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Recently, δ17O and its excess (Δ′17O) have become increasingly significant "triple-oxygen-isotope" indicators of distinctive hydrological processes in hydrology and climatology. This situation mirrors the research regarding δ18O and δ2H in the 1960s towards a solid theoretical base and a surge in application examples and field studies worldwide. Currently, systematic global measurements for δ17O in precipitation are still lacking. As a result, attempts have been made to define a Global δ17O/δ18O Meteoric Water Line (GMWL), often by using regional or local datasets of varying systematicity. Different definitions of the global reference slope (λref) for determining Δ′17O values have been proposed, by ongoing debate around a proposed consensus value of 0.528. This study used worldwide samples archived in the IAEA Global Network of Isotopes in Precipitation (GNIP) to (a) derive a δ17O/δ18O GMWL based on four-year monthly records from 66 GNIP stations, (b) formulate local δ17O/δ18O meteoric water lines (LMWL) for these stations' areas, and (c) evaluate regional and seasonal variations of Δ′17O in precipitation. The GMWL for δ17O/δ18O was determined to be δ′17O = 0.5280 ± 0.0002 δ′18O + 0.0153 ± 0.0013, in keeping with the consensus value. Furthermore, our results suggested that using a line-conditioned 17O-excess is a viable alternative over the global λref in the context of regional hydrology and paleoclimatology interpretations; however, without challenging the global λref as such. [ABSTRACT FROM AUTHOR]

Tritium (3H) in Earth's precipitation is vigilantly monitored since historical nuclear bomb tests because of radiological protection considerations and its invaluable role as a tracer of the global water cycle in quantifying surface, groundwater, and oceanic fluxes. For hydrological applications, accurate knowledge of 3H in contemporary local precipitation is prerequisite for dating of critical zone water and calibrating hydrogeologic transport and groundwater protection models. However, local tritium input in precipitation is hard to constrain due to few 3H observation sites. We present new high-spatial resolution global prediction maps of multi-year mean 3H in contemporary "post-bomb" (2008–2018) precipitation by using a robust regression model based on environmental and geospatial covariates. The model accurately predicted the mean annual 3H in precipitation, which allowed us to produce global 3H input maps for applications in hydrological and climate modelling. The spatial patterns revealed natural 3H in contemporary precipitation sufficient for practical hydrological applications (1–25 TU) but variable across continental regions and higher latitudes due to cumulative influences of cyclical neutron fluxes, stratospheric inputs, and distance from tropospheric moisture sources. The new 3H maps provide a foundational resource for improved calibration of groundwater flow models and critical zone vulnerability assessment and provides an operational baseline for quantifying the potential impact of future anthropogenic nuclear activities and hydroclimatic changes. [ABSTRACT FROM AUTHOR]

Rationale: Stable isotope analyses of environmental waters (δ²H, δ18O) are an important assay in hydrology and environmental research with rising interest in Δ17O, which requires ultra-precise assays. We evaluated isotope analyses of six test water samples for 281 laboratory submissions measuring δ²H and δ18O along with a subset analyzing Δ17O and Δ17O by laser spectrometry and isotope ratio mass spectrometry (IRMS). Methods: Six test waters were distributed to laboratories spanning a wide δ range of natural waters for δ²H, δ18O and Δ17O and Δ17O. One sample was a blind duplicate to test reproducibility and claims of analytical precision. Results: Results showed that ca 83% of the submissions produced acceptable δ18O and δ²H results within 0.2‰ (mUr) and 1.6‰ of the benchmark values, respectively. However, 17% of the submissions gave questionable to unacceptable results. A blind duplicate revealed many laboratories reported overly optimistic precision, and many could not replicate within their claimed precision. For Δ17O, dual-inlet results for IRMS using quantitative O2 conversion were accurate and highly precise, but the results for laser spectrometry ranged by ca 200 per meg (μUr) for each sample, with ca 70% unable to replicate the duplicate to their claimed Δ17O precision. One complicating factor is the lack of certified primary reference waters for Δ17O. Conclusions: No single factor or combination of factors was identifiable for poor or good performance, and underperformance came from issues like data normalization including inadequate memory and drift corrections, compromised working reference materials and underperforming instrumentation. We recommend isotope laboratories include high and low δ value controls of known isotope composition in each run. Progress in Δ17O analyses by laser spectrometry requires extraordinary proof of performance claims and would benefit from the development of adoptable and systematic advanced data processing procedures to correct for memory and drift. [ABSTRACT FROM AUTHOR]

Rationale: A widespread problem observed in global water isotope (δ18 O, δ²H) proficiency tests is compromised working reference materials due to storage-dispensing evaporation effects. Proper storage requires no evaporation or leakage, which causes isotopic drift and bias. Surveys by the International Atomic Energy Agency (IAEA) show most isotope laboratories use glass or plastic bottles to store working reference materials, with frequent opening and closings that pose evaporation risks. Practical small (ca. 2--5 L) storage-dispensing solutions free of air exposure, evaporation, and leakage are needed.We also tested several smaller-scale bottles for day-to-day aliquots. Methods: We tested low-cost, conveniently sized (4 L) adaptations of a common stainless-steel beverage keg with a liquid dispenser, with minor modifications to facilitate low-flow dispensing and pressurization (1--2 bar) with Ar or N2. We tested three kegs (100%, 75%, 50% initial fills) for a 2-year period along with monthly dispensing to assess long-term storage viability for maintaining δ18 O and δ² H integrity and dispensing, and day-to-day aliquot bottles for 6 months. Results: Test results showed these small keg storage systems fully maintained the isotopic integrity of water over the 2-year testing period with no trend in the isotopic data that would reveal evaporative loss or leakage (e.g., pressure or mass loss) regardless of starting fill level. However, evaporated water in the outlet tube assembly must be eliminated by discarding 15--20 mL before dispensing into appropriate daily-use laboratory standard bottles (30--100 mL). Glass bottles for daily aliquots showed good integrity properties, but only if their fill level was >50%. Conclusions: The use of a low-cost pressurized metal beverage keg dispensing system provides a robust solution to enable laboratories to maintain the integrity of their water isotope working reference materials over several years. [ABSTRACT FROM AUTHOR]

Patterns of δ18O and δ2H in Earth's precipitation provide essential scientific data for use in hydrological, climatological, ecological and forensic research. Insufficient global spatial data coverage promulgated the use of gridded datasets employing geostatistical techniques (isoscapes) for spatiotemporally coherent isotope predictions. Cluster‐based isoscape regionalization combines the advantages of local or regional prediction calibrations into a global framework. Here we present a revision of a Regionalized Cluster‐Based Water Isotope Prediction model (RCWIP2) incorporating new isotope data having extensive spatial coverage and a wider array of predictor variables combined with high‐resolution gridded climatic data. We introduced coupling of δ18O and δ2H (e.g., d‐excess constrained) in the model predictions to prevent runaway isoscapes when each isotope is modelled separately and cross‐checked observed versus modelled d‐excess values. We improved model error quantification by adopting full uncertainty propagation in all calculations. RCWIP2 improved the RMSE over previous isoscape models by ca. 0.3 ‰ for δ18O and 2.5 ‰ for δ2H with an uncertainty <1.0 ‰ for δ18O and < 8 ‰ for δ2H for most regions of the world. The determination of the relative importance of each predictor variable in each ecoclimatic zone is a new approach to identify previously unrecognized climatic drivers on mean annual precipitation δ18O and δ2H. The improved RCWIP2 isoscape grids and maps (season, monthly, annual, regional) are available for download at https://isotopehydrologynetwork.iaea.org. [ABSTRACT FROM AUTHOR]

Accurate and precise measurements of low levels of tritium ( 3 H) in environmental waters are difficult to attain due to complex steps of sample preparation, electrolytic enrichment, liquid scintillation decay counting, and extensive data processing. We present a Microsoft Access™ relational database application, TRIMS (Tritium Information Management System) to assist with sample and data processing of tritium analysis by managing the processes from sample registration and analysis to reporting and archiving. A complete uncertainty propagation algorithm ensures tritium results are reported with robust uncertainty metrics. TRIMS will help to increase laboratory productivity and improve the accuracy and precision of 3 H assays. The software supports several enrichment protocols and LSC counter types. TRIMS is available for download at no cost from the IAEA at www.iaea.org/water . [ABSTRACT FROM AUTHOR]

The stable isotope composition of water (d2H, d18O) is a crucial tracer of hydrological processes, hence accurate assays are required to yield sound scientific information. We tested the performance of 235 worldwide laboratories conducting isotope analyses of water by IRMS and laser spectrometers. Eight samples comprised the d-range of natural waters including a highly depleted, enriched, saline, and methanol contaminated sample to assess contamination effects. Results showed 73 % of laboratories gave acceptable results, but 27 % produced unacceptable results. Methanol contamination resulted in extreme outliers for laser spectrometers, but also affected reactor-based IRMS systems. Analysis of results and metadata suggested poor performance stemmed mainly from skill and knowledge-based errors including: calculation mistakes, compromised calibration standards, faulty instrumentation, lack of vigilance to contamination, and inattention to unreasonable isotopic outcomes. To counteract these, we recommend laboratories include 1-2 isotopically known controls in all runs; laser spectrometry laboratories should screen for spectral contamination, and all should evaluate if derived d-excess values are realistic if both isotopes are measured. Together, these strategies should immediately inform the laboratory about fundamental mistakes or compromised samples. [ABSTRACT FROM AUTHOR]

δ 17 O and Δ' 17 O are emerging tracers increasingly used in isotope hydrology, climatology, and biochemistry. Differentiating small relative abundance changes in the rare 17 O isotope from the strong covariance with 18 O imposes ultra-high precision requirements for this isotope analysis. Measurements of δ 17 O by Cavity Ringdown Spectroscopy (CRDS) are attractive due to the ease of sample preparation, automated throughput, and avoidance of chemical conversions needed for isotope-ratio mass spectrometry. However, the CRDS approach requires trade-offs in measurement precision and uncertainty. In this protocol document, we present the following:•New analytical procedures and a software tool for conducting δ 17 O and Δ' 17 O measurements by CRDS.•Outline a robust uncertainty framework for Δ' 17 O determinations.•Description of a CRDS performance framework for optimizing throughput, instrumental stability, and Δ' 17 O measurement precision and accuracy., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 International Atomic Energy Agency. Published by Elsevier B.V.)

Rationale: Stable isotope analyses of environmental waters (δ 2 H, δ 18 O) are an important assay in hydrology and environmental research with rising interest in δ 17 O, which requires ultra-precise assays. We evaluated isotope analyses of six test water samples for 281 laboratory submissions measuring δ 2 H and δ 18 O along with a subset analyzing δ 17 O and Δ 17 O by laser spectrometry and isotope ratio mass spectrometry (IRMS)., Methods: Six test waters were distributed to laboratories spanning a wide δ range of natural waters for δ 2 H, δ 18 O and δ 17 O and Δ 17 O. One sample was a blind duplicate to test reproducibility and claims of analytical precision., Results: Results showed that ca 83% of the submissions produced acceptable δ 18 O and δ 2 H results within 0.2‰ (mUr) and 1.6‰ of the benchmark values, respectively. However, 17% of the submissions gave questionable to unacceptable results. A blind duplicate revealed many laboratories reported overly optimistic precision, and many could not replicate within their claimed precision. For Δ 17 O, dual-inlet results for IRMS using quantitative O 2 conversion were accurate and highly precise, but the results for laser spectrometry ranged by ca 200 per meg (μUr) for each sample, with ca 70% unable to replicate the duplicate to their claimed Δ 17 O precision. One complicating factor is the lack of certified primary reference waters for δ 17 O., Conclusions: No single factor or combination of factors was identifiable for poor or good performance, and underperformance came from issues like data normalization including inadequate memory and drift corrections, compromised working reference materials and underperforming instrumentation. We recommend isotope laboratories include high and low δ value controls of known isotope composition in each run. Progress in Δ 17 O analyses by laser spectrometry requires extraordinary proof of performance claims and would benefit from the development of adoptable and systematic advanced data processing procedures to correct for memory and drift., (© 2021 John Wiley & Sons Ltd.)

Analysis of low-level tritium ( 3 H) in environmental waters requires pre-concentration using electrolytic enrichment prior to decay counting. Accurate and precise electrolytic enrichment factors (EF) are required to determine the sample's environmental 3 H concentration. Two methods are used to determine EFs: i) the Spike Proxy Method (SPM) and ii) the Deuterium Method (DM) with each having several modalities. We conducted a comparative assessment of four EF strategies using 250 mL and 500 mL electrolytic enrichment of three low-level 3 H proficiency water standards (0.5-7 TU) to see which strategy gave the most accurate 3 H results based on z- and Zeta-scores. Our comparative evaluation revealed the DM offers consistently superior 3 H results, with more precise EF determinations compared to the three SPM strategies. The DM gave the best z-scores with an EF relative combined uncertainty of about 0.5‰ and a negligible contribution to the overall uncertainty budget due to the EF determination. Moreover, the DM can improve productivity by eliminating the spike and gravimetric procedures from routine analyses and can give rapid cell enrichment performance feedback prior to decay counting. We recommend low-level tritium laboratories consider adopting the DM into their 3 H sample enrichment and analysis operations., (Copyright © 2021 Elsevier Ltd. All rights reserved.)