Megathrust Earthquake Legacy Linked to Changes in Widespread Potential for Methane and Iron Cycling in Glaciated Wetlands

Abstract Freshwater wetlands are major sources of global methane emissions through biogenic methanogenesis, a process increasingly influenced by climate change. High latitude wetlands are subject to uniquely altered biogeochemical inputs due to disproportionate warming. For example, glacial meltwater delivers metal‐rich sediments that are easily reducible. Additionally, if the wetland is located upon a subduction zone, periodic and dynamic geological forces, such as megathrust earthquakes, can disrupt these systems further. To explore these interactions, we analyzed the genomic potential of microbial communities across a glaciated wetland located in an active forearc region subject to repeated megathrust ruptures. We found that sediment microbial communities contained the complete potential for methanogenesis and iron cycling, yet the relative abundance of key methanogenic genes was reduced in recently deposited freshwater sediments despite high levels of organic matter and iron. These findings suggest that megathrust fault activity and associated uplift exerts broad, abrupt change on microbial metabolic potential, and that overlying sediments reflect modern glacial input which modify the development of metabolic potential. Glacial influence likely disrupts methanogenesis by supporting communities capable of dissimilatory iron reduction, which may increase metal‐dependent methanotrophy. As climate change accelerates glacial melt, extant and newly developing microbial communities will likely respond rapidly to shifting carbon and mineral inputs, altering carbon cycling dynamics in these sensitive ecosystems. Our work links small scale microbial metabolic potential with some of the largest processes on our planet, revealing how cyclical tectonic events can overprint broad scale biogeochemistry by homogenizing microbial metabolisms and disrupting elemental cycling.