Processes Controlling Eutrophication-Induced Acidification in the Northern Gulf of Mexico: Current State and Projected Changes from a Coupled Physical-Biogeochemical Model

The northern Gulf of Mexico receives excessive nutrient inputs from the Mississippi-Atchafalaya River Basin that promote high phytoplankton production and high respiration rates associated with algal decomposition. In combination with vertical stratification, respiration results in seasonal hypoxia, high dissolved inorganic carbon concentrations and low pH in bottom waters on the Louisiana Shelf. In the future, higher atmospheric CO₂ and hydrological and land-use changes in the Mississippi-Atchafalaya River Basin may further compound eutrophication-induced acidification on the Louisiana Shelf. Using a high-resolution, regional circulation-biogeochemical model that simulates the nitrogen cycle, oxygen dynamics and inorganic carbon dynamics in the Northern Gulf of Mexico, we investigate present-day processes controlling acidification on the Louisiana Shelf and project changes for the coming century. Present-day model results show an extended area of acidified bottom waters during summer on the Louisiana Shelf that is primarily due to benthic metabolism. We then discuss projected changes in the size, location and determining factors of acidified bottom waters resulting from climate change.