A modeling study of water and salt exchange for a micro-tidal, stratified northern Gulf of Mexico estuary

摘要

A three-dimensional hydrodynamic model is applied to the Mobile Bay system to study water and salt exchange with the northern Gulf of Mexico via Main Pass (MP) and eastern Mississippi Sound via Pass-aux-Herons (PaH). On average, more water leaves the Bay through MP than through PaH, and the Bay gains salt through MP and loses about the same amount through PaH. However, the volume discharge rate Q_f and salt transport rate F_S vary greatly in response to wind and river discharge with the range of variation 1-2 orders of magnitude larger than the corresponding mean. Stratification plays a key role for salt transport through MP. During periods of large river discharge, the landward shear dispersive transport FE peaking during equatorial tides and the landward tidal oscillatory transport F_T peaking during tropic tides, respectively, balance the seaward advective transport Q_fS_0. During periods of relatively weak stratification, F_S at MP is almost entirely determined by Q_fS_0 and its variability iswell correlated with north-south (along-estuary) wind, associatedwith the barotropic (water level) adjustment. At the shallow, weakly stratified PaH, F_S is almost identical to Q_fS_0, and Q_f is well correlated with east-west wind, with the correlation becoming stronger during the dry period.