δ18O values of tree rings as a proxy of monsoon precipitation in and Northwest China

It is important to understand the history and dynamics of East Asian Monsoon system, which is the key control of environmental conditions in China. This work investigates the relationship between precipitation amount and oxygen isotopic compositions recorded in tree-ring cellulose as a potential tool for reconstruction of summer monsoon strength in and Northwest China. We found a significant positive correlation between the total annual precipitation and the delta(18)O value of tree rings. This correlation results from the fact that summer monsoon precipitation in the study area is relatively more enriched in O-18 than winter precipitation and the total amount of annual precipitation predominantly varies with the amount of summer precipitation brought by summer monsoons. The amount effect, the negative relationship between the precipitation amount and the precipitation delta(18)O, is often used to explain the seasonal isotopic distribution in meteoric water of China. This study presents a case where the delta(18)O value of tree rings and precipitation is positive associated. We point out that the amount effect, which was originally used for tropical convective storms, should not be simplistically considered as a mechanism for determining isotopic variations in China, particularly at high latitude (>30degreesN) and/or inland locations. (C) 2004 Elsevier B.V. All rights reserved.