Modeling of Ocean Acidification in the Massachusetts Bay/Boston Harbor and over the US Northeast Shelf

The U.S. northeast coastal ocean is identified as a region that could be significantly influenced by coastal acidification. The enhanced acidification condition in the region changes with short-term variability caused mainly by the seasonality of lower trophic level biological respiration, precipitation minus evaporation, and changes in coastal river discharge and long-term variability due to climate change-induced interannual-decadal fluctuation of atmospheric CO₂ loading and the inflow of the cool and less salty water from the upstream. To examine biophysical mechanism for ocean acidification, we have developed a Northeast Biogeochemistry and Ecosystem Model (NeBEM) under the framework of the FVCOM-based ERSEM. This model was first validated for the Mass Bay and Boston Harbor through 1-D and 3-D experiments. Driven by the assimilated physical field output from the Mass Bay-FVCOM, NeBEM was robust to capture the seasonal variability of nutrients, phytoplankton, DO, pH and other geochemistry variables on both off-shore and near-shore monitoring stations. A comparison was also made with the existing Mass Bay water quality model (UG-RCA). With improved benthic-water interaction processes, NeBEM showed a better performance than UG-RCA in the near-shore region and inside Boston Harbor. We are extending NeBEM to cover the entire northeast coastal region. NeBEM has provided us a scientific tool to distinguish the relative importance of physical, geochemical and biological processes to the change of ocean acidification in the Mass Bay and over the northeast shelf.