Internal solitary waves on the NW African shelf: A heuristic approach to localize diapycnal mixing hotspots

Type Article
Date 2021-09
Language English
Author(s) Gentil MathieuORCID1, 2, Floc'h France2, Meunier Thomas3, Ruiz-Angulo AngelORCID4, Roudaut Gildas5, Perrot Yannick5, Lebourges-Dhaussy Anne5
Affiliation(s) 1 : Univ Perpignan Via Domitia, Centre de Recherche et de Formation sur les Environnements Méditerranéens, UMR5110, 52 avenue Paul Alduy, F-66860, Perpignan, France
2 : Univ Brest, CNRS, Géosciences Océan, UMR6538, F-29280, Plouzané, France
3 : Woods Hole Oceanographic Institution, Woods Hole, MA, USA
4 : Institute of Earth Sciences, University of Iceland, 102 Reykjavik, Iceland
5 : Institut de la Recherche pour le Développement, Laboratoire de l’Environnement MArin - UMR LEMAR/IRD/UBO/CNRS/Ifremer, Plouzané, France
Source Continental Shelf Research (0278-4343) (Elsevier BV), 2021-09 , Vol. 226 , P. 104492 (10p.)
DOI 10.1016/j.csr.2021.104492
WOS© Times Cited 1
Keyword(s) Internal solitary waves, Diapycnal mixing, Kinetic energy dissipation, Acoustic backscatter, Moroccan shelf, North african upwelling system
Abstract

Turbulent mixing on continental shelves plays roles in the structure and dynamics of marine ecosystems, nutrient cycling, primary production and dispersion of pollutants. Describing and understanding internal wave dynamics enables improved mapping of mixing over continental shelves, especially in complex environments where many processes may interact, such as in upwelling systems. This paper describes internal wave propagation and dissipation in the Moroccan upwelling system using a comprehensive set of hydrographic observations made during two in situ surveys. The acoustic backscatter of the echosounder is shown to be a rapid and convenient survey tool for detecting internal solitary waves (ISWs) on large spatial scales, through the high-frequency oscillation of the zooplankton layer during nighttime conditions. Along ISW trains, enhanced diapycnal mixing episodes are observed with increased dissipation coefficients in the thermocline (O(10-7 W kg-1)), associated with overturning up to 6 m. Mixing due to internal wave soliton packets shows large spatial and temporal variability, but contributes to the overall mixing processes and is responsible for large intermittent variations in the thermocline position. The joint use of a multifrequency echosounder and a current profiler ADCP allows mixing to be quantified (via the Richardson number) on large spatial scales. Validation and use of this method in other coastal regions could be useful to determine regional mixing parameterization in numerical models.

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Gentil Mathieu, Floc'h France, Meunier Thomas, Ruiz-Angulo Angel, Roudaut Gildas, Perrot Yannick, Lebourges-Dhaussy Anne (2021). Internal solitary waves on the NW African shelf: A heuristic approach to localize diapycnal mixing hotspots. Continental Shelf Research, 226, 104492 (10p.). Publisher's official version : https://doi.org/10.1016/j.csr.2021.104492 , Open Access version : https://archimer.ifremer.fr/doc/00711/82262/