Use of δ13С Variations in Organic Matter of Paleosols of Western Transbaikalia for Reconstruction of Paleoprecipitation Dynamics in the Late Glacial and Holocene

Abstract

Analysis of the stable carbon isotopic composition (δ¹³C) of soil organic matter is important for assessing past climate changes and the response of landscape components to them. Soils of nine soil-sedimentary sequences formed in various landscape and geomorphological conditions of western Transbaikalia have been studied. The time of their formation covers the last 15 kyr. The phases of pedogenesis within genetically different landforms were rather synchronous, which enabled us to suppose that they were caused by regional landscape-climatic changes, which also affected δ¹³C of soil organic matter. The range of variations in δ¹³С values is from –20.99 to –27.00‰. Changes in δ¹³С over time are the most contrasting for sections formed under driest steppe conditions and are the smallest for sections in taiga landscapes with the greatest precipitation. However, in general, the trends of changes in δ¹³С in different landscape zones over time are similar: the lowest δ¹³С values are typical for organic matter of Late Glacial paleosols formed 14–15 and 12 kyr BP, as well as for soils of the Late Holocene (3.5–2.0 and 1.0–0.3 kyr BP). Organic matter of soils of the Middle Holocene (9.0–4.0 kyr BP) and of the time interval of 13–14 kyr BP is enriched in ¹³C. Based on the identified dependence of δ¹³C in organic matter of modern soils in the region on the amount of precipitation, we have quantitatively reconstructed precipitation during the past growing seasons. The data obtained enable us to estimate the time intervals of 11.7–10.0 and 4.0–1.5 kyr BP as the most optimal for the formation of soils in Western Transbaikalia. An increase in temperatures and a decrease in atmospheric humidity in Transbaikalia and adjacent areas in the Middle Holocene exerted a negative impact on the pedogenesis intensity.