Wind Modulation of Dissolved Oxygen in Chesapeake Bay

A numerical circulation model with a simplified dissolved oxygen module is used to examine the importance of wind-driven ventilation of hypoxic waters in Chesapeake Bay. The model demonstrates that the interaction between wind-driven lateral circulation and enhanced vertical mixing over shoal regions is the dominant mechanism for providing oxygen to hypoxic sub-pycnocline waters. The effectiveness of this mechanism is strongly influenced by the direction of the wind forcing. Winds from the south are most effective at supplying oxygen to hypoxic regions, and winds from the west are shown to be least effective. Simple numerical simulations demonstrate that the volume of hypoxia in the bay is nearly 2.5 times bigger when the mean wind is from the southwest as compared to the southeast. These results provide support for a recent analysis that suggests much of the long-term variability of hypoxia in Chesapeake Bay can be explained by variations in the summertime wind direction.