ARCUS Student Award | 1st Annual Award

Abstract

The ground thermal and hydrological regime of a site located in the continuous permafrost landscape of Taymyr Peninsula, northern Sibiria was 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 (TDR). 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 is dominated by latent heat fluxes that stabilize soil temperatures at 0 °C for extended periods. During the summer, the thermal regime of the saturated active layer may be understood from assuming density-driven convection as the mechanism of heat transfer. Convective transfer also appears to be dominating during fall, when large amounts of latent heat are released by freeze-back.

Seasonal fluxes of heat and water are calculated using a simple zero-dimensional model of water and energy balance. Although this model neglects processes such as sensible heat fluxes and lateral water flow, it reveals that the dominant heat sink during spring and summer is evaporation. During fall freeze-back, the dominant heat-producing process is phase change.

The soil heterogeneity strongly impacts hydrological and thermal processes in the active layer. Two direct consequences are the development of preferential flowpaths and preferential freezing of the profile during freeze-back.