Vegetation and climate dynamics during the Holocene and Eemian interglacials derived from Lake Baikal pollen records

The last interglacial (LI) and Holocene changes in annual precipitation (Pann), the mean temperature of the warmest (Tw) and coldest (Tc) month and the moisture index (α) were reconstructed from continuous pollen records from Lake Baikal. The Holocene core (52°31′N, 106°09′E) presented in this study was recovered from a depth of 355 m in the 25-km wide underwater Buguldeika saddle separating the southern sub-basin of Lake Baikal from its central sub-basin. The biome reconstruction shows that tundra and steppe biomes have highest scores during ca. 15,000–13,300 cal. years B.P. and that taiga becomes a dominant vegetation type after ca. 13,300 cal. years B.P. Our quantitative reconstruction indicates an onset of relatively warm and wet conditions soon after ca. 10,000 cal. years B.P. The warmest and wettest climate with Tw ∼ 16 °C, Pann ∼ 480 mm and α ∼ 0.9–1 has been reconstructed for ca. 9000–7000 cal. years B.P. In the Lake Baikal region this interval is characterized by the appearance and spread of hunter communities (Kitoi culture). Consistently a hiatus in the regional archaeological record (4900–4200 years B.C. or 6850–6150 cal. years B.P.) coincides with the interval of a major climate deterioration which followed the ‘climatic optimum’. An attempt to find a relationship between the archaeological record and a spread of steppe and meadow communities in the Lake Baikal region demonstrates that despite a long habitation of the area the human impact on vegetation was local rather than regional and likely did not affect the pollen record from Lake Baikal. The reconstructed peaks in the steppe biome scores during the last 9000 years are consistent with short (one to five hundred year) episodes of weak Pacific (summer) monsoon supporting our interpretation that the Holocene vegetation changes around Lake Baikal are associated with large-scale circulation processes controlling regional water balance rather than with human activities. Thus, our study proves the suitability of Lake Baikal pollen data for the reconstruction of natural vegetation and climate dynamics through the whole period from the onset of the LI to the present. Comparison of the recent and the last interglacial suggests that the Holocene ‘climatic optimum’ was less pronounced (e.g. lower summer and winter temperatures and annual precipitation sums) than that of the LI. On the other hand, pollen records demonstrate that the Holocene ‘forest phase’ already lasts some thousand years longer than that of the LI. The interglacial vegetation dynamics derived from the Lake Baikal pollen records can be satisfactorily explained by reconstructed changes in summer and winter temperatures and in available moisture. The interglacial vegetation around Lake Baikal is dominated by the boreal forests, which are associated with a generally warm and wet climate. The high sea level associated with decreased ice volume appears to have had a greater impact on the Siberian environments during the last and the recent interglacial than the direct effect of lower-than-present winter insolation. Reconstructed changes in the winter temperature correlate well with changes in the sea level and global ice volume, while the summer temperatures derived from the Lake Baikal pollen records track changes in the summer insolation.