Understanding the factors that control the magnitude of carbon export from the euphotic zone is one of the most important goals of the US JGOFS Synthesis and Modeling Project (SMP). It is assumed that the magnitude of this export, and its partitioning between particulate and dissolved forms, is determined by the size structure of the food web, but this has never been explicitly tested with models and is subject to debate. A current paradigm is that planktonic systems exist in two contrasting states. Community structure is a function of whether the system is in balance (steady state or State I) or under the influence of transient events - changes in nutrient input, mixing or light - which allow decoupling of phytoplankton and zooplankton growth rates (State II). Export flux and particulate organic matter-dissolved organic matter partitioning are hypothesized to be different between these two states. The high nitrate-low chlorophyll (HNLC) regime is one of the most important ocean types studied during JGOFS. Major process studies were undertaken by US JGOFS in the equatorial Pacific (EqPac) and Southern Ocean (AESOPS) and by Canadian JGOFS in the subarctic north Pacific. Prior to JGOFS, the subarctic north Pacific at Station P was studied by SUPER (Subarctic Pacific Ecosystem Research). The goals of this study are to 1) synthesize and analyze data from HNLC regimes worldwide, 2) use a 1-D model to explore the implications of different grazing formulations for ecosystem function and particulate organic carbon export in HNLC regions, 3) assess the relative importance of particulate and dissolved export, including the role of bacteria and zooplankton as remineralizers, 4) evaluate the elemental stoichiometric relationships that link the various reservoirs, and 5) explore the use of allometric relationships for production and consumption as a tool for understanding and modeling multiple states in HNLC regions. The overall goal is to provide a HNLC synthesis for the SMP of euphotic zone production, consumption and export of carbon and related elements (SMP Element 2), as regulated by variations in environmental conditions.
