Title Thermal instability in freshwater lakes under ice; effect of salt gradients or solar radiation?
Author Kirillin, G.; Terzhevik, A.
Author Affil Kirillin, G., Leibniz-Institute of Water Ecology and Inland Fisheries, Department of Ecohydrology, Berlin, Germany. Other: Russian Academy of Sciences, Karelian Scientific Center, Northern Water Problems Institute, Russian Federation
Source Cold Regions Science and Technology, 65(2), p.184-190, . Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0165- 232X
Publication Date Feb. 2011
Notes In English. 24 refs. GeoRef Acc. No: 309498
Index Terms absorption; boundary layer; buoyancy; convection; diurnal variations; heat transfer; ice; lakes; lake ice; lake water; melting; meltwater; models; salinity; solar radiation; surface waters; temperature; thermal conductivity; Russia; Commonwealth of Independent States; fresh water; gravitational instability; heating; ice-water interface; Lake Vendyurskoye; mechanism; northwestern Russian Federation; rates; Russian Federation; seasonal variations; surface water; thermal anomalies
Abstract The phenomenon of "temperature dichotomy", or anomalous heating of surface water under the ice up to temperatures exceeding 4C is known to take place occasionally in solar-heated ice-covered freshwater lakes and has usually been explained by the stabilizing effect of the weak vertical salinity gradient created by the melt water flux from the ice and supporting the unstable temperature distribution. Here, we report an observation of the local temperature maximum in the upper part of the water column of ice-covered Lake Vendyurskoe (northwestern Russia). The observation was accompanied by vertically resolved measurements of the conductivity allowing estimation of the dissolved salts effect on the vertical density distribution. The results demonstrate insufficiency of the salt gradient to support the vertical stability of water column. Therefore, we suggest the vertically inhomogeneous radiation absorption to be the probable stabilizing mechanism here, similarly to radiatively heated boundary layers in the ocean, the atmosphere and star interiors. An analytical solution of the heat transfer equation is derived describing the temperature profile evolution in ice-covered lakes subject to solar radiation heating above the maximum density temperature. Observed daytime temperature profiles agree well with the analytical model that suggests the absence of convective mixing. According to the model, the temperature maximum is formed within a day that supports the hypothesis about the stabilizing effect of the solar radiation absorption. We conclude that in temperate lakes the warm layer should have diurnal character and should be destroyed during the nighttime by convection. In polar lakes, in turn, the warm layer can exist during essentially longer periods that is supported by application of the model to the previously published data from Lake Peters, Alaska. In this case, the ice melting rate can be significantly affected by the increased temperature gradient beneath the ice. Apart from potential effects on the ice melting rate and the spring plankton development in lakes, the regime represents a rare geophysical example of instability driven solely by radiative heating with many useful analogies in planetary and stellar physics.
URL http://hdl.handle.net/10.1016/j.coldregions.2010.08.010
Publication Type journal article
Record ID 65006609