Under-ice convection dynamics in a boreal lake

Abstract

We investigated radiatively driven under-ice convection in Lake Onego (Russia) during 3 consecutive late winters. In ice-covered lakes, where the temperature of water is below the temperature of maximum density, radiatively driven heating in the upper water column induces unstable density distributions leading to gravitational convection. In this work, we quantified the key parameters to characterise the radiatively driven under-ice convection: (1) the effective buoyancy flux, B * (driver), and its vertical distribution; (2) the convective mixed-layer thickness, h CML (depth scale); and (3) the convective velocity, w * (kinematic scale). We compared analytical w * scaling estimates to in situ observations from high-resolution acoustic Doppler current profilers. The results show a robust correlation between w * and the direct observations, except during the onset and decay of the solar radiation. Our results highlight the importance of accurately defining the upper limit of h CML in highly turbid water and the need for spectrally resolving solar radiation measurements and their attenuation for accurate B * estimates. Uncertainties in the different parameters were also investigated. We finally examined the implications of under-ice convection for the growth rate of nonmotile phytoplankton and provide a simple heuristic model as a function of easily measurable parameters.

Energetics of Radiatively Heated Ice‐Covered Lakes

“…The quantity η solar can be estimated from temperature profiles that resolve the DBL and measurements of under‐ice radiation intensity. Using published observations from three different ice‐covered lakes (Bouffard et al, ; Kirillin et al, ; Volkov et al, ), we obtain the following: …”

Life under ice in Lake Onego (Russia) – an interdisciplinary winter limnology study

“…Therefore, the radiatively driven heating induces gravitationally unstable density profiles that lead to convection. Bouffard et al (2016Bouffard et al ( , 2019 and Bogdanov et al (2019) investigated this type of under-ice convection in Lake Onego during 3 consecutive winters (March 2015-2017). Because the velocities of the convective thermals are often in the submillimetre per second range, only the largest convective cells could be identified by using acoustic velocity profilers (Bogdanov et al 2019).…”

“…However, it was possible to quantify (1) the vertical distribution of the source of the convective instability, (2) the convective mixed-layer thickness, and (3) the convective velocities. The unique aspect of the investigation by Bouffard et al (2019) is the high accuracy and temporal resolution of the daily dynamics, allowing identification of day-night on-off forcing of the convectively mixed layer.…”

“…These convective thermal plumes move nutrients in and out of the light-exposed surface layer. These motions right below the ice are essential for phytoplankton growth because mixing keeps cells in suspension and prevents sedimentation losses (Bouffard et al 2019). Suarez et al (2019) investigated diurnal variations in the vertical distribution of phytoplankton, which are not only driven by convection and below-ice light availability but also by the moderate to high levels of coloured dissolved organic carbon.…”

Mixing processes in small arctic lakes during spring

“…||,Malm et al (1997, 1998), Malm (1998), Mironov et al (2002,Jonas et al (2003),Petrov et al (2006),Kirillin and Terzhevik (2011), Zdorovennov et al (2013). ¶Malm et al (1997) # Bouffard et al (2016# Bouffard et al ( , 2019…”