Long-Chain Alkenones in Sediments of Lake Utichye-3 (Southern Siberia, Khakassia) as a Paleo-Indicator of Climate Change

Abstract

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.