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 continuous permafrost landscape of Taymyr Peninsula, northern Siberia, were studied in 1994 and 1995. The aim was to quantify the seasonal fluxes of water and heat in the active layer from spring thaw to fall freeze‐back. Liquid water content was measured in frozen and unfrozen soils using time domain reflectometry. Liquid water was present in frozen soil at temperatures down to −12°C, and its volumetric fraction increased with temperature before melting occurred. The ground thermal regime during spring thaw and fall freeze‐back was dominated by latent heat fluxes that stabilized soil temperatures at 0°C for extended periods. The transfer of large amounts of latent heat released by freeze‐back in the fall suggested convective heat transfer mechanisms. Seasonal fluxes of heat and water were well described using a simple zero‐dimensional model of water and energy balance. The dominant heat sinks during the spring and summer were sensible and latent heat fluxes into the atmosphere. During fall freeze‐back the dominant heat source was phase change. The soil heterogeneity strongly impacted hydrologic and thermal processes in the active layer. Two direct consequences were the development of preferential flowpaths and the preferential freezing of the profile during freeze‐back.