High-resolution diapycnal mixing map of the Alboran Sea thermocline from seismic reflection images

13 pages, 8 figures, 2 appendices, supplementary material https://dx.doi.org/0.5194/os-14-403-2018-supplementThe Alboran Sea is a dynamically active region where the salty and warm Mediterranean water first encounters the incoming milder and cooler Atlantic water. The interaction between these two water masses originates a set of sub-mesoscale structures and a complex sequence of processes that entail mixing close to the thermocline. Here we present a high-resolution map of the diapycnal diffusivity around the thermocline depth obtained using acoustic data recorded with a high-resolution multichannel seismic system. The map reveals a patchy thermocline, with spots of strong diapycnal mixing juxtaposed with areas of weaker mixing. The patch size is of a few kilometers in the horizontal scale and of 10-15ĝ€m in the vertical one. The comparison of the obtained maps with the original acoustic images shows that mixing tends to concentrate in areas where internal waves, which are ubiquitous in the surveyed area, become unstable and shear instabilities develop, enhancing energy transfer towards the turbulent regime. These results are also compared with others obtained using more conventional oceanographic probes. The values estimated based on the seismic data are within the ranges of values obtained from oceanographic data analysis, and they are also consistent with reference theoretical values. Overall, our results demonstrate that high-resolution seismic systems allow the remote quantification of mixing at the thermocline depth with unprecedented resolution.This work has been fulfilled in the framework of projects POSEIDON (ref: CTM2010-25169) and FRAME (ref: CTM2015-71766-R), both funded by the Spanish Ministry of Economy and Competitiveness (MINECO). The seismic and oceanographic data were acquired in the framework of the IMPULS survey (ref: 2003-05996-MAR), also from MINECO, and the SAGAS survey (ref: CTM2005-08071-C03-02/MAR-SAGAS). This work was also supported by the Grup de Recerca de la Generalitat de Catalunya: Barcelona Center for Subsurface Imaging (2014SGR940)Peer Reviewe