A Numerical Study of the Circulation and Drifter Trajectories in Cobscook Bay

Cobscook Bay is situated in the easternmost part of Maine, US, bordering Canada's maritime province New Brunswick. Vigorous tidal currents mix the water column rich of nutrients, which make this small bay very productive biologically. Rapid growth in salmon aquaculture has a great impact on the ambient coastal environment. Since the intertidal flats account for a sizeable percentage of the total bay surface area at low water, it is necessary to include the wetting/drying process in numerical models when simulating the circulation of Cobscook Bay. The 3D nonlinear finite element ocean model Quoddy with a drying/wetting routine is used in this study to examine the capacity of tides to flush nutrients, pollutants and waste materials from the inner reaches of Cobscook Bay. Driven by major tidal constituents and realistic winds, the modeled circulation agrees well with observed data. Comparisons of time series from the model with in situ observations show that the ellipses at the GoMOOS buoy J are almost rectilinear following the regular cycle of the semidiurnal tide. Water level at Eastport matches observation very well. Several passive drifter experiments are conducted using a Lagrangian particle-tracking program, which agree very well with observed drifter trajectories. The fundamental mechanisms for exchanges between Cobscook Bay and the adjoining Passamaquoddy Bay are strong flooding/ebbing tidal currents and to a lesser degree the flows driven by the instantaneous local winds.