14 Dec 2021

14 Dec 2021

Review status: this preprint is currently under review for the journal OS.

The Levantine Intermediate Water in the western Mediterranean and its interactions with the Algerian Gyres: insights from 60 years of observation

Katia Mallil1,2, Pierre Testor1, Anthony Bosse3, Félix Margirier4, Loic Houpert5, Hervé Le Goff1, Laurent Mortier1, and Ferial Louanchi2 Katia Mallil et al.
  • 1Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN, UMR 7159): CNRS/SU/MNHN/IRD, 75005, Paris, France
  • 2Ecole Nationale Supérieure des Sciences de la Mer et de l’Aménagement du Littoral (ENSSMAL), Laboratoire des Ecosystèmes Marins et Littoraux (EcosysMarL), 16320, Alger, Algeria
  • 3Aix-Marseille Université, Université de Toulon, CNRS, IRD, MIO UM110, 13288, Marseille, France
  • 4School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 5OSE Engineering, 78470, Saint-Rémy-lès-Chevreuse, France

Abstract. The presence of two large scale cyclonic gyres in the Algerian basin influences the general and eddy circulation, but their effect on water mass transfer remain poorly characterized. Our study has confirmed the presence of these gyres using the first direct current measurements of the whole water column collected during the SOMBA-GE2014 cruise, specifically designed to investigate these gyres. Using cruise sections and a climatology from 60 years of in situ measurements, we have also shown the effect of these gyres on the distribution at intermediate depth of Levantine Intermediate Water (LIW) with warmer (~0.15 °C) and saltier (~0.02−1) characteristics in the Algerian basin than in the Provençal basin. The Algerian gyres also impact horizontal density gradients with sinking of the isopycnals at the gyres’ centres. Temporal cross-correlation of LIW potential temperature referenced to the signal observed south of Sardinia reveal timescale of transit of 4 months to get to the centre of the Algerian basin.

The LIW temperature and salinity trends over various periods are estimated to: +0.0017 ± 0.0014 °C.year−1 and +0.0017 ± 0.0003 year−1 respectively over the 1960–2017 period, and accelerating to +0.059 ± 0.072 °C.year−1 and +0.013 ± 0.006 year−1 over the 2013–2017 period.

Katia Mallil et al.

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Katia Mallil et al.

Katia Mallil et al.


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Short summary
Our study aims at documenting the circulation features in the Algerian basin using in situ data. It provides evidence that the Algerian Gyres have an impact on the distribution at intermediate depth of Levantine Intermediate Water. They enable a westward transport from the south of Sardinia toward the interior of the Algerian Basin. The temperature and salinity trends of this water mass are also studied, confirming the acceleration of the warming and salinification during the last decade.