Researchers from the Scottish Association for Marine Science and colleagues have discovered that the polymetallic nodule-covered abyssal seafloor in the Pacific Ocean produces the so-called ‘dark oxygen.’
A polymetallic nodule, collected from the ocean floor, in a lab at Northwestern University. Image credit: Camille Bridgewater / Northwestern University.
Polymetallic nodules — natural mineral deposits that form on the ocean floor — are common on the sediment-covered abyssal plains of oceans worldwide.
They are primarily composed of oxides of iron and manganese, but also contain metals such as cobalt and rare-earth elements that are essential components of many advanced and low-carbon energy technologies.
In the new research, Dr. Andrew Sweetman from the Scottish Association for Marine Science and his colleagues conducted experiments using chambers placed on the seafloor at depths of about 4,200 m to measure the oxygen concentration at multiple locations over 4,000 km apart across the Clarion-Clipperton Zone in the central Pacific Ocean, where polymetallic nodules are found.
Almost all these experiments showed the oxygen concentration steadily increasing over two days.
The researchers conducted follow-up laboratory analysis and propose that the polymetallic nodules are the source of the detected oxygen emissions.
Based upon numerical simulations, they hypothesise that the cause of oxygen generation is the electrical properties of the nodules.
While they note that it is difficult to estimate how much oxygen polymetallic nodules produce on a broader scale, they suggest that this oxygen source could support deep-seafloor ecosystems, which could be impacted if these nodules were to be mined.
“For aerobic life to begin on the planet, there had to be oxygen, and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” Dr. Sweetman said.
“But we now know that there is oxygen produced in the deep sea, where there is no light.”
“I think we, therefore, need to revisit questions like: Where could aerobic life have begun?”
The results appear in the journal Nature Geoscience.
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A.K. Sweetman et al. Evidence of dark oxygen production at the abyssal seafloor. Nat. Geosci, published online July 22, 2024; doi: 10.1038/s41561-024-01480-8
This article is based on a press-release provided by Springer Nature and Northwestern University.