Thorium-234 as a tracer for deep-sea mining sediment plume deposition

Bryan J. O’Malley (), Patrick T. Schwing, Sophia K. Chernoch, Rebekka A. Larson, Michael Clarke, Leigh M. Marsh, Alastair J. M. Lough and Gregg R. Brooks
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Bryan J. O’Malley: 4200 54th Avenue South, Eckerd College, Marine Science
Patrick T. Schwing: 4200 54th Avenue South, Eckerd College, Marine Science
Sophia K. Chernoch: 4200 54th Avenue South, Eckerd College, Marine Science
Rebekka A. Larson: 4200 54th Avenue South, Eckerd College, Marine Science
Michael Clarke: 595 Howe Street, The Metals Company
Leigh M. Marsh: 595 Howe Street, The Metals Company
Alastair J. M. Lough: School of Geography, University of Leeds
Gregg R. Brooks: 4200 54th Avenue South, Eckerd College, Marine Science

Nature Communications, 2025, vol. 16, issue 1, 1-9

Abstract: 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 (234Th), 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 234Th to identify the spatial extent of plume deposition following the NORI-D mining test. Excess 234Th (234Thxs) 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 234Thxs, establishing a geochemical benchmark for plume extent and an operational tool for tracing recent sedimentation under future commercial-scale mining scenarios.

Date: 2025
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DOI: 10.1038/s41467-025-65625-y

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