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Stable hydrogen and oxygen isotopes are widely used as tracers in studying hydrologic processes. Surface water is an important component of the water cycle, and it is an effective vehicle for analyzing regional moisture sources and modern hydrologic processes. We collected surface water samples from August 2018 to August 2023 on the northern slope of the Kunlun Mountains during the Third Xinjiang Scientific Expedition and measured the stable hydrogen and oxygen isotope values. Additionally, we compiled the previous surface water isotope data in the region. We analyzed the spatial distribution characteristics of the stable hydrogen and oxygen isotopes of surface water on the northern slope of the Kunlun Mountains. The results showed that: (1) The surface water isotope values on the northern slope of the Kunlun Mountains showed spatial variations characterized by low values in the west and high values in the east. The local surface water line is δ² H=5.98xδ18 O-6.86 (R²=0.65, n=141). (2) A comparison of the stable isotope values of surface water and precipitation on the northern slope of the Kunlun Mountains reveals that the regional surface water isotope value averages are generally lower than the weighted precipitation isotope values. (3) The spatial distribution of surface water isotopes on the northern slope of the Kunlun Mountains is influenced by the interplay of two key factors: the water vapor advection by westerly winds and the local recycled moisture; additionally, evaporation also changed the regional surface water isotope values. [ABSTRACT FROM AUTHOR]

The spatial patterns of stable hydrogen and oxygen isotopes in precipitation (precipitation isoscapes) provide a geographic perspective to understand the atmospheric processes in modern environment and paleoclimate records. Here we compiled stable isotope data in modern precipitation at 223 sites across China and 48 in surrounding countries, and used regionalized fuzzy clustering to create monthly precipitation isoscapes for China (C-Isoscape). Based on regressions using spatial and climatic parameters for 12 months, the best-fitting equations were chosen for four climate clusters, and then the four layers were weighted using fuzzy membership. The moisture transportation path, controlled by the westerlies and the monsoon, results in different spatial and seasonal diversity of precipitation isotopes. Based on C-Isoscape, we determined a nationwide meteoric water line as δ2H = 7.4δ18O + 5.5 using least squares regression or δ2H = 8.0δ18O + 10.2 using precipitation weighted reduced major axis regression. Compared with previous global products, the C-Isoscape usually shows precipitation more enriched in 18O and 2H in summer and more depleted in winter for northwest China, while the C-Isoscape values are more enriched in heavy isotopes in most months for southwest China. The new monthly precipitation isoscapes provide an accurate and high-resolution mapping for Chinese precipitation isotopes, allowing for future intra-annual atmospheric process diagnostics using stable hydrogen and oxygen isotope in precipitation in the region. [ABSTRACT FROM AUTHOR]

Stable oxygen isotopes in precipitation contain meaningful environmental information on a synoptic scale and can be applied to diagnose hydrometeorological processes. A series of rainstorms occurred at the southern Tianshan Mountains during the period from May to June 2013, and the event-based precipitation was sampled along the mountain range from west to east. Based on δ18O values in precipitation samples as well as the corresponding meteorological parameters, the moisture transport paths during the sampling period were identified. In late-May (stage 1), isotopes in precipitation collected generally showed a depleting trend. In mid-June (stage 2), there was no coherent trend of isotopes in precipitation for these stations, and only isotope values in Aksu showed a continually depleting trend. Checking other meteorological proxies during the sampling period, the event-based precipitation isotopes sensitively reflected the moisture process. In central Asia, both the westerly and monsoon moisture can be delivered to cause extreme precipitation events, and the isotopic information provides an alternative tool to investigate the atmospheric processes. [ABSTRACT FROM AUTHOR]

The local meteoric water line (LMWL) reflects the relationship between stable oxygen and hydrogen isotopes in precipitation, and is usually calculated using an ordinary least squares regression (OLSR). When event-based data are used to calculate a LMWL, the differences in precipitation amount of samples are not considered using OLSR, which in turn may influence the representativeness of the LMWL for local hydrology. Small rain events occur widely in arid Central Asia (annual mean precipitation <150 mm), and where smaller precipitation has lower deuterium excess, this results in LMWLs with slopes and intercepts lower than the global average. Based on an observation network of isotopes in precipitation across the Tianshan Mountains in arid Central Asia, LMWLs for 23 stations are calculated from event-based data from 2012 to 2013 ( n  = 978), using ordinary least squares, reduced major axis and major axis regressions and their precipitation-weighted counterparts. For the northern slope and mountainous areas, the LMWL slope and intercept are close to the Global Meteoric Water Line (GMWL), but the slope and intercept are lower for the southern slope indicating the greater dominance of sub-cloud evaporation. The effect of moisture recycling in the irrigated areas on the northern slope also can be seen where the LMWL slopes are >8. Using a precipitation weighted regression method with event-based data (especially precipitation-weighted reduced major axis regression, PWRMA) is generally consistent with the OLSR regression using monthly data. However, event-based datasets provide a wider range of values to better constrain the regression than can be achieved using monthly data over a short period, providing a sounder basis for determining LMWLs for relatively short-term sampling campaigns in an arid setting. The use of the PWRMA regression is preferred for determining the LMWL for the Tianshan Mountains, and results in a regional meteoric water line of δ D = 7.9 δ 18 O + 10.16. [ABSTRACT FROM AUTHOR]

Stable hydrogen and oxygen isotopes in precipitation are very sensitive to environmental changes, and can record evolution of water cycle. The Lanzhou city in northwestern China is jointly influenced by the monsoon and westerlies, which is considered as a vital platform to investigate the moisture regime for this region. Since 2011, an observation network of stable isotopes in precipitation was established across the city, and four stations were included in the network. In 2013, six more sampling stations were added, and the enhanced network might provide more meaningful information on spatial incoherence and synoptic process. This study focused on the variations of stable isotopes ( δ 18 O and δ D) in precipitation and the environmental controls based on the 1432 samples in this enhanced network from April 2011 to October 2014. The results showed that the precipitation isotopes had great spatial diversity, and the neighboring stations may present large difference in δ D and δ 18 O. Based on the observation at ten sampling sites, an isoscape in precipitation was calculated, and the method is useful to produce isoscape for small domains. The temperature effect and amount effect was reconsidered based on the dataset. Taking meteorological parameters (temperature, precipitation amount, relative humidity, water vapor pressure and dew point temperature) as variables in a multi-linear regression, the result of coefficients for these meteorological parameters were calculated. Some cases were also involved in this study, and the isotopic characteristics during one event or continuous days were used to understand the environmental controls on precipitation isotopes. [ABSTRACT FROM AUTHOR]

According to the simulations of isotope-equipped general circulation models (GCMs) compiled by the Stable Water Isotope Intercomparison Group Phase2 (SWING2), the interannual variability and trend of precipitation isotopic composition in China during 1979–2007 are studied. Six simulations of isotope-enabled GCMs are involved, and monthly series of stable oxygen isotopes in precipitation for each grid are applied to calculate the linear trends from 1979 to 2007. Most isotope-equipped GCM simulations show an increasing trend in δ 18 O, while the GISS-E (NCEP) result shows a decreasing trend. In most areas of north China and northwest China, the GCM-simulations positively correlate with surface temperature. The correlation coefficients between oxygen isotope composition and surface air temperature generally increase from coast to inland. The correlation between observed and simulated δ 18 O in precipitation of northwest China simulated by LMDZ (free) is best ( r = 0.73) among different subregions and isotope-equipped GCMs. The comparison of GCMs simulations and BW model all show the low value region of δ 18 O is in the Tibetan Plateau and the high value in south China. China's meteoric water line simulated using isotope-enabled GCMs (slopes range from 7.63 to 8.26, and intercepts range from 9.25 to 11.92) is similar to the global meteoric water line, and all the correlation coefficients are statistically significant at the 0.01 level. [ABSTRACT FROM AUTHOR]

Reports on a 50-m firn core drilled in Princess Elizabeth Land, Antarctica, during the 1996/1997 Chinese First Antarctic Inland Expedition, which was measured for δ18O and major ions. Indication the firn core was dated with errors within ±3 years because of seasonal variations in major ions; Idea that the study of temperature change over the past 150 years was based on the oxygen isotope in the upper 32.93 m of the firn core; Finding that the temperature decreased by nearly 2°C in the past 150 years; Suggestion the Southern Hemispheric warming, atmospheric circulation, Antarctic Circumpolar Wave (ACW), and the special terrain, including large drainage basins, on the coastal regions were factors in the temperature decline.

Deuterium excess and stable oxygen isotopes in precipitation have been widely applied to trace the source of water vapor. In this study, hydrogen and oxygen isotope analyses of samples were collected on seven sampling stations in Dingxi area from April 2019 to April 2020. The seasonal variation of hydrogen and oxygen stable isotopes as well as the d-excess indicate that the source of water vapor in Dingxi area is mostly from a single source. However, there are different sources of water vapor in the summer. Meanwhile, water vapor sources were analyzed using the Lagrange algorithm, indicating two different principal water vapor sources for precipitation in the area: some locally recycled water vapor in summer and autumn, and most water vapor from the westerly belt. Further studies using the PSCF and CWT analysis methods show that the locally recycled water vapor contributes more to its precipitation in the northwest of Dingxi area. [ABSTRACT FROM AUTHOR]

The proportional contribution of recycled moisture to local precipitation is a geographically dependent parameter that cannot be ignored in water budgets. Stable hydrogen and oxygen isotopes are sensitive to environmental changes and can be applied to investigate the modern water cycle. In this study, a three-component mixing model is used to calculate the contribution of different water vapors (advection, evaporation and transpiration) to summer precipitation in Lanzhou city, Northwest China. The results show that for all sampling sites in Lanzhou, the contribution of advection vapor to precipitation is the largest, followed by the plant transpiration vapor, and the contribution of surface evaporation water vapor is usually the least, with the average values of 87.96%, 9.1% and 2.9%, respectively. The spatial differences of plant transpiration vapor are generally larger than those of advection vapor and surface evaporation vapor, and the high values appear in Yongdeng, Daheng and Gaolan. [ABSTRACT FROM AUTHOR]

The deuterium excess in precipitation is an effective indicator to assess the existence of sub-cloud evaporation of raindrops. Based on the synchronous measurements of stable isotopes of hydrogen and oxygen (δ2H and δ18O) in precipitation for several sites in Lanzhou, western China, spanning for approximately four years, the variations of deuterium excess between the ground and the cloud base are evaluated by using a one-box Stewart model. The deuterium excess difference below the cloud base during summer (−17.82‰ in Anning, −11.76‰ in Yuzhong, −21.18‰ in Gaolan and −12.41‰ in Yongdeng) is greater than that in other seasons, and difference in winter is weak due to the low temperature. The variations of deuterium excess in precipitation due to below-cloud evaporation are examined for each sampling site and year. The results are useful to understand the modification of raindrop isotope composition below the cloud base at a city scale, and the quantitative methods provide a case study for a semi-arid region at the monsoon margin. [ABSTRACT FROM AUTHOR]

The spatial distribution of stable water isotopes (also known as an isoscape) in precipitation has drawn increasing attention during the recent years. In this study, based on the observations at 32 stations, we assessed two widely applied global isoscape products (Regionalized Cluster-based Water Isotope Prediction (RCWIP) and Online Isotopes in Precipitation Calculator (OIPC)) at the Qinghai-Tibet Plateau (QTP) and then established an improved isoscape of oxygen isotopes in precipitation on a monthly basis using a regionalized fuzzy cluster method. Two fuzzy clusters can be determined, which is consistent using three meteorological data. The monthly isoscapes show the seasonal movement of high and low isotopic value regions across the QTP and reveal the influences of monsoon and westerly moisture. According to the cross validation, the δ18O in precipitation in the new monthly isoscapes for the QTP we propose performs better compared to the existing global products. To create a regional isoscape in many other regions, the regionalized fuzzy cluster method can be considered especially for regions with complex controlling regimes of precipitation isotopes. [ABSTRACT FROM AUTHOR]

The deuterium excess (d) in precipitation, determined by the stable hydrogen and oxygen isotopes (δ2H and δ18O), is a widely applied parameter in tracing the water vapor source. Based on the multiple-year observations of stable water isotopes in precipitation at four stations in the Lanzhou city, Northwest China, we analyzed the variations in deuterium excess in precipitation at the Asian monsoon margin region. The mean value of deuterium excess at the study region is 11.0‰ in the dry season and 8.0‰ in the wet season. The d value in precipitation negatively correlates with air temperature and vapor pressure. The low d value during the wet season reflects the monsoon moisture transported from long distances. During the dry season, the continental air masses correspond to the higher d value in precipitation. The moisture regimes based on reanalysis data are generally consistent with the findings using a stable isotopic approach, and the monsoon moisture is highlighted in summer precipitation at these monsoon margin sites. [ABSTRACT FROM AUTHOR]

Water is a key and limiting factor for ecosystem processes (carbon dioxide fixation, vegetation growth, respiration, etc.) and functions (NPP, Net Primary Productivity) in arid and semi-arid areas. As the main regulator, knowledge of plant water use patterns is essential in understanding the SPAC (Soil-Plant-Atmosphere-Continuum) cycle. The tree-planting project in the southern and northern mountains of Lanzhou city aims to improve the ecological environment and promote urban construction. In this study, we analyzed the water use strategies of the dominant plants C. korshinskii and R. soongorica in natural shrubs of southern and northern mountains of Lanzhou city using oxygen stable isotope techniques. The result showed that the flexible water uptake pattern of C. korshinskii and its faster response to precipitation pulse, compared with R. soongorica, might help it to make full use of water and nutrients and adapt to the dry environment. However, R. soongorica progressively switched to suck up deeper soil water and increased the water use proportion from 0.5% to 84.4% as the seasons changed, indicating a greater degree of ecological plasticity. The flexible water use strategies of C. korshinskii and R. soongorica in the same habitat reduced competition for water and nutrients and enhanced adaptability to arid environments. The work presented here provides insights into vegetation restoration and ecological management for the southern and northern mountains of Lanzhou city. [ABSTRACT FROM AUTHOR]

The origin of bottled water can be identified via its stable isotope signature because of the spatial variation of the stable isotope composition of natural waters. In this paper, the spatial pattern of δ2H and δ18O values were analyzed for a total of 242 bottled water samples produced at 137 sites across China that were randomly purchased during 2014–2015. The isotopic ratios of bottled water vary between −166‰ and −19‰ for δ2H, and between −21.6‰ and −2.1‰ for δ18O. Based on multiple regression analyses using meteorological and geographical parameters, an isoscape of Chinese bottled water was created. The results showed that altitude among spatial parameters and precipitation amount and air temperature among meteorological parameters were major natural factors determining the isotopic variation of bottled water. Our findings indicate the potential and the significance of the use of stable isotopes for the source identification of bottled water. An analysis of different origin types (spring, glacier and unmarked) and several different brands of bottled water in the same location reflected different production processes and source signatures. [ABSTRACT FROM AUTHOR]

• Precipitation isotope characteristics of a leeward oasis in central Asia were identified. • Moisture recycling ratio ranged between 17.0% and 63.9% in the central Asian oasis. • Bayesian isotopic mixing model is promising in quantifying moisture recycling. Locally recycled moisture from transpiration and surface evaporation is of great importance in the terrestrial hydrological cycle, especially in the widely distributed oases across arid central Asia. Quantitative assessment of the proportional contribution of recycled moisture to local precipitation, i.e., the recycling ratio, is useful to understand the land-air interaction as well as the anthropogenic impact on the regional water cycle. Here we analyzed the stable hydrogen and oxygen isotopes in precipitation samples collected at six stations across the Kaxgar-Yarkant Oasis in the western Tarim Basin of central Asia from April 2018 to June 2020. Using this data, the moisture recycling ratio in this typical oasis was assessed using a Bayesian three-component isotopic mixing model. For the plain stations, the annual weighted mean δ 18O value in precipitation ranged from −5.94 ‰ to −1.46 ‰, and the mountain station has a lower annual mean precipitation isotopic ratio. The average recycling ratio during the summer months ranged between 17.0 % and 63.9 % for each sampling station in the Kaxgar-Yarkant Oasis, and the proportional contribution from transpiration ranged from 15.1 % to 61.3 %. The contribution of plant transpiration to local precipitation is much larger than that of surface evaporation. The recycled portion in total precipitation amount may increase the local precipitation under an oasis expansion background but is insufficient to change the arid background. In addition, the Bayesian isotopic mixing model is promising to determine the recycling ratio in an arid setting, and provides more spatial details than the climate reanalysis-based calculation. [ABSTRACT FROM AUTHOR]

In arid northwest China where the precipitation intensity is relatively low, the stable hydrogen and oxygen isotopes (δ 2H and δ 18O) in precipitation are usually impacted by the sub-cloud evaporation. To understand the sub-cloud evaporation effect under an arid climate, we used the hourly meteorological data at 14 stations in the Kaxgar-Yarkant River Oasis, a rainshadow oasis of northwest China, and estimated the monthly and hourly isotopic change in falling drops from the cloud base to the ground. The results showed that the hourly meteorological observations are an effective way to assess the spatiotemporal pattern of sub-cloud evaporation effect. Across the 14 stations, the annual mean changes in deuterium excess below cloud base ranged from −19.1‰ to −6.8‰. The impacts of sub-cloud evaporation during spring and autumn are larger than those during winter and weaker than those during summer. The exponential regression (R 2 = 0.96), instead of linear regression (R 2 = 0.85), is better at describing the relationship between the raindrop remaining fraction and the isotopic changes from the cloud base to the ground. The sensitivity analysis of isotopic changes to different relative humidity scenarios shows that the drying scenario may lead to slightly larger sensitivity than the wetting scenario. The impact of sub-cloud evaporation on stable isotope compositions in precipitation may be underestimated when low precipitation events (especially less than 1 mm/h) are not sampled. • Hourly meteorological records are effective to assess sub-cloud evaporation effect on precipitation isotopes. • Arid mountains show a strong sub-cloud evaporation effect like nearby low-lying plains. • The impact of sub-cloud evaporation may be underestimated when low precipitation events are not sampled. [ABSTRACT FROM AUTHOR]

The oxygen isotope compositions in atmospheric water including water vapor and precipitation have been widely used to trace moisture sources and to reconstruct past climates. However, the environmental controls of stable isotopes in atmospheric water depend on the time scales. Because of limited observations in arid Central Asia, factors controlling interannual variations in atmospheric water isotopes are still not clear. Using an isotope-enabled general climate model, we do not find at the annual scale the significant relationship between temperature and δ 18O values during 1979–2020 that is usually observed at the monthly scale. Under a warming background, there is no significant enriching trend in water isotopes. We found a strong positive correlation between westerly (and southerly) water vapor flux and δ 18O values on an interannual scale for the area between 35°N–50°N and 50°E–80°E in the upstream direction. High and low δ 18O years are characterized by different atmospheric circulations of mid-latitude Westerlies, and do not always correspond to the warm and cold years respectively. When the prevailing Westerlies are enhanced, the Westerlies circulation may carry more water vapor from the lower latitudes, leading to higher δ 18O values in Central Asia. The changes in Westerlies circulation are supported by the clustered backward trajectories during enriched and depleted years. The limited precipitation isotope observations also show similar findings as the simulations on an interannual scale. The interannual variations of stable isotopes in atmospheric water in arid Central Asia reflect the changes in the mid-latitude Westerlies circulation. This should be taken into account when interpreting oxygen isotope proxies of paleoclimate records. • Temperature effect of water isotopes exists on a seasonal scale, but is weakened on an annual scale in Central Asia. • On an annual scale, there are positive correlations between westerly (and southerly) water vapor flux and isotope value. • The critical area controlling interannual variability of water isotopes in the Tianshan Mountains is identified. [ABSTRACT FROM AUTHOR]