## 4 Discussion  
Many authors [27, 28, 33, 40, 59, 60] point to the vertical homogenization of the isotopic variance within the snowpack due to diffusion and dispersion of liquid and vapor molecules of water inside the snow masses. In our case, this is clearly manifested in the smoothing of the vertical change in the isotopic composition of the snowpack formed on the earth's surface, in contrast to the isolated snow layers in the barrel and the initial atmospheric precipitation (Figure 3). Since in the winter of 2020-2021, the air temperature during the formation of 2-8 layers of the snowpack was significantly below zero (Table S2), which excluded thawing, the existence of a temperature gradient between the layers of snow is the main reason for such vertical \"smoothing\". The increase in air temperature above zero after the first snowfalls leads to the first snowfalls partially or completely not staying in the snowpack because they melt and penetrate the still unfrozen surface layer of the soil. Under the condition of absence of the influence of soil moisture, it can lead to depletion of heavy isotopes in the bottom layer of the snowpack relative to the initial snowfalls, because the first snowfalls, as a rule, form at higher air temperatures and are more enriched in heavier isotopes. In our case, it is evident by comparing the bottom layer of snow formed in the barrels and directly on the earth surfaces in winter 2020-2021 (Figure 3). The melting of a part of the snowfalls from the bottom layer of the snowpack indicates that at both experimental sites (I and II, Figure 1c) located at a considerable distance from each other (\(\sim\)50 km) isotopic composition of the bottom layer formed on the soil surface was lighter by 3-4% for \(\delta\)18O and by 15-18% for \(\delta\)D relative to the bottom layer in the barrel and precipitation-weighted mean value of snowfalls for the same period. It should be noted that there was short-term warming (one day 11 December 2020) after the first snowfalls, and then thaws were no more in the Altai Territory until the end of February. However, at the end of November, long severe frosts were established with an even lower snowpack height, which led to deep freezing of the soil throughout the studied area, until the end of the winter. The freezing of the initially wet soil contributed to the fact that the soil moisture could not spread from the soil and condense in the bottom layer of the snowpack, which allowed us to notice the depletion in heavy isotopes of the bottom layer of the snowpack relative to the snowfalls. Thus, the initial conditions for the snowpack formation are of great importance for the possibility of the soil moisture inflow into the bottom layer of snow. As a rule, the isotopic composition of the snow bottom layer is enriched in heavier isotopes by soil moisture; for example, [PERSON] et al. (1991) observed that the bottom of snow cores deposited in Fairbanks (Alaska) was enriched in heavier isotopes compared with the bulk snowpack before the beginning of the melt season [27]. The results of our work showed that the amount of soil moisture condensation in the snowpack depends on the condition of the underlying soil. Table 2 shows the data of the isotopic composition of the snowpack (bulk and separately the bottom layer) deposited on frozen and unfrozen soil in the flat part of the Altai Territory at the end of winter 2019-2020. For comparison, the table also presents the precipitation-weighted mean values of the isotopic composition of snowfalls during the same period and rainfalls within two months before the snow cover formation. The data in the table show that the average values of \(\delta\)18O, \(\delta\)D, and d-excess in bulk samples of snowpack deposited on frozen and non-frozen soil practically do not differ, while the bottom layers differ distinctly. This difference for unfrozen soil can only be explained by the water transfer from the soil to the bottom layer of snow.