Evidence of dark oxygen production at the abyssal seafloor

Deep-seafloor organisms consume oxygen, which can be measured by in situ benthic chamber experiments. Here we report such experiments at the polymetallic nodule-covered abyssal seafloor in the Pacific Ocean in which oxygen increased over two days to more than three times the background concentration, which from ex situ incubations we attribute to the polymetallic nodules. Given high voltage potentials (up to 0.95 V) on nodule surfaces, we hypothesize that seawater electrolysis may contribute to this dark oxygen production. Oxygen is generated abiotically at the abyssal seafloor in the presence of polymetallic nodules, potentially by seawater electrolysis, according to in situ chamber and ex situ incubation experiments.