## 1 Introduction  
Data on the stable isotope compositions of oxygen and hydrogen in precipitation and snowpack is actively used to obtain important information about climatic, hydrological, and ecological changes in the environment [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14], including the assessment of the transboundary transfer of atmospheric moisture falling on the studied area as precipitation, and the identification of the sources of this moisture [15; 16; 17; 18; 19; 20; 21; 22; 23; 24]. In contrast to snowfalls, seasonal snow cover of middle and polar latitudes can give integral seasonal (for the winter period) characteristics of the moisture's isotopic composition entering the studied area [24; 25; 26]. At the same time, the sampling of snowpack during the maximum snow accumulation period is simpler to perform in relation to the sampling of atmospheric precipitation and allows you to cover a large area with the necessary sampling network. Unfortunately, it is not correct to directly use the isotopic composition data of the seasonal snow cover for hydrological, climatic, and ecological purposes because many researchers note that during the winter period various processes leading to changes in the initial isotopic composition of snow can occur in the layers of snowpack [27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48]. All this must be taken into account when snowpack samples are used to assess the seasonal moisture supply and further its redistribution among the components of the water runoff in the catchment area after snow melting.  
During the winter period, the main changes in the isotopic composition (\(\delta^{18}\)O and \(\delta\)D) of water in the layers of the snowpack are associated with the penetration and condensation of soil moisture in the snow layer closest to the snow-soil interface [27; 34; 38; 40], movement and condensation of moisture (vapor and water) inside the snowpack due to the existence of a vertical temperature and pressure gradients [33; 38], partial thawing of snow layers [38; 39; 40], as well as vapor exchange between the upper layer of snow and the atmosphere [38; 39; 40]. In addition, a significant effect on the change in the isotope composition of the snowpack can be exerted via canopy for forest areas [8; 41; 42; 43] and for steppe areas due to wind redistribution of snow previously accumulated on the ground [44; 45; 46]. All of these processes have different effects on the vertical redistribution of the initial isotopic composition of atmospheric moisture deposited on the underlying surface, and their combined influence can manifest itself in different ways depending on regional weather conditions. Therefore, studying regional peculiarities and factors influencing changes in the snow's initial stable water isotopes composition in the snowpack is an important task with a wide practical application.  
For the south of Western Siberia (this territory has a stable seasonal snow cover from mid-November to mid-March), the data of the layer-by-layer analysis of the snowpack can be successfully used to study the features of the spatio-temporal distribution of atmospheric moisture deposited during the winter period. In this regard, the purpose of our work was to identify the main factors and assess their contribution to the change in the initial water isotopic composition (\(\delta^{18}\)O and \(\delta\)D) of snowfalls during their storage in seasonal snow cover (until the beginning of the stage of active snow melting) in the south of Western Siberia.