Volcanic ash inputs enhance the deep-sea seabed metal-biogeochemical cycle: A case study in the Yap Trench, western Pacific Ocean

Although volcanic ash deposition into oceans has been a frequent phenomenon for much of geologic history, the potential effects on deep-sea seabed metal-biogeochemical cycles remain enigmatic. In this study, we analyzed mineral compositions, microbial communities, and metal-related functional genes in a sediment core with volcanic ash layers from the Yap Trench in the western Pacific Ocean. The mineralogical analysis showed that volcanic activity introduced large amounts of Fe-rich igneous minerals, such as olivine, pyroxene, hornblende, grossularite, and biotite, into the trench seabed sedimentary environments. Furthermore, some differentiation in microbial communities was observed and potential Fe-metabolizing bacteria (such as Pseudomonas, Alteromonas, Marinobacter, Halomonas, Pseudoalteromonas, and Erythrobacter) were dominant in the volcanic ash layers. Moreover, compared with the background sediment metagenome, the volcanic ash metagenomes were enriched in pathways for siderophore synthesis and uptake, and metal resistant functional genes. These results suggest that volcanic ash can lead to changes in trench-sediment-based microbial communities and stimulate microbial Fe acquisition and other metal-related metabolism. In response, microorganisms could promote decomposition of the metal-rich volcanic minerals and metal release rates from them, subsequently enhancing the deep-sea metal-biogeochemical cycle.