Synthesis & Modeling Project
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.
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.
Friedrichs et al. "Regional
ecosystem model testbeds. A JGOFS synthesis and modeling project."
Duke University Marine Laboratory
135 Duke Marine Lab Road
Beaufort NC 28516-9751
tel: (919) 504-7578
fax: (919) 504-7648
Frances P. Wilkerson