Changes in Atmospheric Humidification in the Steppes of Western Orenburg Region in the Second Half of the Holocene Based on Data from a Study of Soils under Burial Mounds of Different Ages

By studying the morphological properties and physicochemical parameters (humus horizon thickness, organic carbon and carbonate carbon content, forms of carbonate neoformations, and gypsum content) of paleosols buried beneath burial mounds of various archaeological cultures (Pit Grave, Srubnaya, Early Iron Age, and Middle Ages), we were able to reconstruct the evolution of chernozems and chestnut soils (at the type and subtype level) in the steppe zone of the Western Orenburg region during the second half of the Holocene. A clear link was established between soil properties and atmospheric moisture during their formation. Diagnostic signs of aridization (a decrease in the thickness of the humus horizon, the occurrence of carbonate formations closer to the day surface, the presence of gypsum) and humidization of the climate (an increase in the thickness of the humus horizon and humus content, a shift of carbonate formations to a greater depth, their transition to impregnating forms, the disappearance of gypsum) were revealed. The following alternation of epochs of change in climate humidification is shown: 6000–5300 years ago an increase in climate aridization was revealed, 5300–4300 years ago the climate was characterized by milder and less contrasting conditions, 3900–3800 years ago drier climatic conditions prevailed, then humidification gradually increased up to the period 3600–3500 years ago, 2700–1600 years ago. Climatic conditions are characterized by frequent climatic fluctuations (increased aridity alternates with increased humidification and vice versa). Between 800 and 650 years ago, the climate was drier and hotter than the modern period, which gave way to more humid and mild climatic conditions between 650 and 600 years ago. Spatial distribution maps of zonal soil types and subtypes for various historical periods were compiled. The data obtained are key to understanding the genesis of the modern soil cover structure and predicting its changes under current climate change. 

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