Relationships between δ18O in precipitation and air temperature and moisture origin on a south-north transect of the Tibetan Plateau

This project collected and analyzed precipitation samples along a south to north transect of the Tibetan Plateau, from Lhasa in the south, Nagqu and Tuotuohe in the middle, to Delingha in the north, from 2000 to 2003. Results show that overall the positive correlation between delta O-18 in precipitation and temperature gradually strengthens from south to north, with gradual weakening of monsoon activity. In particular, good linear relationships exist between Pb values of precipitation and air temperatures (T) at all the four stations from January to May over the years. In addition, our data show that when air temperature is low enough, the variations of delta O-18 values in precipitation over the whole Tibetan Plateau are controlled mainly by temperature effects. Our data also show that T-delta O-18 effects are of importance throughout the year along the transect, even in the south where the summer moisture mainly comes from monsoon activities. The stable oxygen isotope variations in precipitation along the transect, especially in the south, can reveal the long-term changes of delta O-18 records in the south Tibetan ice cores. In summer, however, the monsoon activities and the great difference between the condensation temperature and the ground temperature weaken the delta O-18-T correlation in precipitation in the south and middle part of Tibetan Plateau. The stable oxygen isotope variations in precipitation can reveal the short-term changes of delta O-18 records in the south Tibetan ice cores. Compared with the results from previous studies, the delta O-18-T correlations in precipitation in 2000-2003 on this transect are poorer than the ones reported from 1991-1999. This may result from higher average annual precipitation and the increasing trend of the monsoon activities in 2000-2003 compare to those in 1991-1999. (C) 2007 Elsevier B.V. All rights reserved.