Methane Carbon Cycling in the Past: Insights from Hydrocarbon and Lipid Biomarkers

Abstract

Methane produced by thermal decomposition of organic matter, biological methanogenesis, and abiotic reactions plays a prominent role in biogeochemical cycles and climate forcing. There are, however, microbiological processes that efficiently mitigate its release into Earth’s surface environments. Lipid biomarkers are powerful tracers for methanotrophic (methane-consuming) organisms and their metabolisms. The particular strength of the biomarker concept, as compared to DNA- or RNA-based techniques, lies in its potential to track the methane-derived processes not only in modern settings but also on a geological time scale. In the past two decades, numerous studies have provided information on the lipid inventories of the key methanotrophic biota. In addition, compound-specific isotopic measurements have become an important tool for the recognition of tracer compounds for the turnover of methane in environmental samples. After a brief introduction about methane sources and sinks, I will provide an overview about the relevant lipid biomarkers that have been reported from aerobic and anaerobic methanotrophs and their habitats. Furthermore, the occurrence and utility of their diagenetic products as molecular fossils for methane carbon cycling in ancient environments will be illustrated.