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

摘要

Oxygen isotopic compositions of rhizoeoncretions and land snail shells were measured to reconstruct the delta O-18 profiles of paleorainwater (delta O-18(p)) for well-dated loess-paleosols in Luochuan, China. To assess the paleoclimatic significance of 6180, factors that control the spatial and temporal 6180 variations of rainwater in East Asian monsoon regions were investigated. Modem records indicate that the spatial delta O-18 variations of modem rainwater (delta O-18(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 delta O-18(m), a linear relationship between delta O-18(m), T and the natural logarithm of P is established by multiple regressing analyses: delta O-18(m) = 1.070 + 0.326 x T-2.041 x InP The 6180 of palcorainwater over the past 130 Ka in Luochuan area is calculated by the modem-spatial delta O-18-T-P relationship using estimated T and P from other paleoclimate records. The calculated delta O-18 match well to those reconstructed from the authigenic carbonates, which implies that the spatial and temporal delta O-18 variations of rainwater in East Asian monsoon regions have similar delta O-18-T-P relationships and the authigenic carbonates in Chinese loess-paleosol sequences can serve as valid records of delta O-18(p), As an application of the delta O-18-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. (c) 2006 Elsevier B.V. All rights reserved.