Asymmetric Baroclinic Response to Tidal Forcing Along the Main Sill of the Strait of Gibraltar Inferred from Mooring Observations
Data collected in the north and south channels of the main sill of the Strait of Gibraltar (Camarinal sill) have been used to investigate processes connected to the internal hydraulics of the exchange through the Strait at tidal frequencies. They strongly suggest the setting up of hydraulic jumps at both the western and eastern flank of the sill, the latter associated with the reversal of the Mediterranean undercurrent during spring tides. The northern site is more sensitive to processes triggered by the formation and release of the jump formed east of the sill during intense enough ebb tide cycles, which is thus better traced at this location, whereas the southern site detects the fluctuations and footprints associated with the hydraulic jump regularly formed to the west of the sill during flood tides more neatly. A detailed inspection of the high resolution bathymetry of the area reveals the existence of two enclosed depressions at either side of Camarinal sill, almost certainly carved by the bottom flow over the millennia, whose shape and morphology are suggestive of this spatial differentiation. In addition to the expected fortnightly periodicity of the spring-neap tidal cycle, the observed hydrodynamic features show a pronounced diurnal inequality caused by the tidal currents of the diurnal constituents.
Data were collected in the frame of the Spanish Government-funded “INGRES-3” (CTM2010-21229/MAR) and “ENCIBA” (CTM2013-40886P) projects. We are particularly grateful to the Instituto Español de Oceanografía, which allocated ship-time of the research vessel Ángeles Alvariño for carrying out the field experiment. This experiment is also part of the PE12-RNM-1540 Regional Government of Junta de Andalucía Excellence project. CN acknowledges a research contract associated with CTM2013-40886P project. JCSG was partially supported by the “Juan de la Cierva” program (contract JCI-2012-13451) and SS acknowledges a post-doc contract linked to PE12-RNM-1540 project.
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