Group Leaders:  Ed Laws and Ray Najjar

Objective:  The goal of the biogeochemical modeling effort is to develop a model of carbon cycling in the ocean that simulates relevant characteristics of pelagic food webs and organic matter decomposition. Those characteristics should be incorporated into a global circulation model (GCM) that simulates the movement of carbon within the ocean and the exchange of CO₂ between the ocean and atmosphere.

Background:  Important aspects of the modeling effort will involve the identification of factors that limit photosynthetic rates at different times and places in the ocean and the relationship between the supply of those limiting factors and new and total production. Other aspects of the biological system that need to be simulated include: remineralization, diatom production, which is closely related to export production in many parts of the ocean, and the contribution of calcification to inorganiccarbon assimilation. An important constraint on the modeling effort is the need to develop a biological component that correctly simulates the important/relevant characteristics of carbon dynamics as influenced by biological processes without becoming so complex that incorporation into a GCM model becomes impractical.

Tasks:  The proposed treatment of marine biogeochemistry in the Ocean Carbon Model Intercomparison Project (OCMIP) is relatively crude. The short-term task for this working group is to create a more robust set of parameterizations to include in the first round of OCMIP simulations for fall/winter 1998.

Membership:
Edward Laws
Ray Najjar
Ken Caldeira
Richard Barber
Robert DeConto

Group Leaders:  Scott Doney, Ray Najjar, Ed Laws

Objectives:

Intermediate Biogeochemistry Model

The next obvious step for the Global Biogeochemistry working group is to develop, evaluate and study a more refined biogeochemical model beyond that used in the OCMIP-2 exercise but short of what might be considered a fully complete "ecosystem-bgc" model based on the ongoing synthesis of the JGOFS process and time-series data.  A number of key issues such as remineralization lengthscales, CaCO₃ and SiO₂ cycles, sediments, and coupling with the physical circulation (e.g. the HBEI issue) need to be addressed in the current generation of modern global GCMS.  Further, more detailed comparisons with the WOCE-JGOFS CO₂ survey data and resulting diagnostic calculations (e.g. surface fluxes, meridional transports, Redfield ratios).

During it's second half day session, the working group began to define the structure of such an "intermediate complexity biogeochemical model". The plan is to have such a model ready on the time-scale of the next few months so that experiments can be completed prior to next summer's workshop.
 
 

Tasks:

The group decided on two immediate tasks:

1. develop a hierarchy of models from geochemical up to full ecosystem, an example could include:  geochemical, + phytoplankton, + POM (lumping PZNDB), + PZND, + PPZZNNDD
2. the small breakout groups formed on Wed. will examine current treatments for the various paramerizations listed above and will make recommendations back to the full group in late summer/early fall.  The breakout groups do not cover all of the key processes included above so some reorganization may be needed.

In follow-up to the 1999 working group discussions, the issue of designing a biogeochemical model  beyond that offered in the OCMIP exercise but short of what might be considered a fully complete "ecosystem-bgc" model based on the ongoing synthesis of the JGOFS process and time-series data.   The list of both model considerations and needs is now better defined below

Model Considerations

1. Model Inputs:
• N
• Si
• Fe
• (P)


2. Model Ouputs

• POC
• DOC
• Silica
• CaCO3 export


3. Water column processes to be modeled

• Remineralization
• dissolution
• denitrification


4. Observations to be compared with model output

• Chlorophyll
• photosynthesis
• DON
• DOP
• POC
• PIC
• Flux of particles

Model Needs

1. Testbeds
• 1-D
• GCM


2. Workshop:  Iron and iron cyling