Field observations on water temperature and stratification in a seasonally ice-covered shallow thermokarst lake

Abstract

In order to better understand the thermodynamic characteristics of seasonally ice-covered shallow lake, the freezing and melting processes, water/ice temperature variation, as well as meteorological conditions were measured in a typical thermokarst lake in central Qinghai-Tibet Plateau from October 2010 until July 2013. The temporal variations of lake temperature, development of thermocline, and the effects of lake on lake water thermal structure were investigated. Results indicated that a significant surface sublimation/ablation took place over the entire season. The daily and seasonal vertical structures of the lake temperature are significantly dominated by the change of air temperature, surface radiative fluxes, wind speed, thermodynamics, and heat fluxes from the lake bottom sediment. During the cycle of ice free-freezing onset-ice growing-melting onset-melting breakoff-ice free, the lake temperature takes up an annual cycle of stratification-overturning-inversion stratification-inversion-normal stratification-overturning-stratification. The thermal stratification consists only of epilimnion (mixing layer) and thermocline. Both layers can be replaced by a strong mixing process caused by strong gusts. Thus, compared with large lakes, the seasonal ice-covered shallow lakes have quite different thermodynamic characteristics.