Thorium-234 as a tracer for deep-sea mining sediment plume deposition.
Where this comes from
- Record sourced from PubMed, PMID 41310330.
- Also identified by DOI 10.1038/s41467-025-65625-y and PMC identifier 12660702.
- Licence recorded as CC BY-NC-ND.
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Abstract
Deep-sea mining for polymetallic nodules is currently exploratory, but commercial-scale operations require indicators of environmental change to support regulatory thresholds and inform adaptive management. In the Clarion-Clipperton Zone, where background sedimentation rates are low, seafloor imagery has validated mining plume deposition but cannot resolve repeated sedimentation as nodules become buried. Thorium-234 (<sup>234</sup>Th), a naturally occurring radionuclide with a 24.1-day half-life and strong particle reactivity, serves as a high-resolution geochemical tracer. Here we apply sedimentary <sup>234</sup>Th to identify the spatial extent of plume deposition following the NORI-D mining test. Excess <sup>234</sup>Th (<sup>234</sup>Th<sub>xs</sub>) activity was low at baseline but elevated after mining and declined to background within 1-2 km of the directly mined area. Results suggest that mining plumes scavenge and redistribute <sup>234</sup>Th<sub>xs</sub>, establishing a geochemical benchmark for plume extent and an operational tool for tracing recent sedimentation under future commercial-scale mining scenarios.