Contribution of inherent organic carbon to the bulk δ13C signal in loess deposits from the arid western Chinese Loess Plateau

The isotopic composition of total organic carbon (TOC) in loess deposits has been widely used to reconstruct palaeovegetation and palaeoclimate for terrestrial ecosystems. The possible significance of the distribution and contribution of organic carbon from dust source regions to loess TOC remains unclear, but may potentially affect interpretation of stable carbon isotope distributions in loess records with respect to local vegetation. Two loess profiles from arid areas in China with sparse vegetation coverage have been investigated. After removing the surface loess affected by recent farming, we detected a narrow range of carbon isotope (δ13C) values from −21.4‰ to −20‰ in the Lanzhou area and from −21.5‰ to −19.7‰ in the Xining area. The values are inconsistent with that of the established vegetation in these areas, where C3 plants are dominant. In contrast, the δ13C values of the loess TOC closely resemble those from dust sources. Together with data from loess TOC and magnetic susceptibility, we demonstrate that the isotopic composition of loess TOC in arid areas was largely controlled by the carbon isotope composition of the dust source, with only a minor contribution from local native vegetation. The results suggest that background carbon isotopic signals should be taken into account when interpreting carbon isotope compositions of loess deposits in arid areas.