Articles | Volume 12, issue 2
Ocean Sci., 12, 433–449, 2016

Special issue: Oceanographic processes on the continental shelf: observations...

Ocean Sci., 12, 433–449, 2016
Research article
11 Mar 2016
Research article | 11 Mar 2016

Turbulence observations in the Gulf of Trieste under moderate wind forcing and different water column stratification

Francesco Marcello Falcieri1, Lakshmi Kantha1,2, Alvise Benetazzo1, Andrea Bergamasco1, Davide Bonaldo1, Francesco Barbariol1, Vlado Malačič3, Mauro Sclavo1, and Sandro Carniel1 Francesco Marcello Falcieri et al.
  • 1Istituto di Scienze Marine – Consiglio Nazionale delle Ricerche, Venice, Italy
  • 2Colorado Center for Astrodynamical Research – University of Colorado, Boulder, CO, USA
  • 3National Institute of Biology, Marine Biology Station, Piran, Slovenia

Abstract. The oceanographic campaign CARPET2014 (Characterizing Adriatic Region Preconditionig EvenTs), (30 January–4 February 2014) collected the very first turbulence data in the Gulf of Trieste (northern Adriatic Sea) under moderate wind (average wind speed 10 m s−1) and heat flux (net negative heat flux ranging from 150 to 400 W m−2). Observations consisted of 38 CTD (Conductivity, Temperature, Depth) casts and 478 microstructure profiles (grouped into 145 ensembles) with three sets of yoyo casts, each lasting for about 12 consecutive hours. Averaging closely repeated casts, such as the ensembles, can lead to a smearing effect when in the presence of a vertical density structure with strong interfaces that can move up or down between subsequent casts under the influence of tides and internal waves. In order to minimize the smearing effect of such displacements on mean quantities, we developed an algorithm to realign successive microstructure profiles to produce sharper and more meaningful mean profiles of measured turbulence parameters.

During the campaign, the water column in the gulf evolved from well-mixed to stratified conditions due to Adriatic waters intruding at the bottom along the gulf's south-eastern coast. We show that during the warm and relatively dry winter, the water column in the Gulf of Trieste, even under moderate wind forcing, was not completely mixed due to the influence of bottom waters intruding from the open sea. Inside the gulf, two types of water intrusions were found during yoyo casts: one coming from the northern coast of the Adriatic Sea (i.e. cooler, fresher and more turbid) and one coming from the open sea in front of the Po Delta (i.e. warmer, saltier and less turbid). The two intrusions had different impacts on turbulence kinetic energy dissipation rate profiles. The former, with high turbidity, acted as a barrier to wind-driven turbulence, while the latter, with low sediment concentrations and a smaller vertical density gradient, was not able to suppress downward penetration of turbulence from the surface.

Short summary
Between January 30th and February 4th we collected the first turbulence observations in the Gulf of Trieste under different wind forcing and water column structure. The vertical profiles of the turbulence kinetic energy dissipation rates showed that the presence near the sea floor of different water masses, inflowing from the open sea, can prevent the complete mixing of the water column. This dumping effect is enhanced when these masses present higher suspended sediment concentrations.