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Ocean Dynamics

, Volume 66, Issue 3, pp 313–327 | Cite as

Strong intrusions of the Northern Mediterranean Current on the eastern Gulf of Lion: insights from in-situ observations and high resolution numerical modelling

  • Nicolas Barrier
  • Anne A. Petrenko
  • Yann Ourmières
Article

Abstract

The Northern Mediterranean Current is the return branch of the cyclonic circulation of the northwestern Mediterranean Sea. Because of geostrophic constraints, this warm and oligotrophic current is forced to flow westward along the continental slope of the Gulf of Lion. But, occasionally, it penetrates on the shelf and strongly impacts the local biogeochemistry and in turn the primary production. By combining in situ observations and high-resolution modelling, it is shown that intrusions on the eastern part of the gulf are mainly forced by easterly or northwesterly wind events, through physical mechanisms that are very different in nature. Easterlies induce a piling of water along the Gulf of Lion coast that drives, through geostrophy, an alongshore shelf-intruding current. This intrusive current occurs independently of the stratification and is concomitant with the wind forcing. On the other hand, intrusions due to northwesterlies only occur during stratified conditions and are related to the development of upwellings along the Gulf of Lion coasts. When the upwelling develops, a northwestward alongshore pressure force balances the Coriolis force associated with the onshore flow at depth. When the winds drop, the upwelling relaxes and the onshore flow weakens. Consequently, the Coriolis force no longer counterbalances the pressure force that ultimately dominates the momentum balance, causing the displacement of the Northern Current on the Gulf of Lion shelf approximately 1 day after the wind relaxation. This time lag between the northwesterlies decrease and the intrusions permits to anticipate possible changes in the biogeochemistry of the Gulf of Lion.

Keywords

Northern Current Gulf of Lion Intrusions Julio Upwelling Cross-shelf exchanges Wind-setup Easterlies Mistral Tramontane Northwesterlies 

Notes

Acknowledgments

The authors thank Gilles Rougier and Denis Malengros for their technical assistance with the Julio mooring. The Glazur64 simulations were performed using GENCI-IDRIS resources (Grant 2014011707). The analysis and plots of this paper were performed with both Python and the NCAR Command Language (version 6.2.1, 2011, Boulder, Colorado, UCAR/NCAR/CISL/VETS, doi: 10.5065/D6WD3XH5). The authors also acknowledge Julie Gatti, whose thesis strongly influenced this work.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Nicolas Barrier
    • 1
    • 2
  • Anne A. Petrenko
    • 1
    • 2
  • Yann Ourmières
    • 1
    • 2
  1. 1.Aix-Marseille Université, CNRS/INSU, IRD, MIO, UM 110MarseilleFrance
  2. 2.Université de Toulon, CNRS/INSU, IRD, MIO, UM 110La GardeFrance

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