LAUSR

Abstract Ferromanganese (Fe Mn) nodules are being widely explored for their significant economic potential. Microbial activity is often emphasized with respect to nodule formation. However, the relationship between microbial activity and Fe Mn nodule growth is still obscure. Here, we investigate the microbial community, elemental distributions, mineral compositions, and pore structural characteristics within Fe Mn nodules from the western Pacific Ocean. Abundant bacterial and archaeal communities were found in the studied nodules, and some species may be related to iron reduction, and manganese oxidation and anammox. Abundant mineralized manganese oxidizing bacteria were also observed in the nodules. In addition, more reduced manganese, more organic carbon, micron-sized pores, and higher bacterial diversity were detected on the younger surface layers of the nodules. These results reveal that more biogeochemical reactions occur in younger areas of nodules than in inner areas. We suggest that micro- and nano-structures within nodules provide a beneficial micro-environment and nutrition channels for biogeochemical activity that contribute Fe Mn nodule growth, and an interdependent relationship occurs between microbial ecosystems and nodules. Our work provides valuable insights into abyssal biogeochemical cycling at the deep-ocean sediment-water reaction interface.