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Tyler B. Coplen

Publications and source records attributed to Tyler B. Coplen.

At least 55 records · Page 3Linked to original sources
USGS2016

Antarctic ice-core water (USGS49) – A new isotopic reference material for δ2H and δ18O measurements of water

As a result of the scarcity of isotopic reference waters for daily use, a new secondary isotopic reference material for international distribution has been prepared from ice-core water from the Amundsen–Scott South Pole Station. This isotopic reference material, designated as USGS49, was filtered, homogenised, loaded into glass ampoules, sealed with a torch, autoclaved to eliminate biological activity and measured by dual-inlet isotope-ratio mass spectrometry. The δ 2 H and δ 18 O values of USGS49 are −394.7 ± 0.4 and −50.55 ± 0.04 mUr (where mUr = 0.001 = ‰), respectively, relative to VSMOW, on scales normalised such that the δ 2 H and δ 18 O values of SLAP reference water are, respectively, −428 and −55.5 mUr. Each uncertainty is an estimated expanded uncertainty ( U = 2 u c ) about the reference value that provides an interval that has about a 95% probability of encompassing the true value. This isotopic reference material is intended as one of two isotopic reference waters for daily normalisation of stable hydrogen and oxygen isotopic analysis of water with an isotope-ratio mass spectrometer or a laser absorption spectrometer. It is available by the case of 144 glass ampoules or as a set of sixteen glass ampoules containing 5 ml of water in each ampoule.

Geostandards and Geoanalytical Research↗
USGS2016

New organic reference materials for hydrogen, carbon, and nitrogen stable isotope-ratio measurements: caffeines, n-alkanes, fatty acid methyl esters, glycines, L-valines, polyethylenes, and oils

An international project developed, quality-tested, and determined isotope−δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope−δ scales. The RMs span a range of δ 2 H VSMOW-SLAP values from −210.8 to +397.0 mUr or ‰, for δ 13 C VPDB-LSVEC from −40.81 to +0.49 mUr and for δ 15 N Air from −5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C 16 n -alkanes, n -C 20 -fatty acid methyl esters (FAMEs), glycines, and l -valines, together with polyethylene powder and string, one n -C 17 -FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a 2 H-enriched vacuum oil. A total of 11 laboratories from 7 countries used multiple analytical approaches and instrumentation for 2-point isotopic normalization against international primary measurement standards. The use of reference waters in silver tubes allowed direct normalization of δ 2 H values of organic materials against isotopic reference waters following the principle of identical treatment. Bayesian statistical analysis yielded the mean values reported here. New RMs are numbered from USGS61 through USGS78, in addition to NBS 22a. Because of exchangeable hydrogen, amino acid RMs currently are recommended only for carbon- and nitrogen-isotope measurements. Some amino acids contain 13 C and carbon-bound organic 2 H-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies.

Analytical Chemistry↗
USGS2016

Atomic weights of the elements 2013 (IUPAC Technical Report)

The biennial review of atomic-weight determinations and other cognate data has resulted in changes for the standard atomic weights of 19 elements. The standard atomic weights of four elements have been revised based on recent determinations of isotopic abundances in natural terrestrial materials: cadmium to 112.414(4) from 112.411(8), molybdenum to 95.95(1) from 95.96(2), selenium to 78.971(8) from 78.96(3), and thorium to 232.0377(4) from 232.038 06(2). The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) also revised the standard atomic weights of fifteen elements based on the 2012 Atomic Mass Evaluation: aluminium (aluminum) to 26.981 5385(7) from 26.981 5386(8), arsenic to 74.921 595(6) from 74.921 60(2), beryllium to 9.012 1831(5) from 9.012 182(3), caesium (cesium) to 132.905 451 96(6) from 132.905 4519(2), cobalt to 58.933 194(4) from 58.933 195(5), fluorine to 18.998 403 163(6) from 18.998 4032(5), gold to 196.966 569(5) from 196.966 569(4), holmium to 164.930 33(2) from 164.930 32(2), manganese to 54.938 044(3) from 54.938 045(5), niobium to 92.906 37(2) from 92.906 38(2), phosphorus to 30.973 761 998(5) from 30.973 762(2), praseodymium to 140.907 66(2) from 140.907 65(2), scandium to 44.955 908(5) from 44.955 912(6), thulium to 168.934 22(2) from 168.934 21(2), and yttrium to 88.905 84(2) from 88.905 85(2). The Commission also recommends the standard value for the natural terrestrial uranium isotope ratio, N ( 238 U)/ N ( 235 U)=137.8(1).

Pure and Applied Chemistry↗
USGS2016

Isotopic compositions of the elements 2013 (IUPAC Technical Report)

The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) of the International Union of Pure and Applied Chemistry (iupac.org) has revised the Table of Isotopic Compositions of the Elements (TICE). The update involved a critical evaluation of the recent published literature. The new TICE 2013 includes evaluated data from the “best measurement” of the isotopic abundances in a single sample, along with a set of representative isotopic abundances and uncertainties that accommodate known variations in normal terrestrial materials.

Pure and Applied Chemistry↗
USGS2016

Updated atomic weights: Time to review our table

Despite common belief, atomic weights are not necessarily constants of nature. Scientists’ ability to measure these values is regularly improving, so one would expect that the accuracy of these values should be improving with time. It is the task of the IUPAC (International Union of Pure and Applied Chemistry) Commission on Isotopic Abundances and Atomic Weights (CIAAW) to regularly review atomic-weight determinations and release updated values. According to an evaluation published in Pure and Applied Chemistry [1], even the most simplified table abridged to four significant digits needs to be updated for the elements selenium and molybdenum. According to the most recent 2015 release of "Atomic Weights of the Elements" [2], another update is needed for ytterbium.

ChemistryViews Magazine↗
USGS2016

A new organic reference material, L-glutamic acid, USGS41a, for δ 13 C and δ 15 N measurements − a replacement for USGS41

Rationale The widely used l -glutamic acid isotopic reference material USGS41, enriched in both 13 C and 15 N, is nearly exhausted. A new material, USGS41a, has been prepared as a replacement for USGS41. Methods USGS41a was prepared by dissolving analytical grade l -glutamic acid enriched in 13 C and 15 N together with l -glutamic acid of normal isotopic composition. The δ 13 C and δ 15 N values of USGS41a were directly or indirectly normalized with the international reference materials NBS 19 calcium carbonate ( δ 13 C VPDB = +1.95 mUr, where milliurey = 0.001 = 1 ‰), LSVEC lithium carbonate ( δ 13 C VPDB = −46.6 mUr), and IAEA-N-1 ammonium sulfate ( δ 15 N Air = +0.43 mUr) and USGS32 potassium nitrate ( δ 15 N = +180 mUr exactly) by on-line combustion, continuous-flow isotope-ratio mass spectrometry, and off-line dual-inlet isotope-ratio mass spectrometry. Results USGS41a is isotopically homogeneous; the reproducibility of δ 13 C and δ 15 N is better than 0.07 mUr and 0.09 mUr, respectively, in 200-μg amounts. It has a δ 13 C value of +36.55 mUr relative to VPDB and a δ 15 N value of +47.55 mUr relative to N 2 in air. USGS41 was found to be hydroscopic, probably due to the presence of pyroglutamic acid. Experimental results indicate that the chemical purity of USGS41a is substantially better than that of USGS41. Conclusions The new isotopic reference material USGS41a can be used with USGS40 (having a δ 13 C VPDB value of −26.39 mUr and a δ 15 N Air value of −4.52 mUr) for (i) analyzing local laboratory isotopic reference materials, and (ii) quantifying drift with time, mass-dependent isotopic fractionation, and isotope-ratio-scale contraction for isotopic analysis of biological and organic materials. Published in 2016. This article is a U.S. Government work and is in the public domain in the USA.

Rapid Communications in Mass Spectrometry↗
USGS2016

Three whole-wood isotopic reference materials, USGS54, USGS55, and USGS56, for δ2H, δ13C, δ15N, and δ18O measurements

Comparative measurements of stable hydrogen and oxygen isotopes in wood are hampered by the lack of proper reference materials (RMs). The U.S. Geological Survey (USGS) has prepared three powdered, whole-wood RMs, USGS54 ( Pinus contorta , Canadian lodgepole pine), USGS55 ( Cordia cf. dodecandra , Mexican ziricote), and USGS56 ( Berchemia cf. zeyheri , South African red ivorywood). The stable isotopes of hydrogen, oxygen, carbon, and nitrogen in these RMs span ranges as δ 2 H VSMOW from –150.4 to –28.2 mUr or ‰, as δ 18 O VSMOW from + 17.79 to + 27.23 mUr, as δ 13 C VPDB from –27.13 to –24.34 mUr, and as δ 15 N AIR-N2 from –2.42 to + 1.8 mUr. These RMs will enable users to normalize measurements of wood samples to isotope–delta scales, and they are intended primarily for the normalization of δ 2 H and δ 18 O measurements of unknown wood samples. However, they also are suitable for normalization of stable isotope measurements of carbon and nitrogen in wood samples. In addition, these RMs are suitable for inter-laboratory calibration for the dual-water suilibration procedure for the measurements of δ 2 H VSMOW values of non-exchangeable hydrogen. The isotopic compositions with 1-σ uncertainties, mass fractions of each element, and fractions of exchangeable hydrogen of these materials are: USGS54 ( Pinus contorta , Canadian Lodgepole pine) δ 2 H VSMOW = –150.4 ± 1.1 mUr (n = 29), hydrogen mass fraction = 6.00 ± 0.04 % (n = 10) Fraction of exchangeable hydrogen = 5.4 ± 0.6 % (n = 29) δ 18 O VSMOW = + 17.79 ± 0.15 mUr (n = 18), oxygen mass fraction = 40.4 ± 0.2 % (n = 6) δ 13 C VPDB = –24.43 ± 0.02 mUr (n = 18), carbon mass fraction = 48.3 ± 0.4 % (n = 12) δ 15 N AIR- N2 = –2.42 ± 0.32 mUr (n = 17), nitrogen mass fraction = 0.05 % (n = 4) USGS55 ( Cordia cf. dodecandra , Mexican ziricote) δ 2 H VSMOW = –28.2 ± 1.7 mUr (n = 30), hydrogen mass fraction = 5.65 ± 0.06 % (n = 10) Fraction of exchangeable hydrogen = 4.1 ± 0.5 % (n = 30) δ 18 O VSMOW = + 19.12 ± 0.07 mUr (n = 18), oxygen mass fraction = 35.3 ± 0.2 % (n = 6) δ 13 C VPDB = –27.13 ± 0.02 mUr (n = 18), carbon mass fraction = 53.3 ± 0.6 % (n = 12) δ 15 N AIR-N2 = –0.3 ± 0.4 mUr (n = 16), nitrogen mass fraction = 0.25 % (n = 4) USGS56 ( Berchemia cf. zeyheri , South African red ivorywood) δ 2 H VSMOW = –44.0 ± 1.8 mUr (n = 30), hydrogen mass fraction = 5.65 ± 0.05 % (n = 10) Fraction of exchangeable hydrogen = 6.6 ± 0.3 % (n = 30) δ 18 O VSMOW = + 27.23 ± 0.03 mUr (n = 12), oxygen mass fraction = 41.1 ± 0.2 % (n = 6) δ 13 C VPDB = –24.34 ± 0.01 mUr (n = 12), carbon mass fraction = 47.3 ± 0.2 % (n = 12) δ 15 N AIR-N2 = + 1.8 ± 0.4 mUr (n = 15), nitrogen mass fraction = 0.27 % (n = 4)

Chemical Geology↗
USGS2016

A revision in hydrogen isotopic composition of USGS42 and USGS43 human-hair stable isotopic reference materials for forensic science

The hydrogen isotopic composition ( δ 2 H VSMOW-SLAP ) of USGS42 and USGS43 human hair stable isotopic reference materials, normalized to the VSMOW (Vienna-Standard Mean Ocean Water)–SLAP (Standard Light Antarctic Precipitation) scale, was originally determined with a high temperature conversion technique using an elemental analyzer (TC/EA) with a glassy carbon tube and glassy carbon filling and analysis by isotope-ratio mass spectrometer (IRMS). However, the TC/EA IRMS method can produce inaccurate δ 2 H VSMOW-SLAP results when analyzing nitrogen-bearing organic substances owing to the formation of hydrogen cyanide (HCN), leading to non-quantitative conversion of a sample into molecular hydrogen (H 2 ) for IRMS analysis. A single-oven, chromium-filled, elemental analyzer (Cr-EA) coupled to an IRMS substantially improves the measurement quality and reliability of hydrogen isotopic analysis of hydrogen- and nitrogen-bearing organic material because hot chromium scavenges all reactive elements except hydrogen. USGS42 and USGS43 human hair isotopic reference materials have been analyzed with the Cr-EA IRMS method, and the δ 2 H VSMOW-SLAP values of their non-exchangeable hydrogen fractions have been revised: where mUr = 0.001 = ‰. On average, these revised δ 2 H VSMOW-SLAP values are 5.7 mUr more positive than those previously measured. It is critical that readers pay attention to the δ 2 H VSMOW-SLAP of isotopic reference materials in publications as they may need to adjust the δ 2 H VSMOW–SLAP measurement results of human hair in previous publications to ensure all results are on the same isotope-delta scale.

Forensic Science International↗
USGS2016

Comment on “Reconciliation of the Devils Hole climate record with orbital forcing”

Moseley et al .’s (Reports, 8 January 2016, p. 165) preferred-Termination-II age is subjective, as evidenced by variation in their Termination-II ages of 2500 years per meter. Termination-II-age bias decreases to zero at ~1.5 meters below the present-day water table, if one assumes linear variation with core-sample height. Maintaining the required gradient of thorium isotope 230 Th over 3.6 meters for 1000 years, much less 10,000 years, seems exceedingly unlikely.

Science↗
USGS2015

LIMS for Lasers 2015 for achieving long-term accuracy and precision of δ2H, δ17O, and δ18O of waters using laser absorption spectrometry

Rationale Although laser absorption spectrometry (LAS) instrumentation is easy to use, its incorporation into laboratory operations is not easy, owing to extensive offline manipulation of comma-separated-values files for outlier detection, between-sample memory correction, nonlinearity ( δ -variation with water amount) correction, drift correction, normalization to VSMOW-SLAP scales, and difficulty in performing long-term QA/QC audits. Methods A Microsoft Access relational-database application, LIMS (Laboratory Information Management System) for Lasers 2015, was developed. It automates LAS data corrections and manages clients, projects, samples, instrument-sample lists, and triple-isotope ( δ 17 O, δ 18 O, and δ 2 H values) instrumental data for liquid-water samples. It enables users to (1) graphically evaluate sample injections for variable water yields and high isotope-delta variance; (2) correct for between-sample carryover, instrumental drift, and δ nonlinearity; and (3) normalize final results to VSMOW-SLAP scales. Results Cost-free LIMS for Lasers 2015 enables users to obtain improved δ 17 O, δ 18 O, and δ 2 H values with liquid-water LAS instruments, even those with under-performing syringes. For example, LAS δ 2 H VSMOW measurements of USGS50 Lake Kyoga (Uganda) water using an under-performing syringe having ±10 % variation in water concentration gave +31.7 ± 1.6 ‰ (2-σ standard deviation), compared with the reference value of +32.8 ± 0.4 ‰, after correction for variation in δ value with water concentration, between-sample memory, and normalization to the VSMOW-SLAP scale. Conclusions LIMS for Lasers 2015 enables users to create systematic, well-founded instrument templates, import δ 2 H, δ 17 O, and δ 18 O results, evaluate performance with automatic graphical plots, correct for δ nonlinearity due to variable water concentration, correct for between-sample memory, adjust for drift, perform VSMOW-SLAP normalization, and perform long-term QA/QC audits easily. Published in 2015. This article is a U.S. Government work and is in the public domain in the USA.

Rapid Communications in Mass Spectrometry↗
USGS2015

A new isotopic reference material for stable hydrogen and oxygen isotope-ratio measurements of water—USGS50 Lake Kyoga Water

Rationale As a result of the need for isotopic reference waters having high δ 2 H VSMOW-SLAP and δ 18 O VSMOW-SLAP values for daily use, especially for tropical and equatorial-zone freshwaters, a new secondary isotopic reference material for international distribution was prepared from water collected from Lake Kyoga, Uganda. Methods This isotopic reference lakewater was filtered through a membrane with 0.2-µm pore size, homogenized, loaded into glass ampoules that were sealed with a torch and autoclaved to eliminate biological activity, and measured by dual-inlet isotope-ratio mass spectrometry. This reference material is available in a case of 144 glass ampoules each containing 5 mL of water. Results The δ 2 H and δ 18 O values of this reference material are +32.8 ± 0.4 and +4.95 ± 0.02 mUr (milliurey = 0.001 = 1 ‰), respectively, relative to VSMOW, on scales normalized such that the δ 2 H and δ 18 O values of SLAP reference water are, respectively, −428 and −55.5 mUr. Each uncertainty is an estimated expanded uncertainty ( U  = 2 u c ) about the reference value that provides an interval that has about a 95 % probability of encompassing the true value. Conclusions This isotopic reference material, designated as USGS50, is intended as one of two reference waters for daily normalization of stable hydrogen and oxygen isotopic analysis of water with an isotope-ratio mass spectrometer or a laser absorption spectrometer, of use especially for isotope-hydrology laboratories analyzing freshwater samples from equatorial and tropical regions.

Lake Kyoga↗
USGS2015

On-line hydrogen-isotope measurements of organic samples using elemental chromium: An extension for high temperature elemental-analyzer techniques

The high temperature conversion (HTC) technique using an elemental analyzer with a glassy carbon tube and filling (temperature conversion/elemental analysis, TC/EA) is a widely used method for hydrogen isotopic analysis of water and many solid and liquid organic samples with analysis by isotope-ratio mass spectrometry (IRMS). However, the TC/EA IRMS method may produce inaccurate δ 2 H results, with values deviating by more than 20 mUr (milliurey = 0.001 = 1‰) from the true value for some materials. We show that a single-oven, chromium-filled elemental analyzer coupled to an IRMS substantially improves the measurement quality and reliability for hydrogen isotopic compositions of organic substances (Cr-EA method). Hot chromium maximizes the yield of molecular hydrogen in a helium carrier gas by irreversibly and quantitatively scavenging all reactive elements except hydrogen. In contrast, under TC/EA conditions, heteroelements like nitrogen or chlorine (and other halogens) can form hydrogen cyanide (HCN) or hydrogen chloride (HCl) and this can cause isotopic fractionation. The Cr-EA technique thus expands the analytical possibilities for on-line hydrogen-isotope measurements of organic samples significantly. This method yielded reproducibility values (1-sigma) for δ 2 H measurements on water and caffeine samples of better than 1.0 and 0.5 mUr, respectively. To overcome handling problems with water as the principal calibration anchor for hydrogen isotopic measurements, we have employed an effective and simple strategy using reference waters or other liquids sealed in silver-tube segments. These crimped silver tubes can be employed in both the Cr-EA and TC/EA techniques. They simplify considerably the normalization of hydrogen-isotope measurement data to the VSMOW-SLAP (Vienna Standard Mean Ocean Water-Standard Light Antarctic Precipitation) scale, and their use improves accuracy of the data by eliminating evaporative loss and associated isotopic fractionation while handling water as a bulk sample. The calibration of organic samples, commonly having high δ 2 H values, will benefit from the availability of suitably 2 H-enriched reference waters, extending the VSMOW-SLAP scale above zero.

Analytical Chemistry↗
USGS2015

Isotopic disproportionation during hydrogen isotopic analysis of nitrogen-bearing organic compounds

Rationale High-precision hydrogen isotope ratio analysis of nitrogen-bearing organic materials using high-temperature conversion (HTC) techniques has proven troublesome in the past. Formation of reaction products other than molecular hydrogen (H 2 ) has been suspected as a possible cause of incomplete H 2 yield and hydrogen isotopic fractionation. Methods The classical HTC reactor setup and a modified version including elemental chromium, both operated at temperatures in excess of 1400 °C, have been compared using a selection of nitrogen-bearing organic compounds, including caffeine. A focus of the experiments was to avoid or suppress hydrogen cyanide (HCN) formation and to reach quantitative H 2 yields. The technique also was optimized to provide acceptable sample throughput. Results The classical HTC reaction of a number of selected compounds exhibited H 2 yields from 60 to 90 %. Yields close to 100 % were measured for the experiments with the chromium-enhanced reactor. The δ 2 H values also were substantially different between the two types of experiments. For the majority of the compounds studied, a highly significant relationship was observed between the amount of missing H 2 and the number of nitrogen atoms in the molecules, suggesting the pyrolytic formation of HCN as a byproduct. A similar linear relationship was found between the amount of missing H 2 and the observed hydrogen isotopic result, reflecting isotopic fractionation. Conclusions The classical HTC technique to produce H 2 from organic materials using high temperatures in the presence of glassy carbon is not suitable for nitrogen-bearing compounds. Adding chromium to the reaction zone improves the yield to 100 % in most cases. The initial formation of HCN is accompanied by a strong hydrogen isotope effect, with the observed hydrogen isotope results on H 2 being substantially shifted to more negative δ 2 H values. The reaction can be understood as an initial disproportionation leading to H 2 and HCN with the HCN-hydrogen systematically enriched in 2 H by more than 50 ‰. In the reaction of HCN with chromium, H 2 and chromium-containing solid residues are formed quantitatively.

Rapid Communications in Mass Spectrometry↗
USGS2015

Categorisation of northern California rainfall for periods with and without a radar brightband using stable isotopes and a novel automated precipitation collector

During landfall of extratropical cyclones between 2005 and 2011, nearly 1400 precipitation samples were collected at intervals of 30-min time resolution with novel automated collectors at four NOAA sites in northern California [Alta (ATA), Bodega Bay (BBY), Cazadero (CZD) and Shasta Dam (STD)] during 43 events. Substantial decreases were commonly followed hours later by substantial increases in hydrogen isotopic composition ( δ 2 H VSMOW where VSMOW is Vienna Standard Mean Ocean Water) and oxygen isotopic composition ( δ 18 O VSMOW ) of precipitation. These variations likely occur as pre-cold frontal precipitation generation transitions from marine vapour masses having low rainout to cold cloud layers having much higher rainout (with concomitant brightband signatures measured by an S-band profiling radar and lower δ 2 H VSMOW values of precipitation), and finally to shallower, warmer precipitating clouds having lower rainout (with non-brightband signatures and higher δ 2 H VSMOW values of precipitation), in accord with ‘seeder–feeder’ precipitation. Of 82 intervals identified, a remarkable 100.5 ‰ decrease in δ 2 H VSMOW value was observed for a 21 January 2010 event at BBY. Of the 61 intervals identified with increases in δ 2 H VSMOW values as precipitation transitioned to shallower, warmer clouds having substantially less rainout (the feeder part of the seeder–feeder mechanism), a remarkable increase in δ 2 H VSMOW value of precipitation of 82.3 ‰ was observed for a 10 February 2007 event at CZD. All CZD and ATA events having δ 2 H VSMOW values of precipitation below −105 ‰ were atmospheric rivers (ARs), and of the 13 events having δ 2 H VSMOW values of precipitation below −80 ‰, 77 % were ARs. Cloud echo-top heights (a proxy for atmospheric temperature) were available for 23 events. The mean echo-top height is greater for higher rainout periods than that for lower rainout periods in 22 of the 23 events. The lowest δ 2 H VSMOW of precipitation of 28 CZD events was −137.9 ‰ on 16 February 2009 during an AR with cold precipitating clouds and very high rainout with tops >6.5 km altitude. An altitude effect of −2.5 ‰ per 100 m was measured from BBY and CZD δ 2 H VSMOW data and of −1.8 ‰ per 100 m for CZD and ATA δ 2 H VSMOW data. We present a new approach to categorise rainfall intervals using δ 2 H VSMOW values of precipitation and rainfall rates. We term this approach the algorithmic-isotopic categorisation of rainfall, and we were able to identify higher rainout and/or lower rainout periods during all events in this study. We conclude that algorithmic-isotopic categorisation of rainfall can enable users to distinguish between tropospheric vapour masses having relatively high rainout (typically with brightband rain and that commonly are ARs) and vapour masses having lower rainout (commonly with non-brightband rain).

California↗
USGS2015

Normalization of stable isotope data for carbonate minerals: implementation of IUPAC guideline

Carbonate minerals provide a rich source of geochemical information because their δ 13 C and δ 18 O values provide information about surface and subsurface Earth processes. However, a significant problem is that the same δ 18 O value is not reported for the identical carbonate sample when analyzed in different isotope laboratories in spite of the fact that the International Union of Pure and Applied Chemistry (IUPAC) has provided reporting guidelines for two decades. This issue arises because (1) the δ 18 O measurements are performed on CO 2 evolved by reaction of carbonates with phosphoric acid, (2) the acid-liberated CO 2 is isotopically fractionated (enriched in 18 O) because it contains only two-thirds of the oxygen from the solid carbonate, (3) this oxygen isotopic fractionation factor is a function of mineralogy, temperature, concentration of the phosphoric acid, and δ 18 O value of water in the phosphoric acid, (4) researchers may use any one of an assortment of oxygen isotopic fractionation factors that have been published for various minerals at various reaction temperatures, and (5) it sometimes is not clear how one should calculate δ 18 O VPDB values on a scale normalized such that the δ 18 O value of SLAP reference water is −55.5 ‰ relative to VSMOW reference water. To enable researchers worldwide to publish the same δ 18 O value (within experimental uncertainty) for the same carbonate sample, we have re-evaluated reported acid fractionation factors for calcite at 25, 50, and 75 °C and propose a revised relation for the temperature dependence of oxygen isotopic acid fractionation factor, α CO 2 ( ACID ) -calcite αCO2(ACID)-calcite , of 1000ln α CO 2 ( ACID ) -calcite=3.48(10 3 /T)-1.47 1000lnαCO2(ACID)-calcite=3.48(103/T)-1.47 Turn MathJax on where T is temperature in kelvin. At 25 °C, α CO 2 ( ACID ) -calcite=1.01025 αCO2(ACID)-calcite=1.01025 , the most commonly accepted value for this quantity. We propose a normalization protocol in which (1) the internationally distributed carbonate isotopic reference materials NBS 18 and NBS 19 are interspersed among carbonate samples analyzed by treatment with phosphoric acid, (2) the δ 18 O values of the calcite reference materials and the carbonate samples are calculated, respectively, by using the α CO 2 ( ACID ) -calcite αCO2(ACID)-calcite relation above and oxygen-isotope acid fractionation factors appropriate for the sample mineralogy and reaction temperature, (3) the δ 18 O values of solid carbonate samples are determined on the VPDB scale ( δ 18 O VPDB ) with IUPAC-recommended scale expansion such that the δ 18 O of SLAP reference water is −55.5 ‰ relative to VSMOW reference water by normalizing δ 18 O values of carbonate samples with 2014-IUPAC-recommended δ 18 O values of NBS 18 and NBS 19, and (4) δ 18 O values on the VPDB scale are converted to δ 18 O values on the VSMOW-SLAP scale by using IUPAC recommendations. To ease calculations in the protocol, a software application titled “Carbon and Oxygen Isotopic Normalization Tool for Carbonates” is available that relies upon IUPAC-recommended δ 13 C and δ 18 O values of carbonate isotopic reference materials ( http://isotopes.usgs.gov/research/topics/carbonatesnormalizationtool.html ).

Geochimica et Cosmochimica Acta↗
USGS2015

Beyond temperature: Clumped isotope signatures in dissolved inorganic carbon species and the influence of solution chemistry on carbonate mineral composition

“Clumped-isotope” thermometry is an emerging tool to probe the temperature history of surface and subsurface environments based on measurements of the proportion of 13 C and 18 O isotopes bound to each other within carbonate minerals in 13 C 18 O 16 O 2 2- groups (heavy isotope “clumps”). Although most clumped isotope geothermometry implicitly presumes carbonate crystals have attained lattice equilibrium (i.e., thermodynamic equilibrium for a mineral, which is independent of solution chemistry), several factors other than temperature, including dissolved inorganic carbon (DIC) speciation may influence mineral isotopic signatures. Therefore we used a combination of approaches to understand the potential influence of different variables on the clumped isotope (and oxygen isotope) composition of minerals. We conducted witherite precipitation experiments at a single temperature and at varied pH to empirically determine 13 C- 18 O bond ordering (Δ 47 ) and δ 18 O of CO 3 2- and HCO 3 - molecules at a 25 °C equilibrium. Ab initio cluster models based on density functional theory were used to predict equilibrium 13 C- 18 O bond abundances and δ 18 O of different DIC species and minerals as a function of temperature. Experiments and theory indicate Δ 47 and δ 18 O compositions of CO 3 2- and HCO 3- ions are significantly different from each other. Experiments constrain the Δ 47- δ 18 O slope for a pH effect (0.011 ± 0.001; 12 ⩾ pH ⩾ 7). Rapidly-growing temperate corals exhibit disequilibrium mineral isotopic signatures with a Δ 47- δ 18 O slope of 0.011 ± 0.003, consistent with a pH effect. Our theoretical calculations for carbonate minerals indicate equilibrium lattice calcite values for Δ 47 and δ 18 O are intermediate between HCO 3 − and CO 3 2− . We analyzed synthetic calcites grown at temperatures ranging from 0.5 to 50 °C with and without the enzyme carbonic anhydrase present. This enzyme catalyzes oxygen isotopic exchange between DIC species and is present in many natural systems. The two types of experiments yielded statistically indistinguishable results, and these measurements yield a calibration that overlaps with our theoretical predictions for calcite at equilibrium. The slow-growing Devils Hole calcite exhibits Δ 47 and δ 18 O values consistent with lattice equilibrium. Factors influencing DIC speciation (pH, salinity) and the timescale for DIC equilibration, as well as reactions at the mineral–solution interface, have the potential to influence clumped-isotope signatures and the δ 18 O of carbonate minerals. In fast-growing carbonate minerals, solution chemistry may be an important factor, particularly over extremes of pH and salinity. If a crystal grows too rapidly to reach an internal equilibrium (i.e., achieve the value for the temperature-dependent mineral lattice equilibrium), it may record the clumped-isotope signature of a DIC species (e.g., the temperature-dependent equilibrium of HCO 3 − ) or a mixture of DIC species, and hence record a disequilibrium mineral composition. For extremely slow-growing crystals, and for rapidly-grown samples grown at a pH where HCO 3 - dominates the DIC pool at equilibrium, effects of solution chemistry are likely to be relatively small or negligible. In summary, growth environment, solution chemistry, surface equilibria, and precipitation rate may all play a role in dictating whether a crystal achieves equilibrium or disequilibrium clumped-isotope signatures.

Geochimica et Cosmochimica Acta↗
USGS2014

Biscayne aquifer drinking water (USGS45): a new isotopic reference material for δ 2 H and δ 18 O measurements of water

RATIONALE As a result of the scarcity of isotopic reference waters for daily use, a new secondary isotopic reference material for international distribution has been prepared from drinking water collected from the Biscayne aquifer in Ft. Lauderdale, Florida. METHODS This isotopic reference water was filtered, homogenized, loaded into glass ampoules, sealed with a torch, autoclaved to eliminate biological activity, and measured by dual-inlet isotope-ratio mass spectrometry. This reference material is available by the case of 144 glass ampoules containing either 4 mL or 5 mL of water in each ampoule. RESULTS The δ 2 H and δ 18 O values of this reference material are –10.3 ± 0.4 ‰ and –2.238 ± 0.011 ‰, respectively, relative to VSMOW, on scales normalized such that the δ 2 H and δ 18 O values of SLAP reference water are, respectively, –428 and –55.5 ‰. Each uncertainty is an estimated expanded uncertainty ( U  = 2 u c ) about the reference value that provides an interval that has about a 95 % probability of encompassing the true value. CONCLUSIONS This isotopic reference material, designated as USGS45, is intended as one of two isotopic reference waters for daily normalization of stable hydrogen and oxygen isotopic analysis of water with an isotope-ratio mass spectrometer or a laser absorption spectrometer.

Rapid Communications in Mass Spectrometry↗
USGS2014

Caution on the use of NBS 30 biotite for hydrogen-isotope measurements with on-line high-temperature conversion systems

RATIONALE The supply of NBS 30 biotite is nearly exhausted. During measurements of NBS 30 and potential replacements, reproducible δ 2 H VSMOW-SLAP values could not be obtained by three laboratories using high-temperature conversion (HTC) systems. The cause of this issue has been investigated using the silver-tube technique for hydrogen-isotope measurements of water. METHODS The δ 2 H VSMOW-SLAP values of NBS 30 biotite, other biotites, muscovites, and kaolinite with different particle sizes, along with IAEA-CH-7 polyethylene, and reference waters and NBS 22 oil that were sealed in silver-tube segments, were measured. The effect of absorbed water on mineral surfaces was investigated with waters both enriched and depleted in 2 H. The quantitative conversion of hydrogen from biotite into gaseous hydrogen as a function of mass and particle size was also investigated. RESULTS The δ 2 H VSMOW-SLAP values of NBS 30 obtained by three laboratories were as much as 21 ‰ too high compared with the accepted value of −65.7 ‰, determined by conventional off-line measurements. The experiments showed a strong correlation between grain size and the δ 2 H VSMOW-SLAP value of NBS 30 biotite, but not of biotites with lower iron content. The δ 2 H VSMOW-SLAP values of NBS 30 as a function of particle size show a clear trend toward −65.7 ‰ with finer grain size. CONCLUSIONS Determination of the δ 2 H VSMOW-SLAP values of hydrous minerals and of NBS 30 biotite by on-line HTC systems coupled to isotope-ratio mass spectrometers may be unreliable because hydrogen in this biotite may not be converted quantitatively into molecular hydrogen. Extreme caution in the use and interpretation of δ 2 H VSMOW-SLAP on-line measurements of hydrous minerals is recommended.

Rapid Communications in Mass Spectrometry↗