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
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.