Phytoplankton production and community structure in an unstable frontal region

Results are presented for a two-phytoplankton model of an unstable frontal ecosystem. Vertical transport results in both an increased flux of nitrate to surface waters and to a transport of phytoplankton communities at a rate too rapid to track equilibrium. The former leads to an increase in primary production within the region by 10%. The latter is responsible for transient heterogeneity in distributions, especially of phytoplankton ratios. Although the inclusion of two size classes of phytoplankton does not appear to change significantly the total primary production compared to a single phytoplankton model, it does allow for a dynamic partitioning of phytoplankton biomass and production between the classes. This partitioning is controlled by biological responses to transport, dictated here by inter-class differences in nutrient limitation and mortality. Biological responses to upwelling are also shown to be dependent on the background nitrate profile.