Variation characteristics and controlling factors of precipitation δ18O in Kuoqionggangri Glacier region,source of the Lhasa River
In the water cycle,water bodies show different characteristics of stable hydrogen and oxygen isotopes(δ18O and δ2H)in different processes of evaporation,transport,convection,and condensation due to the influ-ences of isotope fractionation.Therefore,δ18O and δ2H is widely used in the study of paleoclimate and modern hydrological processes.Previous studies mainly focused on the variations of precipitation stable isotopes in the low-altitude regions in the Lhasa River basin,a critical area for the studies of the progressing and evolution of monsoon and westerly wind systems.In contrast,studies on δ18O and δ2H data obtained from the alpine regions are largely lacking.In this study,we analyzed 347 event scale precipitation samples collected at three sampling sites in the Kuoqionggangri Glacier region from July 2020 to July 2023.The spatial and temporal variations of precipitation δ18O,the local meteoric water lines,the relationship between precipitation δ18O and meteorological factors,and the relationship between precipitation δ18O and convective activity are investigated to understand the influences of the Indian monsoon and westerly wind on the precipitation δ18O and 82H in the Kuoqionggangri Gla-cier region at the source of the Lhasa River of the southern Qinghai-Xizang Plateau.Besides,the backward tra-jectory of water vapor was further demonstrated through correlation analysis and cluster analysis,so as to reveal sources of water vapor.The results showed that there was little difference in temperature,relative humidity,and precipitation among the three fixed points located in different altitudes in this study area from July 2020 to July 2023(the glacier terminus(5 544.5 m a.s.1.),the basin source(5 374.0 m a.s.1.)and the basin export(4 941.3 m a.s.1.)).In addition,the precipitation δ18O and local meteoric water lines were similar among these three sampling sites from July 2020 to August 2020.This suggested that the climate conditions remained relative-ly identical within the Kuoqionggangri glacier region.According to the above results,we put emphasis on data of the precipitation δ18O collected at the basin export from July 2020 to July 2023.The results revealed a two-stage pattern of changes in daily precipitation δ18O:a higher value before mid-June followed by a lower value.The monthly precipitation δ18O shows the highest value in June and the lowest value in September.The slope and intercept of the local meteoric water line during the monsoon period(8.12,11.78)were obviously smaller than those during the non-monsoon period(8.79,23.18),indicating that the water vapor source of the precipitation during the monsoon period possessed a higher relative humidity compared with that during the non-monsoon peri-od.The slope and intercept of the local meteoric water line around the year(8.27,15.10)were more similar to those in the monsoon period.This phenomenon might be due to the large contribution of precipitation in the mon-soon period around the year in this region.Monthly precipitation δ18O exhibited a significant dependence on tem-perature in the monsoon period.Specifically,the monthly precipitation δ18O and temperature are positively corre-lated.Daily precipitation δ18O were significantly dependent on precipitation amount around the year.Specifical-ly,the daily precipitation δ18O and precipitation amount are negatively correlated.The convection activity taking place 1～6 days before the precipitation event would deplete the precipitation δ18O.This influence on the precipita-tion δ18O was mainly concentrated in the monsoon period.Results of the backward trajectory tracking analysis in-dicated that water vapor transported by the Indian monsoon contributed the most to the precipitation of the region throughout the year,which depleted the precipitation δ18O.This study preliminarily reveals the spatial and temporal variations of precipitation δ18O and its main influencing factors in the alpine mountains of the southern Qinghai-Xizang Plateau.Results of the current work can provide basic data for the study of water cycle in the alpine regions.
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