A thirty-year retrospective analysis of Chesapeake Bay warming

Temperature variations in shallow, coastal marine environments are much greater than in open-ocean environments and substantially affect biogeochemical processes. Multidecadal warming trends directly impact these processes by increasing bottom-water oxygen demand and reducing oxygen solubility, together increasing the extent of hypoxia. An analysis of monthly/bi-monthly cruise observations from the Chesapeake Bay show that over the past 35 years, surface and bottom waters of the main stem have warmed at a nearly uniform rate with the rate of warming varying strongly from the head of the Bay (~0.4°C) to the mouth (1-2°C). To fully assess the relative importance of various mechanisms contributing to this observed Bay warming, we use a 3-D hydrodynamic–biogeochemical estuarine model based on the Regional Ocean Modeling System (ROMS) linked to an independent regulatory watershed model. Variousmodeling scenarios are conducted in which we examine the impacts of individual and simultaneous changes in atmospheric temperature, river temperature, ocean temperature and sea level. Preliminary results show that observed warming in the summer and cooling during late fall are consistent with atmospheric temperature trends over these same time periods. Contributions from riverine warming are generally only important within major tributaries, and the effect of shelf warming is most apparent in the southern Bay. Surprisingly, sea level rise has acted to modulate Bay temperature trends and reduce summer warming. Isolating these four warming mechanisms in various model scenarios can help us understand and predict how these warming mechanisms may continue to affect Chesapeake Bay hypoxia in the future.