THERMAL AND HYDROLOGIC DYNAMICS OF THE ACTIVE LAYER AT A CONTINUOUS PERMAFROST SITE (TAYMYR PENINSULA, SIBERIA)

The ground thermal and hydrologic regimes of a site located in the con tinuous permafrost landscape of Taymyr Peninsula, northern Siberia, we re studied in 1994 and 1995. The aim was to quantify the seasonal flux es of water and heat in the active layer from spring thaw to fall free ze-back. Liquid water content was measured in frozen and unfrozen soil s using time domain reflectometry. Liquid water was present in frozen soil at temperatures down to -12 degrees C, and its volumetric fractio n increased with temperature before melting occurred. The ground therm al regime during spring thaw and fall freeze-back was dominated by lat ent heat fluxes that stabilized soil temperatures at 0 degrees C for e xtended periods. The transfer of large amounts of latent heat released by freeze-back in the fall suggested convective heat transfer mechani sms. Seasonal fluxes of heat and water were well described using a sim ple zero-dimensional model of water and energy balance. The dominant h eat sinks during the spring and summer were sensible and latent heat f luxes into the atmosphere. During fall freeze-back the dominant heat s ource was phase change. The soil heterogeneity strongly impacted hydro logic and thermal processes in the active layer. Two direct consequenc es were the development of preferential flowpaths and the preferential freezing of the profile during freeze-back.