A study reports evidence of dark oxygen production (DOP) at the abyssal seafloor in the Pacific Ocean, attributed to polymetallic nodules. In situ benthic chamber experiments showed oxygen levels increasing to over three times background concentrations, with DOP rates ranging from 1.7 to 18 µmol O₂ m⁻² d⁻¹. This production was confirmed using the Winkler method and was not due to experimental artifacts, as no significant differences were found between treatments or chambers. DOP was also observed in ex situ incubations, suggesting it occurs in multiple locations across the Clarion-Clipperton Zone (CCZ). The study hypothesizes that DOP may result from seawater electrolysis, driven by high voltage potentials on nodule surfaces. The potential energy for this process comes from the electrochemical gradient within nodule layers, possibly involving metal catalysts like manganese oxides. The 'geo-battery' hypothesis is supported by the link between DOP and nodule surface area, with larger nodules having more active sites. However, DOP activity may vary with nodule spatial density and type, and upscaling results by area is cautioned. The study also explores other potential mechanisms, including radiolytic oxygen production and chemical reduction of manganese (IV) oxide, but these contribute negligibly to DOP. Understanding DOP's mechanisms and spatial distribution is crucial for assessing its role in abyssal ocean ecosystems and broader Earth history. The findings contrast with previous deep-sea benthic oxygen flux studies and suggest that DOP may provide oxygen for benthic respiration. The study highlights the need for further research to understand the variability and implications of DOP in deep-sea environments.A study reports evidence of dark oxygen production (DOP) at the abyssal seafloor in the Pacific Ocean, attributed to polymetallic nodules. In situ benthic chamber experiments showed oxygen levels increasing to over three times background concentrations, with DOP rates ranging from 1.7 to 18 µmol O₂ m⁻² d⁻¹. This production was confirmed using the Winkler method and was not due to experimental artifacts, as no significant differences were found between treatments or chambers. DOP was also observed in ex situ incubations, suggesting it occurs in multiple locations across the Clarion-Clipperton Zone (CCZ). The study hypothesizes that DOP may result from seawater electrolysis, driven by high voltage potentials on nodule surfaces. The potential energy for this process comes from the electrochemical gradient within nodule layers, possibly involving metal catalysts like manganese oxides. The 'geo-battery' hypothesis is supported by the link between DOP and nodule surface area, with larger nodules having more active sites. However, DOP activity may vary with nodule spatial density and type, and upscaling results by area is cautioned. The study also explores other potential mechanisms, including radiolytic oxygen production and chemical reduction of manganese (IV) oxide, but these contribute negligibly to DOP. Understanding DOP's mechanisms and spatial distribution is crucial for assessing its role in abyssal ocean ecosystems and broader Earth history. The findings contrast with previous deep-sea benthic oxygen flux studies and suggest that DOP may provide oxygen for benthic respiration. The study highlights the need for further research to understand the variability and implications of DOP in deep-sea environments.