A yet-to-be peer-reviewed paper claims that the production of oxygen by polymetallic nodules through hydrolysis is not possible based on laws of physics. Specifically, the Dark Oxygen hypothesis requires that the 2nd law of thermodynamics be broken for hydrolysis to occur. The preprint version of that paper is located here (Link) (To be fair to Sweetman, he has detected oxygen and is speculating that it may be occurring due to hydrolysis, but he has also speculated that it could be due to the presence of oxygen-generating bacteria on the nodules)
The Sweetman hypothesis on Dark Oxygen is controversial. We know that previous tests have not detected the presence of oxygen production from nodules. Yet, our commitment is to follow the science, and that means following the scientific method. The scientific method requires that independent testing be done to confirm an experiment’s results. Until that independent testing confirms the results, the hypothesis should be treated for what it is – a hypothesis. Unfortunately, many media sources treated the Dark Oxygen hypothesis as if it was a validated fact when that was clearly not the case. We believe that they have done so for political reasons.
An even more important point, and one that has largely escaped consideration, is that the oxygen production that Sweetman hypothesizes about is fleeting (over very short time periods) and very limited in scale. We spoke with Sweetman about this and he confirmed that this is something that people do not appreciate. He speculated that it could be the removal of a fine amount of sediment from the nodules by the lander that causes the temporary production of oxygen – if that is what is really happening. In any case, as we have noted previously, the amount of oxygen generated in a forested terrestrial environment would be many orders of magnitude greater than what is speculated to be happening on the abyssal plains. In addition, the forested environment is also capturing and sequestering CO2 at a much greater rate than on the abyssal plains. So, if we want to talk about ecosystem services in this context, it is clear that strip mining forests is far more damaging than picking up nodules.
Dark Oxygen is interesting from a scientific standpoint, but it has little bearing on the debate around deep sea nodule harvesting.