Exploration of Deep Ocean Ferromanganese Nodule Fields Using Radon as a Tracer

Ferromanganese nodules (Fe-Mn nodules) are considered as potential sources of in-demand metals (such as manganese, cobalt, nickel, copper, and rare-earth elements) that are used in high-technology industries. The resource potential of Mn nodules in the world ocean remains uncertain due to technological and financial challenges. Here we propose an effective tracer: the natural radioactive radon isotope (Rn-222) to assess the abundance of Fe-Mn nodules on the sea floor. Significant linear relationships were observed between benthic excess Rn-222 fluxes and concentrations with Fe-Mn nodule occurrence and coverage on the global seafloor. Benthic excess Rn-222 flux >10(7) dpm/m(2)/yr or bottom water Rn-222 concentrations >2,000 dpm/m(3) indicate the possibility of Fe-Mn nodules occurrence at >80% and seabed coverage of >25%. Our results indicate radon, relatively easy to measure, could serve as a novel and efficient tool for targeting Fe-Mn nodule resources in the global abyssal ocean.