Collaborative Research: Ecosystem Structure, Biogeochemical Fluxes and Vulnerability to Climate Change Perturbations

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This project is part of the U.S. JGOFS Synthesis and Modeling Project (SMP) aimed at the SMP objective of understanding Mechanistic Controls of Local Carbon Balances, specifically the role of food web structure in controlling particle flux, particle export, nutrient regeneration and DOC production in oceanic systems. The collaborators will use data generated from the JGOFS process studies to consolidate field measurements into formal, quantitative descriptions of size and function-based food web groups and the material flows between them. They will use inverse techniques to infer unknown (unmeasured) material flows in the food webs. Finally they will use the trophic networks derived to test the stability of the plankton-biogeochemical ecosystem following potential perturbations to simulate changes due to ocean warming or increased stratification. Scientific reviews strongly support the assertion that understanding how the biological pump operates requires detailed knowledge of the relationships between food web structure, productivity, new production and biological fluxes. The amount of material leaving the surface layer is usually dependent on how it is partitioned among the plankton community. In an idealized plankton community, most of the primary production that passes through bacterioplankton and microzooplankton is likely to be recycled in the surface layer. In contrast, a significant portion of the primary production that passes through the mesozooplankton may become part of the sinking flux of organic matter via fecal pellet production and active transport below the euphotic zone due to vertical migration. Although many of the relevant processes were measured in JGOFS, the resulting data have never been rigorously condensed in a series of depictions of foodwebs consistent with all the data. This food web synthesis, a collaborative effort between Hugh Ducklow, George Jackson and Mike Roman, aims to further an ecosystem-based synthesis of JGOFS results. The goal is the construction or 'recovery' of a series of solutions to foodweb networks consistent with observations from the four major US JGOFS Process Studies in the North Atlantic (NABE); the Equatorial Pacific (EQPAC); the Arabian Sea and the Southern Ocean Process Study (AESOPS -- Ross). The project is based on the assumption that improved understanding of ecosystem structure and function depends critically on knowledge of the component rate processes, or inter-compartmental exchanges. There now exists a body of formal techniques and theory for analyzing the holistic properties of such flux networks. The research plan consists of four elements: 1. Consolidate field measurements into descriptions of size and function-based food web groups and the measured flows between them. 2. Use inverse techniques to infer unknown (unmeasured) material flows in the food web. 3. Use biomass and rate information to examine stability properties and how they differ, and how characteristic flow structures generate basin scale contrasts in particle export, nutrient regeneration, and DOC production in oceanic systems. 4. From the derived stability properties, infer the vulnerability of different foodweb structures (different ocean provinces) to ocean warming and changing stratification.