Seminar: Dr. Peter Douglas

Please join us as we welcome Dr. Peter Douglas, a Professor in the Department Earth and Planetary Sciences at McGill University for a seminar titled "Clumped isotope measurements as a new tracer of methane sources and sinks." Coffee will be served.

Abstract

Methane is an important greenhouse gas, and isotopic measurements have long been a valuable tool for tracing methane sources and sinks, both on a local and a global scale. Despite this, there are key ambiguities in conventional isotopic fingerprinting of methane. Recently, the measurement of multiply-substituted isotopologues, or clumped isotopes, has provided a new dimension of isotopic data that has the potential to provide important new insights into methane biogeochemistry. Clumped isotopes refer to methane molecules that contain multiple rare isotopes, such as 13CH3D or 12CH2D2, which recent developments in isotope ratio mass spectrometry and laser spectroscopy have made it possible to analyze at natural abundances. When methane forms in isotopic equilibrium, clumped isotope values are directly controlled by the formation temperature, providing an excellent tool for differentiating methane derived from different geological settings. However, methane produced by microbes in Earth surface environments is subject to a strong kinetic isotope effect that overwhelms this equilibrium thermodynamic signal. While the kinetic isotope effect complicates using this measurement for thermometry in some cases, it also has the potential to provide new insights into the metabolism of methanogenic microbes in different environments. I will provide an overview of clumped isotope measurements made to date and their ability to distinguish different methane sources and sinks, and then explore in more detail measurements of methane from high-latitude lakes, which recent studies suggest are an important source of atmospheric methane. Finally, I will discuss how clumped isotope measurements can be integrated with other isotope measurements to improve our understanding of global methane budgets.