| In situ observations including long-term moored measurements and multi-year gulf-wide ship survey data are used along with realistic coupled bio-physical ocean model simulations to study interannual variability of surface wind, river runoff, and hydrographic conditions in the Gulf of Maine and their couplings with the Alexandrium fundyense blooms in the region. Complex transport pathways in the GOM are examined by numerical surface particle trackings based on realistic circulation hindcast, and are further quantified using Lagrangian probability density function, the connectivity matrix, source and destination functions. Results show that the interannual variability in coastal connectivity has a strong impact on the spatial distribution of A. fundyense blooms. Comparisons of coastal currents to toxicity closure maps of A. fundyense blooms also suggest a linkage between alongshore transport and the downstream extent of toxicity.;During the 10-year (2002-2011) period this study has focused on, several years stand out by having anomalous hydrographic conditions in response to local and upstream/offshore forcing variability. Due to limitations in initial, boundary, and surface forcing conditions, it is often a challenging task to predict these anomalous conditions using regional ocean models. As a proof-of-concept study, an advanced 4-dimensional variational data assimilation (4D-Var) method is applied to hindcast the anomalous water mass and circulation conditions in summer 2012. By assimilating satellite and in situ observations in the GOM, the 4DVar system dynamically adjusts and incrementally refines model boundary condition, initial condition and surface forcing, thereby allowing for significant improvement in the prediction skill of our GOM regional ocean model.;The GOM regional circulation model is coupled with A. fundyense population dynamic model to study the germination, initiation, and development of an extensive A. fundyense bloom in 2008. As our previous bloom hindcast studies for 2005 and 2006, the coupled model is found to be capable of reproducing the hydrodynamics and the temporal and spatial distributions of A. fundyense cell concentration reasonably well. Model hindcast solutions are further used to diagnose 3-dimensioal structures of the bloom, and physical and biological factors controlling the bloom dynamics. Results support the hypothesis that cyst abundance is a first-order predictor of overall magnitude of the A. fundyense bloom, and that ocean advections have significant impact on the cell concentration in the western Gulf of Maine. |
