Age and Dynamics of the Lithalsa in the Sentsa River Valley, Eastern Sayan, Based on 14С Dating and Isotope–Geochemical Methods

Lithalsas are found on mires in the discontinuous permafrost in the circumpolar area of the northern hemisphere and in mountainous regions. The age and growth mechanism of lithalsa in the continental intermountain region of the East Sayan Mountains were uncertain and debated. We represent the results of a detailed analysis of four representative lithalsas, including 14C dating, C‐N content of buried peat lenses, and organic matter from soils, as well as results of stable isotope measurements (δ18O and δ2H) in the lithalsas' ice lenses. It was found that the studied lithalsas are not older than 600 years; the youngest mound began to form about 170 years BP. Main water sources for lithalsa ice formation were shallow lakes and the Sentsa River during spring floodings; freezing occurred mainly in open system conditions. However, the rate of freezing ice lens was not the same for the studied lithalsas, as well as the rate of their growth. Multiple freezing cycles were established for the highest lithalsa. High values of the C/N ratio in organic and peat horizons allow us to suppose the rapid freezing of organic matter during lithalsa growth. The findings confirm that non‐climatic factors, like flooding, are crucial for lithalsa dynamics.