Circulation over the continental shelf of the western and southwestern Gulf of Mexico

The circulation over the continental shelf break of the western and southwestern Gulf of Mexico is inferred from the analysis of drifter trajectories and 12–19 months of continuous current measurements at seven different locations. The interpretation of the data is backed up by satellite altimetry, coastal sea level from tide gauges and wind model outputs. In accordance with previous numerical results, subinertial surface currents are driven by the wind along the shelves of the states of Tamaulipas and Veracruz. Northern wind regimes would force southward currents, whereas southern wind regimes would force northward currents at the surface but southward near the bottom, through a process involving Ekman drift and geostrophic balance. Our results show, however, that alongshore current variations are not correlated with the wind over the Western Campeche Bank. In addition, we identify other sources of current forcing. The transient eddies that collapse along the continental shelf can force strong alongshore currents and overwhelm the influence of established wind regimes. Their erratic occurrence is likely to be a major factor of interannual variability of the alongshore currents. Also, we point out the existence of coastally trapped waves generated by the wind in the northern shelf of Tamaulipas and propagating down to the Western Campeche Bank. The period of these waves ranges between 6 and 10 days, with phase speeds in the 4 m/s range.