Turbulence related quantities in the surface layer of Lake Garda
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The purpose of this study is the investigation of turbulence related quantities in Lake Garda. The research is based on in-situ observations of the vertical shear and temperature micro-structure in the surface layer, using a vertical microstructure profiler (microCTD). The aim is to quantify the dissipation of energy due to turbulent motion under the assumption of locally isotropic and homogeneous turbulence, and to identify and describe the main sources of turbulent mixing. The Nasmyth spectrum method is used to compute the dissipation of Turbulent Kinetic Energy (TKE) rate, while the mixing coefficient is computed using the Osborn theory. The analysis is carried out for the months of March, April and May and focuses on the northern, narrow part of the lake: here, the Earth's rotation forces a secondary closed circulation characterized by strong vertical transport at the sides of the basin. The observations, supported by the atmospheric forcing analysis, are used to infer the role of turbulent mixing in the phytoplankton growth and productivity. The result reveals a large unevenness in the horizontal distribution of phytoplankton in early Spring: in the eastern part of the lake the Chlorophyll is completely depleted by the upwelling of cold deep water, while on the other side of the basin, significant amounts Chlorophyll are found at extreme depths due to the Ekman downwelling.