Microbial growth efficiency in the mesopelagic
Organic carbon sinking from the ocean’s surface can meet three fates in the dark waters below: it can be assimilated into biomass, respired back to carbon dioxide, or continue sinking to the seafloor. Quantifying these fates—the ocean’s biological pump—is essential to constructing a carbon and energy budget for the ocean’s interior, and predicting changes in this budget into the future. The growth efficiency of microorganisms, that is, what fraction of the carbon they consume becomes cellular biomass, is an essential parameter to developing balanced budgets of carbon storage in the ocean’s interior. The goal of this project is to develop novel cultivation techniques to establish bacterial and archaeal culture systems for understanding carbon, nitrogen, and energy flow in the mesopelagic in the subtropical North Pacific, using Station ALOHA as a model system. Efforts will be directed at determining quantitative physiological parameters such as growth efficiencies, substrate affinities, and temperature optima that can feed directly into predictive models of microbial ecosystem structure and function. The ultimate goal of this work is to construct an energy budget for the mesopelagic (from the base of the photic zone to 1000 m depth) to understand and predict the efficiency of the biological pump.