Export pathways for river discharged fresh water in the northern Gulf of Mexico

Abstract

A numerical simulation of the Gulf of Mexico (GoM) using the Navy Coastal Ocean Model (NCOM) is used to identify the pathways by which fresh water discharged by major rivers in the northern Gulf is exported away from the region. The NCOM, a new primitive equation ocean model with a hybrid sigma/geopotential level vertical coordinate, is described along with its application to the GoM region. Trajectories from surface drifters are analyzed to show evidence of the seasonally shifting alongshore and cross‐shelf transport in the region. The model results are used to determine the preferred locations and times of year for cross‐shelf and along‐shelf export of low‐salinity water from the northern GoM. The annual cycle of local wind stress plays an important role in shifting the export pathway of the fresh water discharged from the major rivers (primarily the Mississippi River) toward the east in the spring/summer, where it can be transported offshore by the currents associated with deep ocean mesoscale eddies, and toward the west in the fall/winter, where it is transported southward along the Mexican coastline as a coastally trapped current.