Circulation over the continental shelf in the northern Gulf of Mexico

More than 750 surface drifters were deployed over the northern continental shelf in the Gulf of Mexico (gulf) from 1993 through 1998. Drifters were mostly air-deployed on a schedule giving continuous data over much of the Texas-Louisiana and west Florida shelves for an entire year. The drifter data are analyzed to give descriptive, statistical, and dynamical views of the northern gulf circulation on synoptic to seasonal scales. Circulation on both the Texas-Louisiana and west Florida shelves is characterized by coherent along-shore and across-shore modes which explain more than 50% of the variance. A pronounced seasonal cycle exists on the Texas-Louisiana shelf, but not the west Florida shelf. Both shelves display synoptic signals due to local wind forcing. Strong connectivity between the shelves occurs during isolated period of strong winds associated with the passage of tropical storms. Eddies impinging upon the shelf are responsible for moving drifters cross-shore. Offshore flows generally occur prior to reversals in the along-shore direction. Regions with near zero mean velocities but large total energy exist. Drifters leave these areas and move thorough much of the Gulf and into the Atlantic within 90 days despite negligible annual mean Eulerian velocities.