Mountain lakes in East Siberia have been studied for recent changes in water chemistry, turbidity and diatom assemblages preserved in bottom sediments. We performed a regional analysis of the relative effect of climate and glacier changes on change in diatom diversity and supply of meltware in proglacial lakes. We analysed sediment records from East Siberian glacier lakes using geochemical and diatoms proxies. We found that dramatic changes in communities and abundance of diatoms and biogenic proxy could be induced by low nutrient concentrations in glacial lakes and high turbidity due to active degradation of glaciers and snow patches as a result of the global increase in temperature in the Northern Hemisphere. Our evidences show that diatoms have been gradually decreased since ca. the 1880s. A significant tendency towards diatom reducing occurred at high summer regional temperatures. This tendency may be attributed to the fact that glaciers and snow patches thawed actively in East Siberia during ca. 1880-1958, which was induced by the beginning of the Recent Warming (ca. 1850-1860) and a long period of relatively warm regional climate from ca. 1900 to 1960.

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A simple, reliable, and high-performance method has been proposed for direct determination of the isotopic composition of authigenic uranium in silica lacustrine sediments. The method is based on studying the kinetics of the selective extraction of authigenic uranium from sediments with weak solutions of ammonium hydrocarbonate followed by the ICP-MS analysis of the nuclides. To estimate the contamination of authigenic uranium by terrigenous one, the contents of 232Th and some other clastogenic elements in the extracts were measured simultaneously. The selectivity of extraction of authigenic uranium from the sediments treated with a 1% NH4HCO3 solution appeared to be no worse than 99%. The method was used to analyze the isotopic composition of authigenic uranium at several key horizons of a core dated before. The measurements directly prove that the 234U/238U values in Baikal water varied depending on climate, which contradicts the previous statements. The measured 234U/238U ratios in paleo-Baikal water match the values reconstructed from isotopic data for total uranium in the sediments on the supposition that the U/Th ratio is constant in the terrigenous part of the sediment. Direct experimental determination of total and authigenic nuclides in sediments enhances the potentiality of the method for absolute 234U-230Th dating of carbonate-barren lacustrine sediments, including those from Lake Baikal, within the intervals corresponding to the periods of glaciation, where the sediments contain a large fraction of terrigenous component. Given the fractions of terrigenous and authigenic uranium are accurately determined, we have an opportunity to study the variability of the sources of terrigenous matter and to refine the previous model for reconstructing the climate humidity in East Siberia.

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East Siberia is very sensitive to moisture regimes because it is located in a margin area, where moisture from the North Atlantic is strongly depleted, and the penetration of the East Asian monsoon is weak and rare. In winter months, the Siberian anticyclone strongly blocks and reduces the external influences on the region. The high latitude of the study area at 52°N is probably sensitive to variation in insolation and solar activity. We analysed a 42-cm-long sediment record from Lake Mountain located in East Siberia (Russia) for geochemical, mineralogical, subfossil diatoms, chironomids, and pollen to provide a reconstruction of the climate history of the area for the last 850 years. According to our reconstruction, a clear decrease in summer temperatures occurred in East Siberia after ca. 1400 and we linked this temperature drop with the beginning of the Little Ice Age. The coldest summer occurred about ca. 1570-1700 and 1830-1900. We assumed that the most significant changes of the lake bio-productivity and the catchment area were occurred about ca.