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[1] A detailed study of the climatic significance of d 18O in precipitation was completed on a 1500 km southwest-northeast transect of the Tibetan Plateau in central Asia. Precipitation samples were collected at four meteorological stations for up to 9 years. This study shows that the gradual impact of monsoon precipitation affects the spatial variation of d 18 O-T relationship along the transect. Strong monsoon activity in the southern Tibetan Plateau results in high precipitation rates and more depleted heavy isotopes. This depletion mechanism is described as a precipitation ''amount effect'' and results in a poor d18 O-T relationship at both seasonal and annual scales. In the middle of the Tibetan Plateau, the effects of the monsoon are diminished but continue to cause a reduced correlation of d 18 O and temperature at the annual scale. At the monthly scale, however, a significant d 18 O-T relationship does exist. To the north of the Tibetan Plateau beyond the extent of the effects of monsoon precipitation, d18 O in precipitation shows a strong temperature dependence. d18 O records from two shallow ice cores and historic air temperature data were compared to verify the modern d O in the ice core record in the monsoon regions of the southern Tibetan Plateau suggest past monsoon seasons were probably more expansive. It is still unclear, however, how changes in large-scale atmosphere circulation might influence summer monsoon precipitation on the Tibetan Plateau.

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