Different Magmatic-Hydrothermal Fluids at the Same Magma Source Support Distinct Microbial Communities: Evidence From In Situ Detection

Submarine magmatic-hydrothermal systems are dominated by volcanism and generate unique biocenoses. However, the relationships between the microbial communities and the broad range of chemical and physical variability within the systems are poorly understood. Here, a high-precision in situ Raman quantitative technique was used for the hydrothermal fluids at the Onsen site and a newly found site named Faxian in a magmatic-hydrothermal system at the DESMOS caldera, Manus back-arc basin. The maximum in situ H-2 concentration (8.56 mmol/kg) at the Onsen site is the highest value ever reported in similar hydrothermal systems. In contrast, the diffuse fluid at the Faxian site was characterized by rich H2S (7.78 mmol/kg) but without H-2. The differences in mixing contents of seawater induced different geochemical reactions and fluxes of hydrogen and hydrogen sulfide. Furthermore, the existence of hydrogen- and sulfide-oxidizing genes suggests that the oxidation of hydrogen and hydrogen sulfide are the energy sources of the microbial communities at the two sites even within the same magma source. The in situ quantitative analyses of different types of fluids provide implications on the materials fluxes in the magmatic-hydrothermal system, and the relationships between widespread submarine volcanic activities and life in early Earth.