The team discovers “dark oxygen” at the bottom of the sea

Children always ask, “Why?” It’s natural to want to know more as they are the first time they’re experiencing things. But as children grow into adults, they often dismiss something new that challenges their experiences and understanding.

This happened when we discovered a source of oxygen production in the deep sea, but we ignored it for nine years.

In 2013, I was conducting an experiment to measure undersea carbon cycling in the Clarion Clipperton Zone in the Pacific Ocean. This is very unusual, so two years later, when I returned to the same site, I took some optode (oxygen sensor).

These are designed to measure oxygen consumption, but instead showed oxygen production in the exact opposite direction I was expecting. Instead of questioning why we get these results, we rejected the reading as a result of a sensor failure.

We all teach from very early in education that oxygen is produced only through photosynthesis and that light is necessary. Until 2021, when we measured oxygen production in the second way, I realized that I had found an exception: dark oxygen – oxygen produced without sunlight.

In the summer of 2024, my team and I published their findings in the magazine Nature Geoscience.

The discovery of dark oxygen has changed our understanding of the deep ocean and potentially life on Earth. However, it remains to be seen how this oxygen is produced, to what extent, and whether it is ecologically significant for the deep-sea ecosystem in which it occurs.

Our paper suggests that the source may be rock-like formation, polymetal nodules made up of many different metals, including manganese, which make a difference in electrical potential when interacting with seawater.

These proposed that they could generate enough voltages to divide seawater into hydrogen and oxygen. A new Chinese study just showed that oxygen could potentially be produced when these manganese nodules are formed.

More “why” questions

This year we will explore some of these scientific questions. Showing that oxygen production is possible in the absence of photosynthesis, this discovery will change the way we see the possibilities of living on other planets.

Certainly, we are already talking to NASA experts who believe that dark oxygen can reconstruct our understanding of how life is maintained in other oceanic worlds like Enceladus and Europe.

It is also in the process of analyzing the potential for dark oxygen in the Central Pacific Ocean and developing dedicated and autonomous land or rigs. This will be the UK’s first opportunity to fall below 6,000m deep.

These vehicles carry specialist instrumentation to a depth of 11,000 meters. The pressure is multiple metric tons per square centimeter (which is equivalent to 100 heads sitting on you).

We investigate whether hydrogen is released during the creation of dark oxygen and whether it is used as an energy source for unusually large communities of microorganisms in parts of the deep ocean. We would also like to learn more about how climate change affects biological activity in the deep sea.

This project is the first of its kind to explore these processes firsthand. My team can study the deep seabed in the Hadal Zone, an area that reaches 6,000-11,000 meters deep and accounts for about 45% of the entire ocean. This habitat, filled with deep sea trenches, is still not well understood.

The discovery of dark oxygen clearly has potential implications for deep-sea mining. Deep sea mining is necessary to extract polymetal nodules containing metals such as manganese, nickel and cobalt, and to produce lithium-ion batteries for electric vehicles and mobile phones.

Although it remains to be seen how such an industry will affect the seabed, our research over the next few years will help answer many of the questions raised, perhaps better informing us where the seabed should be better protected from deep sea mining. One thing is for sure, whatever we find, I try to give a sense of childish enthusiasm and ask, “Why?”

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