Ten years of marine current measurements in Espartel Sill, Strait of Gibraltar

Abstract

More than 10 year of Acoustic Doppler Current Profiler observations collected at the western-most sill (Espartel sill) of the Strait of Gibraltar by a monitoring station have been carefully processed to pro-vide the most updated estimation of the Mediterranean outflow. A comprehensive quality control of thefactors affecting the uncertainty of the measurements has been carried out and great care has been paid toinfer the current at the bottom layer, where direct observations are lacking. The mean outflow in the south-ern channel of the sill section has been estimated as 20.82 Sv (1 Sv 5 1 3 10 6 m3 s21 ), with an average con-tribution of the eddy fluxes of 20.04 Sv. This figure is an overestimation, as the mooring measurements,assumed valid for the whole section, ignore the lateral friction. On the other hand, it only gives the flowthrough the southern channel and disregards the fraction flowing through shallower northern part. Bothdrawbacks have been addressed by investigating the cross-strait structure of the outflow from hindcastsproduced by the MITgcm numerical model, run in a high-resolution domain covering the Gulf of C adiz andAlboran Sea basins. An overall rectifying factor of 1.039 was found satisfactory to correct the first estimate,so that the final mean outflow computed from this data set is 20.85 Sv, complemented with an uncertaintyof 60.03 Sv based on the interannual variability of the series. The temporal analysis of the series shows anoutflow seasonality of around the 8% of the mean value, with maximum outflow in early spring.