Synthesis & Modeling Project
James Murray
Bruce Frost
Harilaos Loukos
Suzanne Strom
Food-web regulation of particulate export flux in high nitrate-low chlorophyll (HNLC) regions

NSF ('99), 36 months

PROJECT DESCRIPTION: 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 are determined by the size structure of the food web, but this has never been explicitly tested with models and is subject to debate.  The current paradigm is that there are two ecosystem states in which the biological community structure is a function of whether the system is in balance (steady state or State I) or influenced by transient events - changes in nutrient input, mixing or light - which allow decoupling of phytoplankton and zooplankton growth rates (State II).  Export flux and deep water remineralization is hypothesized to be different between these two states.

US JGOFS conducted its field studies in specific important ocean locations, but the US JGOFS synthesis needs to be conducted by ocean type.  The high nitrate-low chlorophyll (HNLC) regime is one of the most important ocean types studied during JGOFS.  Major process studies were conducted 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).  We propose to develop models to test hypotheses regarding grazing and particle export and remineralization starting with the most extensive data from the equatorial Pacific.  These models will be tested with data from other HNLC regimes, including the subarctic north Pacific and the Southern Ocean. Our goal is to provide a HNLC synthesis for SMP of euphotic zone production, consumption and export of carbon and related elements and transport and remineralization of these elements (SMP Element 2).

The goals of this study are to address the following key elements missing from current and past modeling efforts. 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 POC 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.  We plan to accomplish goals 2 - 5 by conducting a series of steady state and perturbation simulations.  The perturbed environmental  variables will be light, mixing and nutrients.  The simulated evolution of HNLC community structure and export will be compared with the observational data compiled under goal 1.


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James W. Murray
School of Oceanography
University of Washington
PO Box 357940
Seattle, WA 98195-7940
tel: (206) 543-4730
fax: (206) 685-3351

Bruce W. Frost
School of Oceanography
Campus Box 357940
University of Washington
Seattle, WA 98195-7940
tel: (206) 543-7186
fax: (206) 543-0275

Harilaos Loukos
7600 Sand Point Way NE
Seattle, WA 98115-0070

Suzanne Strom
Shannon Point Marine Center
1900 Shannon Point Road
Anacortes, WA 98221
tel: (360) 293-2188, (360) 650-7400
fax: (360) 293-1083