Okenone in Bottom Sediments as a Proxy for Changes in the Water Level of a Saline Stratified Lake
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Okenone in Bottom Sediments as a Proxy for Changes in the Water Level of a Saline Stratified Lake D. Y. Rogozina,b,*, V. V. Zykova, A. O. Bulkhina,b, and Academician A. G. Degermendzhia Received February 21, 2020; revised March 19, 2020; accepted March 20, 2020
Abstract—Long-term measurements show that the sedimentation dynamics of okenone (a carotenoid of purple sulfur bacteria) reflects the abundance of purple sulfur bacteria, the hydrogen sulfide content, and the stratification stability in the closed saline meromictic Shira Lake (Southern Siberia, Russia). The profile of fossil okenone in bottom sediments has been compared with the data on the water surface level in the lake over the last 100 years. The peaks of okenone correspond to lake transgressions, and the drops in the okenone content coincide with periods of stable or decreasing water level. Our observations show that fossil okenone may be used as a qualitative proxy of meromictic conditions and as a quantitative proxy of the water level dynamics in closed stratified lakes. Therefore, okenone can be used for qualitative reconstructions of the water balance and climate humidity in arid zones. Keywords: okenone, purple sulfur bacteria, meromixis, water level, stratification, climate reconstruction DOI: 10.1134/S1028334X20070168
Closed lakes in areas with arid and semi-arid climate are sensitive to changes in the precipitation– evaporation balance. Changes in their volume and, thus, the determination of the water level dynamics in such lakes by bottom sediments provides valuable information for the reconstruction of climate humidity in the given area. Paleolimnological studies are mainly based on indirect proxies, which reflect changes in water salinity, for example, the species composition of diatoms, the composition of chemogenic minerals (carbonates), etc. The search for new proxies of the water level dynamics is urgent for higher accuracy of paleoclimate reconstructions and therefore for more reliable forecasts of future climate scenarios. Photosynthetic pigments (carotenoids and chlorophylls) are preserved well in bottom sediments and are used to characterize changes in the trophic status of the reservoir and in the taxonomic composition of phototrophic organisms at the level of the main groups (higher plants, green algae, cyanobacteria, diatoms, cryptophytes, etc.) [1]. Besides, carotenoids of phototrophic sulfur bacteria are used to detect periods when hydrogen sulfide is present in water, i.e., periods of the meromictic status of the reservoir [2]. This work is devoted to a more comprehensive analysis of the quantitative reconstruction of water a Institute
of Biophysics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia b Siberian Federal University, Krasnoyarsk, 660041 Russia *e-mail: [email protected]
level dynamics in a stratified reservoir on the basis of the content of carotenoids of phototrophic sulfur bacteria in bottom sediments. The aim of paleoreconstruction is inverse: changes in the reservoir ecosystem and ul
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