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Characterization of the sub-mesoscale energy cascade in the Alboran Sea thermocline from spectral analysis of multichannel seismic data

AuthorsSallarès, Valentí ; Mojica, J.F. ; Biescas, Berta ; Klaeschen, Dirk
Issue Date21-Apr-2016
PublisherEuropean Geosciences Union
CitationGeophysical Research Abstracts 18: EGU2016-12624 (2016)
AbstractLarge-scale ocean dynamics is linked to small-scale mixing by means of turbulence, which enables the exchange of kinetic energy across the scales. At equilibrium, the energy flux that is injected at the production range must be balanced by mixing at the dissipation range. While the physics of the different ranges is now well established, an observational gap exists at the 103 -101 m scale that prevents to characterize the transition from the anisotropic internal wave motions to isotropic turbulence. This lack of empirical evidence limits our understanding of the mechanisms governing the downward energy cascade, hampering the predictive capability of ocean circulation models. Here we show that this observational gap can be covered using high-resolution multichannel seismic (HR-MCS) data. Spectral analysis of acoustic reflectors imaged in the Alboran Sea (Western Mediterranean) thermocline evidences that this transition is caused by shear instabilities. In particular, we show that the averaged horizontal wavenumber (kx) spectra of the reflector¿s vertical displacements display three subranges that reproduce theoretical spectral slopes of internal waves [λx>100 m, with λx=kx−1], Kelvin-Helmholtz (KH)-type shear instabilities [100 m> λx>33 m], and turbulence [λx<33 m]. The presence of the transitional subrange in the averaged spectrum indicates that the whole chain of events is occurring continuously and simultaneously in the surveyed area. The availability of a system providing observational data at the appropriate scales opens new perspectives to incorporate small-scale mixing in predictive ocean modelling research
DescriptionEuropean Geosciences Union General Assembly 2016 (EGU2016), 17-22 April 2016, Vienna, Austria.-- 1 page
Publisher version (URL)https://meetingorganizer.copernicus.org/EGU2016/orals/20364
Identifiersissn: 1607-7962
Appears in Collections:(ICM) Comunicaciones congresos
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