The very first transformation of the Mediterranean outflow in the Strait of Gibraltar

Time series collected in the Camarinal and Espartel sills, the two main sills of the Strait of Gibraltar, have been analyzed to assess the first transformation of the Mediterranean outflow. In Espartel, west of Camarinal sill, the outflow has been estimated from a 6 year long time series of acoustic Doppler current profiler observations. The near bottom water flowing out at Espartel is around 0.1 units saltier and 0.1°C warmer than at Camarinal, which is explained by entrainment and mixing of Atlantic water by the outflow inside the basin bounded by both sills. The constancy of heat and salinity transport implies an Atlantic water entrainment of 0.03 Sv, which is about 4% of the outflow observed at Espartel (0.77 Sv) and a flow of 0.74 Sv at Camarinal (96% of the flow at Espartel). It is also shown that the high energy dissipation rate associated with internal tides is enough to sustain the entrainment and a thorough mixing of the entrained water.