Mid Holocene ecosystem peak and late Holocene shift to littoral refugia in an arid Altai lake: non-pollen palynomorph record

This study reconstructs the local environmental conditions of Lake Tarkhata (Altai Mountains) during the Middle and Late Holocene based on the analysis of non-pollen palynomorphs preserved in lacustrine sediments. A total of approximately 60 NPP morphotypes were identified, including algae, fungal remains, invertebrates, testate amoebae, and conifer stomata, providing detailed insights into within-lake processes and hydrological changes. Several previously undescribed NPP morphotypes were morphologically described in this study. The results show that the composition of NPP assemblages reflects a transition from an early system with clear cyanobacterial dominance to a more diverse and structurally complex lake ecosystem. The highest diversity, maximum complexity, and peak biological productivity are recorded not during the Holocene climatic optimum, but in the interval ∼ 4.6–2.8 cal kyr BP, despite a decrease in moisture availability inferred from palynological evidence from the same core. This indicates an asynchrony between climatic trends and ecosystem response. This stage is interpreted as the result of internal reorganization of the lake system associated with falling water levels and expansion of littoral habitats. In contrast, the end of the Late Holocene is characterized by declining productivity and increasing dominance of shallow-water microenvironments. Thus, effective moisture was the primary factor controlling lake ecosystem dynamics, while ecosystem responses were non-linear and not always synchronous with regional climate change.