Angel Cuesta, Marcel Jaspars

Physical principles need to be respected when interpreting controversial findings such as the production of abyssal oxygen. Such extraordinary claims must be analysed carefully before a large research effort is mounted and valuable human and financial resources are wasted based on flawed data. We are aware of the sensitivities around polymetallic nodules and their potential value as a source of essential metals for various applications, in particular in batteries for electric vehicles. This utility is however in conflict with the value of polymetallic nodules to deep-sea ecosystems. Although that value is unclear, the potential for damage caused by deep seabed mining must be considered in a habitat where metabolic processes are slow and recovery from damage may take centuries. The July 2024 issue of Nature Geoscience contained a brief communication suggesting the dark production of oxygen at the abyssal seafloor.1 This claim was soon followed by healthy scepticism.2–4 But those critiques missed the main point, namely, that the claimed abyssal production of dark oxygen, as proposed by Sweetman et al.,1 is simply thermodynamically impossible. In addition, Sweetman et al.’s findings contradict earlier reports,5 but this lack of agreement was not mentioned by them.