Baroclinic M₂ tidal circulation in Algeciras Bay and its implications for the water exchange with the Strait of Gibraltar: Observational and 3-D model results

Abstract

[1] The M 2 tidal circulation in Algeciras Bay (Strait of Gibraltar) is analyzed using a 3-D, nonlinear, baroclinic, hydrodynamic model, in conjunction with observed data series. Results show the influence of the density stratification on the vertical structure of the M 2 currents in Algeciras Bay, although its tidal dynamics shows major differences with respect to the Strait of Gibraltar. Whereas the M 2 currents in the Strait present mainly barotropic behavior, the baroclinic effects prevail in Algeciras Bay. A notable finding is the presence of a tidal M 2 counter-current system between the upper Atlantic and the lower Mediterranean water layers within the Bay, with amplitudes of up to 25 cm s À1 . The interface between the two layers oscillates in antiphase relation with respect to the freesurface elevation, with amplitudes of almost 20 m. The presence of the submarine Algeciras Canyon was found to be determinant in the three-dimensional structure of tidal currents within the Bay, strengthening the baroclinic tidal regime of currents. This situation has quantitative consequences for the flow-exchange processes between Algeciras Bay and the outer Strait, with rates 20 times higher than those obtained when considering only the barotropic behavior, as well as inflow/outflow lateral recirculation volumes during half a tidal cycle that account for more than 20% of the net accumulated volume. This flowexchange system was found to be affected by the nonlinear interaction processes between the first baroclinic period of resonance of Algeciras Bay and the M 2 tide.

Water renewal in semi‐enclosed basins: A high resolution Lagrangian approach with application to the Bay of Algeciras, Strait of Gibraltar

“…After the pioneer study by de Buen (), the interest of the scientific community turned to the Strait of Gibraltar itself, displacing the Bay to the background. During the last decade of the 20 th century, it attracted the interest of physicists (e.g., Watson and Robinson ) and biologists (e.g., Naranjo et al and references therein), but it is only recently that more extensive multidisciplinary studies have been published (Álvarez et al ; Periáñez ; González et al ; Sammartino et al ; Sánchez Garrido et al ; Chioua et al ). A recurrent concern about the Bay is the chronic degree of pollution caused by the intense activities of the local Port and industries, which has been assessed even higher than the one found in the coast of Galicia in the northwest of the Iberian Peninsula after the Prestige oil spill (Morales‐Caselles et al ).…”