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.
Given high voltage potentials (up to 0.95 V) on [the polymetallic] nodule surfaces, we hypothesize that seawater electrolysis may contribute to this dark oxygen production.
ok, thats pretty damn cool.