A multi-site, year-round turbulence microstructure atlas for the deep perialpine Lake Garda

Abstract

A multi-site, year-round dataset comprising a total of 606 high-resolution turbulence microstructure profiles of shear and temperature gradient in the upper 100 m depth is made available for Lake Garda (Italy). Concurrent meteorological data were measured from the fieldwork boat at the location of the turbulence measurements. During the fieldwork campaign (March 2017-June 2018), four different sites were sampled on a monthly basis, following a standardized protocol in terms of time-of-day and locations of the measurements. Additional monitoring activity included a 24-h campaign and sampling at other sites. Turbulence quantities were estimated, quality-checked, and merged with water quality and meteorological data to produce a unique turbulence atlas for a lake. The dataset is open to a wide range of possible applications, including research on the variability of turbulent mixing across seasons and sites (demersal vs pelagic zones) and driven by different factors (lake-valley breezes vs buoyancy-driven convection), validation of hydrodynamic lake models, as well as technical studies on the use of shear and temperature microstructure sensors.

Intense upper ocean mixing due to large aggregations of spawning fish

“…> 10 −6 W kg −1 ), however, the measured spectra show excellent agreement with the empirical universal forms for intense turbulence over the resolved wavenumber range (Supplementary Figure 1), supporting the robustness of the estimation. This methodology is described in more detail elsewhere 54 . During night-time biomixing periods, fish impacts on the profiler were often apparent in the shear and pseudo-shear (accelerometer) records (Supplementary Figure 2).…”

Observations of Modified Warm Deep Water Beneath Ronne Ice Shelf, Antarctica, From an Autonomous Underwater Vehicle

“…For the relatively low rates of dissipation found beneath Ronne Ice Shelf (ε < 10 −9 W m −2 ), integrating up to 10 cpm resolved a sufficient portion of the shear variance in 58.1% of spectra, while integrating to $${k}_{95}$$ was sufficient in a further 41.7% of cases. Each estimate of ε was then iteratively adjusted using the empirical Nasmyth spectrum to correct for the shear variance found beyond $${k}_{I}$$ and at the low‐wavenumber end of the spectrum (Lueck, 2016; Piccolroaz et al., 2021). Turbulence has a correlation time and length scale, and therefore 88 ε estimates that differed by more than a factor of 4 between shear probes for the same segment, or more than a factor of 10 between neighboring segments, were discarded.…”

“…The RSI MicroRider package had four microstructure probes sampling at a rate of 512 Hz: two orthogonally positioned shear probes that provide an estimate of the rate of turbulent kinetic energy dissipation (TKE; ε), and two thermistor probes that provide an estimate of the rate of thermal variance dissipation (χ). The microstructure data were processed following standard methods (e.g., Inall et al., 2022; Kimura et al., 2016; Piccolroaz et al., 2021; Scott et al., 2021). Under the assumption of small‐scale isotropy, ε can be estimated as $$${\varepsilon}=\frac{15}{2}\nu \left\langle {\left(\frac{{\partial u}^{\prime }}{\partial z}\right)}^{2}\right\rangle =\frac{15}{2}{\nu}\int \nolimits_{0}^{{k}_{I}}{\psi }_{S}(k)\,dk,$$$ where ν is the temperature‐dependant kinematic viscosity of seawater and $$\left\langle {\left({\partial u}^{\prime }/\partial z\right)}^{2}\right\rangle $$ is the variance of the velocity shear fluctuations perpendicular to ALR's path (Osborn, 1974) derived from integrating the velocity shear spectrum $${\psi }_{S}$$ in wavenumber space $$k$$ up to $${k}_{I}$$.…”

“…The microstructure data were processed following standard methods (e.g. Inall et al, 2022;Kimura et al, 2016;Piccolroaz et al, 2021;Scott et al, 2021).…”

“…The RSI MicroRider package had four microstructure probes sampling at a rate of 512 Hz: two orthogonally positioned shear probes that provide an estimate of the rate of turbulent kinetic energy dissipation (TKE; ε), and two thermistor probes that provide an estimate of the rate of thermal variance dissipation (χ). The microstructure data were processed following standard methods (e.g., Inall et al, 2022;Kimura et al, 2016;Piccolroaz et al, 2021;Scott et al, 2021). Under the assumption of small-scale isotropy, ε can be estimated as…”