On the modeling of the seasonal variation in the three-dimensional circulation near Georges Bank

The sustainability of valuable fish populations and their associated ecosystems is currently receiving significant attention; in light of concerns regarding increased fishing pressure, pollution, catastrophic events, other human intervention, and possible global change scenarios. The situation is critical on Georges Bank, where both the United States and Canadian governments recently invoked severe fishing restrictions. Understanding the physical circulation is vital to resource management on Georges Bank, as early life stages of key marine species rely on it for survival.;In this thesis, 3-D circulation fields on realistic Georges Bank topography are computed and studied to gain insight regarding contributions from various physical processes to seasonal variations in circulation. The dynamics considered result from the dominant principal lunar tide, density variations, wind stress, up-stream conditions, and turbulence parameterization. The annual cycle is modeled as the progression through bimonthly, quasi-static circulation fields. Seasonal variations, resulting from associated differences in physical forcing, are important as key marine species spawn at various times throughout the year.;Analysis of six bimonthly solutions (computed using a fixed density, two-frequency, harmonic, finite element method (FEM) model) indicates important contributions to seasonal intensification of the Georges Bank gyre from tidal rectification, prescribed density gradients, and mean wind stress; with recirculating transport increasing by a factor of six from winter to late summer. Overall, these solutions are in approximate agreement with observations. Comparison of bimonthly circulation fields computed using a more advanced time-stepping model with harmonic model results illustrates the importance of incorporating advanced turbulence closure, tidal-time evolution of density, and improved treatment of nonlinearities. Other issues addressed pertain to advancement of 3-D coastal ocean FEM models; including discretization and boundary conditions for advanced turbulence closure. The applicability of computed flow fields is indicated by their use in studies addressing population dynamics on Georges Bank (e.g. Werner et al. (1993), Lough et al. (1994), Tremblay et al. (1994)).