CONCENTRATIONS OF STABLE ISOTOPES AND THEIR RESPONSES TO MOISTURE AND ENVIRONMENTAL CHANGES FOR PRECIPITATION EVENTS DURING THE SUMMER MONSOON PERIOD IN CHENGDU, SOUTHWEST CHINA

Samples of hydrogen and oxygen stable isotopes in precipitation were collected and analyzed during the summer monsoon in 2017 and 2018 in Chengdu. Specifically, δD and δ¹⁸O showed consistent temporal changes, and the depletion and enrichment of isotopes reflect the changes in monsoon intensity. Local meteoric waters lines (LMWLs) based on the precipitation events and monthly precipitation weighted average were obtained. The slope and intercept of the LMWLs in both years were slightly higher than those of the global meteoric water line (GMWL), although they were close to each other. The changes of d-excess and isotope composition reflect the seasonal changes in the moisture source. Precipitation with a low (high) d-excess value and a more (less) negative δ¹⁸O corresponds to moisture from ocean (inland) sources. The fluctuations in d-excess and δ¹⁸O reflect the alternation of different monsoons and the mixing of moisture from different sources. The source information indicated by d-excess and δ¹⁸O is in good agreement with the results of the air mass trajectory model. Significant negative correlations between δ¹⁸O and precipitation were observed during the summer monsoon period of the two years. The variations in δ¹⁸O–P regression equations are related to changes in the moisture source and transport path influenced by monsoon activities. No significant temperature effect was observed during the study period. Moreover, a negative correlation was shown between δ¹⁸O and temperature in 2018, which may be attributed to masking of the precipitation effect and the influence of complicated atmospheric circulation processes. The results of this study show that the isotopes in precipitation and in biological and geological proxies are closely related to moisture sources and climatic conditions and can be used as an effective tool to reflect monsoon activities and paleoclimate changes.

Keywords: stable isotopes; precipitation; subtropical monsoon climate; d-excess; moisture source; HYSPLIT model; paleoclimate