No deep-sea oxygen after all? Mining company criticizes research results

At the beginning of August, a study that claimed to have demonstrated unexpected oxygen production by manganese nodules on the seabed caused a stir. This research is now being heavily criticized. Both independent scientists and a deep-sea mining company are expressing considerable doubts about the results.

Key points of the criticism

Deep-sea mining company The Metals Company, which funded some of the research team's voyages, accuses the authors led by Andrew Sweetman of the Scottish Association for Marine Science of serious methodological flaws and selective reporting in their study published in Nature Geoscience. The company has published its counter-arguments on Earth ArXiv.

A central point of criticism concerns an unreported control experiment. An experiment in which chambers without sediment or nodules were used also showed an increase in oxygen concentration. This information was not mentioned in the original study. Further criticism is directed at the stress measurements on the nodules. Lars-Kristian Trellevik from the mining company Adepth emphasizes that a voltage close to the value required for water electrolysis was only briefly measured on a single nodule.

Michael Clarke, a marine biologist at The Metals Company, told Science: "None of the lines of evidence presented by Sweetman stand up to scrutiny." Critics argue that the observed oxygen could be explained by trapped air bubbles or current leaking from the measuring devices.

Sweetman dismissed the criticism and said his team was in the process of drafting a response: "We have nothing to hide." He argues that the results of the control experiment could be explained by the injection of cold surface water. He also emphasizes that the electrolysis is probably intermittent: "We say it's possible."

Independent assessments

Independent researchers are cautious. Adrian Glover, a deep-sea ecologist at the Natural History Museum in London, sees the exchange as a normal scientific process.

Matthias Haeckel from the GEOMAR Helmholtz Center for Ocean Research Kiel reported in the Science article that his team had not observed any oxygen production during similar measurements. He points out that almost 20 years ago his team also thought they had observed oxygen production on the sea floor, which later turned out to be trapped air bubbles.

What is piquant about the discussion is that ecological concerns and economic interests collide in deep-sea mining: The Metals Company has a major economic interest in mining the manganese nodules required for battery production in the deep sea. Oxygen production in the deep sea would stand in the way of these plans. Sweetman is now proposing follow-up expeditions to search for hydrogen as a by-product of water splitting in order to confirm the results of his study.

(vza)