Geostrophic circulation and tidal effects in the Gulf of Gabès

Abstract. The mean kinematic features in the Gulf of Gabès region is analyzed based on 30 years of altimetry data (1993–2022) and the outputs of a high resolution ocean model for the year 2022. A comparison of the seasonal variability in three different geographical areas within the gulf is presented. In the northern and southern parts of the gulf, anticyclonic structures prevail, while the central area is dominated by divergence. Similarity in the flow topology is found in these three areas of the gulf due to the signature of hyperbolic regions. In winter and fall, the mean flow is oriented northward while it is reversed in spring and summer. The tidal perturbation influences sea level, kinetic energy and hyperbolic geostrophic structures, leading to the generation of a cyclonic current located in the central part of the gulf and to the presence of persistent strain gradients amplifying hyperbolic structures. The Finite Time Lyapunov Exponent (FTLE) computed using altimetry data highlights the link between physical and biogeochemical processes, with the Gulf of Gabès mean circulation features acting as transport barriers for phytoplankton dispersion.