Hydrogen isotope ratios of leaf wax n-alkanes in loess and floodplain deposits in northern China since the Last Glacial Maximum and their paleoclimatic significance

The hydrogen isotopic composition of leaf-wax n-alkanes (δDn-alkane) is increasingly used as a proxy for estimating δD of past precipitation (δDp). However, aridity can also affect sedimentary δDn-alkane, complicating the interpretation of paleo-δDn-alkane records. In order to evaluate the effects of the complex interactions and balance between precipitation hydrogen isotope composition and aridity on sedimentary δDn-alkane records, we present two δDn-alkane records from the North China Plain and the western Chinese Loess Plateau across a steep east-west climatic gradient in the East Asian Summer Monsoon area since the Last Glacial Maximum. The estimated δDp changes, based on a present-day relationship between δDp and rainfall amounts, can explain much of the δDn-alkane variations in the North China Plain, but do not explain the large variations of δDn-alkane in the western Chinese Loess Plateau. Comparison of δDn-alkane records with observed δDn-alkane values in modern plants and published pollen data indicates that changes in vegetation play a minor role in the variations of δDn-alkane. Instead, δDn-alkane values are coincident with aridity both temporally and spatially, i.e. the higher δDn-alkane values the drier climate and vice versa. Aridity effects are more evident in the western Chinese Loess Plateau than in the North China Plain. Therefore, on glacial-interglacial scale, sedimentary δDn-alkane records from the North China Plain mostly reflect changes in δDp values, whereas those from the western Chinese Loess Plateau largely reflect the effects of aridity, mainly due to a greater evapotranspirational deuterium-enrichment caused by a drier climate in the western Chinese Loess Plateau than in the North China Plain. Further calibrations from modern sediments are required to better define the quantitative relationship between the δDn-alkane and climate in northern China.