Abstract

--- - Depth-resolved geochemical and metagenomic analyses of a model hot spring in Yellowstone reveals the presence of an archaeal-dominated subsurface microbiome, which likely contributed to a dramatic acidification of the spring in 2018. - Despite over a century of study, it is unknown if continental hydrothermal fields support high-temperature subsurface biospheres. Cinder Pool is among the deepest hot springs in Yellowstone and is widely studied due to unique sulfur geochemistry that is attributed to hydrolysis of molten elemental sulfur at similar to 18 m depth that promotes several chemical reactions that maintain low sulfide, low oxygen, and a moderate pH of similar to 4.0. Following similar to 100 years of stability, Cinder Pool underwent extreme visual and chemical change (acidification) in 2018. Here, we show that depth-resolved geochemical and metagenomic-based microbial community analyses pre- (2016) and post-acidification (2020) indicate the changes are likely attributable to feedbacks between geological/geochemical processes, sulfur oxidation by subsurface Sulfolobales Archaea, and the disappearance of molten sulfur at depth. These findings underscore the dynamic and rapid feedback between the geosphere and biosphere in continental hydrothermal fields and suggest subsurface biospheres to be more prevalent in these systems than previously recognized.