Victoria Gill

Back in 2024, on a drizzly summer day, an email landed in my inbox. It was a tip-off about a new study that was about to be published in a big journal. I'm a science journalist, I get sent lots of new research every week. But the subject line grabbed me. It said, evidence of dark oxygen production at the abyssal seafloor.

So I opened it and read an extraordinary claim. Oxygen had been discovered two and a half miles down, produced at the bottom of the Pacific Ocean. In complete darkness. In a place where it couldn't possibly be made. School science textbooks tell us that oxygen is made by plants in sunlight. And there's no sunlight at the seabed 4,000 meters down.

So this was a tantalizing claim. If true, it could upend hundreds of years of scientific knowledge. Everything we know about how oxygen, that vital ingredient for life, is made. So I reported on it.

So I've come back to it, to investigate. And what I've discovered is much more than an interesting scientific claim. I want to tell you about what I've found. It's a story about a scientific surprise. This is like someone finding anti-gravity, or it was going to be a very controversial thing to get out there. A story of swirling controversy. You don't need to judge whether it's wrong, because it's already from the start impossible.

A story that collides head on with a billion dollar mission to mine metals in the deep sea. There's enough basically to replace every car on the planet with an electric vehicle at the moment. It's a row about science that became personal. We've been called fraudsters. It's harassment. It's vilification. And a story about how mysterious the deep ocean is. This is Dark Breath. I'm Victoria Gill.

I want to start at the beginning. Meet Andrew Sweetman, professor of seafloor ecology. He's the scientist at the centre of all this. I find him in a building packed with deep sea research equipment at the Scottish Association for Marine Science in Oban, northwest Scotland. Over here we have two of our 13 deep ocean landers. These are what are called seafloor respirometers. And this one has just arrived actually.

Olen melko iloinen, että olemme täällä ja eivät ole säällä tänään, koska täällä on melko kivaa. Tervetuloa Skotlandiin novemberiin.

Andrews deep sea landers are basically autonomous chemistry labs that carry scientific equipment to the seabed. The key bit of equipment on the lander is a chamber that clamps down and encloses a section of the seafloor so that samples and measurements can be taken from inside it. That's what Andrew and his team were using when they first registered a strange signal two and a half miles down on the Pacific seabed back in 2013.

They expected the exact opposite. Oxygen should be declining, consumed by the microbes and tiny creatures that live at the seabed. But somehow it appeared that oxygen was being produced. Andrew Sweetman first saw the phenomenon in 2013, then he says he saw it again in 2015 and again in 2018. After every cruise I would send components back to the manufacturer to say, look, these aren't working. I cannot figure out where this oxygen is coming from.

They would send them back a couple of months later saying, everything's fine, we've checked them. Then, in 2021, it happened again. Another scientist on that research trip was Andrews then PhD student, Daniela de Jonga.

Pääasiassa minun tekeminen oli kemiallisesti tarkistaa oksigen määrää. Andrew ja Daniela tekevät seuraavan kokemuksen lauluksella. He analysoivat laulukkoa, jonka saatiin sisällä ympäristöön. Pitäkää sinne, koska metodi on tärkeä. Kun laulukko on sisällä sisällä sisällä sisällä sisällä sisällä sisällä sisällä sisällä sisällä,

Up until this point, Andrew had dismissed the strange oxygen phenomenon again and again. You saw the oxygen going up and you disregarded that. I disregarded that for about nine years.

So Andrew and his team had seemingly made a huge discovery. Oxygen somehow being produced in complete darkness at the seafloor. But they didn't feel jubilant. We tried to think through all these sort of method issues that could potentially be there and tried to work through them all. But none of that explained what we were seeing.

And it was. But even more than the sheer surprise of the finding, there's another element of this story, a bit of context that made the stakes even higher. Because the site that Andrew was investigating is special. It's called the Clarion Clipperton Zone, a huge expanse of seafloor between Hawaii and Mexico that's littered with small black potato-sized lumps that formed naturally over millions of years. And they contain metals. Andrew thinks the apparent production of dark oxygen could have something to do with these lumps.

Deep sea mining companies want the metals in these nodules to power the green economy. It's been called a trillion dollar race to mine metals on the seafloor. There's enough basically to replace every car on the planet with an electric vehicle at the moment.

That's Michael Clark, environmental manager for The Metals Company, a Canadian deep sea mining operation. The Metals Company has a permit to explore and do research in the Clarion-Clipperton zone. In the future they want to mine there. When Andrew Sweetman made his dark oxygen discovery in 2021, he was working for Michael and The Metals Company.

Michael says Andrew Sweetman left the project early and that the metals company then engaged a third party to go back out to the same area with more sophisticated landers. That third party, he says, found no dark oxygen. The dark oxygen discovery made headlines around the world. And with that global coverage came intense scrutiny from other scientists. Some shared critiques of Andrew and his team online.

Andrew Sweetman and his team drew criticism from scientists and non-scientists alike. Comments have appeared on social media questioning the research and the conclusions, but I've also seen comments about the competence and the integrity of Andrew and his team. Some posts I've read on social media platforms, including LinkedIn and Reddit, have used terms like fabricating science, shoddy and even fraud to describe his claim of dark oxygen production.

His former employer also weighed in. In September 2024, a post on X from the metals company's CEO Gerard Barron's account described dark oxygen as bad science and Andrew Sweetman as having, quote, a dark ego. It went on to say of Andrew that, quote, this wannabe Einstein chose to go public with his unsupported extraordinary claims about dark oxygen production. A follow-up post included a short video of Russell Brand comparing himself to Jesus.

We asked the metals company about these posts in an email, but they didn't respond. I've been a science journalist for a long time, and I've spoken to many researchers who disagree over the conclusions that can be drawn from a set of data. But this row has at times felt hostile. It could be because dark oxygen crashed into a much bigger debate about whether we should mine the deep sea at all.