Fig. 9: Schematic of microbial succession and biogeochemical processes in serpentinite mud at the Mariana forearc.
From: Biomarker evidence of a serpentinite chemosynthetic biosphere at the Mariana forearc
This schematic depicts lipid biomarker transitions from pelagic sediment communities to extremophiles adapted to high pH and redox conditions in serpentinite mud. The Mariana forearc biosphere is fueled by alkaline serpentinization fluids enriched in H2, CH4, DIC, and organic acids, sustaining specialized microbial communities. Lipid and stable carbon isotope data reveal a shift from relict methanogenic archaea, likely engaged in hydrogenotrophic methanogenesis, to a later ANME-SRB community mediating anaerobic oxidation of methane (AOM). Changes in substrate availability likely drove this transition. Distinct lipid signatures, including unsaturated diethers, acyclic GDGTs, and ether-based glycolipids, highlight adaptations to pH stress, phosphate limitation, and fluctuating redox conditions. The presence of in-situ branched GDGTs suggests previously uncharacterized bacterial communities persisting in these ultra-oligotrophic conditions. The Mariana forearc serpentinite biosphere, shaped by episodic fluid flow and substrate shifts, provides insights into deep-sea subsurface habitability. DIC = dissolved inorganic carbon, ANME anaerobic methanotrophic archaea, SRB sulfate-reducing bacteria, AOM anaerobic oxidation of methane, GDGT glycerol dialkyl glycerol tetraether.
