In Situ Observations of the Small-Scale Dynamics at Camarinal Sill—Strait of Gibraltar

Abstract

Recently, PROTEVS GIB20 experiment was performed in the Strait of Gibraltar. Part of this experiment was dedicated to observe the high frequency dynamics near Camarinal Sill (CS), considered as a mixing hotspot in the region. Mooring lines equipped with current profilers and temperature/salinity probes provided data which evidence two dynamical regimes depending on the tidal current intensity; in neap tide floods, local internal hydraulic control is never observed over CS while in spring tide, local internal hydraulic control depicts a tide-dependent and spatially variable pattern. In spring tide floods, measurements revealed the development of a hydraulic jump over the sill and its advection on the lee side. Cross sill sections with CTD casts and acoustic images confirmed this dynamics and depicted a well developed hydraulic jump on the eastern flank of the sill during spring tide ebbs. The north-south and temporal variability of the internal hydraulics was analyzed from several zonal sections over CS, the mean topographic feature of the Strait of Gibraltar. We highlighted a complex series of local hydraulic jumps constrained by topography and a significant north-south variability. The spatiotemporal variability of local hydraulics questions the two dimensional representation of the exchange flow in the Strait of Gibraltar. During neap tide flood, the dynamics of the Mediterranean outflow was investigated from a fixed station. We imaged the development of instabilities at the interface between Atlantic and Mediterranean waters jointly with the generation of much thicker billows deeper. Finally, we discuss our findings in relation to other straits dynamics.