This is a proposal for 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.  A central goal of JGOFS, and of ocean biogeochemistry overall, is understanding how ocean ecosystems control carbon flux between the atmosphere, ocean and sediments.  Among the major elements of the SMP is the following: "Modeling the major mechanisms responsible for observed local inventories and fluxes of carbon and other substances is essential to the development of larger-scale models.  There is therefore a need for mass balances for carbon and other associated substances at the process study and time-series sites as well as quantification of the principal controlling mechanisms" (NSF Announcement of Opportunity 98-133).  Bacteria are a major (and perhaps the dominant) component of biomass in many ocean systems. They metabolize amounts of carbon equivalent to ~50% of local primary production in the euphotic zone on a daily basis. A principal achievement of JGOFS was new recognition of the importance of dissolved organic carbon (DOC) in the ocean carbon cycle.  Bacteria are practically the sole agents of 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. The proposed research will contribute to the SMP goals by achieving improved quantitative understanding of the roles of bacteria in euphotic zone production and export of carbon and related biologically-active substances, an area targeted by the announcement of opportunity.

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, we hope to meet two principal goals: 1) 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.

The proposed research represents a collaborative effort between an observational marine microbial ecologist (Ducklow) and two ocean biogeochemical/ecological modelers (Fasham and Anderson). Ducklow participated in the four US JGOFS Process Studies and BATS and is responsible for most of the bacterial data collected by US JGOFS.   Fasham participated in NABE, and with Anderson, developed the prototype ecosystem models used in the current generation of ocean carbon models.  Our research will proceed in two parallel stages:  We will use simple mass balance budgets, flow analytical and numerical simulation models with JGOFS data on primary production and respiration, DOC turnover and particle fluxes to constrain estimates of bacterial stocks and fluxes in each of the process studies and time series.  With the "improved" JGOFS bacterial data generated by these exercises, we will develop new bacterial formulations and microbial components for ecosystem models to be used in the SMP.  We will also produce standardized data sets on bacterial processes for use by other modelers.