A test of stable carbon isotope record characteristics of phreatic and outcrop profiles

Current research on stable carbon isotopes in Chinese loess mostly focuses on the natural outcrops located on the sides of gullies formed by rainfall erosion on the Loess Plateau. In those environments, late processing may influence the carbon isotopic composition of loess-paleosol. This issue is not widely reported in the literature.A comparative analysis of carbon isotopes in phreatic and outcrop profiles was performed for two sites located on the Chinese Loess Plateau (CLP). The results for the Luochuan and Xifeng sites indicate that the distribution characteristics for carbon isotopes (δ13CTOC and δ13CTIC) of phreatic and outcrop profiles present a consistent trend of changes on the glacial–interglacial scales, respectively. High δ13CTOC values are found in paleosol (S0 and S1) and weak paleosol (L1SS1), and low values are found in the loess stage; however, the high δ13CTIC values are found in less pedogenically altered loess layers, and low δ13CTIC values are found in paleosol horizons. Therefore, late processing does not appear to influence the stable carbon isotope composition of the loess from natural outcrop profiles on glacial–interglacial scales for studied profiles. This finding indicates that the carbon isotope composition of easily excavated natural outcrop profiles can accurately record the characteristics of paleo-vegetation and paleo-climate on glacial–interglacial scales.