Lake ecology and catchment vegetation changes reconstructed for the last 18,400 years in South-Western Yakutia, Siberia

Since many lakes in Yakutia, eastern Siberia, are of thermokarst origin, it can be challenging to reach ages of paleorecords beyond the Holocene, hence limiting the understanding of long-term key interactions between climate change, vegetation dynamics, biodiversity shifts, and lake development. However, with a new paleoenvironmental multiproxy project at an intermontane basin we aim to reconstruct lake-vegetation feedbacks since the Late Glacial Maximum (LGM). For that purpose, a 10.8 m long sediment core has been extracted from the deepest part (22.3 m) of the Lake Khamra (59.99095° N, 112.98345° E) and dated back to 18.4 cal ka BP. Lake Khamra is situated in South-Western Yakutia, the transitional zone of discontinuous to continuous permafrost, it is also in the zone of mixed evergreen-deciduous forest. We applied sedimentological and XRF-derived geochemical parameters in addition to palynological analyses of plant fossils and metabarcoding analyses of diatoms and plants sedimentary ancient DNA (sedaDNA). Our genetic analyses of diatoms revealed 45 unique sequence types. A high distribution of several small fragilarioid types indicates the initial formation of the lake, started in the LGM (15.4 cal ka BP), and high abundance of planktonic taxa since 8 cal ka BP indicates lake deepening in the Mid-Holocene. SedaDNA composition of 38 unique sequence types of aquatic and 155 unique sequence types of terrestrial plants revealed the agreement with pollen and non-pollen palynomorph derived vegetation composition. LGM vegetation was represented as wet tundra and both analyses revealed refugia of Larix. Tundra vegetation only appeared in LGM. The Holocene warming led to the forest establishment and therefore lake vegetation feedback intensification, seen from the turnover of diatoms. Diatoms assemblages of LGM which were represented by only few epiphytic taxa significantly increased the richness, as well as increasing of planktonic and benthic diatom assemblages. The lake expansion resulted in a diversification of emergent aquatic plants. And again, because the lake is not of thermokarst origin it shows more stable insight to environmental variability. This study provides a better understanding of the climate, lake system dynamics, and vegetation in Siberia, and simultaneously fills in the very scarce paleolimnological data in eastern Siberia.