Abiotic hydrogen (H ₂ ) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere

Free hydrogen (H₂) is a basal energy source underlying chemosynthetic activity within igneous ocean crust. In an attempt to systematically account for all H₂ within young oceanic lithosphere (<10 Ma) near the Mid-Ocean Ridge (MOR), we construct a box model of this environment. Within this control volume, we assess abiotic H₂ sources (∼6 × 10¹² mol H₂/y) and sinks (∼4 × 10¹² mol H₂/y) and then attribute the net difference (∼2 × 10¹² mol H₂/y) to microbial consumption in order to balance the H₂ budget. Despite poorly constrained details and large uncertainties, our analytical framework allows us to synthesize a vast body of pertinent but currently disparate information in order to propose an initial global estimate for microbial H₂ consumption within young ocean crust that is tractable and can be iteratively improved upon as new data and studies become available. Our preliminary investigation suggests that microbes beneath the MOR may be consuming a sizeable portion (at least ∼30%) of all produced H₂, supporting the widely held notion that subseafloor microbes voraciously consume H₂ and play a fundamental role in the geochemistry of Earth's ocean-atmosphere system.