Dynamics of the surface wetness of mires in the southern taiga subzone of Western Siberia in the middle and late Holocene

The research is devoted to the comparative analysis of the dynamics of the surface wetness of mires located within the southern taiga subzone of Western Siberia. Synchronous changes in the surface wetness of different mires in the same area during their development in the Holocene are most likely due to the influence of hydroclimatic fluctuations on them. The aim of our work was to identify synchronous changes in the surface wetness in different mires within a single region in the course of their development in the Holocene and to search for the conformity with regional paleoclimatic changes. The objects were four different mires on the territory of the southern taiga of West Siberia: 1) the Temnoye raised mire, located on the second terrace of the Tom River; 2) the Bakcharsky watershed mire (a peat core was taken from the hollow of the ridge-hollow complex); 3) the Samara mire, which occupies the first floodplain terrace of the Bakchar river; 4) the Petropavlovskoye raised mire, located on the right-bank terrace of the Ob river (Table 1 and Fig. 1). For the first three mires, we calculated a quantitative reconstruction of the water-table depth using transfer function models on the basis of testate amoebae analysis of peat. We developed two models of transfer functions for the area of the southern taiga of Western Siberia, separately, for ombrotrophic and minerotrophic mires using a weighted average (Figs. 2 and 3). In the fourth mire, reconstruction of paleoprecipitation was carried out using Klimanov's information-statistical method. The calibrated age of peat deposits in the number system Before Present was used in the work (Table 2). The studied mires differ from one another in the degree of surface wetness. The surface wetness of the Temnoye and Petropavlovskoye mires is much less than that of the Samara mire and the hollow from the Bakcharsky mire. The results of the construction of depth-age models of the studied peat cores indicated that peat accumulated with different speeds during the formation of mire sediments, in most cases slowing down of peat accumulation occurred non-simultaneously in different mires (Fig. 4). The time resolution of the reconstructions of the surface wetness in the studied mires varied from 51 to 650 years and, on average, was 193 years in the hollow from the Bakcharsky mire, 104 years in the Temnoye mire, 243 years in the Samara mire, and 188 years in the Petropavlovskoye mire (Fig. 5). As a result of a comparative analysis of the development of the studied mires over the last 8.500 years, we identified six periods of synchronous increase in their surface wetness: 8500-8400, 5700-5600, 5200-4600, 2600-2300, 1300-1100, and 900-700 yr BP, as well as 11 periods of synchronous drying of the mire surface: 6700-6600, 6100-6000, 4600-4400, 4300-4100, 4000-3800, 35003400, 3200-3000, 2700-2600, 2100-1900, 1500-1300, and 1100-900 yr BP (Fig. 6). These periods are consistent with the corresponding changes in paleoprecipitations. In general, the dynamics of the surface wetness in the studied mires corresponded to the climatic characteristics of different periods in the Holocene, revealed in West Siberia. Thus, in the Atlantic period synchronous wet stages in the studied mires were shown; in the Subboreal period mainly synchronous dry stages were singled out, and in the Subatlantic period the wet and dry synchronous stages alternating one by one were revealed in the studied mires. The periods with low time resolution in reconstructions complicate the detection of synchronous changes in the surface wetness of mires. We concluded that the higher the time resolution, the more likely it is that the compared water-table depth values existed in different mires at the same time, therefore, the greater the objectivity of data synchronization from different objects. The problem of low time resolution can be avoided by increasing the number of objects studied, or by a smaller sampling step in the peat cores. The synchronous changes in the surface wetness of mires and paleoprecipitations, which we have identified, reflect the fluctuations in the climate humidity in the Holocene. Our results indicate the sensitivity of the studied ombrotrophic and minerotrophic mires to hydroclimatic fluctuations during their development. In the future, it is planned to continue the research and include a comparative analysis of quantitative data of paleoecological reconstructions from other mires on the territory of the southern taiga subzone of West Siberia, as well as to increase the time resolution of the reconstructions. This will make it possible to clarify and detail information on century to millennial-scale climate variations on the studied territory in the Holocene.

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