Environment changes reconstruction by pedohumic method in the Central-Tuvan hollow during holocene period

The paleosols formed from 9860±160 to 605±55 years ago in the Central-Tuvan hollow were investigated by the pedohumic method with the aim to reconstruct the environment of the past.According to diagnostics of certain horizons types and their forming conditions corresponding to climate warming and cooling and taking into account the reported data on spore-pollen spectra of the sediments of different Holocene age the most detailed present scheme of soil formation environment changes in the Central-Tuvan hollow was suggested. It was revealed that during Holocene warming periods soils were forming in the steppe environment and during those of cooling soil formation occurred in the steppe-forest and taiga.Diagnostics of soil formation types and conditions for Holocene beginning period (9,9-8,5 thousand years ago) was first carried out for Tuva territory. This period has not been studied either from paleopedogenesis point of view or from that of paleoecosystems and paleoclimates. Well-compared dates and characteristics of Baryk and Shanchy sections made it possible to reconstruct environment changing in that time and to reveal two periods of warming and one of cooling between them. The cooling period was so deep and strong that it led to dark coniferous taiga zone being lowered to 700 m above sea level where steppe cenosis predominated over warm intervals. The following Holocene period that started 7 thousand years ago is characterized on the scheme with the combination of pedogenesis features studied for paleosols and sediments and of reported data of spore-pollen spectra.Three waves of climate drying are distinguished: in the beginning of atlantic and subboreal periods and in the second half of subatlantic one. The first arid age was followed by climate warming and two last ones were characterized by significantclimate cooling led to depression of wooden vegetation on all altitude levels, which is confirmed by sediment spore-pollen spectra and by the data of Seserlig-1, Biche-Bases-1 and Ondum-11 paleosols sections studying. Dry periods interchanged with moistening phases at the end of atlantic period and on the border between subboreal and subatlantic periods that were first followed by cold conditions and then changed into warmer ones. Cold and humid stages occurred with the forest zone getting wider that was replaced by steppe cenosis under climate warming. Pedogenic features of the investigated paleosols within Seserlig-1 section convincingly prove this statement demonstrating interchanging of forest-steppe and steppe environment.The data on paleosols and sediment humus characteristics and reported spore-pollen spectra do not contradict each other and register a general trend of environment changing in the direction of warming and relative aridization increasing that served as background for fluctuations of warmth supply and moistening.

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