The research of biochemical thermo- and salt-sensitive markers - long-chain alkenones in sediments of lakes of the North Minusinsk valley is an important contribution to the understanding of climatic changes in this region. We found that the total concentration of alkenones in the top layers of bottom sediments of saline lakes increases significantly at a salinity of about 20 g l-1. Also, it was found that the average chain length of alkenones in the surface sediments rises with increasing salinity and thus can be used as an indicator of salinity, and the ratio of alkenones C37/C38 varies widely, suggesting that this index can be used as a paleo-indicator of salinity. The high correlation between ,  and  indices with salinity indicates their potential for paleosalinity reconstruction. The obtained functional dependences were additionally verified in the core of bottom sediments of Lake Utichie-3 and confirmed the possibility of using alkenones as a paleo-indicator of climatically determined salinity changes in endorheic lakes. The taxonomic composition of haptophyte algae and alkenone composition in the studied lakes were comparable to lakes in prairie regions of North America.

Long-chain alkenones are produced exclusively by certain species of microalgae Isochrysidales of the order of haptophytes (Haptophyta). These are polyunsaturated methyl and ethyl ketones C35–C42 with 2–4 trans double bonds in the aliphatic chain. The length of the hydrocarbon chain and the degree of unsaturation of double bonds of a given class of lipids can vary depending on the environmental conditions of their producers. This class of substances is well preserved in the bottom sediments (BSs) of seas and lakes and therefore can serve as a paleoindicator of climate change. Currently, studies are being conducted to identify the functional dependences of the composition of long-chain alkenones on the temperature and salinity of water in continental water bodies. In arid regions, saline closed-basin lakes sensitively react by changing the volume of water and its salinity to variations in the “precipitation–evaporation” balance, and, consequently, the sediments of such lakes are sources of information about climate humidity variations in the past. In this work, we analyzed the vertical profile of long-chain alkenones in the upper part of the BSs of the Utichye-3 salt lake located in the steppe region of southern Siberia and compared it with changes in the surface level and salinity of the lake water recorded over a period of about 100 years. It has been shown that the content of long-chain alkenones in sediments can increase during periods of high salinity. Consequently, the composition of alkenones can be used to reconstruct changes in salinity from BSs of closed-basin lakes, and, therefore, to reconstruct dry periods in the history of the climate of the steppe zone of southern Siberia.

Abstract. The core-top calibration study of 22 lakes indicates that in salt lakes the total alkenones increase sharply at a salinity of about 20 g/L, while alkenones are absent in the sediments of freshwater lakes. For the first time, this study shows that the Uk40 and Uk40 unsaturation indices are positively correlated with salinity and thus can be used to reconstruct salinity. The C37/C38 ratio is negatively correlated with salinity, and therefore this parameter can be used as an indicator of salinity. Also, the %C37:4 indicator is not correlated with salinity. It was found that the average chain length of alkenones increases with salinity, but the correlation was weak. Analysis of the alkenone composition and 18S rRNA suggests that all lakes are inhabited by Group II haptophytes, except for one freshwater lake, where the Group I of LCA-producing haptophytes was found. The taxonomic composition of haptophyte algae and the alkenone composition in the lakes were comparable to those in the lakes of the Canadian Prairies, apparently due to the similarity of climatic factors and the ionic composition of lake water in the two regions.