Summer circulation and exchange in the Saginaw Bay-Lake Huron system

Abstract

We use a three-dimensional, unstructured grid hydrodynamic model to examine circulation and exchange in the Saginaw Bay-Lake Huron system during the summer months for three consecutive years (2009-2011). The model was tested against ADCP observations of currents, data from a Lagrangian drifter experiment in the Saginaw Bay, and temperature data from the National Data Buoy Center stations. Mean circulation was predominantly cyclonic in the main basin of Lake Huron with current speeds in the surface layer being highest in August. Circulation in the Saginaw Bay was characterized by the presence of an anticyclonic gyre at the mouth of the outer bay and two recirculating cells within the inner bay. New estimates are provided for the mean flushing times (computed as the volume of the bay divided by the rate of inflow) and residence times (computed as e-folding flushing times based on dye concentration modeling treating the bay as a continuously stirred tank reactor) for Saginaw Bay. The average flushing time (over the 3 months of summer and for all 3 years) was 23.0 days for the inner bay and 9.9 days for the entire bay. The mean e-folding flushing time was 62 days (2 months) for the inner bay and 115 days (3.7 months) for the entire bay for the summer conditions examined in this work. To characterize the behavior of river plumes in the inner Saginaw Bay, trajectory data from GPS-enabled Lagrangian drifters were used to compute the absolute diffusivity values in the alongshore and cross-shore directions. Key Points We model circulation and thermal structure in Saginaw Bay and Lake Huron New estimates for residence times and exchange between the bay and the main lake Estimated diffusivities using Lagrangian drifters and particle transport models © 2014. American Geophysical Union. All Rights Reserved.