Quantifying Impacts of Mean Annual Lake Bottom Temperature on Talik Development and Permafrost Degradation below Expanding Thermokarst Lakes on the Qinghai–Tibet Plateau

Abstract

Variations in thermokarst lake area, lake water depth, lake age, air temperature,permafrost condition, and other environmental variables could have important influences on themean annual lake bottom temperature (MALBT) and thus affect the ground thermal regime andtalik development beneath the lakes through their direct impacts on the MALBT. A lake expandingmodel was employed for examining the impacts of variations in the MALBT on talik developmentand permafrost degradation beneath expanding thermokarst lakes in the Beiluhe Basin on theQinghai–Tibetan Plateau (QTP). All required boundary and initial conditions and model parameterswere determined based on field measurements. Four simulation cases were conducted withdifferent respective fitting sinusoidal functions of the MALBTs at 3.75 °C, 4.5 °C, 5.25 °C, and 6.0 °C.The simulated results show that for lakes with MALBTs of 3.75 °C, 4.5 °C, 5.25 °C, and 6.0 °C, themaximum thicknesses of bowl-shaped talik below the lakes at year 300 were 27.2 m, 29.6 m, 32.0 m,and 34.4 m; funnel-shaped open taliks formed beneath the lakes at years 451, 411, 382, and 356 afterthe formation of thermokarst lakes, with mean downward thaw rates of 9.1 m/year, 10.2 m/year,11.2 m/year, and 12.0 m/year, respectively. Increases in the MALBT from 3.75 °C to 4.52 °C, 4.25 °Cto 5.25 °C, and 5.25 °C to 6.0 °C respectively resulted in the permafrost with a horizontal distance tolake centerline less than or equal to 45 m thawing completely 36 years, 32 years, and 24 years inadvance, and the maximum ground temperature increases at a depth of 40 m below the lakes at year600 ranged from 2.16 °C to 2.80 °C, 3.57 °C, and 4.09 °C, depending on the MALBT. The groundtemperature increases of more than 0.5 °C at a depth of 40 m in year 600 occurred as far as 74.9 m,87.2 m, 97.8 m, and 106.6 m from the lake centerlines. The simulation results also show that changesin the MALBT almost have no impact on the open talik lateral progress rate, although the minimumdistances from the open talik profile to lake centerlines below the lakes with different MALBTsexhibited substantial differences.