MODELING NUTRIENT AND PLANKTON PROCESSES IN THE CALIFORNIA COASTAL TRANSITION ZONE .3. LAGRANGIAN DRIFTERS

Two types of numerical Lagrangian drifter experiments were conducted, using a set of increasingly complex and sophisticated models, to inves tigate the processes associated with the plankton distributions in the California coastal transition zone (CTZ). The first experiment used a one-dimensional (1-D; vertical) time-dependent physical-bio-optical m odel, which contained a nine-component food web. Vertical velocities, along the track of simulated Lagrangian drifters, derived from a three -dimensional (3-D), primitive equation circulation model developed to simulate the flow observed within the CTZ; were used to parameterize t he upwelling and downwelling processes. The second experiment used 880 simulated Lagrangian drifters from a 3-D primitive equation circulati on model which was coupled to tile same food web and bio-optical model used in the first experiment. Parameterization of tile biological pro cesses in both experiments were based upon data obtained during the CT Z field experiments. Comparison of simulations with data provided insi ght into the role of the biological and physical processes in determin ing the development of the subsurface chlorophyll maximum and other re lated features. In both studies, the vertical velocities experienced b y a simulated Lagrangian drifter as it was advected offshore while ent rained within a filament played a major role in determining the depth to which the euphotic zone and the chlorophyll maximum developed. Also , as the drifters moved offshore, tile food web changed from a coastal , neritic food web to an offshore, oligotrophic food web due to the de crease in nutrient availability. The temporal development of the food web constituents following the simulated drifters was dependent upon t he environment to which the drifter was exposed. For example, the amou nt of time upwelled or downwelled and the initial location in the CTZ region greatly affected tile development of tile food web.