We seek to quantify and relate primary productivity, remineralization and net community production (NCP) in the mixed layer across different ecosystem/carbon cycling states (ECCs). More specifically, our measurements will contribute towards the determination of upper ocean ecosystem characteristics that are important in controlling the vertical transfer of organic matter to ocean depths. Through a combination of biogenic O2 gas and inorganic carbon and nitrogen inventory measurements, we will quantify the biological rate processes and fluxes in both autotrophic and heterotrophic members of the marine microbial community. Estimates of Gross
Primary Productivity (GPP) and respiration rates will be used in conjunction with mixed-layer integrated rates of NCP to quantify the overall carbon export from the mixed layer. In addition to the composition of the microbial community present (i.e., phytoplankton, bacteria and archaea) there is increasing evidence that their physiological status is also important in predicting carbon export. Thus, in tandem with our rate measurements, we will determine the marine microbial community composition through targeted DNA sequencing as well as sequencing of environmental RNA to determine gene expression that can be used to infer the physiological status of the microbial plankton community. Together, the integration of these measurements will allow for an unprecedented ability to examine how the form and function of upper ocean microbial ecosystems shape the carbon export potential across different ECCs. Using our combined measurements, we will test the following hypotheses: i) Specific phytoplankton and bacteria contribute disproportionately to NCP, ii) NCP is highest when there is low coupling between members of a given marine microbial community, iii) GPP and respiration rates in the mixed layer co-vary in tightly coupled microbial communities, and iv) the physiological status of phytoplankton will have a large influence on the NCP and is an important component to predicting NCP.