Collaborative Research: Bacterial Production Uncoupled from Primary Production: Implications for DOM Fluxes in the Southern Ocean (JGOFS)

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95-31977 Kirchman This research project is part of the US Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program aimed at (1) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological and biogeochemical factors and processes which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. This research will investigate the role and quantitative importance of bacteria in the transformation of organic matter as part of the JGOFS Southern Ocean Process Study. Researchers hypothesize that extreme seasonal and spatial variation in the Southern Ocean leads to transient uncoupling between bacteria and primary producers as mediated through the dissolved organic matter pool. The principal goal of the research will be comprehensive spatial and temporal coverage of core measurements (bacterial abundance, biomass, and production). This will allow an integrated quantitative assessment of the fraction of primary production consumed by bacteria. Equally important is the study of the mechanisms controlling the rate and time frame in which primary production is processed by bacteria. This is critical to complement the core measurements and address these issues. Specifically, total bacteria counts will be complemented with counts of nucleoid-containing cells and respiring cells to determine the fraction of the bacterial assemblage that is active. Incubation experiments in collaboration with other researchers will examine variation in DOM lability and the growth yield of bacteria. This project will provide a quantitative and mechanistic understanding of variability in a major pathway of carbon flow, the microbial loop, in the Southern Ocean.