the reliability of their data. “We decided to take a backup method that worked differently to the optode sensors we were using, and when both methods came back with the same result, we knew we were onto something ground-breaking and unthought-of,” Sweetman added.
This discovery challenges our understanding of oxygen production
The key to this discovery lies in polymetallic nodules—mineral deposits found on the ocean floor composed of metals such as cobalt, nickel, copper, lithium, and manganese. These nodules, essential for modern technology, including batteries, are found at depths of 10,000 to 20,000 feet below the ocean surface. “The polymetallic nodules that produce this oxygen contain metals such as cobalt, nickel, copper, lithium, and manganese—which are all critical elements used in batteries,” said Geiger, co-author of the study. “Several large-scale mining companies now aim to extract these precious elements from the seafloor at depths of 10,000 to 20,000 feet below the surface. We need to rethink how to mine these materials so that we do not deplete the oxygen source for deep-sea life.”
This discovery challenges our understanding of oxygen production and raises important questions about deep-sea mining and its potential impact on marine ecosystems. As scientists continue to explore the ocean’s depths, this “dark oxygen” phenomenon may reveal new insights into the origins of life and the sustainability of deep-sea environments.
The findings, described by Sweetman as one of the “most exciting” in ocean science, mark a significant step forward in our understanding of Earth’s complex and mysterious ecosystems. As researchers delve deeper into these phenomena, the ocean floor may yet hold more secrets waiting to be uncovered.