Our proposed microbial analyses of Guaymas Basin and Sonora Margin subsurface sediments are guided by the working hypothesis that microbial communities will change in composition and metabolic potential, as hydrothermal activity decreases across the ridge flanks, chemical and thermal gradients are attenuated, and substrate availability changes. We propose that the distinctly different lithological and hydrothermal histories of these sediments, and their depositional contexts and changing quality and quantity of buried organic matter will affect the microbial community composition and activity.PI: Andreas Teske