An international team of scientists is embarking on an ambitious $5.2 million expedition to investigate one of oceanography’s most controversial discoveries: mysterious oxygen production occurring 4,000 meters below the Pacific Ocean surface, in complete darkness where photosynthesis should be impossible. Armed with custom-built deep-sea robots and sophisticated pressure chambers, researchers will return to the Clarion-Clipperton Zone in May 2026 to determine whether potato-sized metallic rocks are indeed functioning as natural “geo-batteries” that split seawater into oxygen and hydrogen.
The Controversial 2024 Discovery
The investigation centers on startling findings first published in Nature Geoscience in July 2024 by marine ecologist Andrew Sweetman and his colleagues at the Scottish Association for Marine Science. During routine seafloor respiration experiments, their benthic chamber landers (devices that seal off sections of the ocean floor to measure changes in oxygen levels) detected something completely unexpected.
Rather than the anticipated oxygen decline as organisms consumed the gas through respiration, oxygen concentrations tripled over 48 hours. Initial reactions assumed equipment malfunction. After extensive troubleshooting ruled out technical errors, the team concluded they had observed genuine oxygen production in an environment where sunlight cannot penetrate and photosynthesis cannot occur, a phenomenon they termed “dark oxygen production.”
The measurements revealed production rates between 1.7 and 18 millimoles of oxygen per square meter per day, substantial amounts equivalent to 0.5 to 180 percent of gross community production measured in the photosynthetically productive Equatorial Pacific. If confirmed, this would represent the discovery of an entirely new oxygen-generating process on Earth, challenging the long-standing paradigm that the abyssal seafloor functions exclusively as an oxygen sink.
However, the discovery immediately sparked scientific controversy. According to a critical analysis published in Frontiers in Marine Science, numerous previous investigations of seafloor oxygen fluxes in the same Clarion-Clipperton Zone using functionally similar benthic chambers consistently measured only oxygen consumption at rates matching the global abyssal average. None detected oxygen production.
The Geo-Battery Hypothesis
The proposed mechanism centers on polymetallic nodules, ancient mineral formations that accumulate on certain abyssal plains over millions of years. These potato-to-grapefruit-sized rocks contain valuable metals including manganese, nickel, copper, cobalt, and rare earth elements. The Clarion-Clipperton Zone alone contains an estimated 21 billion tons of these nodules, representing decades worth of global battery metal demand.
Sweetman collaborated with Franz Geiger, a chemist at Northwestern University who previously demonstrated that rust combined with saltwater can generate electricity. When Geiger’s laboratory tested nodules shipped from the seafloor, they measured voltage potentials reaching 0.95 volts on single nodule surfaces, comparable to a typical AA battery, which requires just 1.5 volts.
The hypothesis suggests these voltage gradients arise from uneven distribution of metal ions across nodule surfaces, creating electrical charge separation similar to battery electrodes. This electrochemical potential could theoretically split water molecules through seawater electrolysis, liberating oxygen and hydrogen, the same principle used in industrial hydrogen production, but occurring naturally.
Jeff Marlow, a geobiologist at Boston University and team member investigating the new expedition, noted that microbes could also contribute. Certain extremophile bacteria possess metabolic pathways capable of light-independent oxygen production through mechanisms like chlorite dismutation or nitric oxide dismutation. The truth likely involves complex interactions: perhaps electrochemistry and biology work separately, perhaps in tandem.
Specialized Equipment for Deep-Sea Investigation
The Nippon Foundation, a Tokyo-based charitable organization, is funding the follow-up studies with a $5.2 million grant. Project scientists unveiled their specialized instrument suite at a London press conference in January 2026, describing capabilities specifically designed to address criticisms of the original study.
The new benthic landers incorporate pH sensors to measure proton concentrations in seawater, high levels would indicate water molecule splitting and oxygen formation. The original landers lacked this capability, representing a significant limitation that skeptics highlighted. The updated probes will simultaneously measure oxygen concentration changes, pH fluctuations, and collect water samples for laboratory analysis.
According to the original Nature Geoscience study, researchers will deploy at least two different lander designs, each with distinct measurement capabilities, to cross-validate findings and eliminate potential instrument-specific artifacts.
Back at Northwestern University, Geiger’s laboratory will subject recovered nodules to extreme conditions matching the deep-sea environment using custom pressure chambers that recreate 400 atmospheres of pressure. Special transmission electron microscopes operating in liquid cells will map chemical states of surface metals in the presence of saltwater at the atomic scale.
Custom electrode arrays will measure voltage differences across hundreds of locations on individual nodules to determine whether they genuinely generate sufficient electrical potential for water splitting. These experiments aim to move beyond correlation toward demonstrating mechanism – the critical distinction between suggesting nodules might produce oxygen and proving how they accomplish it.
Deep-Sea Mining Hangs in the Balance
The timing of this research carries profound implications beyond pure science. The International Seabed Authority, the United Nations body regulating international seabed activities, is currently negotiating deep-sea mining regulations. Sixteen companies have already secured exploration contracts in the Clarion-Clipperton Zone, and several are pushing to begin commercial extraction operations.
The dark oxygen discovery was announced during the ISA’s 29th annual session and subsequently cited by the UN Scientific Advisory Board as a potential complication for mining regulations. If polymetallic nodules genuinely produce oxygen that sustains deep-sea ecosystems, removing them through mining could eliminate a crucial life-support system for organisms adapted to one of Earth’s most extreme environments.
Mining advocates counter that ocean floor ecosystems receive adequate oxygen from surface waters through ocean circulation. However, according to research covered by Yale Environment 360, studies of 1980s mining test sites reveal ecosystems that haven’t recovered after four decades – areas where not even bacterial communities have regenerated in previously mined zones, while unmined adjacent areas support flourishing marine life.
Deep-sea ecologist Sabine Gollner of the Royal Netherlands Institute emphasizes that we lack names for 90 percent of animal species inhabiting nodule fields. The rocks provide essential habitat for corals, sponges, and diverse microorganisms. Once removed by mining, nodules require millions of years to reform, meaning any dependent biodiversity and ecosystem functions would be lost essentially permanently from human perspectives.
May 2026: Return to the Abyss
By May 2026, the research team will board the vessel Nautilus and sail to the exact locations where dark oxygen was originally detected. The expedition represents a critical test not just of a specific hypothesis, but of how science responds to extraordinary claims.
Sweetman acknowledges that the findings diverge dramatically from established deep-sea ecology paradigms. Extraordinary claims require extraordinary evidence, precisely what the new expedition aims to provide through rigorous methodology designed to address every criticism of the original work.
The expedition will build “microscale maps” of microbes, minerals, and metabolic activity within and around nodules, seeking to understand whether biological processes complement or drive the observed oxygen production. Researchers will examine whether oxygen production varies across different nodule compositions, sizes, or locations within the Clarion-Clipperton Zone.
Marine biologist Lisa Levin noted particular interest in determining whether similar phenomena occur around ferromanganese crusts on seamounts, another target for deep-sea mining but found in lower-oxygen environments. If dark oxygen production helps sustain life in oxygen-depleted microenvironments, it could represent an even more critical ecosystem service than currently recognized.
The scientific community remains divided. Some researchers view the evidence as compelling and the mechanism plausible, while others point to decades of contradictory measurements from the same regions. The May expedition aims to resolve this debate definitively through comprehensive measurements that either confirm, refute, or refine the dark oxygen hypothesis.
As humanity stands at a crossroads between exploiting deep-sea resources and preserving poorly understood ecosystems, the dark oxygen investigation exemplifies how scientific discovery can reshape policy debates. Whether polymetallic nodules prove to be natural batteries sustaining abyssal life or merely curious geological formations, the answer will profoundly influence decisions affecting millions of square kilometers of ocean floor and the fate of mining operations worth billions of dollars.
Original Study Citation: Sweetman, A.K. et al., “Evidence of dark oxygen production at the abyssal seafloor,” Nature Geoscience (2024). DOI: 10.1038/s41561-024-01480-8
