Environmental Science and Engineering Seminar

Nitrous oxide (N₂O) is a potent greenhouse gas and ozone-depleting compound, and marine oxygen minimum zones (OMZs) are disproportionate hotspots of its cycling and emissions to the atmosphere. Yet predicting N₂O dynamics in these regions remains difficult because the nitrifying and denitrifying microbes that mediate N₂O production and consumption are diverse, spatially structured, and often represented only implicitly in ocean biogeochemical models. In this talk, I present a redox-informed framework for modeling microbial metabolisms across marine biogeochemical gradients. This approach represents diverse aerobic and anaerobic microbes as metabolic functional types whose growth, resource demands, and biogeochemical transformations are constrained by the chemistry and energetics of the reactions they catalyze. In this framework, nitrogen cycling emerges from ecological interactions among functional types rather than from prescribed transformation rates. Functional types compete for shared chemical resources, while the products of one metabolism can become the substrates for another, creating cross-feeding networks that organize nitrogen transformations across oxygen, organic matter, and nutrient gradients. I then embed this model in an eddy-resolving simulation of the Eastern Tropical South Pacific to examine how circulation, environmental variability, and biogeochemical forcing shape microbial community structure and, in turn, N₂O cycling. The model reproduces the characteristic vertical structure of N₂O, with low concentrations in the anoxic core and accumulation in the surrounding oxyclines. This structure arises because metabolic cross-feeding among denitrifier functional types tightly couples N₂O production and consumption in the anoxic core, while aerobic competition, grazing, and physical transport progressively decouple production from consumption at redox boundaries. The resulting imbalance sustains supersaturated N₂O layers at the periphery of the OMZ that can be ventilated through coastal upwelling and mixing, demonstrating how microbial niche structure within OMZs can regulate emissions at the ocean–atmosphere interface. Together, these results provide a mechanistic basis for predicting how cellular-scale redox metabolisms shape greenhouse-gas cycling in a changing ocean.