The mysterious Mr Sweetman and the unlikely story of dark oxygen

France, June 2025

I am in France, in the city of Nice, where a political event of the utmost importance is taking place. At the UN’s International Conference on Oceans, the groundwork is being laid for decisions that will affect the future of humanity in areas such as fisheries, fish farming, maritime transport, underwater technology, the commitments that each government will make to protect the marine environment and, of course, much of the discussion revolves around the silent protagonist of the global chessboard: the deepwater mining.

In his introductory speech, Emanuel Macron said: “One of our difficulties is to protect the seabed and ocean depths on the high seas. We have built a coalition to promote a moratorium on deep-sea mining and I can tell you all that this is absolutely essential. And why do I say that? I’m not against economic activity, on the contrary, however I think it’s madness to embark on a kind of economic activity that has the potential to disrupt benthic biodiversity, that will destroy it, that will lead to a release of carbon dioxide, it’s madness to interfere in environments that we know nothing about.

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“I am the first to admit that I am not in favour of mining, but at the same time I am not against it. I believe that in the future we may need to extract minerals from the depths of the sea. But my opinion is that if we do, we need to have as much information as we can possibly have before we go ahead.”

It is obscurantist to precede the economic exploitation of exploration. A moratorium on deepwater mining is an international, vital need. Let’s launch major exploration expeditions, let’s learn more, let’s harness science, but let’s not exploit the deep seabed! Let’s protect our ecosystems, because we don’t know what might happen next, because that’s where there are key carbon stocks, because that’s where there are species that nobody knows about yet. This fight is vital for all of us. And I want to make it clear that the depths of the sea are not for sale, just as Greenland is not for sale, just as Antarctica or the high seas are not for sale, just as fishing licences for developing countries are not for sale, just as scientific data or the safety of coastal populations are not for sale. We are talking about a common good. We are talking about a project that concerns us all, so let’s get started.”

What exactly is Macron referring to?

Deepwater mining is an industry that is being born right now. It is a process of finding and extracting minerals in the depths of the sea. The activity is not yet legal and the global debate is about when and under what conditions it will happen. Macron, in this excerpt from his speech, refers to the need for a moratorium, i.e. a temporary, worldwide pause in this debate until scientists have more knowledge of what is happening in the depths of the sea, which is the field of extraction of various minerals and ores.

A few days later, when asked by LiFO at a press conference whether there is any indication that the goal of a temporary halt to deep-sea mining will be achieved after this conference, one of the political leaders who support the idea, Palau’s Prime Minister Surangel Whipps Jr, replied, “In July, the International Seabed Authority will meet. We hope to continue the relevant assessment process for the moratorium that has already begun. What we ask is that there be no rush. There is no need for haste. Let us first make sure that we have the proper scientific knowledge, that we really know the consequences. That is what we are asking for.”

The International Seabed Authority is a very important player on the mining chessboard. It is an independent international authority whose purpose is to regulate operations involving minerals on the international seabed. Its function is defined by UNCLOS, the United Nations Convention on the Law of the Sea. Within this convention, legal regulation is also sought for the deep sea, which is difficult to regulate because it does not actually belong to any one country but is ‘the common heritage of mankind’.

The stakes

The subject of the debate is actually very practical: what is the procedure, what are the conditions and what are the competent authorities in order to start the commercial activity of certain companies that want to extract minerals from a part of the planet about which we know almost nothing? The emphasis placed on ‘science’ by the political world is no accident: quite simply, until now the technology to explore the depths of the sea did not exist and even now that it does, it is a very expensive sport. These two facts raise other questions, such as: who owns the knowledge? Does it belong to the company that has the money to hire scientists and keep their findings for personal use? What about the know-how acquired by the military? What about the scientific data that companies are not interested in and try to “disappear” so as not to jeopardize their commercial activity?

And this is where Andrew Sweetman, whose research accidentally went viral and brought this complicated conversation to the “for you page” of TikTok, comes in.

Andrew Sweetman and dark oxygen</h3

To understand what the professor shares below with the LiFO audience, a little context is necessary.

Professor Andrew K. Sweetman leads the Benthic Ecology and Biogeochemistry Research Group and is Chair of the Benthic Ecology and Biogeochemistry Section of the Scottish Association for Marine Science in the UK. He has been a researcher at several leading research institutions worldwide, including Woods Hole Oceanographic Institution and Florida State University, University of Maine, University of Hawaii at Manoa and University of Bergen.

In July 2024, Andrew Sweetman and his team publish a study in the journal Nature Geoscience, in which they argue something unprecedented: that there is evidence of “dark oxygen” in the ocean depths. This means oxygen production without photosynthesis. If Sweetman and his team are right, a new field of possibilities is created in areas that are both unexplored and commercially important.

Funding for this research was provided in part by The Metals Company, which is seeking permission from the US president to begin deep-water mining as soon as possible in the Clarion Clipperton area, where Sweetman found evidence of dark oxygen. Shortly after Sweetman’s research was published, TMC withdrew funding. The company’s CEO, Gerard Barron, said, “After a decade of research using the same methods, no credible scientist has ever found ‘dark oxygen’. Grandiose claims require grandiose evidence. We are still waiting.” Sweetman, who initially, and for nine years, doubted the evidence for the existence of dark oxygen himself, believing that what he saw could not possibly exist, found funding for the next three years from the Japanese foundation The Nippon Foundation, with the research focus on how dark oxygen is produced.

– I have read that when you had the first data on the existence of dark oxygen, you ignored it. I’d like to hear the story from you.
Yeah, well, the story goes like this: it all started in 2013, when we collected some samples from the seafloor that had bubbles. They were like a soda can. I saw the bubbles, but I didn’t know what they were. When I went back to the site two years later, I took oxygen detectors with me because I wanted to measure oxygen consumption. I was on the bottom and my instruments were showing an increase in oxygen. In all the experiments I had done up to that point, this was impossible. I had never seen it before. I immediately thought the instruments were broken, defective. I sent them back to the company for testing. The company said everything was fine, they were working properly. I went back in, measured again, said “they don’t work. They’re showing an oxygen increase.” The company told me again that they have been rigorously tested and are working properly. When I went back, nine years later, I took back-up equipment with me. When the oxygen detectors showed an oxygen increase again, we threw them away. They cost £10,000 each, we had three, we threw £30,000 worth of equipment in the bin. But I didn’t trust the method. So we tried another method. Again, increasing oxygen. And then I said, “Oh, my God, there’s something here that’s creating oxygen.” For nine years I was unaware of a very interesting process.

– At the United Nations International Conference on Oceans, when deep-sea mining was being commented on politically in relation to the moratorium, there was always the word “science” in there somewhere and the idea that they should wait for it before they started mining.
I’ll be the first to admit that I’m not for mining, but at the same time I’m not against it. I believe that in the future we may need to mine minerals from the deep sea. But my opinion is that if we do, we need to have as much information as possible before we proceed. As I’ve said to many journalists, all those of us who are involved in dark oxygen are asking for is three to five years to understand what it is, how important it is. It may not be important. And if it’s not important, we don’t have to worry about it. But we need that information before we fall on our faces. I think this is the most mature way to do it. And these few years are all we ask for.

– What would the presence of dark oxygen mean for ecosystems in the ocean depths?
There are no data yet to answer this question. Right now we know very little and in any case we cannot answer with certainty the question of how deep-sea mining will affect benthic ecosystems. We do know that dark oxygen exists. We have a huge amount of data showing that it exists. We still don’t know how it can exist. Is it an electrochemical process? Is it microbiological? Is it a mixture of the two? These are the answers we’ll have on page 500. Right now we’re on page 5. And that’s why some of us have started working on projects that will provide some of these answers.

– Your major funder pulled out when the survey was published. What happened?
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Yes. Suddenly they didn’t want to work with us. You will need to ask them why. When the survey was published, we were approached by The Nippon Foundation and told that they wanted to support our effort to understand what was going on.

– There has been strong criticism of your research and you personally. I have read reviews commenting on your methods and other types of criticisms attacking you.
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There have been a total of five rebuttals. Of these, none have been published in a reputable peer-reviewed journal and one is currently under consideration. We have, technically, proven that dark oxygen exists. The refutations, therefore, have not been published because they are scientifically incorrect. People say “there are published refutations against dark oxygen”, but that’s a lie. They are only on the internet, in pre-publication status. You could upload recipes to the servers that are uploaded. You could upload anything. Just because something is published on the internet doesn’t mean it’s accurate. We have proven 100% that the process happens. We just don’t know what’s causing it. People say there’s a lot of controversy, but that’s not true. We know with much, much certainty that what we’re seeing is happening. Just because we don’t understand it doesn’t mean it’s not real.

– Why didn’t someone find it before you?
It’s possible we’re not the first. I remind you, I ignored it for 9 years. It’s possible others found it and just ignored it.

– Yes, but wouldn’t you know it? Wouldn’t it have been heard? Wouldn’t it have been, at least, internal gossip in your academic and research circles?
Not necessarily. However, since the study was published, I have been contacted by some scientists who have written to me saying that they found something strange and that it is related to what we found. The other issue is that the equipment we use is terribly expensive and very difficult to use.

– Is it difficult to do research in your field?
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I think people don’t understand that research, for example, research in the Clarion-Clipperton area, is not done the way we did it and with the kind of equipment we used. Most surveys send a robot to the bottom and evaluate its results. Do you know how many experiments there are in the area with the expensive equipment we use? A Korean team did one. A French team did two. We’ve done fifty-four. So, another answer to “why now?” is that there simply aren’t enough surveys with proper equipment at these depths.

– Do you feel any pride in your research? Or responsibility?
Definitely responsibility. Pride? I wouldn’t say so. You know, after all, the discovery was made by accident. I don’t think the word “pride” is appropriate. It’s just a discovery. Sometimes they happen by accident. People find something and it takes them nine years to figure it out. Other times, it takes a lifetime. But yes, I feel responsible. When we found it, we knew we’d meet a lot of resistance. It’s been particularly difficult. I’ve been accused of being a liar, of being a fraud. We’ve been compared to convicted rapists. It hasn’t been a relaxed, stress-free year for me. Sometimes it’s been a very, very lonely year. But, you know, even if I knew in advance all the problems, all the accusations, all the negative reviews, all the things that would be said about us, I would still publish the survey. I think that’s the important thing.

This article was written as part of the 2025 UNOC Fellowship organized by Internews’ Earth Journalism Network. It was first published in Greek in LiFO on July 16, 2025.