The carbon isotopes ratio in small lakes bottom sediments located in the forest-steppe and steppe zones of southern Siberia

Sobolev Institute of Geology and Mineralogy of the Russian Academy of Sciences (IGM SB RAS), 630090, Novosibirsk, Russia

^* Corresponding author: strahova@igm.nsc.ru

Abstract

Isotopic variations of carbon of the carbonates and organic matter in bottom sediments of lakes of two lake systems located in the South of Siberia are studied: Baraba (Baraba steppes) and Tazheran (Tazheran steppes). Isotopic studies of δ¹³C carbonates and organic matter of the lacustrine bottom sediments of the Tazheran and Baraba systems indicate two main mechanisms of authigenic carbonates formation: chemogenic deposition and biochemogenic deposition due to bacterial destruction of organic matter. The dependence of the δ¹³C_org and δ¹³C_carb, the degree of water salinity is not revealed. Forms by chemogenic carbonates are similar to water isotopic values, i.e. with dissolved bicarbonate - ion reservoir. However, in most of the studied lakes the light isotopic composition δ¹³C_carb was revealed, as carbonates are formed in the environment with a high content of isotope-light CO₂ formed by the oxidation of carbon dioxide emitted by bacteria-decomposers in the mineralization process of the original organic matter in the stagnant waters in the anaerobic environment.