Modeling Nutrient and Plankton Processes in the California Coastal Transition Zone: 3. Lagrangian Drifters

Two types of numerica,1 Lagrangian drifter experiments were conducted, using a, set of increa, singly complex and sophisticated models, to investigate the processes associa, ted with the plankton distributions in the California coastal transition zone (CTZ). The first experiment used a one-dimensional (l-D; vertical) time-dependent physical-bio-optical model, 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 the upwelling a, nd downwelling processes. The second experiment used 880 simulated Lagrangian drifters from a 3-D primitive equation circulation model which was coupled to the same food web a, nd bio-optical model used in the first experiment. Para, meterization of the biologica,1 processes in both experiments were based upon data, obtained during the CTZ field experiments. Comparison of simulations with da,ta, provided insight into the role of the biological and physical processes in determining the development of the subsurface chlorophyll maximum and other rela, ted features. In both studies, the vertical velocities experienced by a simulated La, gra, ngian drifter as it wa, s advected offshore while entrained within a filament played a mador role in determining the depth to which the euphotic zone and the chlorophyll maximum developed. Also, as the drifters moved offshore, the food web changed from a coastal, nefftic food web to an offshore, oligotrophic food web due to the decrease in nutrient availability. The temporal development of the food web constituents following the simulated drifters was dependent upon the environment to which the drifter was exposed. For example, the amount of time upwelled or downwelled and the initial location in the CTZ region greatly affected the development of the food web.