THERMAL REGIME OF A SHALLOW LAKE IN WINTER

• Main Authors: Galina Zdorovennova, Roman Zdorovennov, Nikolai Palshin, Tatyana Efremova, Galina Gavrilenko, Sergey Bogdanov, Arkady Terzhevik
• Format: Article
• Language: English
• Published: Karelian Research Centre of the Russian Academy of Sciences 2016-05-01
• Series: Transactions of the Karelian Research Centre of the Russian Academy of Sciences
• Subjects: water temperature; shallow lake; fluctuations; ice-covered period; heat flux
• Online Access: http://journals.krc.karelia.ru/index.php/limnology/article/view/314
• ISSN: 1997-3217; 2312-4504

<p>The thermodynamics of the water column and the bottom layer of a small shallow lake Vendyurskoe were identified from the analysis of temperature measurements by high resolution equipment during the winter 2014-2015. Estimates of the heat flux from the bottom sediments into the water revealed a sharp decrease in its value from 2-5 W·m^-2 before lake freezing up to 1-1.5 W·m^-2 in the first days of the ice-covered period, and then a slow decrease to 0.4 W·m^-2by the end of the winter. Temperature oscillations of different amplitudes and periods are observed against the background of its seasonal increase. The oscillations ΔT varied with time and depth in a wide range, with areas of "background" values of a few thousandths of a degree alternating with "active" intervals where ΔT value increased by an order of magnitude or more. The sharpest changes in near-bottom temperature led to an increase in the heat flux from the background values of 0.5-1.1 W·m^-2 to 3-5 W·m^-2. "Background" temperature oscillations corresponded to 1-2 mm vertical displacement of the isotherms, and vertical rates of about 10^-5 m·s^-1, whereas “active” oscillations corresponded to displacements of up to several cm and rates 1-2 orders of magnitude higher. "Active" intervals were observed when atmospheric forcing on the lake (sharp fluctuations of atmospheric pressure and wind intensification) increased. Significant fluctuations of the depth of isotherms and the dependence of the temperature oscillation amplitude on the depth suggest they are of baroclinic nature, i.e. may be caused by internal waves in a stratified lake.</p>