Spatial and temporal variability of tidal flow in the Strait of Gibraltar

Recent observations collected at different places in the Strait of Gibraltar are used to investigate the temporal and spatial variability of tidal currents in this region. The analysis of a five-year long time series of velocity observations at the Espartel sill (western end of the strait) shows that harmonic constants fluctuate seasonally exhibiting smaller amplitude in winter. This fact, along with an increased subinertial flow during the winter induces a marked decrease in the relative importance of the tide to the total flow compared to the summer. New computations of tidal transport at the key sections of Espartel and Camarinal, together with historical information reported for the Eastern Exit of the strait, have been analyzed jointly to highlight the internal along-strait divergence of the tidal transport in each layer and the transfer of the tidal signal from one layer to the other. This study covers the whole length of the strait, thus extending previous results reported for the central-eastern strait. Most of the topographically forced divergence is accounted for by large vertical displacements of the interface, although velocity observations collected on the continental shelf of the northern strait suggest that coastal recirculation plays some role in the volume conservation at tidal frequencies.

► We examine the relative importance of the tides on the total flow. ► Harmonic constants fluctuate seasonally exhibiting smaller amplitude in winter. ► Increased subinertial flows during the winter induce a decrease of tidal residuals. ► Tidal transport computations highlight the transfer of tidal signal between layers. ► Coastal recirculation plays some role in the tidal volume conservation.