Salt and water movement was measured in unsaturated frozen soil columns incubated under a thermal gradient for 3, 6, or 9 weeks. Both water and salt moved from the warmer to cooler areas in the soil, creating a twofold concentration difference over a 24-cm distance. Movement of CaC12, LiI, and K2SO4 was studied in detail Cation exchange reactions and salt solubilities at high concentrations affected the movement. Although the results suggested that mass flow of dissolved salts in a liquid film of water was the principal transfer mechanism, both vapor and salt diffusion were sometimes significant. Thermal diffusion and salt sieving did not appear to be important.Since the vapor pressure of ice controls the water potential in frozen soil, the amount of unfrozen water and matric suction could be calculated from a water release curve and data from ice suspensions in salt solutions. These results led to the conclusion that mass flow in the liquid phase is described by Darcy's law. Thus, salt flow as well as net water transfer can probably be predicted in unsaturated frozen soil using information available from unfrozen systems.Additional Index Words: salinity, salt diffusion, thermal diffusion, salt separation, frost heaving. M OIST UNSATURATED SOIL freezes downward from the surface in the fall and is subject to varied thermal gradients throughout the winter (Benz et al., 1968). As the soil water freezes, small ice crystals form in the pore spaces. Not all of the water freezes under temperatures commonly experienced in the field. A liquid-like film 10 to 40A thick remains at the ice-air interface. Liquid films of varying thicknesses also remain in the soil particleice interfaces and in the soil particle-air interfaces (Anderson, 1970).Since ice crystals freeze out of a solution in a pure state, all soluble salts are forced into the unfrozen water films and may form relatively concentrated brines. The vapor pressure of ice is less than that of pure liquid water. Consequently, water will continue to crystallize from the soil solution until the combined osmotic and matric forces reduce the solution's vapor pressure to that of the ice (Hoeckstra, 1966;Low et al., 1968). Under natural conditions in the field, temperature gradients always exist, and liquid water tends to move from warmer to cooler areas (Fergusen et al., 1964). A spontaneous vapor pressure gradient in this same direction is fixed by the temperature of the ice phase. While some movement is in the vapor phase, most of the flow is in the unfrozen liquid films (Hoeckstra, 1966;Benz et al., 1968 apparent that salt will also move from warmer to cooler areas in the unsaturated frozen soil.Most of the liquid phase movement occurs along the water films adsorbed to the soil particles. While there are liquid films in the ice crystal air interfaces, they comprise a small fraction of the total unfrozen water in unsaturated soil because of the relatively small surface area of the ice crystals compared to that of the soil particles (Anderson, 1970). As the water ...