Numerical simulations of buoyancy driven flow on the Texas-Louisiana continental shelf

A realistic hydrodynamic numerical model of the Mississippi/Atchafalaya river plume system is used to examine the effects of seasonal hypoxia on the Texas-Louisiana continental shelf in the context of physical processes. Circulation over the Texas-Louisiana continental shelf is dominated by the Mississippi/Atchafalaya River plume system. The Mississippi/Atchafalaya River plume system is unique in that there are two large fresh water sources, with the Mississippi River plume forming a surface trapped plume near the shelf edge, whereas the Atchafalaya empties into a broad, shallow shelf and forms a bottom trapped plume. Results show that simple parameterizations of respiration can reproduce the spatial and temporal structure of hypoxia on the shelf. Also, the model suggests that different kinds of respiration are important over different shelf regions: bottom respiration is important in controlling hypoxia over the broad, shallow region south of Atchafalaya Bay, water column respiration is important in creating hypoxia in the Louisiana Bight, west of the Mississippi River Delta. Thus, physical processes are critical in the creation, maintenance, and destruction of seasonal hypoxia on the Texas-Louisiana shelf.