Mid-Holocene environmental conditions in the Altai Mountains: paleolimnological data

The paper discusses the results of the study of Middle Holocene paleorecords from lake-bottom sediment cores of the Altai lakes and adjacent areas. To reconstruct the climate and vegetation of the late Holocene, cores from lakes Maloye Yarovoye, Kuchuk, Tenga, Balyktukel, Igistukel, Kanas, and Khoton-Nur were analyzed. The middle Holocene of the Steppe Altai is characterized by a relatively high proportion of Pinus sylvestris pollen and a maximum presence of Ulmus pollen. Coniferous forests with admixture of deciduous species were distributed along river valleys in the most humid areas of the Ob-Irtysh interfluve and the Pre-Altai plain. The proportions ofpollen of Scots pine and elm decreased significantly after 3 ka BP. The results of the study show a pronounced onset of aridity in this area between 4.8-4.5 ka BP. Information on the natural conditions of the central part of the Russian Altai is provided by two palaeorecords from lakes of the Ulagan Plateau; the samples were studied by high resolution XRF analysis and, palynological and sedimentary plant DNA studies. According to the palynological record from Lake Kanas, the Middle Holocene vegetation of the Mongolian Altai is characterized by the maximum forest development. The pollen record from Lake Khoton-Nur also characterizes the vegetation in this part of the Mongolian Altai in the range of 8-5 ka BP as predominantly dark coniferous forests dominated by Siberian spruce. Thus, despite some inconsistencies in local reconstructions, the Northgrippian period of the Altai is characterized by the greatest humidity and distribution of forest vegetation. The reduction of forests and the decrease of the average annual precipitation started after 5 ka BP. The largest distribution of broadleaved species in southern West Siberia and Altai occurs between 7.2-2.6 ka BP. After the Little Ice Age, no presence of broad-leaved species in the paleorecords of Altai lakes has been noted.