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Tyler B. Coplen

Publications and source records attributed to Tyler B. Coplen.

At least 19 recordsLinked to original sources
USGS2026

Triple oxygen isotope compositions of isotopic reference waters: Implications for VSMOW-Scale and VSMOW-SLAP-Scale Δ′¹⁷O calibration

Triple oxygen isotope ratios of waters are commonly reported on the VSMOW–SLAP scale, whereas comparison with theoretical calculations and assessment of instrumental scale distortion require accurate constraints on the measured isotopic compositions of the primary isotopic reference materials (iRMs) themselves. In particular, the measured δ 17 O VSMOW and Δ ′ 17 O VSMOW values for SLAP and its substitute, SLAP2, remain insufficiently constrained and reported values differ among laboratories. Here, we measured triple oxygen isotope ratios for two primary iRMs (VSMOW and SLAP) and twelve secondary iRMs (VSMOW2, SLAP2, GISP, GRESP, USGS45, USGS46, USGS46a, USGS47, USGS48, USGS49, USGS50 and USGS53) using BrF 5 fluorination and dual-inlet isotope-ratio mass spectrometry. For SLAP, we obtained δ 18 O VSMOW = -55.50 ± 0.15‰ and δ 17 O VSMOW = -29.66 ± 0.08‰, giving Δ ′ 17 O VSMOW = 34 ± 6 per meg (all expanded uncertainties, k = 2). The corresponding values for SLAP2 agree within uncertainty. When expressed on the conventional VSMOW–SLAP scale, our Δ ′ 17 O VSMOW–SLAP values for all secondary iRMs with available literature values agree with previously published values within uncertainty, confirming interlaboratory comparability on that scale. In contrast, waters with low δ 18 O values, Δ ′ 17 O VSMOW values are systematically higher than the corresponding Δ ′ 17 O VSMOW–SLAP values. These results further suggest that accurate determination of the VSMOW-scale isotopic composition of SLAP and/or SLAP2 across laboratories is essential, particularly for low- δ 18 O samples, for which the difference between VSMOW-scale and VSMOW–SLAP-scale Δ ′ 17 O values becomes large, and for meaningful comparison between measured data and theoretical calculations.

Geostandards and Geoanalytical Research↗
USGS2026

Reaffirming the consistency of the original stock of NBS 19 limestone and its byproduct with finer grain size for δ13C and δ18O calibrations—Both distributed internationally

Rationale Approximately 3–4 kg of NBS 19 limestone, prepared in 1982 by the U.S. Geological Survey (USGS), serves as a primary reference for the carbon isotope scales VPDB and VPDB-LSVEC and the oxygen isotope scale VPDB. Its consensus values are +1.95‰ for δ 13 C and −2.2‰ for δ 18 O measurements. After more than three decades of distribution, the number of units labeled “NBS 19” shrunk substantially, and the remaining material was quarantined, with a small fraction retained at the USGS and a larger fraction entrusted to the International Atomic Energy Agency (IAEA) for secure storage. Given the critical role of NBS 19, verifying the integrity of its δ 13 C and δ 18 O values across these storage locations is essential. Method Samples from IAEA and USGS stock materials were selected to ensure traceability of carbon and oxygen isotopes to NBS 19 distribution units from various storage locations. To achieve this, distribution units labeled as NBS 19 from both the IAEA and the National Institute of Standards and Technology (NIST) were included. During evaluation, two distinct grain sizes were identified within these units. Grain size was assessed using sieves on five selected samples. The δ 13 C and δ 18 O values of finer and coarser fractions (both labeled NBS 19) were measured at USGS using continuous-flow isotope-ratio mass spectrometry on 100- and 200-μg samples. Results Expanded 95% measurement uncertainties ( k = 2) for δ 13 C and δ 18 O determinations are 0.027‰ and 0.038‰ or better, respectively, for quarantined NBS 19 stocks and finer byproduct calcite, which we term “NBS-19 byproduct,” regardless of storage location. Between the 1990s and circa 2011, NBS-19 byproduct labeled “NBS 19,” distributed by NIST and the IAEA, shows these findings. Conclusions NBS 19 primary isotopic reference material should be used for calibration of new isotopic reference materials rather than NBS-19 byproduct secondary isotopic reference material.

Rapid Communications in Mass Spectrometry↗
USGS2026

Three new calcium formate reference materials for δ13C measurements and a redetermination of the R(13C/12C) ratio for VPDB based on proton nuclear magnetic resonance measurements

Rationale Isotope ratio mass spectrometry (IRMS) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy are independent techniques for determining the isotope ratio R ( 13 C/ 12 C) in organic compounds. However, the lack of suitable reference materials has limited intercalibration of results from these methods. Methods Three high-purity calcium formate isotopic reference materials were developed, each ideal for accurate isotope ratio measurements by both 1 H NMR and isotope-ratio mass spectrometry (IRMS). For each material, R ( 13 C/ 12 C) was determined by 1 H NMR, and the relative isotope abundance ( δ 13 C VPDB-LSVEC ) by IRMS. The combined IRMS and NMR results were used to determine the R ( 13 C/ 12 C) value of Vienna Peedee belemnite (VPDB). Results The combined datasets yield a value for R ( 13 C/ 12 C) of 0.0111050 ± 0.0000047 ( k = 2) for VPDB, which is 6.7‰ lower than the commonly cited value of 0.011180, but similar to other recent determinations. These three calcium formate reference materials exhibit high accuracy across both analytical methods and provide robust tools for instrument calibration, method validation, and inter-laboratory comparison in carbon stable isotope ratio analysis. Conclusions An accurate R ( 13 C/ 12 C) value for VPDB strengthens the link between relative ( δ 13 C VPDB-LSVEC ) values from IRMS and R ( 13 C/ 12 C) isotope ratios from NMR and other techniques. These three calcium formate isotopic reference materials (USGS106, USGS107, and USGS108) are available from the US Geological Survey and provide reference materials for calibration, method validation, and inter-laboratory comparison in carbon isotope ratio analysis.

Rapid Communications in Mass Spectrometry↗
USGS2025

Correction to “Stable isotope reference materials and scale definitions – outcomes of the 2024 IAEA experts meeting”

This article corrects the following: Camin, F., Besic, D., Brewer, P., Allison, C., Coplen, T., Dunn, P., Gehre, M., Gröning, M., Meijer, H.-A.-J, Hélie, J.-F., Iacumin, P., Kraft, R., Krajnc, B., Kümmel, S., Lee, S., Meija, J., Mester, Z., Mohn, J., Moossen, H., Qi, H., Skrzypek, G., Sperlich, P., Viallon, J., Wassenaar, L. and Wielgosz, R. (2025). Stable Isotope Reference Materials and Scale Definitions—Outcomes of the 2024 IAEA Experts Meeting. Rapid Commun Mass Spectrom, 39: e10018, https://doi.org/10.1002/rcm.10018. In the above article, the text of note 3 in Section 4.2 is incorrect. The correct text is shown below: 3. Whilst limited amounts of the original VSMOW and SLAP scale-defining reference materials may still be available, to enable continuous wide distribution of RMs for VSMOW-SLAP scale realization (normalization, calibration) the scale-maintaining reference materials VSMOW2 and SLAP2 are available. VSMOW2 and SLAP2 have δ(18O) values identical to VSMOW and SLAP, respectively, but with an uncertainty with respect to VSMOW and SLAP. We apologize for this error. The CIAAW-IUPAC endorsed all isotope delta scale definitions appearing in Camin et al. (2025) and agreed to publish the current and all future updates and corrections to these definitions on its website (www.ciaaw.org).

Rapid Communications in Mass Spectrometry↗
USGS2025

Isotopic compositions of modern seawater at the Mariana and Yap trenches

The isotopic composition of ocean water is crucial in studying water masses and mixing in deep oceans, isotope mass balance in ocean water regulated by high-temperature and low-temperature hydrothermal alterations, and the exchange of water among crust-ocean-mantle reservoirs. We collected 40 water samples from Challenger Deep and the water column above at the Mariana Trench (down to 10,923 m) and 12 from the Yap Trench (down to 6,300 m) in the western Pacific Ocean in three hadal cruises from 2016 to 2018. The δ 2 H values at the Mariana and Yap Trenches average 0.1 ± 0.2 ‰ (1σ error). The δ 2 H records from this study, together with existing databases, manifest that deep waters have δ 2 H values varying between −2 and +2 ‰ (except for the Weddell Sea, the Greenland, Iceland, and Norwegian Seas, and the Mediterranean Sea), with increasing values from the Southern Ocean to the Pacific and Indian Oceans, and to the Atlantic Ocean. The average δ 18 O value of water samples from both trenches is –0.04 ± 0.03 ‰ (1σ error). The correlation between δ 18 O and salinity distinguishes abyssal water masses at the study region, UCDW (Upper Circumpolar Deep Water) and LCDW (Lower Circumpolar Deep Water). These water samples from the Mariana and Yap Trenches gave an average 17 O excess value of −6 ± 1 ppm (1σ error). Our 52 data records of 17 O excess expand the 38 existing records for the deep ocean. Both δ 2 H and 17 O excess of modern ocean have rolled as anchor points to reconstruct compositions of Earth’s early ocean.

ACS Earth and Space Chemistry↗
USGS2025

Determination of provenance soil type using inductively coupled plasma mass spectrometry (ICP-MS) analyses of Pinus ponderosa ash

This study demonstrates the feasibility of determining soil provenance from tree ash composition using elemental analysis and chemometric techniques. To date, no published studies have applied chemometric approaches to classify ash for provenance determination following forest fires. In this work, Pinus ponderosa ash was analyzed to distinguish samples based on soil type and geographic location. Pinus ponderosa , a widely distributed pine species in the western United States where wildfires are prevalent, was selected as a model system. Needles were collected from trees grown in five distinct soil types across northern Arizona and Colorado, then dry-ashed under controlled conditions. Classification was performed using three preprocessing techniques and five machine learning algorithms, including hierarchical modeling structures to optimize separation. Partial least squares discriminant analysis (PLS-DA) following a Box-Cox transformation yielded the highest classification accuracy, achieving a prediction kappa value of 0.98 for soil type identification. However, classification performance decreased when distinguishing both soil type and geographic location, indicating that additional variability may influence predictive accuracy in broader applications. These findings highlight the potential of inductively coupled plasma mass spectrometry (ICP-MS) and machine learning for post-wildfire forensic analysis and environmental monitoring.

Applied Spectroscopy↗
USGS2025

Characterization of DOC in riparian wetland pore water and its interference in stable water isotope analysis of δ2H and δ18O

Wetlands play an important role in carbon retention, which is greatly dependent on hydrological conditions. Therefore, the interest in wetland hydrology has increased over recent decades. In wetland hydrology, stable water isotopes ( δ 2 H, δ 18 O) have found increasing use, as laser-based instruments have become readily available and allow for faster analysis and lower costs. However, the use of laser-based determinations of stable hydrogen and oxygen isotopes in wetland pore waters might be challenging because of dissolved organic carbon (DOC), especially as wetland pore waters often contain elevated DOC concentrations. To study the potential interference of DOC on laser-based stable water isotopes determination, we determined concentration, fluorescence and absorbance characteristics of DOC in pore waters collected from six restored and six near-natural riparian wetlands. The water samples’ δ 2 H and δ 18 O values were determined by two laser absorption spectrometers (LAS) and, for reference, in parallel by dual-inlet isotope-ratio mass spectrometry (DI-IRMS). The two LAS methods showed significant deviations from the DI-IRMS-determinations. Variations in the specific UV absorbance index (SUVA 254 , the quotient of the absorbance at 254 nm and the DOC concentration), which indicates the aromaticity of the DOC, partially accounted for interference for δ 2 H measurements. Elevated SUVA 254 index values were especially linked to restored wetlands. Studies that investigate pore waters with high DOC aromaticity but where the DOC is not characterized, and which require a high accuracy of the δ 2 H-values for interpretation of the hydrological system, may be severely affected by DOC interference.

Journal of Hydrology↗
USGS2025

Stable isotope reference materials and scale definitions – Outcomes of the 2024 IAEA experts meeting

The participants of the 12 th International Atomic Energy Agency (IAEA) meeting on stable isotope reference materials reached a consensus, acknowledging the existence and use of two carbon isotope delta scales: the VPDB (Vienna Peedee belemnite) scale and the VPDB-LSVEC (LSVEC - lithium carbonate prepared by H. J. Svec). Conversion models between the two scales can be established and used but introduce uncertainty. A format for isotope delta scale definition was agreed upon and was used to define the two carbon isotope delta scales and the two main oxygen isotope delta scales, VSMOW-SLAP (Vienna Standard Mean Ocean Water–Standard Light Antarctic Precipitation) and VPDB. Confirmation or identification of a second-scale–defining point is still necessary for the nitrogen and sulfur isotope delta scales. Efforts are encouraged to improve consistency among laboratories in the isotopic analysis of “non-exchangeable hydrogen” in bulk organic materials and oxygen in carbonates using the phosphoric acid reaction. Additional topics discussed include (1) need for improvement in reference materials for accurate greenhouse gas isotopic analyses; (2) reference materials under production by the IAEA, the US Geological Survey (USGS), and the US National Institute of Standards and Technology (NIST); (3) methods for value and uncertainty assignment of reference materials; and (4) calculation of carbon-13 isotope delta and oxygen-18 isotope delta of CO 2 measured by dual-inlet isotope ratio mass spectrometry.

Rapid Communications in Mass Spectrometry↗
USGS2025

Geographic determination of Pinus ponderosa using DART TOFMS, ICP-MS, and LIBS handheld analyzer

Due to legal requirements on international imports, it is important for law enforcement and regulatory agencies to identify the geographical provenance of timber. Current methods for geographic identification utilize data generated by direct analysis in real time time-of-flight mass spectrometry (DART TOFMS), genetics, and isotope-ratio mass spectrometry (IRMS), but identification methods based on genetics and IRMS data require months to years to create usable databases. This study used machine learning algorithms to compare the results of DART TOFMS, inductively coupled plasma mass spectrometry (ICP-MS), and a handheld laser-induced breakdown spectroscopy (LIBS) analyzer for use in geographic identification of five populations of Pinus ponderosa spaced between 14 to 72 km apart. The results of the study showed comparable performances from machine learning algorithms applied to the ICP-MS and LIBS data with accuracy and kappa values over 90% while the DART TOFMS had an accuracy of 76% and a kappa value of 70%. This study demonstrated that data from the LIBS handheld analyzer is a viable and intriguing alternative to ICP-MS and DART TOFMS analyses in generating training databases and further indicates that trace elemental analysis via ICP-MS is a promising method for generating databases used to identify the origin of timber.

California, Oregon↗
USGS2024

Using stable oxygen isotope dual-inlet isotope-ratio mass spectrometry to elucidate uranium transport and mixed 230Th/U calcite formation ages at the seminal Devils Hole, Nevada, natural laboratory

Rationale Vein calcite in Devils Hole has been precipitating continuously in oxygen-isotope equilibrium at a constant temperature for over 500 000 years, providing an unmatched δ 18 O paleoclimate time series. A substantial issue is that coeval calcite (based on matching δ 18 O values) has uranium-series ages differing by 12 000 years. Methods An unparalleled high-accuracy δ 18 O chronology series from continuously submerged calcite was used to correct the published uranium-series ages of non-continuously formed calcite in two cores, cyclically exposed by water-table decline during glacial–interglacial transitions. This method relies on the premise that the δ 18 O values of coevally precipitated calcite are identical, allowing matching calcite δ 18 O values to establish formation ages. Results Exposed calcite can have apparent ages that are 12 000 years too young due to unrecognized uranium mobility and resulting mixed ages identified in over 50 mixed uranium-series ages from previous studies. Secondary uranium in fluids, sourced from the formation or dissolution of porous carbonate deposits (folia) with high uranium-238 ( 238 U) concentrations, has migrated up to 10 mm into vein calcite. Conclusions The continuously submerged Devils Hole δ 18 O chronology is not explained by orbital forcing. Rather, this chronology represents a regional climate record in the southern Great Basin of sea-surface-temperature (SST) variations off California, variations that preceded the last and penultimate deglaciations by 5000 to approximately 10 000 years. Temporal discrepancies between the continuously submerged Devils Hole chronology and other regional δ 18 O records (e.g., the Leviathan chronology) can be explained by unrecognized cryptic, pernicious uranium mobility, leading to model estimations that may be thousands of years younger than actual ages. Consequently, paleo-moisture availability, water-table, and groundwater recharge models based on these mixed uranium-series ages are too young by as much as 12 000 years. The potential for post-formation uranium addition in subaerial cores and speleothems underscores the need for caution in uranium-series dating, highlighting δ 18 O time-series comparisons as a method for identifying mixed ages.

Nevada↗
USGS2023

Evaluation of spectral collection strategies for identification of Dalbergia spp. using handheld laser-induced breakdown spectroscopy

The illegal timber trade has significant impact on the survival of endangered tropical hardwood species like Dalbergia spp. (rosewood), a world-wide protected genus from the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Due to increased threat to Dalbergia spp., and lack of action to reduce threats, port of entry analysis methods are required to identify Dalbergia spp. Handheld laser-induced breakdown spectroscopy (LIBS) has been shown to be capable of identifying species and establishing provenance of Dalbergia spp. and other tropical hardwoods, but analysis methods for this work have yet to be investigated in detail. The present work investigates five well-known algorithms—partial least squares discriminant analysis (PLS-DA), classification and regression trees (CART), k -nearest neighbor ( k -NN), random forest (RF), and support vector machine (SVM)—two training/test set sampling regimes, and data collection at two signal-to-noise (S/N) ratios to assess the potential for handheld LIBS analyses. Additionally, imbalanced classes are addressed. For this application, SVM and RF yield near identical results (though RF takes nearly 100 longer to compute), while the S/N ratio has a significant effect on model success assuming all else is equal. It was found that forming a training set with replicate low S/N analyses can perform as well as higher precision training sets for true prediction, even if the predicted samples have low signal to noise! This work confirms handheld LIBS analyzers can provide a viable method for classification of hardwood species, even within the same genus.

Journal of Chemometrics↗
USGS2023

Equilibrated gas and carbonate standard-derived dual (Δ47 and Δ48) clumped isotope values

Carbonate clumped isotope geochemistry has primarily focused on mass spectrometric determination of m/z 47 CO 2 for geothermometry, but theoretical calculations and recent experiments indicate paired analysis of the m/z 47 ( 13 C 18 O 16 O) and m/z 48 ( 12 C 18 O 18 O) isotopologues (referred to as Δ 47 and Δ 48 ) can be used to study non-equilibrium isotope fractionations and refine temperature estimates. We utilize 5,448 Δ 47 and 3,400 Δ 48 replicate measurements of carbonate samples and standards, and 183 Δ 47 and 195 Δ 48 replicate measurements of gas standards from 2015 to 2021 from a multi-year and multi-instrument data set to constrain Δ 47 and Δ 48 values for 27 samples and standards, including Devils Hole cave calcite, and study equilibrium Δ 47 -Δ 48 , Δ 47 -temperature, and Δ 48 -temperature relationships. We compare results to previously published findings and calculate equilibrium regressions based on data from multiple laboratories. We report acid digestion fractionation factors, Δ* 63-47 and Δ* 64-48 , and account for their dependence on the initial clumped isotope values of the mineral.

Geochemistry, Geophysics, Geosystems↗
USGS2022

Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)

Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative examples.

Pure and Applied Chemistry↗
USGS2022

Standard atomic weights of the elements 2021 (IUPAC Technical Report)

Following the reviews of atomic-weight determinations and other cognate data in 2015, 2017, 2019 and 2021, the IUPAC (International Union of Pure and Applied Chemistry) Commission on Isotopic Abundances and Atomic Weights (CIAAW) reports changes of standard atomic weights. The symbol A r °(E) was selected for standard atomic weight of an element to distinguish it from the atomic weight of an element E in a specific substance P, designated A r (E, P). The CIAAW has changed the values of the standard atomic weights of five elements based on recent determinations of terrestrial isotopic abundances: Ar (argon): from 39.948 ± 0.001 to [39.792, 39.963] Hf (hafnium): from 178.49 ± 0.02 to 178.486 ± 0.006 Ir (iridium): from 192.217 ± 0.003 to 192.217 ± 0.002 Pb (lead): from 207.2 ± 0.1 to [206.14, 207.94] Yb (ytterbium): from 173.054 ± 0.005 to 173.045 ± 0.010 The standard atomic weight of argon and lead have changed to an interval to reflect that the natural variation in isotopic composition exceeds the measurement uncertainty of A r (Ar) and A r (Pb) in a specific substance. The standard atomic weights and/or the uncertainties of fourteen elements have been changed based on the Atomic Mass Evaluations 2016 and 2020 accomplished under the auspices of the International Union of Pure and Applied Physics (IUPAP). A r ° of Ho, Tb, Tm and Y were changed in 2017 and again updated in 2021: Al (aluminium), 2017: from 26.981 5385 ± 0.000 0007 to 26.981 5384 ± 0.000 0003 Au (gold), 2017: from 196.966 569 ± 0.000 005 to 196.966 570 ± 0.000 004 Co (cobalt), 2017: from 58.933 194 ± 0.000 004 to 58.933 194 ± 0.000 003 F (fluorine), 2021: from 18.998 403 163 ± 0.000 000 006 to 18.998 403 162 ± 0.000 000 005 (Ho (holmium), 2017: from 164.930 33 ± 0.000 02 to 164.930 328 ± 0.000 007) Ho (holmium), 2021: from 164.930 328 ± 0.000 007 to 164.930 329 ± 0.000 005 Mn (manganese), 2017: from 54.938 044 ± 0.000 003 to 54.938 043 ± 0.000 002 Nb (niobium), 2017: from 92.906 37 ± 0.000 02 to 92.906 37 ± 0.000 01 Pa (protactinium), 2017: from 231.035 88 ± 0.000 02 to 231.035 88 ± 0.000 01 Pr (praseodymium), 2017: from 140.907 66 ± 0.000 02 to 140.907 66 ± 0.000 01 Rh (rhodium), 2017: from 102.905 50 ± 0.000 02 to 102.905 49 ± 0.000 02 Sc (scandium), 2021: from 44.955 908 ± 0.000 005 to 44.955 907 ± 0.000 004 (Tb (terbium), 2017: from 158.925 35 ± 0.000 02 to 158.925 354 ± 0.000 008) Tb (terbium), 2021: from 158.925 354 ± 0.000 008 to 158.925 354 ± 0.000 007 (Tm (thulium), 2017: from 168.934 22 ± 0.000 02 to 168.934 218 ± 0.000 006) Tm (thulium), 2021: from 168.934 218 ± 0.000 006 to 168.934 219 ± 0.000 005 (Y (yttrium), 2017: from 88.905 84 ± 0.000 02 to 88.905 84 ± 0.000 01) Y (yttrium), 2021: from 88.905 84 ± 0.000 01 to 88.905 838 ± 0.000 002

Pure and Applied Chemistry↗
USGS2021

Insights on geochemical, isotopic, and volumetric compositions of produced water from hydraulically fractured Williston Basin oil wells

Tracing produced water origins from wells hydraulically fractured with freshwater-based fluids is sometimes predicated on assumptions that (1) each geological formation contains compositionally unique brine and (2) produced water from recently hydraulically fractured wells resembles fresher meteoric water more so than produced water from older wells. These assumptions are not valid in Williston Basin oil wells sampled in this study. Although distinct average 228 Ra/ 226 Ra ratios were found in water produced from the Bakken and Three Forks Formations, average δ 2 H, δ 18 O, specific gravity, and conductivity were similar but exhibited significant variability across five oil fields within each formation. Furthermore, initial produced water (“flowback”) was operationally defined based on the presence of glycol ether compounds and water from wells that had produced <56% of the amount of fluids injected and sampled within 160 days of fracturing. Flowback unexpectedly exhibited higher temperature, specific gravity, conductivity, δ 2 H, and δ 18 O, but lower oxidation–reduction potential and δ 11 B, relative to the wells thought to be producing formation brines (from wells with a produced-to-injected water ratio [PIWR] > 0.84 and sampled more than 316 days after fracturing). As such, establishing an overall geochemical and isotopic signature of produced water compositions based solely on chemical similarity to meteoric water and formation without the consideration of well treatments, well completion depth, or lateral location across the basin could be misleading if these signatures are assumed to be applicable across the entire basin. These findings have implications for using produced water compositions to understand the interbasin fluid flow and trace sources of hydraulic fracturing fluids.

Montana, North Dakota↗
USGS2021

Devils Hole calcite was precipitated at ±1°C stable aquifer temperatures during the last half million years

Subaqueous carbonates from the Devils Hole caves (southwestern USA) provide a continuous Holocene to Pleistocene North American paleoclimate record. The accuracy of this record relies on two assumptions: That carbonates precipitated close to isotope equilibrium and that groundwater temperature did not change significantly in the last 570 thousand years. Here, we investigate these assumptions using dual clumped isotope thermometry. This method relies on simultaneous analyses of carbonate ∆ 47 and ∆ 48 values and provides information on the existence and extent of kinetic isotope fractionation. Our results confirm the hypothesis that calcite precipitation occurred close to oxygen and clumped isotope equilibrium during the last half million years in Devils Hole. In addition, we provide evidence that aquifer temperatures varied by less than ±1°C during this interval. Thus, the Devils Hole calcite δ 18 O time series exclusively represents changes in groundwater δ 18 O values.

Nevada↗
USGS2021

USGS44, a new high-purity calcium carbonate reference material for δ13C measurements

Rationale The stable carbon isotopic ( δ 13 C) reference material (RM) LSVEC Li 2 CO 3 has been found to be unsuitable for δ 13 C standardization work because its δ 13 C value increases with exposure to atmospheric CO 2 . A new CaCO 3 RM, USGS44, has been prepared to alleviate this situation. Methods USGS44 was prepared from 8 kg of Merck high-purity CaCO 3 . Two sets of δ 13 C values of USGS44 were determined. The first set of values was determined by online combustion, continuous-flow (CF) isotope-ratio mass spectrometry (IRMS) of NBS 19 CaCO 3 ( δ 13 C VPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1‰), and LSVEC Li 2 CO 3 ( δ 13 C VPDB = −46.6 mUr exactly), and normalized to the two-anchor δ 13 C VPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI)-IRMS of CO 2 evolved by reaction of H 3 PO 4 with carbonates, corrected for cross contamination, and normalized to the single-anchor δ 13 C VPDB scale. Results USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-μg amounts. It has a δ 13 C VPDB-LSVEC value of −42.21 ± 0.05 mUr. Single-anchor δ 13 C VPDB values of −42.08 ± 0.01 and −41.99 ± 0.02 mUr were determined by DI-IRMS with corrections for cross contamination. Conclusions The new high-purity, well-homogenized calcium carbonate isotopic reference material USGS44 is stable and has a δ 13 C VPDB-LSVEC value of −42.21 ± 0.05 mUr for both EA/IRMS and DI-IRMS measurements. As a carbonate relatively depleted in 13 C, it is intended for daily use as a secondary isotopic reference material to normalize stable carbon isotope delta measurements to the δ 13 C VPDB-LSVEC scale. It is useful in quantifying drift with time, determining mass-dependent isotopic fractionation (linearity correction), and adjusting isotope-ratio-scale contraction. Due to its fine grain size (smaller than 63 μm), it is not suitable as a δ 18 O reference material. A δ 13 C VPDB-LSVEC value of −29.99 ± 0.05 mUr was determined for NBS 22 oil.

Rapid Communications in Mass Spectrometry↗