The Gulf of Mexico is an ideal natural laboratory for studying the complexity of biological communities associated with gas hydrates. The development of growth-fault networks provide conduits for the migration to the sea floor of hydrocarbons formed in deep reservoirs. The resulting hydrocarbon seeps and solid gas hydrates on the sea floor support a diverse and abundant micro- and macro-biota. In addition, biologically mediated processes of hydrocarbon oxidation and sulfate reduction lead to the deposition of massive quantities of carbonates that modify sea floor geology and are critical to development of invertebrate communities. The long-term goal of this project is to understand the feedback relationships between carbon and sulfur cycling and community dynamics in gas hydrate systems in the Gulf of Mexico.
This will be a one-year pilot study involving investigators from the University of Missouri - Columbia, Texas A & M University, and the University of Tennessee. The first goal is to obtain basic information on the abundance, diversity, and activity of microorganisms, which are poorly understood relative to the geochemistry and to the invertebrate communities in gas hydrate systems. The second goal is to organize two workshops bracketing the research aspects of the project to foster future collaboration. The workshops will enhance dialog between different disciplines and prepare scientists in several fields to address questions at a systems level using interdisciplinary skills. The pilot study will be centered on testing of hypotheses using field and laboratory measurements. The investigators hypothesize that (1) the gas hydrate system harbors a distinct microbial community, which has high population density and high rates of sulfate reduction, hydrocarbon (including methane) oxidation, and H2 S oxidation compared to the normal marine environments; (2) methane oxidation coupled to sulfate reduction below the sediment surface provides reduced sulfur compounds that diffuse upward and serve as the energy source for sulfur-oxidizing bacteria at the sediment or gas hydrate surface where oxygen is available; (3) microbial oxidation of methane and other hydrocarbons strongly affects carbonate diagenesis. The experimental approach includes (1) culture-independent DNA-based molecular methods, lipid biomarkers, microscopic, and radioactive isotope tracer techniques to determine microbial abundance, activity, and species diversity, and (2) stable carbon and sulfur isotope fractionation, and pore-water chemistry to understand the kinetics and mechanisms of element cycles. Results of this project are expected to speak broadly to the evolution of biocomplexity in the marine biosphere given the wide occurrence of gas hydrates throughout geological time.
