COUPLED PHYSICAL AND BIOLOGICAL MODELING OF THE SPRING BLOOM IN THE NORTH-ATLANTIC .1. MODEL FORMULATION AND ONE-DIMENSIONAL BLOOM PROCESSES

This is the first of two papers that introduce a mesoscale eddy resolv ing coupled physical and biological model system. The physical model c onsists of a quasigeostrophic interior with,a fully coupled surface bo undary layer. The nitrogen based biological model includes nitrate, ph ytoplankton, heterotroph and ammonium fields. This interdisciplinary m odel system is used to examine aspects of the 1989 JGOFS North Atlanti c Bloom Experiment data set. This-paper deals mainly with one dimensio nal processes and a companion paper addresses three dimensional phenom ena. The data set consists of two time series of observations taken fr om different water masses in the mesoscale environment. The general fe atures of the two time series are well represented by a one dimensiona l model when the mesoscale spatial variability in the initial conditio n is treated explicitly within the one dimensional framework. However, a significant bias is evident in the first time series as the samplin g pattern began in a warm feature and moved toward colder ones. Mistak ing spatial for temporal variability in this case results in an appare nt sink of heat and source of nitrate in the data. Removing this bias with the one dimensional model results in an f-ratio that is almost a factor of two higher (0.64) than computed by other authors based on nu trient inventories and primary productivity measurements (0.37). The s econd time series was conducted in the interior of a mesoscale feature and spatial biasing is minimal. The model forms a seasonal thermoclin e and nitracline that compare quite well with the data in both magnitu de and vertical extent. A subsurface ammonium maximum is generated by the model from an initially homogeneous profile that also agrees well with the data. Simulated primary productivity profiles match C-14 incu bations except on the final day of the simulation when surface nutrien ts appear in to have been exhausted slightly prematurely. Computed f-r atios are consistent with independent estimates based on uptake measur ements. A systematic parameter dependence and sensitivity analysis is carried out on these results. The most sensitive parameters are the ph ytoplankton and heterotroph maximum growth rates. Detailed analysis of the behavior of the system indicates tight coupling between phytoplan kton production and heterotrophic consumption even in the early stages of the bloom.