This integrated biogeochemical and microbiological research program will explore the pathways
of and environmental controls on the consumption and production of methane, other alkanes,
DIC, LMW organic acids and sedimentary organic matter that fuel the Guaymas sedimentary microbial ecosystem. The hydrothermal sediments of Guaymas Basin provide a spatially compact, high-activity location for investigating novel modes of methane cycling and carbon assimilation into microbial biomass. In the case of anaerobic methane oxidation, the high temperature and pressure tolerance
of Guaymas Basin methane-oxidizing microbial communities, and their potential to uncouple
from the dominant electron acceptor sulfate, vastly increase the predicted subsurface habitat
space and biogeochemical role for anaerobic microbial methanotrophy in global deep subsurface diagenesis. Further, microbial methane production and oxidation interlocks with S and N transformations, which we will explore on the organism and process level in hydrothermal sediment microbial communities and mats of Guaymas Basin. In general, our first-order research tasks (rate measurements, radiotracer incorporation studies, genomes, in situ microgradients) will define the key microbial capabilities, pathways and processes that mediate chemical exchange between the subsurface hydrothermal/seep environment and the deep ocean waters.

In the proposed project, we will investigate genomic potential, physiological capabilities and biogeochemical roles of key uncultured organisms from Guaymas sediments, especially the high-temperature anaerobic methane oxidizers that occur specifically in hydrothermally active sediments; for this purpose, sediment cores from hydrothermal hot spots [to be determined with the Alvin heatflow probe] will be collected with HOV Alvin. We will focus on the role of methane-oxidizing archaea and other Guaymas microbiota in C transformations, but also explore their potential involvement in S and N transformations. First-order research topics include quantifying anaerobic methane oxidation under high T, P and in situ methane concentration, and with alternate electron acceptors; sulfate and sulfur-dependent microbial pathways and isotopic signatures under these conditions; and nitrogen transformations in methane-oxidizing microbial communities, hydrothermal mats and sediments. To complement these microbial and biogeochemical studies, we are planning to employ the AUV Sentry, build and operated by the Woods Hole Oceanographic Institution, for a mapping and photomosaic survey of the Southern Guaymas Trench and its adjacent regions. This survey should enlarge the commonly visited microbial sampling area, which is needlessly limited to a small area in the southern Guaymas Basin.