DIFFUSION AND REACTIONS IN THE VICINITY OF PLANKTON - A REFINED MODELFOR INORGANIC CARBON TRANSPORT

Inorganic carbon uptake by phytoplankton depletes the immediate cell e nvironment and disturbs the carbonate system equilibrium. Uptake is ba lanced by both diffusional transport across and chemical reactions wit hin the depleted boundary layer. In this study, we have derived a mode l that simulates inorganic carbon diffusion and reactions in the vicin ity of phytoplankton cells. To allow a general application of the mode l, the reaction kinetics of the carbonate system are reviewed and temp erature-and salinity-dependence of the various rate constants are disc ussed. A consistency condition for some of the kinetic rates is derive d. The effective thickness of the diffusive boundary layer in spherica l and planar geometry is discussed. In addition, the effect of cell sh ape on diffusive transport to phytoplankton is examined and a simple m eans to account for this effect in model calculations is presented. In a second step, the complete description of the diffusion-reaction sys tem is simplified to consider two special cases in which (1) algal pro duction relies on CO2(aq) as the single source of inorganic carbon, an d (2) CO2, HCO3-, or CO32- are utilized independently for organic matt er production combined with calcite precipitation. In the size range t ypical for phytoplankton cells model predictions of these simplified v ersions are nearly identical to those of the complete model, indicatin g that the simplified models represent good approximations of the comp lete diffusion-reaction system. (C) 1997 Elsevier Science B.V.