Constraining and Understanding Bacterial Biomass and Production Variability in Ocean Ecosystems

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DucklowThis work is a part of the Synthesis and Modelling Program (SMP) of US JGOFS aimed at modelling and synthesis of data on carbon fluxes and transformations mediated by oceanic bacterioplankton. Bacteria are a major (and perhaps the dominant) component of biomass in many ocean systems and are practically the sole agents of dissolved organic carbon (DOC) turnover in aquatic ecosystems. Further, they contribute to particle formation and breakdown through intense biosynthetic and hydrolytic processes, thus influencing vertical sedimentation rates and patterns. An unprecedented amount of data on bacterioplankton abundance and production rates was obtained during JGOFS but it has yet to make its mark in ocean biogeochemistry. At the time the JGOFS studies were designed in the mid-1980's, conceptual models of bacterial processes were crude, and numerical models were largely nonexistent. Development of both types of models has advanced in the JGOFS decade, but mostly without benefit of empirical constraints. JGOFS bacterial data, on the other hand, have some significant shortcomings: extrapolations of biomass levels from abundance (and more recently biovolume) measurements are uncertain by perhaps an order of magnitude. Carbon-based rates of production derived from isotopic precursor incorporation rates are similarly uncertain. By participating in the JGOFS SMP, by improving and constraining existing models with new data, and by developing new models, both conceptual and numerical, the investigators plan to meet two principal goals: l) reduce the uncertainties of, and add meaning to the observations; and 2) improve our understanding of how bacteria influence carbon fluxes and ecosystem functions in ocean plankton systems. This research represents a collaborative effort between an observational marine microbial ecologist (Ducklow) and two ocean biogeochemical/ecological modelers (Fasham and Anderson).