Serpentinization and Subduction Mass Transfer Processes: Implications for Chemosynthetic Life in Modern and Ancient Forearcs

Convergent margins are key engines of mass transfer between Earth’s surface and interior, governing long-term fluxes of volatiles, redox-sensitive elements, and carbon. Subduction transports large quantities of water and carbon into the mantle, while fluid release and metasomatic reactions move these components into the mantle wedge and, in places, toward the surface. Central to this exchange is mantle wedge serpentinization, the slab-derived hydration of mantle wedge peridotite that alters redox conditions and generates reduced compounds such as H2 and CH4, directly linking deep Earth processes to carbon cycling and energy availability for subseafloor biosphere.In the modern Mariana forearc, serpentinite mud volcanoes provide a rare natural laboratory to directly interrogate the products and consequences of mantle wedge serpentinization. Our recent geochemical, isotopic, and lipid biomarker findings demonstrate that the availability of abiotic geofuels produced during serpentinization exerts a first-order control on the subsurface chemosynthetic microbial communities on a temporal scale (Kumawat et al., 2025). We present in situ stable oxygen isotope measurements of serpentine from several Mariana mud volcanoes, combined with published pore fluid δ18O compositions. They define systematic spatial trends in serpentinization temperature, from cold, trench-proximal settings to progressively hotter conditions deeper in the mantle wedge. Using our newly developed serpentine–water calibration, our data imply that these thermal gradients regulate redox evolution and the production of reduced volatiles and organic components, establishing dynamic energy landscapes that sustain life under high pH, nutrient limitation, and episodic substrate delivery.While mantle wedge serpentinization, serpentinite mud volcanism, and associated biospheres are increasingly well-constrained in the modern Mariana forearc, their occurrence and significance in the geological record remains largely unconstrained. We also present geochemical evidence for Early Cretaceous serpentinite mud volcanism preserved within the paleo-forearc basin within the Coast Ranges of California. Elevated fluid-mobile element inventories, systematic oxygen isotope record of serpentine, and textural evidence for mud-supported serpentinite transport are complemented by an extensive methane-seep fossil record and lipid biomarker signatures indicative of chemosynthesis-based ecosystems. Together, these observations suggest that mantle wedge serpentinization and focused fluid discharge have been major volatile and energy providers in Mesozoic convergent margins.By integrating modern forearc observations with ancient geological archives, this work highlights serpentinization as a persistent and efficient mechanism for mass transfer, redox modulation, and volatile cycling at convergent margins. These processes not only shape mantle metasomatism and arc evolution but also link deep Earth volatile pathways to the limits of habitability in the deep biosphere through Earth history. Kumawat, P., Albers, E., Bach, W. et al. Biomarker evidence of a serpentinite chemosynthetic biosphere at the Mariana forearc. Commun Earth Environ 6, 659 (2025). https://doi.org/10.1038/s43247-025-02667-