Synthesis & Modeling Project
Richard Barber 
Fei Chai 
Richard Dugdale 
Frances Wilkerson 
Tsung-Hung Peng 

New and export productivity regulation by Si and Fe in the Equatorial Pacific Ocean

NSF: OCE-9712359/ 9802061/ 9802060/ 9802062 36 months

PROJECT DESCRIPTION: To identify and quantify the principal processes that control the partitionin g of carbon among oceanic reservoirs and between the ocean and atmosphere on local and regional scales, with a view towards synthesis and prediction on a global scale, is a specific goal of the U.S. JGOFS Synthesis and Modeling Project.  As a contribution towards achieving this goal, Drs. Barber, Peng, Chai, Dugdale and Wilkerson will develop an ecosystem model for the equatorial Pacific Ocean, with a focus on how silicate and iron affect new and export productivity and the partitioning of carbon between the atmosphere, surface ocean and deep ocean.  The study will use an ecosystem model embedded in a state-of-the-art general circulation model for the equatorial Pacific Ocean to investigate how new and export productivity responds to changing physical and chemical forcing.  The domain of the model is between 30S and 30N, 120E and 70W, with real geometry and topography, but analysis will focus on the equatorial region from 5N to 5S.  The recent upgrade of supercomputers at North Carolina Supercomputing Center (NCSC) (CrayT90) and Arctic Region Supercomputing Center (ARSC) (Cray-YMP) and the award of several hundred hours of CPU time to Peng, Chai and Barber make it possible to embed an ecosystem model with modest complexity in a high resolution, three dimensional prognostic ocean model,and to conduct numerous experiments on the ecosystem model structure and parameters in a timely and efficient manner.

Phase 1 of the project will modify an existing five-compartment ecosystem model by adding three more compartments (silicate, diatoms and mesozooplanktonic grazers) following the approach of Dugdale et al.  The preliminary objective of this three-dimensional Si/N/light model is to reproduce High  Nitrate-Low Silicate-Low Chlorophyll (HNLSLC) conditions.  With size-depend ent growth rate responses in small phytoplankton and diatoms and varying grazing vulnerability, the role of new diatom production regulating on Si and Fe can be thoroughly investigated.  Also in Phase 1, TCO2 and total alkalinity (ALK) will be added in order to calculate pCO2. The pre-industrial atmospheric CO2 (280 ppm) will be used to hindcast air-sea flux of CO2 in the equatorial Pacific.  New production regulating on silicate should provide a more accurate calculation of CO2 compared to using nitrate as a regulating nutrient.

In Phase 2 the effect of iron is added to the model making a, the initial slope of the photosynthesis vs. irradiance curve, a function of iron. The values of a are based on equatorial observations of natural and experimental iron additions. Independently, Ks for Si(OH4) is made a function of iron, an effect that involves only diatoms.  The `balance to bloom` transition will be simulated with the two iron effects to reproduce the IronEx 1 and 2 phytoplankton responses to a transient iron addition.  This modeling study will provide estimates of new and export productivity, and a formal description of Si and Fe as regulating mechanisms in the equatorial Pacific Ocean.  When new and export productivity is modeled accurately and validated with JGOFS studies, it will possible to predict with increased confidence how climate change may alter, via biogenic export, maintenance of the air-sea dpCO2 and hence the ocean's uptake and release of CO2.


DATA: Information on the 1-D upper ocean eocosystem model developed for the central and eastern Pacific Ocean can be found at: http://rocky.umeoce.maine.edu/1deco-new/1deco.htm. Download a TAR of model results (1.2M).

Data from this project can also be found via the Live Access Server of the University of Maine Ocean Modeling Group


Chai, F.; R.C. Dugdale; T-H Peng; F.P. Wilkerson; R.T. Barber (2002): One Dimensional Ecosystem Model of the Equatorial Pacific Upwelling System, Part I: Model Development and Silicon and Nitrogen Cycle. Deep-Sea Res. II 49: 2713-2745.

Dugdale, R.C.; R.T. Barber; F. Chai; T.H. Peng; F.P. Wilkerson (2002): One Dimensional Ecosystem Model of the Equatorial Pacific Upwelling System, Part II: Sensitivity Analysis and Comparison with JGOFS EqPac Data. Deep-Sea Res. II 49:2747-2768.

Dugdale, R.C.; A.G. Wischmeyer; F.K. Wilkerson; R.T. Barber; F. Chai; M. Jiang; T.H. Peng (2002): Source of meridional asymmetry of nutrients to the equatorial upwelling ecosystem and modeling of the impact on ocean-atmosphere CO2 flux. Deep-Sea Res. II 49:2515-2531.

Peng, T.-H.; F. Chai (2001): Modeling the Carbon Cycle in the Equatorial Pacific Ocean. The Conference Proceeding on Marine Environment, the Past, Present and Future. C.-T. Arthur Chen (editor), page 240-255.

also, Published Abstracts

Chai, F.; M.S. Jiang; R.T. Barber; R. Dugdale; T.-H. Peng; Y. Chao (2001): Modeling Carbon Cycle in the Pacific Ocean. Oceanography, Vol. 14, No.1, page 13.

Dugdale, R.C.; A.G. Wischmeyer; F.K. Wilkerson; R.T. Barber; F. Chai; M.S. Jiang; T.-H. Peng (2001): Dependence of equatorial Pacific export production and pCO2 on silica trapping in the Southern Ocean; implications for Paleo-oceanography and Paleo-climatology. Oceanography, Vol. 14, No.1, page 19.

Barber, R.T.; R.C. Dugdale; F.K. Wilkerson; F. Chai; M.S. Jiang; T.-H. Peng (2001): Modeling the ecosystem responses and CO2 drawdown of transient in situ iron-enrichment experiments in the equatorial Pacific Ocean. Oceanography, Vol. 14, No.1, page 6-7.


RELATED PROJECTS: Friedrichs et al.  "Regional ecosystem model testbeds. A JGOFS synthesis and modeling project."

Chai et al.  "Biogeochemical modeling of carbon partitioning in the Pacific: the role of Si and Fe in regulating production by siliceous and calcifying phytoplankton"


Richard Barber 
Duke University Marine Laboratory 
135 Duke Marine Lab Road 
Beaufort NC 28516-9751 
tel: (919) 504-7578 
fax: (919) 504-7648 

Fei Chai 
School of Marine Sciences 
5741 Libby Hall 
University of Maine 
Orono, ME 04469-5741 
tel: (207) 581-4317 
fax: (207) 581-4388 

Richard Dugdale 
Romberg Tiburon Center for Environmental Studies 
San Francisco State University 
PO Box 855 
3150 Paradise Drive 
Tiburon, CA 94920-0855 
tel: (415) 338-3518 
fax: (415) 435-7120 

Frances P. Wilkerson
Romberg Tiburon Center 
San Francisco State University 
PO Box 855 
3150 Paradise Drive 
Tiburon, CA 94920 
tel: (415) 338-3519 
fax: (415) 435-7120 

Tsung-Hung Peng
Ocean Chemistry Division 
4301 Rickenbacker Causeway 
Miami, FL 33149-1026 
tel: (305) 361-4399 
fax: (305) 361-4392