Along‐shelf current variability on the Catalan inner‐shelf (NW Mediterranean)

Abstract

We examine the circulation over the inner‐shelf of the Catalan Sea using observations of currents obtained from three Acoustic Doppler Current Profilers (two at 24 m and one at 50 m) during March–April 2011. The along‐shelf current fluctuations during that period are mainly controlled by local wind stress on short time scales and by remote pressure gradients on synoptic time scales. Different forcing mechanisms are involved in the along‐shelf momentum balance. During storm conditions, wind stress, sea level gradients and the nonlinear terms dominate the balance. During weak wind conditions, the momentum balance is controlled by the pressure gradient, while during periods of moderate wind in the presence of considerable stratification, the balance is established between the Coriolis and wind stress terms. Vertical variations of velocity are affected by the strong observed density gradient. The increased vertical shear is accompanied by the development of stratified conditions due to local heating when the wind is not able to counteract (and break) stratification. The occasional influence of the Besòs River plume is observed in time scales of hours to days in a limited area in near the city of Barcelona. The area affected by the plume depends on the vertical extent of the fresher layer, the fast river discharge peak, and the relaxation of cross‐shore velocities after northeast storm events. This contribution provides a first interpretation of the inner‐shelf dynamics in the Catalan Sea.