Climatic optimum as a factor of the economic crisis of steppe nomads in the 4th century ad

Introduction. Archaeological sites of the 4th century AD absent on most of the area of the Late Sarmatian culture. This may be both due to the difficulties of their identification and absence of chronological indicators and due to migrations of nomads from the steppe zone. Perhaps unfavorable climatic conditions for nomadic cattle breeding affected the decrease in the number of nomadic population in the 4th century AD. Methods and materials. The paleosoil data allow reconstructing the ecological situation in dry and desert steppes in the first centuries AD. The initial stage of the Late Sarmatian era (the late 2nd - the early 3rd centuries AD) was marked byarid conditions with cold winters with little snow, which were favorable for cattle breeding in the steppe zone. In the late 3rd century and at the turn of the 3rd - 4th centuries, the processes of humidization began - an increase in climate humidity, which favorably affected the ecological situation in the steppe: high grass, area watering. Such situation provided successful livestock grazing in summer. However, in winter, an increase in humidity led to heavysnowfalls and snowstorms, an increase in snow cover, frequent winter thaws, rain, fog, that were replaced by periods of cooling. At this time, grass icing and ice crust formation occured. Analysis. In those conditions, the number of days, when cattle grazing was impossible, increased. As a consequence, there was weakening and disease of the livestock, until the complete loss of the herd. This was followed by the decrease of population. Results. The humidization processes primarily affected the Southern Urals and in the final of the 3rd century reached the Volga- Don steppes. This could be the reason for the outflow of the Late Sarmatian population from the Southern Urals to the Volga regions. In the 4th century AD, the steppes from the Urals to the Lower Don were practically depopulated. The beginning of the humid period, which was unfavorable for the nomadic economy, had a positive effect on settled agricultural societies. The Early Alanian culture of the Central Caucasus demonstrates the dynamics of active development throughout the Late Sarmatian period, including in the 4th c. AD. The duration of this humid period is difficult to estimate, however, in the Hun Epoch, steppes remained almost uninhabited, as evidenced by the small number of sites of this time.