Microstructure observations of the summer-to-winter destratification at
a coastal site in the Gulf of Naples
Florian Kokoszka
Stazione Zoologica Anton Dohrn, Naples, Italy, Stazione Zoologica Anton Dohrn, Naples, Italy, Stazione Zoologica Anton Dohrn, Naples, Italy
Corresponding Author:[email protected]
Author ProfileBruno Ferron
Univ. Brest, CNRS, IFREMER, IRD, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Plouzané, France, Univ. Brest, CNRS, IFREMER, IRD, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Plouzané, France, Univ. Brest, CNRS, IFREMER, IRD, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Plouzané, France
Author ProfilePascale Bouruet-Aubertot
Sorbonne Université (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN, Paris, France, Sorbonne Université (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN, Paris, France, Sorbonne Université (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN, Paris, France
Author ProfileJustine Mc Millan
Rockland Scientific International Inc., Victoria, Canada, Rockland Scientific International Inc., Victoria, Canada, Rockland Scientific International Inc., Victoria, Canada
Author ProfileAbstract
A dissection of the physics of seasonal cycle of oceanic upper layer
stratification is necessary to improve climate predictions of
biogeochemical cycles. We present a time series of vertical profiles of
ε, the dissipation rate of turbulent kinetic energy, obtained from a
microstructure profiler during the destratification period
(summer-to-winter) at a mid-latitude 75m-deep coastal site. Significant
correlation is obtained in the mixed layer depth (MLD) with a model
combining effects of wind, wave, and buoyancy forcings, estimated from
bulk parameters ~10 hours before observations, and used
to identify the dominant forcings leading to MLD deepening.
Intermittency at surface is correlated with seasonal storminess, and we
observe a quadratic relation between kurtosis and skewness for ε
statistics. By splitting the time series into layers, we observe the
co-location of patches of higher ε with the shear maxima of the two
first baroclinic modes, and significant correlations with surface wind
stress in the transitional layer the past 24 hours, and at longer scale
(4.25 days) in the baroclinic layer, suggesting that internal waves
activity influences the setup of mixing intensity despite the lack of
tidal forcing. The low-passed microstructure shear distribution seems to
support this hypothesis despite possible signal contamination. In the
highly stratified layers associated to salt-fingering (MLD’s basis and
below), the buoyancy Reynolds number indicates a buoyancy regime control
with low mixing value (0.2 x 10e-5 m²/s). More turbulent flows are
identified in both surface and bottom layers (0.6 - 0.8 x 10e-5 m²/s),
suggesting a seasonal erosion of the stratification by the boundary
processes.