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Deep-sea polymetallic nodules: uses in research

Also: manganese nodules, ferromanganese nodules, Clarion-Clipperton Zone, dark oxygen

Polymetallic nodules are potato-sized lumps of iron and manganese oxides lying on the deep ocean floor. They hold metals such as nickel, cobalt and copper, which makes them a target for future deep-sea mining, and a disputed 2024 study suggested they may even release oxygen in the dark.

Known properties: Deep-sea polymetallic nodules

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Timeline

  1. 2020 Nodules as a source of critical metals
  2. 2024 Dark oxygen on the abyssal seafloor

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Nodules as a source of critical metals

Hein, Koschinsky and Kuhn reviewed how nodules of iron oxyhydroxides and manganese oxides take up metals such as nickel, cobalt, copper, titanium and rare earth elements, why they are a target for mining, and why the ecosystems that mining would affect must be better understood before operations begin.

As reported in: Hein, Koschinsky, Kuhn (2020). Deep-ocean polymetallic nodules as a resource for critical materials. Nature Reviews Earth & Environment. doi:10.1038/s43017-020-0027-0

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earth science

lab earth science 2024 Disputed

Dark oxygen on the abyssal seafloor

Sweetman and colleagues reported that oxygen rose to more than three times background levels over two days inside seafloor chambers on a Pacific nodule field. They attributed it to the nodules and, noting voltages of up to 0.95 V on nodule surfaces, hypothesized that splitting of seawater by electricity may contribute.

Disputed: other researchers have questioned the evidence that the nodules produce oxygen (see Downes et al. 2025, doi:10.3389/fmars.2025.1721853).

As reported in: Sweetman, Smith, de Jonge et al. (2024). Evidence of dark oxygen production at the abyssal seafloor. Nature Geoscience. doi:10.1038/s41561-024-01480-8

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