Test Stable Carbon Isotopic Composition of Soil Organic Matters as a Proxy Indicator of Past Precipitation: Study of the Sand Fields in Northern China

Abstract Understanding the stable carbon isotopic composition (δ 13 C) of surface soil organic matter under various climates is crucial for quantitative reconstruction of past climatic changes. Although the relationship between precipitation and plant δ 13 C is well understood at global and regional scale, studies relating δ 13 C of surface soil organic matter to precipitation in northern China remain controversial. In this study, 90 surface soil samples were collected from the desert/loess transition zone of Northern China, where vegetation is sensitive to climatic changes. The stable carbon isotopic composition of organic matter in these soil samples was analyzed in order to examine its palaeoclimatic implications. Our results show that the δ 13 C varied from −26.56 to −19.41‰ among the investigated sites, with an average of −23.54‰. There was a strong negative correlation between the δ 13 C of surface soils and the mean annual precipitation (MAP) ( R 2  = 0.52, p 13 C of C 3 plants was the main factor that determined the δ 13 C of soil organic matter. The C 4 /C 3 biomass ratio may also contribute to the δ 13 C changes, but this effect was relatively minor in our study area. Our findings suggest that a general transform function between the proxy index δ 13 C value and climates may not be applicable at one specific site, and that a comprehensive investigation is needed when reconstructing the past climate change using the δ 13 C of buried soils.