Microbial methane oxidation in aerated subterranean ecosystems: an upscaling and intervention framework for climate change mitigation.

Aerated subterranean ecosystems are emerging as globally widespread yet understudied sinks for atmospheric greenhouse gases (GHGs), especially methane. Subterranean GHG cycling is driven by atmospheric exchange between the surface and subsurface, and by uptake by aerotrophic bacteria inhabiting cave surfaces. Despite growing evidence for these novel biogeochemical processes, aerated subterranean ecosystems remain largely omitted from Earth system models, GHG budgets, ecosystem service valuations, and climate change mitigation efforts. Here, we synthesise the current understanding of the subterranean microbial methane sink and provide a framework for upscaling uptake based on ventilation and biological determinants. We propose that enhanced subterranean aerotrophy could provide a novel pathway for atmospheric methane removal by leveraging caves and cave proxies as passive methane biofilters. We speculate that decommissioned mines might provide a similar opportunity. Based on this mechanistic understanding, we discuss key uncertainties and outline a research agenda to direct future research on subterranean ecosystems as a new potential lever for climate change mitigation.