Ice cores retrieved from the Third Pole provide invaluable information about past and present environmental changes. Here we present, for the first time, a continuous tritium and plutonium isotope profile of the Puruogangri ice field, Tibetan Plateau, China, for the last 70 years. The age-depth profile has been composed by different time anchors such as the onset of thermonuclear weapon tests, the so-called bomb peak of tritium, the Chernobyl event, and the time of ice coring. The accumulation rate of ice calculated from the age-depth relation shows a decrease after 1963. It was 57, 15, and 22 cm/year in the periods of 1954-1963, 1963-1986, and 1986-2023, respectively. The concentrations of plutonium isotopes (239Pu: up to 2.7 fg/g) are slightly lower than those of the Belukha ice core, Siberian Altai, Russia, and almost the same as the Miaoergou glacier, eastern Tien Shan, China. Contrary to this latter ice core profile, the Puruogangri plutonium profile reflects that the Chinese weapon test started in 1966. This is confirmed by the tritium time series as well. 240Pu/239Pu atomic ratios vary between 0.14 and 0.23, with an average of 0.177 +/- 0.024. The overall obtained local fallout of 239Pu and 240Pu is 13.2 and 9.0 Bq/m2 (4.0 and 1.1 ng/m2), respectively.

Although Yunnan, located in southwestern China, is recognized as a transitional zone between the Indian Summer Monsoon and the East Asian Monsoon, the extent to which distinct moisture sources and associated transport pathways influence precipitation isotopic variability in this region remains poorly quantified. Here, we analyzed a four-and-a-half-year precipitation isotope dataset from Kunming and differentiated between precipitation sourced from the Bay of Bengal (BoB) and the South China Sea (SCS). We observe a strong seasonal delta O-18 contrast of 7.4 parts per thousand in BoB-sourced precipitation, which accounts for similar to 61% of the moisture supply for Kunming precipitation. In contrast, SCS-sourced precipitation exhibits a weak seasonality of only 1.8 parts per thousand in delta O-18. Our analysis indicates that seasonal changes of evaporative conditions in BoB source and upstream meteorology along its transport path produce this pattern, while relatively stable SCS source and transport conditions result in minimal seasonal variability. Simulation results demonstrate that SCS-sourced delta O-18 largely follows Rayleigh distillation, whereas BoB-sourced delta O-18 deviates from this simple model, indicating the influence of additional processes. We further find that the tropospheric temperature gradient is a key thermodynamic driver of precipitation delta O-18, showing a persistent negative correlation across seasons and moisture sources. In addition, precipitation d-excess responds differently to the two moisture sources. D-excess in BoB-sourced precipitation partially reflects source-region and transport-path conditions, while SCS-sourced precipitation shows no such consistent relationships. Overall, this work quantifies the distinct isotopic fingerprints of these two major moisture sources to southwestern China, providing an advance for modeling regional water cycles and interpreting isotopic paleoclimate archives.

Lakes on the Yunnan Plateau, southwest China, have experienced rapid water quality deterioration during the past few decades. Investigating lake hydrological regimes holds great significance for protecting water resources and mitigating eutrophication. However, a comprehensive assessment of lake water balance on a regional scale is still lacking. Here we conducted water isotope surveys on the nine largest representative lake basins of the plateau and assessed lake water balance using an isotope mass balance (IMB) model. To ensure accurate application of the IMB model, we employed a Bayesian approach to infer the isotopic composition of lake inflow (delta I) and developed an improved method to constrain isotopic composition of atmospheric vapor (delta A), a critical yet rarely measured parameter in the model. Results demonstrate that lake water exhibits substantial evaporative enrichment relative to lake inflow, with mean delta 18O enrichments ranging from 6.6 %o at Dianchi to 10.7 %o at Chenghai. The 2022 annual evaporation-to-inflow (E/I) ratios for individual lakes, in ascending order, are: Erhai (0.36 f 0.05), Dianchi (0.38 f 0.08), Qilu (0.42 f 0.11), Xingyun (0.50 f 0.11), Yilong (0.50 f 0.16), Yangzong (0.54 f 0.10), Fuxian (0.60 f 0.09), Lugu (0.70 f 0.16), and Chenghai (1.01 f 0.23), with an average ratio of 0.56. E/I variations reveal a significant spatial diversity of water balance patterns among these lakes. Most of the lakes are restricted drainage systems characterized by either long water residence times or high relative evaporation rates, where evaporation losses dominate the water balance. Isotope enrichments in deep lakes relative to the 1990s attest to water balance dynamics, and tracking these dynamics remains essential as our lake water balance categorization only captures a spatial snapshot.

Oxygen isotope records from various East Asian geological archives are vital tools for reconstructing past monsoon variations, yet their climatic interpretations remain the subject of considerable debate. While seasonality is inherently linked to monsoon patterns, a comprehensive understanding of precipitation S18O (S18Op) seasonality across East Asia and its connection to monsoon activities has remained elusive. We present an integrative analysis combining observation-based monthly S18Op maps, isotope-enabled model simulations, and multi-year daily observations. Our results reveal three distinct modes of S18Op seasonality across East Asia, closely linked to the seasonal march and retreat of the monsoon. Specifically, the western Pacific subtropical high (WPSH) serves as a primary source of isotopically enriched vapor due to suppressed convection in this highpressure system. In conjunction with the northward progression of WPSH from spring to summer, the S18Op peak first appears in southern East Asia and subsequently shifts toward northern regions. In contrast, the southward retreat of WPSH in late summer and autumn leads to a secondary S18Op peak. The low S18Op values observed between these peaks reflect the progression of monsoon convection. These findings demonstrate that S18Op faithfully captures the seasonal dynamics of the East Asian Monsoon, offering a pathway to resolve ongoing debates regarding the interpretation of speleothem S18O records. Furthermore, these insights highlight the potential of utilizing spatially distributed paleo S18Op records to uncover the timing and structure of past East Asian Monsoon variability.

It remains uncertain whether precipitation oxygen isotopes (δ18O) reliably capture East Asian Meiyu monsoon variability. Analyzing daily δ18O across the Yangtze-Huai River Basin from 28-34°N, we reveal a distinct spatial dichotomy. In the middle and northern Meiyu regions, δ18O robustly tracks Meiyu precipitation. Conversely, the southern Meiyu margin is decoupled from Meiyu variability, primarily reflecting upstream convection processes further south. We identify the western Pacific subtropical high (WPSH) as the central driver, creating a dynamic dipole: its northwestward extension enhances moisture transport and deep convection along its northwestern flank (driving isotopic depletion in the northern Meiyu region), while imposing subsidence and convective inhibition under its body (suppressing isotopic depletion in the southern Meiyu region). Importantly, these mechanisms persist on interannual timescales. Consequently, while northern δ18O records effectively capture Meiyu variability, southern records reflect distinct vertical constraints, necessitating spatially differentiated paleoclimate interpretations.

To investigate the spatial and temporal modes in European winter precipitation isotopes and their climatic controls, we performed an empirical orthogonal function (EOF) analysis on the Piso.AI dataset, a recently released machine-learning-based monthly gridded precipitation isoscape across Europe. The first two EOF modes, EOF1 and EOF2, explain 56.83 % and 12.94 % of the total variance, respectively. EOF1 shows spatially uniform changes in delta D, influenced by regional variations in temperature and water vapor transport. EOF2 reveals a dipole delta D pattern between northern and southern Europe, reflecting regional differences in climate and moisture sources. These spatial-temporal patterns are corroborated by results from delta 18O and isotope-enabled model simulations, enhancing the robustness of our findings. The Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) significantly impact the first delta D mode through their modulation of European temperatures and the strength of water vapor transport from lower latitudes, with a strong correlation of 0.86 for AO. The second mode captures unique climate variability independent of NAO and AO. These findings enhance understanding of atmospheric circulation and water vapor transport processes that control isotope changes across Europe. Furthermore, they offer insights into paleoclimate reconstruction, highlighting the potential for using spatially distributed isotopic records to reconstruct past AO activities. Additionally, they suggest the possibility of developing new climate reconstructions by leveraging the differences in isotopic signatures between northern and southern Europe.

Due to the impact of various climate systems, including the Asian Summer Monsoon (ASM) and westerlies, it is challenging to identify specific climate variables from the ice core delta 18O records of the Tibetan Plateau (TP). Here, we disentangle the major climate modes by applying the singular spectrum analysis method to a delta 18O time series in a shallow ice core retrieved from central TP. This method allows us to identify three major climate modes: the trend component, the El Ni & ntilde;o Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). The trend component mainly reflects warming in the middle and upper troposphere over the south of the TP rather than the low land surface temperature changes. Furthermore, we found that water vapor delta 18O in these upper atmospheric layers positively correlates with temperature. We propose that the up-and-over transport of such water vapor to the TP contributes to the temperature signal in the ice core delta 18O record, which also helps understand the increasing trend in TP ice core delta 18O records during the last deglaciation. ENSO and PDO affect the intensity of the ASM through two phases: warm phases tend to weaken the monsoon, leading to higher delta 18O values, whereas cool phases strengthen the monsoon, resulting in lower delta 18O values. Our findings suggest that multiple climate forcings can have their specific isotopic imprints in isotopic archives and highlight the importance of analyzing the integrated effects of diverse climatic drivers. The analyses also shed light on separating different climate signals from paleoclimate records.

Abstract. The Tibetan Plateau (TP) serves as a water tower for major rivers in Asia, and mountain valleys in southeastern TP are key channels for moisture entering the TP. Water resources on the TP are experiencing spatially opposite changes due to climate change, and understanding the sources and dynamics of atmospheric moisture is vital. To investigate the role of ocean surface evaporation, continental air mass intrusion, and rain-vapor interaction, we present a three-year daily time series of near-surface water vapor isotope compositions (δ18O and d-excess) from the South-East TP station. We find that apparent negative correlations between d-excess and relative humidity over the Indian Ocean mainly reflect their similar seasonality. When analyzed for different seasons, the correlation is insignificant or only explains a marginal fraction of variance. Therefore, caution is required when interpreting the d-excess as a conservative tracer of ocean surface evaporation. Instead, local and upstream specific humidity is the main factor determining non-monsoon season d-excess variability due to the intrusion of cold and dry air from upper levels. During the summer monsoon season, d-excess and δ18O mainly reflect the effect of raindrop evaporation on humidity during transport which decreases lower vapor δ18O but increases d-excess values. These findings provide new insights into the significance of using water isotopes to track moisture sources and dynamics over the TP with seasonally alternating circulation systems. Particularly, the findings for d-excess will improve the understanding of different moisture sources and guide the interpretation of d-excess derived from other water bodies and ice cores.

Atmospheric CO2 represents a crucial greenhouse gas, while in situ observation excluded a full recognition of the spatial scape of such data, and thus prevent a detailed understanding of the specific source contribution to the atmosphere. In this study, we employed a mobile vehicle-based WS-CRDS (wavelength-scanned cavity ring-down spectroscopy) analyzer to conduct continuous measurements of near-surface atmospheric CO2 concentration and delta 13C-CO2 across extensive regions of mainland China during winter, aiming to investigate their spatial patterns, possible driver, and trace emission sources. Our findings reveal distinct spatial heterogeneity in CO2 concentrations at regional scales. In particular, we observed 53 ppm higher CO2 concentration in urban areas than in suburban areas, and averaged around 1.35 parts per thousand lower delta 13C to the center of big cities, owing to the increasing CO2 concentration in association with emission from human activities and depleted carbon isotope from fossil sources. Keeling plot analysis revealed more depleted delta 13C values in northern cities with around -25.96 +/- 2.85 parts per thousand, than around -24.35 +/- 2.87 parts per thousand in southern cities, owing to heating practice in northern China. Source delta 13C comparison indicates that coal and liquid fossil fuels (encompassing gasoline and diesel) constitute the predominant energy sources in most urban areas, representing a key factor influencing the observed winter spatial distribution patterns.

The Southeast Tibetan Plateau (SETP) has experienced a significant drying trend in recent decades, which is likely linked to shifts in moisture sources. To investigate the roles of ocean surface evaporation, continental air mass intrusion, and precipitation-vapor interactions, we present a three-year daily time series of near-surface vapor delta 18O and d-excess data from the SETP station. Our analysis reveals that apparent negative correlations between d-excess and relative humidity over the Indian Ocean are primarily due to anticorrelated seasonal cycles, which become insignificant or marginal when examined seasonally. This result underscores the need for caution in interpreting d-excess as a conservative tracer of ocean surface evaporation. Instead, we identify local and upstream specific humidity as the primary determinants of non-monsoon season d-excess variability, which is influenced by the intrusion of cold and dry air from upper levels. During the summer monsoon season, both d-excess and delta 18O reflect the effect of raindrop evaporation during transport, which decreases delta 18O but increases d-excess. These findings offer new insights into the use of water isotopes to track moisture sources and circulation changes across the SETP, especially under varying seasonal circulation systems. In particular, the findings for d-excess will contribute to our understanding of shifts in moisture sources and provide a framework for interpreting d-excess in various hydroclimatic applications, including ice core studies.

Mass spectrometry and laser spectroscopy have been widely employed for precise water vapor isotope measurements. Nevertheless, these techniques are limited by logistical challenges in fieldwork, consequently constraining the temporal and spatial resolution of measurements. Specifically, water vapor isotope measurements are primarily limited to near-surface levels, while measurements in the free troposphere are notably scarce. Portable sampling devices, such as air bags and glass bottles, have therefore become necessary alternatives for collecting, storing, and transporting gaseous samples in diverse environments prior to analysis with less portable instruments. In drone-based high-altitude vapor sampling, air bags are preferred for their lighter weight and greater flexibility compared to glass bottles. Nevertheless, they present specific challenges, such as potential sample contamination and isotopic fractionation during storage, primarily due to the inherent permeability of air bags. Here, we developed a theoretical model for water vapor diffusion through the sampling bag surface, with parameters calibrated through laboratory experiments. This model enables the reconstruction of the initial isotopic composition of sampled vapor based on measurements obtained within the bag and from the surrounding environment. This diffusion model underwent rigorous validation through experiments conducted under varying humidity and isotopic composition differences between the inside and outside of the air bag, confirming its reliability. We applied this correction method to air samples collected at various pressures up to the upper troposphere using an air bag-mounted drone that we developed, thereby estimating the initial isotopic composition and uncertainty based on our observations. Our correction method enhances the reliability and applicability of water vapor isotope observations conducted using drones equipped with air bags, and provides a detailed assessment of all potential sources of error and quantifies the uncertainty range of the observations. This approach leverages the strengths of drone-based air bag sampling while mitigating its limitations, thus facilitating the convenient collection of isotopic data throughout the troposphere.

Isotopic analysis serves as a critical tool in understanding the complexities of the water cycle and quantifying the influence of distinct atmospheric processes.This research focuses on the spatio-temporal distribution of the HDO/H2O ratio in water vapor on Earth and Mars, identifying the processes that control these variations.Utilizing isotopic data from General Circulation Model LMDZ simulations for Earth and Planetary Climate Model (PCM) simulations for Mars, we investigate the similarities and differences in water vapor transport and phase changes within each planet's atmosphere. Key findings include a marked isotopic enrichment from ice sublimation in both planets, with a stronger effect observed on Mars due to longer crystal residence times. In contrast, Earth exhibits a buffering effect by the near-surface ocean not present on Mars. Our hypothesis that a unified conceptual framework can interpret isotopic distributions on both planets is supported, suggesting shared fundamental processes with adaptations to each planet's unique conditions.This comparative analysis not only highlights the similarities and differences in the water cycles of Earth and Mars, but also demonstates the adaptability of our conceptual framework to various planetary environments. These insights enhance our comprehension of planetary hydrological cycles and contribute to a deeper understanding of their underlying microphysical mechanisms.

There is increasing evidence that plants enhance stomatal conductance and transpiration with rising temperatures to prevent leaf overheating especially in environments with ample water availability. We investigated the interplay among environmental parameters, plant water status and leaf physiology as drivers of monthly variations of leaf water oxygen and hydrogen isotopic enrichment above plant source water (O18OL, O2HL, respectively) over two years in four common tree species with contrasting leaf shapes and water-uptake patterns in a humid subtropical climate in Southwest China. We hypothesized that O18OL and O2HL variation throughout the year is primarily driven by air temperature seasonality through modulation of stomatal regulation of transpiration at seasonal timescale. We found tight coupling and inverse links of O18OL and O2HL with air temperature and leaf water content in each target species, which is consistent with the expected effect of enhanced stomatal conductance and transpiration on leaf water isotopic composition under warmer conditions. Leaf dry matter oxygen isotopic data provide further evidence of general increases in time-integrated stomatal conductance and transpiration with increasing ambient air temperature and leaf water content across species. These results support that trees can achieve effective transpirational leaf cooling under high ambient temperatures when soil water availability is also high, at both short and long timescales. Our analysis also shows that the correlations of O18OL and O2HL with meteorological parameters are largely unaffected by leaf morphology but can be slightly modified by water-uptake pattern among species. Finally, this study highlights the key influence of temperature-modulated seasonal changes in stomatal conductance on leaf water isotopic enrichment fluctuations through time, which sheds light on plant-environment interactions and ecosystem water fluxes in humid subtropical regions.

Water uptake depth is often coordinated with leaf morphology, nutrient and water-use traits across dryland plant species, but such trait coordination remains largely unexplored in plants from more humid but nutrient-poor habitats. We assessed how the year-round water uptake pattern influences the leaf economics spectrum (LES) and isotopic water-use traits across five representative native tree species inhabiting limestone soils and sandstone-derived yellow soils in humid subtropical SW China. We used xylem water isotopes (δ18O, δ2H) to infer water uptake depth; leaf δ13C and Δ18O as proxies for time-integrated water-use efficiency and stomatal conductance, respectively; and key LES traits (specific leaf area, Nmass and Narea) as indices of carbon-nutrient economy. Soil water uptake depth strongly influenced the inter-specific variations in leaf economic and water-use traits, especially during the dry winter-spring period. Shallow-rooted species using water stored in fertile topsoil layers exhibited lower carbon investment per leaf area, higher leaf N and water contents, and higher δ13C values. Conversely, deep-rooted species using deeper soil/bedrock water exhibited thicker and more sclerophyllous leaves combined with lower leaf N, water contents and δ13C values. Across species, leaf δ13C increased with N content, revealing that N-induced differences in photosynthetic capacity are the dominant control over interspecific variation in intrinsic water-use efficiency. Shallow-rooted species exhibited lower foliar Δ18O values (indicative of looser stomatal regulation and water-spender strategy), potentially facilitating nutrient uptake from fertile topsoil. Specifically, Zanthoxylum bungeanum played a central role in shaping the broad water-spender-to-water-saver continuum observed across the target species. Our findings highlight how shallow-rooted tree species can adopt a resource-acquisitive strategy through coupled enhancement of soil water and nutrient capture, stomatal conductance, photosynthetic capacity and water-use efficiency. We provide novel insights into key ecophysiological mechanisms that may help maintain tree species diversity and coexistence in humid but nutrient-poor subtropical habitats.

Glaciers in the Karakoram exhibit stability or near-balanced mass changes, in stark contrast to the widespread glacier retreat observed globally. However, the limited availability of observational data, coupled with the lack of in-depth exploration of ablation physical mechanisms, has hindered a comprehensive understanding of the factors driving the anomalous behavior of these glaciers. This study employs an energy‒mass balance model, validated against observational data, and focuses on the representative Pasu Glacier to identify the key factors contributing to the near-balanced glacier mass budget observed over 2000–2020. The analysis revealed an average mass balance of −0.030 ± 0.247 m w.e. per year for Pasu Glacier in 2000–2020, with an average equilibrium line altitude of 4150 m. While snowfall was the primary determinant of mass balance for interannual and seasonal variations, turbulent heat exchange also played a significant role in the glacier's energy balance process. Through an analysis of altitude gradients and long-term variations in mass‒energy gain and loss and comparisons with other glaciers in High Mountain Asia (HMA), we concluded that 1) the balanced state of Pasu Glacier was largely attributed to the magnitude and extent of the accumulation of precipitation at high elevations, 2) reduced snowfall in highly accumulated areas (−0.79% per year), increasing melting intensity (0.026 m w.e. per year), and prolonged melting duration (∼24 d during 2000–2020) indicated a negative tendency of glacier mass budgets, and 3) Pasu Glacier exhibited similar characteristics of continental glaciers in terms of energy balance and polar continental glaciers in terms of mass gain, which have contributed to the stability of Pasu Glacier in 2000–2020. Our findings provide valuable insight into the dominant factors contributing to the balanced state of Pasu Glacier and can be applied to addressing other glacier changes in the Karakoram.

Understanding the spatiotemporal variability of atmospheric dust over the Tibetan Plateau (TP) and its response to large-scale climate patterns is critical for comprehending regional climatic and environmental changes. Here, we present an annually resolved Ca2+ concentration record from the Qiangtang No. 1 Glacier spanning 1800-2011 CE to investigate the influence of the Pacific Decadal Oscillation (PDO) on dust deposition in the central TP. Correlation and wavelet analyses demonstrate a significant relationship between the QT Ca2+ record and reconstructed PDO indices derived from Asian proxies, with both exhibiting coherent pentadecadal periodicities. Combined with other TP dust records, our analyses reveal that the PDO has a regionally contrasting influence on interdecadal dust variability over the TP. Specially, the PDO exhibits a significant positive correlation with dust concentration records in the central and southern TP, whereas a negative correlation in the northwestern TP. This spatial pattern persists at least over the past millennium, as evidenced by long-term ice core dust records. During the positive PDO phases, intensified aridity in South Asia and enhanced atmospheric transport contribute to elevated atmospheric dust loading over the southern TP, while wetter conditions in Central Asia and weakened westerly circulation likely result in reduced dust level over the northwestern TP. These findings on the PDO's spatially heterogeneous influences offer new insights into how the PDO modulates the long-term dust variability across the TP.

Root water uptake and leaf-level intrinsic water-use efficiency (WUEi) and their temporal variations are important determinates of plant water balance and carbon fixation, yet these processes in humid forest trees are much less explored. We investigated the monthly variations in xylem and soil water isotopes (delta 18O, delta 2H), leaf carbon isotope (delta 13C), soil, xylem and leaf water contents as well as the seasonal variations in leaf oxygen isotope (delta 18O) and N contents for the dominant overstory species (Pinus massoniana) and a neighboring common understory species (Camellia japonica) in a subtropical humid pine forest within April 2021-June 2022. Water stable isotopes revealed that the two species exhibited similar water uptake patterns over time and both shifted water uptake toward deeper and shallow soil layers during the wet and relatively dry seasons, respectively. Evident soil water partitioning only occurred during a spring drought when only C. japonica shifted water uptake toward deeper soil layers, indicating high interspecific competition for shallow water. For P. massoniana, the reliance on shallow water positively correlated with WUEi (leaf delta 13C) through negatively affecting leaf relative (to xylem) water content and stomatal conductance (proxied by leaf 18O enrichment above source water). In contrast, C. japonica exhibited non-sensitive WUEi response to temporal changes in water uptake depth, and its low leaf N contents indicate severe N limitation on photosynthesis and WUEi. Our results highlight the tight coupling between water uptake depth and WUEi for the overstory species, but not for the understory species likely associated with the stronger water and particularly N limitation it was experiencing. Our analysis of temporal changes in water uptake depth and WUEi (leaf delta 13C) provides a useful framework to evaluate belowground constraints on resource acquisition and leaf-level water use strategies for plants in humid forests.