季节性冰封热融浅湖水温原位观测及其分层特征

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

为探究季节性冰封浅湖热力学特征,于2010年10月至2013年7月对高原腹地一典型热融湖塘冰层生消、水/冰温及气象条件开展原位观测,分析了水温分布时间变化、温跃层以及冰生消对水温结构的影响。结果发现:冰面升华显著,贯穿整个冰期;水温日变化、季节变化和垂直结构受气温、大气辐射、风速、冰生消和湖底沉积层热贡献影响显著;在"无冰期—结冰前—冰生长期—冰融化期—融化后—无冰期"年循环过程中水温垂直结构分别呈现出"分层—翻转—逆温分层—逆温与正温共存—翻转—分层"的循环过程。分层期水温结构仅由上部混合层和温跃层构成,且偶因强风搅动而全湖翻转混合。可见,相比大中型湖泊,季节性冰封浅湖热力学结构差异显著。

In order to better understand the thermodynamic characteristics of seasonally ice-covered shallow lake,the ice 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 ice on lake water thermal structure were investigated. Results indicated that a significant surface sublimation / ablation took place over the entire ice 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,ice thermodynamics,and heat fluxes from the lake bottom sediment.During the cycle of ＂ice free-freezing onset-ice growing-melting onset-melting ice 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 icecovered shallow lakes have quite different thermodynamic characteristics.