Reconstruction of Paleoecological Conditions from Isotopic Signatures in Bottom Sediments of Lake Bolshoye Eravnoye (Transbaikalia)

Paleoecological reconstructions for the intracontinental regions of Transbaikalia are crucial for understanding ecosystem responses to global climatic changes. The study presents the results of a comprehensive analysis of a sediment core (2 m) from Lake Bolshoye Eravnoye (Eravninskaya Basin). Based on three AMS ¹⁴C dates, the core sample spans a period of approximately 38 thousand years, making it one of the longest temporal records for shallow lakes in the region. Analysis of elemental and isotopic composition along with grain-size distribution allowed for the identification of four sedimentation phases that reflect the ecosystem’s response to shifts in climatic conditions. The findings demonstrate that during warm and humid periods, allochthonous organic matter dominated (C/N = 15–19, δ¹³C from –26.1 to –24.0 ‰). In contrast, cold and arid phases (Last Glacial Maximum) were marked by an increased role of autochthonous organic matter with minimal hydrodynamic activity attributed to persistent ice cover. The most pronounced environmental changes occurred at the Pleistocene-Holocene transition: a sharp increase in hydrodynamic energy and a shift in organic matter sources are interpreted as a response to permafrost degradation and increased moisture availability. The Holocene section of the record is characterized by high productivity and dynamism, reflecting the climatic instability of this period. The data presented provide, for the first time, such a long and detailed paleoecological record for small lakes of the Eravninskaya Basin. This significantly contributes to refining the paleogeographic history of Transbaikalia and underscores the high sensitivity of its lake ecosystems to global climatic trends.