Why I’m leading an expedition in search of ‘dark oxygen’

An international team made headlines in 2024 after they discovered that the metallic nodules now sought by deep-sea mining firms were producing ‘dark oxygen’ in the depths of the Clarion Clipperton Zone (CCZ) in the Pacific. Such nodules contain high levels of metals like nickel, cobalt and lithium, which find uses in green technologies such as rechargeable batteries.

The origin of ‘dark oxygen’ at the ocean’s depth is largely unknown. The nodule’s themselves may be producing oxygen, with the team previously suggesting that the nodule’s charged surface may create the right conditions for water electrolysis.

The Nippon Foundation – a Japanese organisation with an interest in the world’s oceans – has just given a $5.2 million (£3.7 million) grant for a three-year long project to better understand this phenomenon. This includes deploying three purpose-built landers in the CCZ up to six thousand metres below sea level later this year.

Mason Wakley spoke to Andrew Sweetman, a biogeochemist at the Scottish Association for Marine Science, who is leading the project.