Quentin-Boris Barral (OPLC) will defend his thesis Thursday, July 21, 2022 at 2:00 pm At the University of Toulon - Campus La Garde - Building X - Amphi X.300

On the following topic:

Characterization of the North Balearic front: variability and role of water mass circulation in the Western Mediterranean

 under the direction of

Mr. Bruno ZAKARDJIAN, University Professor, University of Toulon (France), thesis director


Co-supervised by Mr. Franck DUMAS, Research Officer, SHOM, Brest (France) and Mr. Pierre GARREAU, Research Officer -HDR, LOPS, IFREMER, Brest (France)

before a jury composed of

Mrs. Claude ESTOURNEL, Director of Research-CNRS, LEGOS-Toulouse Rapporteur

Mrs Sabrina SPEICH, Professor, LMD-ENS-IPSL Paris Rapporteur

Mrs. Karina von SCHUCKMANN, Research Associate-HDR, Mercator-Ocean, Toulouse Examiner

Mr. Baptiste MOURRE, Research Fellow, SOCIB, Palma de Majorca (Spain) Examiner

Mr. Samuel SOMOT, Research Officer, CNRM, Météo-France Toulouse (France) Examiner

Mr. Franck DUMAS, Research Officer, SHOM, Brest (France), Invited

Mr. Pierre GARREAU, Research Fellow -HDR, LOPS, IFREMER, Brest (France), Guest

Mr. Bruno ZAKARDJIAN, University Professor, University of Toulon (France), Thesis Director





In the Western Mediterranean, the Balearic front (BF) marks the confrontation of less salty Atlantic waters (AWs) and more salty Mediterranean waters (mAWs); the Liguro-Provençal front results from the transport of warm Tyrrhenian waters in the Northern Current; the Pyrenees front (PF) is the result of the north-south contrast of the wind forcing around the Pyrenees. The North Balearic Front (NBF) located between the Balearic Islands, Corsica and Sardinia, seems to separate the Provencal and Algerian basins, and is less well defined. Some studies consider it as a thermal front, others as a salinity front, or associated with a possible closing circulation between Menorca and Corsica of the "North Gyre" (a cyclonic loop of currents), or even as a southern limit to winter convection. This thesis characterizes this front. A detection method is applied to satellite observed sea surface temperature (SST) data and to those of a simulation (the MEDRYS1V2 reanalysis, 1992-2013), as well as to its simulated sea surface salinity (SSS) data. Two areas of recurrent presence of fronts appear: two frontal areas. The first one connects the Pyrenees and Corsica by thermal fronts in summer-autumn at the near surface (0-50m). It constitutes the eastern extension of the PF when its water masses are advected to the subsurface by the regional circulation. The second connects Menorca and Sardinia by haline fronts without seasonal variability. It characterizes the eastern continuation of the BF and the confrontation between mAWs, and AWs displaced by Algerian eddies (AEs). Consequently, these two distinct fronts, previously confused in the sense of the NBF, are here named the Pyrenees-Corsica and Balearic-Sardinia Frontal Zones. The Pyrenees-Corsica Thermal Frontal Zone is not influenced by deep water formation (DWF). On the other hand, the Balearic-Sardinian Haline Frontal Zone shows spatial variability on an interannual scale. It moves southward for about 100 km in DWF years, and without, regains its stable position to the north under the influence of AEs.  A diagnostic algorithm for detecting water masses in the western basin has been developed to quantify them in the reanalysis. It evaluates their characteristics, their specific cores, volumes and circulations. The first result is the latitudinal seasonal oscillation of the North Gyre closing current. Also detected are unrealistic episodes of circulation and deep water mixing (1998-1999, 2003 and 2010). Nevertheless, the reanalysis is resilient to them, so that an interannual dynamic is observed on the deep water: the DWF dislocates the deep and cyclonic Algerian Gyre. Differentiating these two regimes (with or without DWF) shows that all water masses are affected by the destabilization of the gyre. At the surface, the AWs are no longer subject to cyclonic entrainment and their zonal circulation migrates south, explaining the displacement of the Balearic-Sardinian Frontal Zone. Otherwise, the West Mediterranean Transition (WMT, due to the DWF of 2005) led to a realistic overflow of deep water in the Sardinia Channel in 2009. The algorithm shows that this deep west-east transit caused an east-west return at the surface. This event brings mAWs through the Sardinia Channel instead of the usual East-Corsica Channel. It brought part of the AWs to the Provençal basin in 2009, moving in an atypical but realistic way the Balearic-Sardinian Frontal Zone to Corsica.


Keywords: Front, Water mass, Reanalysis, Seasonal variations, Annual variability, Deep Water Formation, Eddies, Mediterranean