Influence of Diurnal Sea Breeze on Residence Time and Associated Biogeochemical Processes in the Mississippi Sound and Bight

Courtney Bouchard1, Mustafa Kemal Cambazoglu2, Michael S Dinniman3, Patrick J Fitzpatrick4, Eileen E Hofmann3 and Jeremy David Wiggert5, (1)University of Southern Mississippi, Stennis Space Center, MS, United States, (2)The University of Southern Mississippi, School of Ocean Science and Engineering, Stennis Space Center, MS, United States, (3)Old Dominion University, Center for Coastal Physical Oceanography, Norfolk, VA, United States, (4)Mississippi State University, Geosystems Research Institute, Stennis Space Center, MS, United States, (5)The University of Southern Mississippi, Division of Marine Science, Stennis Space Center, MS, United States
The northern Gulf of Mexico is home to one of the largest seasonal hypoxic events in the world located along the Texas/Louisiana shelf. Significant attention has been placed on the event that extends westward, from the Mississippi River outflow onto the Texas Shelf. A smaller, yet notable, hypoxic event also manifests to the east of the Birdfoot Delta near the barrier islands that separate the Mississippi Sound and Bight. Recent studies have found that this area is less influenced by the high nutrient loads within Mississippi river water than previously thought; rather it is more directly influenced by the local riverine sources flowing into Mississippi Sound. To understand the interlinked circulation and biogeochemical processes of the region, a coupled physical-biogeochemical model has been developed based on the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System. The model provides insights into the seasonal variations of the biogeochemical and physical interactions in this coastal ecosystem that is heavily influenced by freshwater plumes. Seasonal dye experiments were set up to examine the exchange pathways between the estuarine waters of Mississippi Sound and the inner shelf of Mississippi Bight. A high temporal (hourly) and spatial (0.01 deg) resolution wind field that resolves the diurnal sea breeze is applied for this study and twin experiments with full resolution winds and temporally filtered winds have been performed to investigate the influence of the diurnal sea breeze on the flushing of estuarine waters onto the shelf. The rate of freshwater flow into the system is a primary control on the productivity and biogeochemical cycling in the region’s bays and estuaries. Results from these numerical experiments provide a detailed perspective on residence times and the associated biogeochemical processes that contribute to the appearance of the poorly understood hypoxic events that appear in the coastal waters of Mississippi Bight.