Interactions between life and planets in the modern
The modern day methane cycle: Methane and caves
Methane is a greenhouse gas in earth’s atmosphere, a natural resource for humanity as the major constituent of natural gas, and is an abundant molecule in the universe. Rocks that frequently host caves, like limestones and basalts, which are shown in blue and pink in the banner figure, are estimated to cover 20 % of earth’s land surface. My doctoral research sought to resolve the mechanism that is responsible for removing methane from cave air. Using the techniques of stable isotope analysis, qPCR, and 16S rRNA analysis in caves from Indiana to Vietnam my work has shown that methane is consumed in caves by the action of methanotrophic bacteria.
Fig 1. The stable isotopic composition of methane records the processes that affect methane, like its formation and consumption, similar to the way to the way that a resume records a person’s professional life. This data set collected from 36 caves around the world shows that the methane present in cave air was being consumed by methanotrophic bacteria and was influenced by two smaller sources of methane from two different biochemical pathways. Figure originally from Webster et al., 2018.
Despite our work showing that subatmospheric methane concentrations in cave air are caused by methanotrophic bacteria, the annual amount of methane consumed by caves remains unanswered. I am developing research to answer questions about the size of the cave methane sink through multiple lines of inquiry. Major collaborators of mine in this research are Arndt Schimmelmann and Jay Lennon.
Kevin D. Webster, Ph.D. 