APPLICATION OF BIOMARKERS AND CARBON ISOTOPES TO COLD SEEP BIOGEOCHEMICAL PROCESSES

Methane flux generally controls cold seep biogeochemical processes and ecosystem. Anaerobic oxidation of methane (AOM) is the major sink of CH₄, which is mediated by methane-oxidizing archaea and sulfate-reducing bacteria, and the mechanisms of AOM can be traced using biomarkers and their carbon isotope ratios. Biomarkers for these microbes are depleted in ¹³C, and the δ¹³C values of sulfate-reducing bacteria biomarkers are enriched compared to those of archaeal biomarkers, indicating CH₄ carbon has flowed from archaea to bacteria during AOM. Methane flux also determines the microbial community structure of cold seeps, with the ANME-2 cluster dominating when CH₄ flux is high. Cold seep microbial community structure changes can be traced by the two biomarker indices, OH-AR and BIPH, with higher values for both when ANME-2 cluster dominates. Thus, biomarkers and their δ¹³C values can not only provide evidence suppoting the occurrence of AOM, but they can also be used to study environments and microbial consortium structure for both modern and ancient cold seeps.