Oxygen-isotope record of paleorainwater in authigenic carbonates of Chinese loess-paleosol sequences and its paleoclimatic significance

Abstract

Oxygen isotopic compositions of rhizoconcretions and land snail shells were measured to reconstruct the δ 18O profiles of paleorainwater ( δ 18O p) for well-dated loess-paleosols in Luochuan, China. To assess the paleoclimatic significance of δ 18O p, factors that control the spatial and temporal δ 18O variations of rainwater in East Asian monsoon regions were investigated. Modern records indicate that the spatial δ 18O variations of modern rainwater ( δ 18O m) are closely related to near surface temperature ( T) and the amount of precipitation ( P). In order to separate the effects of T and P on the δ 18O m, a linear relationship between δ 18O m, T and the natural logarithm of P is established by multiple regressing analyses: δ 18 O m = 1.070 + 0.326 × T − 2.041 × ln ⁡ P The δ 18O of paleorainwater over the past 130 Ka in Luochuan area is calculated by the modern-spatial δ 18O– T– P relationship using estimated T and P from other paleoclimate records. The calculated δ 18O match well to those reconstructed from the authigenic carbonates, which implies that the spatial and temporal δ 18O variations of rainwater in East Asian monsoon regions have similar δ 18O– T– P relationships and the authigenic carbonates in Chinese loess-paleosol sequences can serve as valid records of δ 18O p. As an application of the δ 18O– T– P relationship, P variation in the past 130 ka in Luochuan was evaluated. The reconstructed P is in good agreement with other studies using different approaches. Our results suggest higher precipitation in Marine Isotope Stages 1, 3 and 5, reflecting intense summer monsoon influences during these periods of time.