Sea level variability and tidal resonance in the Gulf of Gabes, Tunisia

Sea level variability in the Mediterranean Sea is dominated at meso- and synoptic scales by meteorologically induced motion except, in some regions where tidal resonance occurs. One such region is the Gulf of Gabes where tidal amplitudes can reach 1 m during spring tides. Sea level fluctuations were recorded at four stations around the Gulf of Gabes, during 86 days in 2003 and at three stations, within the Boughrara lagoon in the southern Gulf, during about 30 days in 1999. Spectral analysis reveals that tides are responsible for most of the variance found in sea level fluctuations. Harmonic analysis results are discussed and amplitude and phase estimates for the four major constituents (K1, O1, M2, and S2) are compared to estimates from previous studies. Based on simple dynamical arguments, it is shown that the Gulf of Gabes has the right dimensions to entertain tidal resonance for most semi-diurnal tidal harmonics. The low-frequency sea level fluctuations are finally described in relation to atmospheric forcing. They are spatially coherent and respond to both easterly winds at periods near 6.5 and 14 days and as an inverse barometer at periods close to 4–6 days.