Synthesis & Modeling Project
Fei Chai 

Richard C. Dugdale 
Richard T. Barber 
Tsung-Hung Peng 
Francis P Wilkerson 

Biogeochemical modeling of carbon partitioning in the Pacific: the role of Si and Fe in regulating production by siliceous and calcifying phytoplankton

For Period: 4/1/2002 - 3/31/2005

PROJECT DESCRIPTION: Physical and biological interactions play a complex role in the partitioning of carbon between the atmosphere, upper ocean, deep ocean and sediments. At present, interdisciplinary models offer the best means to test hypotheses about how carbon partitioning is regulated in various oceanic regions on time scales of years to centuries. The work proposed here is a new interdisciplinary modeling effort that brings together advances made in several areas important to the oceanic carbon cycle, and builds upon our current modeling effort. Our existing 1-D model for the equatorial Pacific upwelling system includes total dissolved inorganic carbon (TCO2), three nutrients (nitrate, ammonium and silicate), two phytoplankton components (diatoms and picoplankton), two grazing components (mesozooplankton and microzooplankton), and two detrital components (detrital N and Si). Based upon results from the existing model, we propose to investigate two related hypotheses: 1) that switches between diatoms and other phytoplankton groups (e.g. non siliceous picoplankton and calcifying phytoplankton) control carbon partitioning, such switches vary spatially and temporally and are regulated by Si and Fe in combination; 2) that changes in Si trapping in the Southern Ocean affect Si(OH)4 concentrations and Si and C uptake by equatorial phytoplankton that affect TCO2 thereby altering air-sea exchange of CO2 at the equator.

To test these hypotheses, we propose to 1) add a calcifying phytoplankton component to the existing phytoplankton compartments in the biogeochemical model to investigate the role of biogenic calcite formation with its potential to affect alkalinity and hence air-sea CO2 flux and downward carbon flux out of the euphotic zone; 2) include carbon system dynamics so that it will be possible to model alkalinity and inorganic carbon speciation due to calcite production and dissolution; 3) spatially expand the improved biogeochemical model developed for the equatorial Pacific to include the Polar Front of the Southern Ocean to the equatorial region; and 4) improve application of the Fe-sensitive growth parameters of the model to enable model experiments to be conducted to understand ecosystem response to Fe enrichments in the equatorial Pacific Ocean and the Southern Ocean. Accomplishing these objectives will provide an improved modeling approach to evaluate partitioning of carbon in the ocean and the importance of biological production by different phytoplankton in affecting surface TCO2 and thereby global air-sea flux of CO2.


DATA: no data submitted


PUBLICATIONS: no publications listed


RELATED PROJECTS: Barber et al.  "New and export productivity regulation by Si and Fe in the Equatorial Pacific Ocean."


Fei Chai 
School of Marine Sciences 
University of Maine 
5741 Libby Hall 
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

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

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

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