Experts argue that a widely discussed 2024 study may conflict with basic thermodynamics, intensifying the debate over the claim of deep-sea dark oxygen challenged. Polymetallic nodules on the deep seafloor could produce oxygen in darkness, suggesting a new oxygen source in the abyss and raising questions about deep-sea ecosystems and seabed mining.
Now, a group of marine scientists and electrochemists says the claim may rest on flawed measurements and an implausible mechanism. Metallic nodules’ claim to act as natural batteries splitting water into oxygen and hydrogen is “fundamentally at odds with thermodynamics,” according to Live Science’s summary. A 2025 critique in Frontiers in Marine Science also reviewed the original evidence, questioning whether the observed oxygen increases were genuine seafloor processes.
The Original Study Claimed Oxygen Without Sunlight
The 2024 paper reported rising oxygen levels in benthic chamber experiments in the Clarion-Clipperton Zone, a deep Pacific region known for its polymetallic nodules. Because the seafloor there receives no sunlight, the authors argued that the oxygen must come from a non-photosynthetic source. They proposed that the nodules themselves might drive electrolysis-like reactions and generate oxygen in the dark.
That claim stood out because it contradicted decades of deep-sea oxygen flux studies that showed oxygen consumption at the seafloor, not unexplained oxygen production. Critics argue the anomaly should have prompted greater caution, especially given its unusual results compared to earlier work.
Reviewers Point to Data and Method Problems
The new criticism focuses on several issues. One of the biggest is that some of the chamber experiments cited in the debate reportedly did not contain actual manganese nodules, or contained only small manganese oxide particles. If oxygen rose in chambers without nodules, critics argue, then nodules cannot explain the effect. The Frontiers in Marine Science critique also says that elevated oxygen levels were observed in settings that appeared more consistent with experimental artefact than with a real geochemical process.
Critics also say the proposed electrolysis mechanism lacks a convincing energy source. In their view, the reaction as described would require more energy than the nodules could realistically provide under abyssal conditions. That is why some researchers now argue the paper’s conclusions cannot be trusted in their current form. The criticism has become strong enough that some experts have called for the paper to be retracted.
The Controversy Matters Beyond One Paper
The dark oxygen challenged dispute has drawn unusual attention because the original claim landed in a politically sensitive area. Polymetallic nodules, central to deep-sea mining debates, could influence scientists’ and regulators’ views on ecological risk if they aid oxygen production. This shift from a methodological disagreement to a broader debate about evidence, replication, and environmental policy explains the argument’s evolution.
The original research team has not abandoned the question. Scientists led by Andrew Sweetman plan further deep-sea expeditions in early 2026 using new equipment to test the “dark oxygen” idea more directly.. For now, though, the new criticism has shifted the balance of the discussion. Instead of asking what dark oxygen means for ocean life, many researchers are asking whether it even exists.