Polyunsaturated long-chain alkenones in bottom sediments of the meromictic Lake Shira (southern Siberia) as a paleo-indicator of climate change

Abstract

To understand long-term climate variability and its connection with modern global warming, this study analyzed the composition of long-chain alkenones in the bottom sediments of Lake Shira (North-Minusinsk valley) over the past 3000 years. In the ICE2023, Shira-I-21 and Shira-II-21 cores, gas chromatography-mass spectrometry revealed methyl- and ethyl-alkenones, predominantly C₃₇ and C₃₈, with double bonds ranging from two to four. The vertical profiles show substantial fluctuations in total concentration (1-355 µg/g), likely associated with changes in water level, salinity, and organic matter preservation conditions. Alkenone peaks coincide with light (carbonate-rich) layers, reflecting phases of lake level decline and increased salinity. Elevated alkenone concentrations in the clay-rich sections of the core may indicate enhanced adsorption and preservation. The results confirm the potential of long-chain alkenones as a proxy for paleo-salinity and, consequently, paleo-humidity in arid regions of Siberia.