Abstract
A one-dimensionalchemical-biological model is constructedto evaluate the capacity of surface
watertoabsorbatmospheric carbon dioxide. Themodel variables aretheconcentration of phytoplankton,
zooplankton, bacteria, particulate anddissolved non-biological organic material (carbon, nitro
gen, andphosphorus), nutrient (PO4, NO3, NH4), total CO2, alkalinity, anddissolved oxygen. The
model contains the verticaladvection with the constantupwellingrate and a verticaldiffusion process.
Forphytoplankton, processes such as photosynthesis, mortality, extracellular release, sinking andres
piration areconsidered. Forzooplankton, grazing, respiration and mortality processes, andforbacte
ria theprocesses of uptake of non-biological organic materials, mortality, andrespiration aretakeninto
account. Decomposition of non-biological organicmaterials, sinking, nitrification, and exchangeof
C02 and 02 with air are also includedin the model.
The model is examined for North Pacific surface water (42°N, 175°E) and compared with the
observed NOPACCS data (Northwest Pacific Carbon Cycle Study). The result reproduces the obser
vation exceptfordissolved oxygen. Theestimated carbon mass balance shows thatmostof the total
inorganic carbon utilized forprimary production is supplied within thesurface layers byregeneration
as well as from lowerlayer by verticaldiffusive flux. The supplyfrom air to be utilizedfor primary
producion is only a few percent, Sensitivity analysis shows that vertical water velocity shouldbe
smaller than 10^-6 (cm s^-1), and a verticaldiffusioncoefficientshould be about 1 (cm^2 s^-1) to reproduce
observedresults. Amongbiological parameters, the mortality rate of zooplankton and bacteriahave
littleeffecton thebiological pump,whilethe formation rateof calciumcarbonate cell affects the result
significantly. The limits andproblems of the present one-dimensional model are alsodiscussed.
