r/GeologyExplained

A few years ago, researchers working more than 4 km below the Pacific noticed something that seemed impossible: oxygen levels inside their seafloor experiments were going up, not down.

The result was published in Nature Geoscience in 2024 and quickly became known as “dark oxygen”, the idea that oxygen might somehow be produced on the deep seafloor without sunlight or photosynthesis.

One proposed explanation was especially strange: polymetallic manganese nodules scattered across the Clarion-Clipperton Zone might behave like natural “geobatteries,” creating electrical potentials capable of driving chemical reactions that produce oxygen.

But the claim has become increasingly controversial.

Critics argue that the oxygen increases could be experimental artifacts caused by the benthic chambers themselves. Others have challenged the voltage measurements and the proposed electrolysis mechanism, while a later reanalysis questioned whether the oxygen signal was actually related to the nodules at all. In April 2026, Nature Geoscience added an Editor’s Note stating that concerns about the paper are under review.

So, is dark oxygen a genuinely new geochemical process occurring on the abyssal seafloor, or an extremely convincing measurement artifact?

Would be interested to hear what people here think, particularly about the chamber-artifact explanation versus the idea that some manganese-rich material really is producing oxygen.

The Silverpit argument has been running twenty-three years. It just got shocked quartz, and I still don't think it's settled.

Early 2000s: Philip Allen is working through 3D seismic from the southern North Sea and hits a set of concentric rings he can't account for. He pins the image to his office wall, hoping someone walking past will explain it to him. Simon Stewart, in the building on unrelated business, sees it and says it looks like an impact structure. Nature, 2002.

Then John Underhill points out that Zechstein salt withdrawing at depth produces circular collapse features all over that basin, and said that's all this was. The Geological Society staged a debate on 6 October 2009, audience mostly industry seismic interpreters, twenty minutes of argument, then a vote. 80:20 against impact. Silverpit went quiet for thirteen years.

What restarted it was an unsolicited email. Ronnie Parr at the North Sea Transition Authority read the Nadir crater papers and wrote to Uisdean Nicholson telling him to go back and look at Silverpit. He also pointed him at new high-resolution seismic that a carbon-storage survey had happened to shoot straight across the disputed central uplift.

The 2025 Nature Communications paper runs on that survey plus drill cuttings from a 1985 British Gas well. Two grains, quartz at 463 m, potassium feldspar at 494 m, carry shock lamellae recording 10–13 GPa, which no natural process on Earth produces except a hypervelocity impact. Two grains is still two grains, though, and Matthew Huber at the Planetary Science Institute has already told Eos as much: with that little you can reasonably ask whether they were reworked in from somewhere else, and he expects the paper to get argued over. Nicholson's team has an answer for the shallower grain. Not, so far, for both.

Full writeup on Geoscopy, including why the crater shrank from 20 km to 3.2 km and what the modelling says about the chalk being flash-baked into CO₂