A study published this summer in Nature Geoscience captured widespread attention in both Norwegian and international media by claiming the discovery of oxygen production at the seafloor. If verified, this finding could point to a previously unknown source of oxygen generation on Earth, separate from photosynthesis.
The researchers behind the study conducted experiments using a specialized instrument lowered to the seafloor, which enclosed a section of the seabed and surrounding seawater. Typically, in such scenarios, oxygen levels in the water decrease as microorganisms consume it. However, in an unexpected twist, when measurements were taken in the Clarion-Clipperton Zone a vast area in the Pacific Ocean known for its abundance of metal-rich nodules oxygen levels were observed to increase instead.
These manganese nodules, scattered across the seafloor, have drawn interest from companies looking to extract metals critical for battery production and other technologies. The study proposed an intriguing hypothesis: that these nodules might function as natural batteries, generating enough electrical energy to split water molecules through electrolysis, thereby producing both hydrogen and oxygen.
Growing skepticism and criticism
Despite the study’s bold claims, it has recently come under scrutiny. Lars-Kristian Trellevik, Chief Scientific Operations Officer (CSOO) of Adepth Minerals, a Norwegian company focused on seabed mineral extraction, has raised serious doubts about the study’s findings. Trellevik and his colleagues have published a critical article challenging the study's credibility, suggesting that the observed rise in oxygen levels could be due to other factors, such as disturbance of the seafloor during the experiment or the presence of oxygen in the equipment when the measurements were initiated. Andrew Sweetman, a professor at the Scottish Association for Marine Science who led the original study, acknowledged the irregularities in the oxygen production data, cautioning against drawing broad conclusions from their results. He noted that oxygen production was not continuous and that measurements only began three to 24 hours after the instrument had settled on the seafloor.
Concerns over lack of hydrogen measurements
One of the key criticisms from Adepth Minerals is the study’s failure to measure hydrogen production. If electrolysis was indeed occurring, as the study hypothesized, hydrogen would have been generated alongside oxygen. Sweetman admitted that hydrogen was not measured in the initial experiments but expressed hope that future research would address this gap.
Questions about voltage and electrolysis
Trellevik and his team also questioned the reported voltage measurements, which are crucial for supporting the electrolysis hypothesis. The study reported a maximum voltage of 0.95 volts, but Trellevik argued that this is insufficient for electrolysis, which typically requires at least 1.23 volts. This discrepancy calls into question the study’s interpretation of the data and its broader claims about oxygen production.
Lack of control data
Another significant point of contention is the absence of control data—specifically, measurements from seafloor areas devoid of nodules. Adepth Minerals suggested that the voltage detected could have originated from other sources, such as an electrical fault in the underwater instruments rather than from the nodules themselves.
Sweetman countered this argument by noting that if an electrical fault had indeed caused electrolysis, the oxygen production would have been constant, which was not observed in their data.
Disputing claims on early atmospheric oxygen
Adepth Minerals further criticized the study’s speculation that the findings could provide insights into the early oxygenation of Earth's atmosphere and biological evolution. The study suggested that similar processes might have contributed to the initial oxygenation of the atmosphere. However, Trellevik and his team argued that "dark oxygen" generated in such a manner could not have played a role in early atmospheric oxygen levels, as the formation of oxides like those found in manganese nodules would have required pre-existing oxygen. Trellevik emphasized that while the study’s findings are indeed sensational, the evidence presented is too weak to support the far-reaching conclusions that were drawn. As the scientific community continues to scrutinize these claims, the study serves as a reminder of the importance of rigorous testing and verification in groundbreaking research.