# Seismic shifts in the geochemical and microbial composition of a Yellowstone aquifer

## TL;DR

Earthquakes in Yellowstone can change underground chemistry and support microbial life by releasing hydrogen and carbon.

## Contribution

This study shows seismic activity can dynamically alter subsurface microbial communities through geochemical changes.

## Key findings

- Earthquake swarms correlate with increased hydrogen, organic carbon, and sulfide in aquifer fluids.
- Seismic energy alters microbial composition, increasing chemolithotrophic bacteria like Dethiobacteraceae and Desulfotomaculum.
- Mechanical fracturing of rhyolite releases organic carbon and hydrogen, suggesting a large subsurface reservoir.

## Abstract

Seismic energy, like that released by earthquakes, can fracture rock and thereby alter subsurface fluid flow paths, release substrates from inclusions, and expose fresh mineral surfaces capable of reacting with water. However, it is unclear how such seismic-induced changes influence microbial communities. Volcanically active areas experience frequent seismic activity and thus represent ideal locations to examine the influence of seismic-induced geochemical change on subsurface microbial communities. Here, we demonstrate that energy released in an earthquake swarm in 2021 correlated with extensive temporal change in the geochemical and microbial composition of aquifer fluids sampled from ∼100 m depth in a borehole in Yellowstone National Park. Increased energy absorbed at the borehole over time was correlated with increased concentrations of hydrogen, dissolved organic carbon, and sulfide and was associated with depletion of δ13C in dissolved organic carbon, increased concentrations of cells, and increased abundances of chemolithotrophic, putative hydrogen-oxidizing Dethiobacteraceae and Desulfotomaculum bacteria. Dissipation of the earthquake swarm was associated with decreased concentrations of hydrogen, sulfide, and cells. These results suggest the subsurface biosphere dynamically responds to seismic-induced geochemical change at the level of activity and growth. Laboratory mechanical comminution of rhyolite, the primary bedrock in Yellowstone, released organic carbon and hydrogen and generated hydrogen when exposed to water. This indicates the presence of a large subsurface reservoir of organic carbon and hydrogen that can be released or generated by seismic induced bedrock fracturing. Taken together, these data indicate seismic-induced generation of chemical disequilibria can support the persistence of complex subsurface microbiomes.