Spatiotemporal Variations of δ13С and δ18О Values of Secondary Carbonate Accumulations in Soils of the Baikal Region

The formation of secondary carbonates is one of the most important pedogenic processes, characterizing a response of soils to changes in the natural environment in the past and enabling the assessment of the current pathways of carbon dynamics. This work assesses the features of morphology and distribution of secondary carbonates, which are a typical component in steppe soils of the Baikal region, but to a lesser extent than in taiga soils. The differences in the conditions of formation of modern soils are reflected in variations in the values of δ13С and δ18О, being the lowest for secondary carbonate accumulations in taiga soils that are formed under more favorable hydrothermal conditions during the growing season, and being the highest for pedofeatures in steppe soils, due to the low productivity of phytocenoses, low biological activity of soils in a dry growing season, and a short period of optimal combination of temperature and moisture. During the Holocene, the main phases of carbonate profile formation in soils were confined to the Middle Holocene. Single phases of carbonate redistribution in soils are recorded for the Early and the beginning of the Late Holocene. During the Upper Pleistocene, phases of carbonate redistribution were associated with phases of cryogenesis at the upper and lower boundaries of the Upper Osinsk stage of soil formation, fixing regional manifestations of global climate changes at the end of MIS 3. Along with the Karginian, a stage of carbonate redistribution and development of carbonate pedofeatures in the regional soils is also recorded during Late Glacial climate warming events. The morphology and isotope-geochemical properties of Upper Pleistocene carbonate cutans indicate the active occurrence of the Al-Fe-humic process under cold humid conditions during the formation of MIS 3 and MIS 2 soils. Thus, the secondary carbonates are an important archive of the polygenetic development of the regional soils.