Scientia Marina, Vol 76, No S1 (2012)

Mixing dynamics on the inner shelf of the Ebro Delta

Imma Bastida
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Jesús Planella
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Elena Roget
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Jorge Guillén
Institut de Ciències del Mar, Marine Geology Department, CSIC, Spain

Pere Puig
Institut de Ciències del Mar, Marine Geology Department, CSIC, Spain

Xavier Sánchez
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain


Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes at the BBL and suggests that sub-critical reflection of internal waves could play an important role in boundary mixing. Our data also suggest that during the campaign, after two consecutive short episodes of high winds, the first baroclinic mode shifted to the second one.


bottom boundary layer; nepheloid layer; inner shelf; turbulence; turbidity; internal waves; mixing

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