I work to better understand the interactions between microorganisms, their biogeochemical environment, and the Earth’s climate. A relatively small number of metabolic pathways drive the global cycles of climatically important elements, and bacteria and archaea mediate the majority of this cycling. My work hypothesizes that the activity of microbes within an ecosystem is sufficiently predictable to provide insight into the formation of large-scale biogeochemical features, such as anoxic oxygen minimum zones and patterns of nitrification. The predictability results from an assumption that much of the large-scale function of the microbial community can be understood by reducing that activity to its underlying chemistry and to the physiology of a microbial cell. Interactions of diverse microbial populations with each other and the environment results in the geochemical distributions that we observe. I work to develop simple models with mechanistic description of microbial growth and respiration to examine these distributions, their connections to rates of microbial activity and the biogeography of the microbial communities, and their sensitivity to changes in climate.