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Long-term variability of the coastal ocean stratification in the Gulf of Naples: Two decades of monitoring the marine ecosystem at the LTER-MC site, between land and open Mediterranean sea
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  • Florian Kokoszka,
  • Baptiste Le Roux,
  • Daniele Iudicone,
  • Fabio Conversano,
  • Maurizio Ribera d'Alcalá
Florian Kokoszka
Stazione Zoologica Anton Dohrn

Corresponding Author:[email protected]

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Baptiste Le Roux
Ecole Centrale de Nantes
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Daniele Iudicone
Stazione Zoologica Anton Dohrn
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Fabio Conversano
Stazione Zoologica Anton Dohrn
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Maurizio Ribera d'Alcalá
Stazione Zoologica Anton Dohrn
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Abstract

We analyze 20 years (2001-2020) of temperature and salinity profiles at the LTER-MC coastal station in the Gulf of Naples, Mediterranean Sea. Surface and bottom layer show increases of temperature (+0.01 and +0.03°C/year, 2005-2019); water-columns budgets (heat, freshwater) show pseudo-periodic oscillations every 3 to 5 years, and weak linear trends. Seasonal minimum of salinity occurs two months later than the runoff peak, pointing to the importance of horizontal circulation in regulating the inshore-offshore exchanges and the residence time of freshwater contribution. Inter-annual variations of the mixed layer depth (MLD) exhibit a shallowing (-1.27m/year during winter) and a shortened time span of the fully mixed water-column. A visible decadal shift in the external forcings suggests an influence of winterly wind stress in 2010-2019, that prevailed over dominant buoyancy fluxes in 2001-2009. Changes are visible in the large-scale indices of the North Atlantic and Western Mediterranean Oscillations and highlight the role of wind direction, offshore or inshore oriented, in disrupting the stratification driven by freshwater runoff. A random forest regression confirms that role and quantifies the MLD drivers importances. This allows for a reliable prediction of the stratification using external variables independent from the in situ observations.