ON THE SENSITIVITY OF ECOSYSTEM BOX MODEL SIMULATIONS ON MIXED-LAYER DEPTH ESTIMATES

A certain class of pelagic ecosystem box models uses the mixed layer d epth as the main physical forcing. This paper investigates the influen ce of the definition and derivation of the mixed layer depth on the si mulation results. For this investigation the model of Fasham et al. (1 990) (Journal of Marine Research, 48, 591-639) is used to simulate the phytoplankton bloom during the Fladenground Experiment in spring 1976 (FLEX'76). The time of establishment of the thermocline, the mean dep th and the temporal variability of the mixed-layer depth differ substa ntially between the estimates under consideration. Exactly those featu res influence the model results fundamentally. All processes and state variables of the ecosystem model examined for a series of representat ions of mixed layer development during FLEX '76 differ widely from eac h other and from observations. Temporal variability of the mixed-layer depth causes a variability of the onset of the plankton bloom of abou t two weeks. Consequently, this class of ecological models cannot repr oduce the dynamics of the spring bloom ecosystem appropriately; for th is purpose vertical mixing processes need to be represented explicitly . Copyright (C) 1996 Elsevier Science Ltd.