Abstract
Abstract. The 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 10–15 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.
Highlights
Diapycnal diffusivity around the thermocline plays a major role in controlling the strength and pattern of the ocean circulation because it determines heat and salt heterogeneity at different spatial scales
The Alboran Sea is characterized by the continuous exchange between Mediterranean Water (MW) and Atlantic Water (AW) through the Strait of Gibraltar
The goal is being able to identify features and processes occurring in the transition between the internal wave and the turbulence subranges, such as the intensity and scales of variability in the mixing patches, the location and size of the mixing patches, and their potential relationship with oceanographic features such as IWs or wave instabilities
Summary
Diapycnal diffusivity (kρ) around the thermocline plays a major role in controlling the strength and pattern of the ocean circulation because it determines heat and salt heterogeneity at different spatial scales. Several recent works have demonstrated that it is possible to map kρ using measures of the horizontal wave number (kx) spectra of the vertical displacements of thermohaline boundaries imaged with MCS acquisition systems (Sheen et al, 2009; Holbrook et al, 2013; Fortin et al, 2016) These studies use conventional, relatively low-resolution systems with source energy concentrating below ∼ 50 Hz. In addition, due to the long wavelength source wavelet, conventional MCS systems are not well suited to image the shallowest ocean layers (i.e., < 200 m), but rather deeper water levels (> 400 m depth).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
