Stable vegetation and environmental conditions during the Last Glacial Maximum: New results from Lake Kotokel (Lake Baikal region, southern Siberia, Russia)

摘要

This paper presents a new decadal-resolution fossil pollen record from Lake Kotokel (52°47′N, 108°07′E, 458 m a.s.l.) and provides a reconstruction of the Last Glacial Maximum (LGM) vegetation and environments in the study area during this interval of globally harsh climate. Lake Kotokel is situated close to the eastern shoreline of Lake Baikal, in the boreal forest zone of southern Siberia. The analysed 190 cm long section 6 of the bottom core KTK10 (KTK10/6) consists of compact, undisturbed, greenish-grey to dark-grey, slightly laminated silty clay indicating continuous lacustrine sedimentation throughout the LGM period ca. 26.8-19.1 cal. Ka BP. The age model is supported by 11 calibrated AMS dates. The results of pollen analysis and pollen-based biome reconstruction show that steppe and tundra vegetation composed of grasses and various herbs dominated ca. 26.8-19.1 cal. Ka BP. Occurrence of conifer tracheids and stomata throughout the record, together with small quantities of boreal conifer and broadleaf tree and shrub taxa pollen, suggests the presence of single trees or small forest stands in the lake vicinity, most likely in the river valleys. Application of the biomisation method and the resulting numerical scores of the most characteristic biomes (steppe, tundra and cold deciduous forest) show minor fluctuations, signifying stability of the regional vegetation cover during the analysed LGM interval. In contrast to the regional biomes, the local environmental indicators demonstrate greater sensitivity of the lake system to decadal- and century-scale climate variability. The highest pollen percentages of Ranunculaceae, representing littoral/meadow vegetation communities, are registered ca. 23.8-23.4 cal. Ka BP. This and an increase in coarse-grained sand particles together with slightly increased total inorganic carbon (TIC) values representing calcite in the KTK10/6 sediment provide evidence of a much shorter than present distance between the coring site and the shoreline and a reduced lake area, in line with a drier-than-present LGM climate. A general stability of the grassland vegetation in the study region ca. 26.8-19.1 cal. Ka BP and relatively constant total organic carbon (TOC) values support the hypothesis that this productive vegetation could stably serve as a perennial food resource for large populations of herbivores, thus providing favourable environments for the local hunter-gatherers inhabiting the Lake Baikal region during the LGM interval.