Definitive evidence of the Mediterranean Outflow heterogeneity. Part 2: all along the Strait of Gibraltar

Abstract. We have demonstrated in Part 1, with only a CTD transect across the Strait at 6°05' W, that the Mediterranean Outflow (MO) was definitely heterogeneous there. A yo-yo CTD time series has also provided astounding examples of both the marked layering that the Mediterranean Waters (MWs) display on the vertical at the Strait entrance (5°43' W), i.e. just upstream from the Camarinal sills (5°45' W), as well as the tremendous instability processes occurring in all layers. We focus herein on similar data collected within the Strait at both 5°50' W and 6°05' W (downstream from the Camarinal and Espartel sills, resp.) during five campaigns of the 1985–1986 GIBEX. We first show additional transects supporting the demonstration we made at 6°05' W, and we demonstrate that the marked heterogeneity of the MO within the Strait is clearly on the horizontal; as we expected, densest (resp. lightest) MWs flow on the bottom on its left-hand (resp. right-hand) side and all MWs are juxtaposed side by side. We also demonstrate that the density range within the MO in the western side of the Strait (6°05' W) is at least 0.5 kg m⁻³, which is the density range, in the vicinity of the Cape St Vincent (8°30' W), of the four veins formed by the MO splitting. We show that the lightest component of the MO has started to be split as soon as Camarinal sills and sink all along the Strait. The splitting of the MO into veins is thus mainly due to its intrinsic heterogeneity, which is a direct consequence of the Sea functioning and of the mixing, within the Strait itself, of the MO with this or that type of Atlantic Waters (AWs). Therefore, the bathymetry in the Strait, and even in the Strait exit surroundings (near 6°20' W), has no major effect on the MO characteristics in the whole Ocean. We also focus on a yo-yo CTD time series collected during ~24 h at 6°05' W which shows that markedly different MWs have been passing by, clearly demonstrating that the horizontally heterogeneous MO is significantly meandering within the Strait. Finally, we confirm one of our previous results that, provided the temporal variabilities of both the MWs and the AWs are not too large, significant relationships can possibly be established between the characteristics of the MWs at the Strait extremities, or at least that the slope of the mixing lines on a q-S diagram provides significant information. Parts 1 and 2 of our trilogy must be assimilated before reading Part 3.