In July 2024, a scientific paper was published in Nature that claimed Dark Oxygen Production (DOP) was occurring on the ocean floor and may be associated with polymetallic nodules. The authors hypothesized that the oxygen production could be the result of electrolysis – the splitting of water into hydrogen and oxygen.
Without a doubt, the finding warrants further investigation.
Several scientists who have conducted similar studies, but using remotely operated vehicles instead of the deep-sea landers used in the Nature study, have not observed the same result and instead have only observed oxygen consumption rather than production.
A number of scientists have said they believe the oxygen measurements are real but are not sure electrolysis is the right explanation. One of the ways to find out is to measure hydrogen along with oxygen. If electrolysis is occurring, there should be two hydrogen atoms for every oxygen atom. To date, hydrogen measurements have not accompanied the oxygen measurements, and this is an important next step to confirm if the hypothesis is true.
Several groups have called into question the DOP paper based on what they say are flaws in methodology. For example, scientists familiar with the study note that control experiments conducted as part of the study showed oxygen production rose even when nodules were not present, yet for some reason this was not reported. Further investigation is warranted, in particular to establish if the results can be replicated or explained in a different way. It is also important to understand if the amount of oxygen being produced is significant and how widespread the phenomenon is.
Scientists have been studying ocean oxygen levels for many years and they have found that the primary source of oxygen in the deep Pacific Ocean is from the cold, oxygen-rich waters of the Southern Ocean around Antarctica. This oxygen is transported northward by deep ocean currents, with oxygen levels decreasing with distance from the source. This pattern suggests that oxygen produced by dark ocean production doesn’t significantly affect ocean oxygen levels, or that DOP might not be happening at all in these areas.
Human impacts to any ecosystem service need to be mitigated and managed. For commercial-scale polymetallic nodule collection, it is generally recognised that establishing a network of set-aside areas that are representative of the areas impacted by mining is the best way to ensure ecosystem health and function are maintained on a regional scale. Even if DOP is real, it is envisaged this approach to environmental management would remain valid.
Research in this space is ongoing and updates will be posted here in due course.
References
Evidence of dark oxygen production at the abyssal seafloor, Sweetman et al, 2024
How far does light travel in the ocean? National Ocean Service
Questioning Dark Oxygen Production in the Deep-Sea Ferromanganese Nodule Field, Nakamura, 2024