The existence of unfrozen water in soils at negative temperatures was first found by Bouyoucus experiments (1916), and then confirmed by Young (1932) on clays. Systematically investigations start to determine the soils freezing point (Andrianov, 1936) and showed the existence of previously super cooling of samples, and then the sharp increasing of temperature. The highest temperature point after the leap was determined as a freezing point of soils. Later calorimetric experiments, mostly on artificial frozen samples, were done on Tsitovich's (1945) Principe of equilibrium state of ice and water. It was shown: under any temperature increasing in frozen soils, the ice particular melted (Tsitovich, 1947; Nersesova, 1951) and the freezing point in soils dependent from their physical and chemical characteristics (Bozhenova, 1954). For the first time were determined the main regularities the unfrozen water changes as function of negative temperatures (Tsitovich, 1947; Nersesova, 1953, 1954; Nersesova, Tsitovich, 1966; Martinov, 1956; Khakimov, 1957; Tsitovich, Nersesova, 1957, 1963). Afterward the similar correlation were received by other scientific teams (Williams, 1964; Williams, Smith, 1984; Koopmans, Miller, 1966; Anderson, 1966-1968; Anderson et al, 1971, 1972; Anderson, Morgenshtern, 1973; Banin et al, 1968, 1973, 1974). Anderson with colleagues using the methods of NMR and roentgen determined the ice nucleation on the first stage of soil freezing and calculated the thickness of unfrozen water films, surrounding mineral/organic soil particles. The last advances were received by Ershov et al (1977, 1982, 1990) on the base of great number of different samples. They showed the regularities in forming freezing point and changes in quantity of unfrozen water at negative temperature as function of their physical and chemical characteristics and temperature of cooling. The explanation of experiments based on previously fundamental research of phase transfers during freezing and thawing corresponding with energy (heat) detachment or absorption (Fundamental Geocryology, 1959; Ananyan, 1959; Savelyev, 1063; Dostovalov, Kudryavtsev, 1967).
In our experiments with native samples using the modern technique (the temperature measurements at each second and their summarizing as average for 0.5 and 2.0 minutes) shows other regularities: the freezing of soil samples cannot take place without their previously super cooling (except the soils closed to dry state) and if super cooling didn't reach the critical negative temperature correspondent to the leap, the samples will not freeze during any time; the temperature after the leaps sometimes increase to (+0.1) - (+0.2) oC and, according the existing wording, the freezing point lay at positive temperatures; the temperature leaps take place not only before freezing point but at any spectrum of negative temperature typical for cryolithosphere (on the background of trend samples cooling and freezing); the frequency of leaps dependent from the rate of freezing: lower the environmental temperatures - the rather the frequency; each next leap take place at more lower temperature, as well as each next leap take place with lower amplitude; leap's temperature changes also take place in any negative spectrum on the background of trend samples warming and thawing - in this case all overwriting processes going with opposite symbol: the frequency of leaps dependent from the rate of warming - higher the environmental temperatures - the rather the frequency; each next leap take place at more higher temperature, as well as each next leap take place with higher amplitude; on the last stage of samples thawing the temperature leap to direction below 0 oC take place after the temperature reach the positive symbol.
At first time by experiments was shown the real development of freezing - thawing processes. Received new principal regularities of energetic on phase transfers under freezing and thawing. They are logical continue of existing fundamental ideas. If we agree with these well known theories and curves showed the regularities of unfrozen water changes under negative temperatures, we need to agree with received data. In experimental field some of them supported by new roentgen data (Grechishchev, 1996) and in natural conditions - by observations on meteorological stations (here the depths of soil freezing and penetration of 0 oC isotherm are different), as well as by special investigations in Arctic tundra (Zimov et al, 1994) and Antarctic deserts (Meier et al, 1987). The results received means, at least, the necessarily to determine for each type of soils the freezing point. For example, in winter some of them or some parts of their profiles may exist only in super cooling and not in freezing state.
David A. Gilichinsky Laboratory for Soil Cryology Institute of Soil Science & Photosyntesis Russian Academy of Sciences 142292, Pushchino, Moscow Region, RUSSIA Telephone: 7-096-77-32604 Fax: 7-096-77-90532 E-mail: gilichin@issp.serpukhov.su