Changes in the Southern Urals environment: Holocene records of the deep-water lake, regional correlations, and global climate events

Palaeoenvironmental studies of the Southern Ural provide a link between the Holocene records of Europe and Asia, and the steppe and forest zones of the continent. Owing to a lack of well-dated Holocene sequences and the strong influence of local factors, the overall pattern of Holocene environmental changes in the Southern Ural forest zone is still a matter of debate. To solve this problem, Lake Turgoyak, which is influenced to a minimum extent by local factors, was studied, and the Holocene sequences of the Southern Urals were correlated with each other and with the global climate events. The sedimentary records of Lake Turgoyak were found to reflect almost all changes that were partially noted in the records of the earlier studied lakes. The main changes in the Lake Turgoyak ecosystem occurred at 12.1 cal ka BP, 11.8 cal ka BP, 11.1 cal ka BP, 8.1−7.8 cal ka BP, 2.5 cal ka BP, and 0.5−0.11 cal ka BP, as well as since the second half of the 20th century. Regional correlations of the sedimentary records of the six lakes make it possible to distinguish the environmental changes that occurred in the Southern Urals at more than 12.3 cal ka BP. Climate warming began at 12.1 cal ka BP, however, an effective moisture increased only after 11.7−11.5 cal ka BP. The climate amelioration trend increased after 11.2 ka and 8.2 ka dry and cool events. The optimum, warm, and humid conditions were characteristic of the period from 7.8 to 6.5 cal ka BP. An increase in effective moisture due to climate cooling began at 5.1 cal ka BP and more clearly after the 4.2 ka event and since 2.5 cal ka BP. The Little Ice-Age, marked by the return of cool and dry conditions, was recorded only in the Turgoyak and Syrytkul sedimentary records. Correlation with global climate changes demonstrated that the events recorded in Greenland ice cores (11.2 ka and 8.2 ka) exerted more significant influence on the Southern Urals than the 4.2 ka event which is strongly recorded in proxy climate records from the middle and low latitudes.