Geobiology
Biomarker evidence of a serpentinite chemosynthetic biosphere at the Mariana forearc
This study uncovers a unique chemosynthetic biosphere at the Mariana forearc through the analysis of geochemical and lipid biomarkers.
Imagine a place deep in the ocean where special rocks constantly react with water, releasing energy-rich gases like a natural, non-stop battery. This process also makes the water extremely alkaline, like a weak bleach. Scientists found tiny microbes living in the mud there, surviving by 'eating' these gases. They acted like detectives, analyzing the fatty molecules (lipids) left behind by these microbes in the mud. These 'molecular fossils' told them not only that life was there, but also what it was eating. They discovered that the microbes' diet changed over time, switching between making methane and eating methane, depending on what other 'food' was available. They also saw that these microbes build special, tough cell walls to protect themselves from the harsh, alkaline conditions.
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Serpentinization systems at the Mariana forearc emit reduced volatiles, serving as analogs for early Earth ecosystems.
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Microbial life persists in high pH, nutrient-scarce environments through adaptation mechanisms.
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Geochemical and lipid biomarkers evidence a shift from hydrogenotrophic methanogenesis to sulfate-dependent anaerobic methane oxidation.
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Membrane adaptations help microbes survive extreme conditions within serpentinite mud.
Present-day serpentinization systems, such as that at the Mariana forearc, are prominent sources of reduced volatiles, including molecular hydrogen (H2) and methane (CH4), and are considered analogs for chemosynthetic ecosystems on early Earth. However, seepage of serpentinization fluids through mud volcanoes at the Mariana forearc seafloor is defined by high pH, and nutrient scarcity, creating challenging conditions for microbial life. We present geochemical and lipid biomarker evidence for a subsurface biosphere shaped by episodic substrate availability, highlighting microbial persistence across steep geochemical gradients within serpentinite mud. Light stable carbon isotope compositions from diagnostic lipids reveal a temporal shift from hydrogenotrophic methanogenesis to sulfate-dependent anaerobic methane oxidation. Membrane adaptations, including unsaturated diether, acyclic and branched tetraether, and ether-based isoprenoidal and non-isoprenoidal glycosidic lipids, reflect microbial strategies for coping with this extreme environment. Our findings establish the Mariana forearc as a unique serpentinite-hosted biosphere, where life operates at the fringes of habitability. Serpentinization systems of the Mariana forearc host chemosynthetic microbial life shaped by substrate availability and membrane adaptations, as revealed through geochemical and lipid biomarker analyses of sediment cores.