Subterranean karst environments as a global sink for atmospheric methane

- Methane (CH4) was sampled in the air of 36 caves from the USA and New Zealand.
- Subatmospheric CH4 concentrations were measured in 35 of the 36 caves.
- The data indicate caves are acting as a global atmospheric CH4 sink.
- δ13CCH4 and δ2HCH4 values demonstrate caves have multiple CH4 sources.
- Acetate fermentation and carbonate reduction are widespread in the environment.