Nutrients and grazing in modeling the deep chlorophyll maximum

A representation of nutrients uptake and grazing processes, based on the sp ecific uptake rate of multiple nutrients and specific predation rate in 1-p redator_n-prey systems, is applied to a model for simulation of deep-chloro phyll maximum (DCM) in seas. In the original model a formulation for uptake processes was obtained from a mononutrient system. A detailed analysis of differences between the original and a modified model is performed. The mod ification increases the peak, but does not change the depth of DCM. Replaci ng the expression for grazing processes contributed to the differences betw een results more than a change in the uptake formulation. This is a consequ ence of two facts, (a) nutrient cycling plays a secondary role in the model , making nitrate dominant and ammonium a superfluous variable; while (b) pr ey concentrations are closer to their half-saturation constants. Since the original model was calibrated using improper formulations in uptake and gra zing processes, a new calibration was performed. (C) 2001 Elsevier Science B.V. All rights reserved.