MICROBIAL COMMUNITIES AND DIFFERENTIAL METHANE FLUX IN ARCTIC GAS HYDRATE MOUNDS

Seafloor seeps are a source of methane, an important greenhouse gas if it enters the atmosphere in large quantities. Methanotrophy in seeps is important globally as it limits methane emissions to the hydrosphere by oxidizing large amounts of the hydrocarbon in sediments. Our goal is to determine how increased methane flux from seeps influences the sediment microbial community composition. We hypothesize that differences in the structure of sediment microbial communities will be evident in sites where recent episodic increases in methane flux have occurred as determined by modeled diffusion of porewater sulfate. Amplifiable DNA was extracted from 48 sediment samples recovered from seeps near Svalbard in the Arctic Ocean that differ in the degree to which the porewater chemistries are or are not at steady-state. Porewater sulfate determinations from the sites that are actively emitting methane exhibit concave-up profiles suggestive of increasing methane flux whereas one mound with no flare exhibits a profile suggestive of steady-state diffusive fluid kinetics. DNA sequencing and analysis is underway and will allow a comparison of microbial communities from below, within, and above the sulfate methane transition zone to estimates of methane flux histories at the respective sites. These data will improve our understanding of the complex interplay between physical and biological processes occurring in these biogeochemically important sites.