Undersea Mystery: The Quest for ‘Dark Oxygen’ Stirs International Waters

A group of scientists led by British marine ecologist Andrew Sweetman is planning a new underwater expedition to explore ‘dark oxygen’ potentially formed on the ocean floor. Sweetman and his team have introduced two new devices capable of diving to depths of up to 11 kilometers, equipped with special sensors to measure the ‘respiration of the seafloor.’ The research will focus on polymetallic nodules (small formations on the ocean floor containing valuable metals like manganese, nickel, cobalt, and copper) located in the Clarion-Clipperton Zone-an extensive area between Hawaii and Mexico.

Scientists speculate that the nodules have sufficient electrical charge to split seawater into hydrogen and oxygen through electrolysis. The Nippon Foundation, a prominent supporter of marine research, is actively involved in this project, financing the expedition set for May 2026. Results from this study are expected within 24-48 hours after the devices are retrieved aboard the research vessel.

The outcomes of Sweetman’s previous research in 2024 hinted at the existence of ‘dark oxygen,’ sparking debates in the scientific community and causing concern among companies planning to mine valuable metals from the ocean floor. Some researchers suggested the detected oxygen might have been just air bubbles trapped in the measuring devices. Sweetman refutes these claims, stating that the team conducted tests ruling out such possibilities.

The new devices, designed to withstand pressures 1,200 times atmospheric pressure at Earth’s surface, bear resemblance to space exploration equipment. Despite criticism from the mining company The Metals Company, which partially funded the 2024 research, Sweetman emphasizes that the expedition’s goal is not to halt deep-sea mining but to gather as much information as possible to minimize its environmental impact. Recent reviews by Nippon Foundation and other stakeholders indicate potential rapid shifts in marine policies that affect mining permissions, especially pertaining to environmental sustainability.

Final results of the research will not be available before June, with further experiments possibly taking several months. Marine biogeochemist Matthias Haeckel from the German GEOMAR Helmholtz Centre for Ocean Research indicated that his research showed no signs of oxygen production by nodules. However, he noted that Sweetman would join his expedition at the end of 2026 to compare their methods carefully.