Stable isotopic composition of carbonate pedofeatures in soils along a transect in the southern part of European Russia

Stable isotopic analysis of carbonates is widely used for paleoreconstructions in various regions of the world. Only few and sparse information on stable isotopic composition of soil components are available for Russia. The aim of this research was to obtain for the first time systematic data on stable isotopic compositions of C and O in carbonate pedofeatures in modern soils of the European part of Russia. This territory is known as a classical example of natural bioclimatic zonation with an increasing of MAT from 4.5 to 9.4 °C and variation of MAP from 300 to ~ 600 mm. We also aimed to compare the isotopic values of hard carbonate nodules with soft carbonates. Key-sites were located in Lipetsk, Kursk, Voronezh, Rostov, Manych and Stavropol regions in Russia; Samara key-site was studied in Ukraine. O isotopic compositions of soil carbonates vary depending upon geographical position, carbonate morphologies and age. The overall range of isotopic compositions varies by approximately 5–7‰, from − 12.6 to − 5.2‰ for С and − 10.8 to − 5.6 for O. otopic compositions of C and O in pedogenic carbonates indicate that carbonates were formed under various environments. The general trend of C isotopic compositions correlates with MAP and MAT i.e. show the climatology gradient similar to latitudinal gradient described for other regions. The most complicated isotopic pictures were described in Voronezh, Kursk, Stavropol and Samara key-sites, which may be explained by the recent or past climatic changes, ground or perched water, or shallow paleosols containing old carbonates. Isotopic composition of soft carbonates is usually slightly different from those of hard nodules, which may reflect the different mechanism/rate of formation for nodules and soft masses, and reveal several generations of carbonates. Carbonates with younger and older radiocarbon age were identified. Meanwhile, the carbonates with older radiocarbon age generally have similar stable isotopic compositions as the carbonates with younger 14C-age. Three bioclimatic types of environment were identified according to the stable isotopic compositions of carbonates: wetter and warmer (MAT 5.4–9 °C, MAP 550–600 mm), wetter and cooler (MAT 5.2–5.4 °C, MAP ~ 600 mm), and drier and warmer (MAT 8.5–9.4 °C, MAP 300–500 mm). This information may be used for the future paleoreconstructions in paleosols of the central-southern parts of European Russia.