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1. A simple CO 2 equilibration method for measuring blood oxygen isotope compositions

   https://doi.org/10.1002/rcm.9256  

   Green, Daniel R. ; Olack, Gerard ; Tütken, Thomas ; Leichliter, Jennifer ; Winkler, Daniela E. ; Clauss, Marcus ; Vonhof, Hubert ; Colman, Albert S. ( February 2022 , Rapid Communications in Mass Spectrometry)

   Blood water oxygen isotope compositions can provide valuable insights into physiological processes and ecological patterns. While blood samples are commonly drawn for medical or scientific purposes, blood fractions are infrequently measured for oxygen isotopic compositions (δ¹⁸O) because such measurements are time consuming and expensive.

   We sampled blood from sheep, goats, and iguanas raised in field and animal laboratories into serum, EDTA, heparin, and uncoated plastic vials commonly used in medical and scientific research, then separated red blood cell (RBC) and plasma or serum blood fractions. These were injected into helium‐flushed Exetainer tubes where they naturally outgassed endogenous CO₂(goat blood), or into He‐ and CO₂‐flushed tubes (iguana blood). The CO₂gas was sampled on a GasBench II system, and δ¹⁸O was measured by an isotope ratio mass spectrometer (IRMS).

   Repeated δ¹⁸O measurements were stable over multiple days. The addition of desiccated blood solids to water standards had little impact on their δ¹⁸O measurements, suggesting that organic molecular constituents within blood serum and plasma do not interfere with blood water δ¹⁸O values. We observed slight but statistically significant δ¹⁸O offsets between plasma, serum and RBC fractions. Mass‐dependent body water turnover times for iguanas were derived from the data.

   We demonstrate that a simple blood‐CO₂equilibration method using the GasBench can quickly, reliably and accurately characterize water δ¹⁸O in the plasma, RBC, and whole blood fractions of mammalian and reptilian blood samples (precision ≤ 0.1‰). This method will expand the application of blood stable isotope analysis in physiological and medical research.

    

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2. Influence of sample volume on nitrate N and O isotope ratio analyses with the denitrifier method

   https://doi.org/10.1002/rcm.9224  

   Zhou, Mengyang ; Granger, Julie ; Chang, Bonnie X. ( December 2021 , Rapid Communications in Mass Spectrometry)

   Analyses of the isotope ratios of nitrogen (¹⁵N/¹⁴N) and oxygen (¹⁸O/¹⁶O) in nitrate (NO₃⁻) with the denitrifier method require relatively high sample volumes at low concentrations (≤1 μM) to afford sufficient analyte for mass spectrometry, resulting in isotopic offsets compared to more concentrated samples of the same isotopic composition.

   To uncover the origins of isotopic offsets, we analyzed the N and O isotope ratios of NO₃⁻reference materials spanning concentrations of 0.5–20 μM. We substantiated the incidence of volume‐dependent isotopic offsets, then investigated whether they resulted from (a) incomplete sample recovery during N₂O sparging, (b) blanks – bacterial, atmospheric, or in reference material solutions – and (c) oxygen atom exchange with water during the bacterial conversion of NO₃⁻to N₂O.

   Larger sample volumes resulted in modest offsets in δ¹⁵N, but substantial offsets in δ¹⁸O. N₂O recovery from sparging was less complete at higher volumes, resulting in decreases in δ¹⁵N and δ¹⁸O due to associated isotope fractionation. Blanks increased detectably with volume, whereas oxygen atom exchange with water remained constant within batch analyses, being sensitive to neither sample volume nor salinity. The sizeable offsets in δ¹⁸O with volume are only partially explained by the factors considered in our analysis.

   Our observations argue for bracketing of NO₃⁻samples with reference materials that emulate sample volumes (concentrations) to achieve improved measurement accuracy and foster inter‐comparability.

    

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3. Variability and Controls on δ 18 O, d‐excess, and ∆′ 17 O in Southern Peruvian Precipitation

   https://doi.org/10.1029/2020JD034009  

   Aron, Phoebe G. ; Poulsen, Christopher J. ; Fiorella, Richard P. ; Levin, Naomi E. ; Acosta, Rene P. ; Yanites, Brian J. ; Cassel, Elizabeth J. ( December 2021 , Journal of Geophysical Research: Atmospheres)

   The isotopic composition of precipitation is used to trace water cycling and climate change, but interpretations of the environmental information recorded in central Andean precipitation isotope ratios are hindered by a lack of multi‐year records, poor spatial distribution of observations, and a predominant focus on Rayleigh distillation. To better understand isotopic variability in central Andean precipitation, we present a three‐year record of semimonthly δ¹⁸O_pand δ²H_pvalues from 15 stations in southern Peru and triple oxygen isotope data, expressed as ∆′¹⁷O_p, from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with δ¹⁸O_pand that seasonal δ¹⁸O_pvariations are related to upstream rainout and local convection. Spatial δ¹⁸O_pvariations and atmospheric back trajectories show that both eastern‐ and western‐derived air masses bring precipitation to southern Peru. Seasonal d‐excess_pcycles record moisture recycling and relative humidity at remote moisture sources, and both d‐excess_pand ∆′¹⁷O_pclearly differentiate evaporated and non‐evaporated samples. These results begin to establish the natural range of unevaporated ∆′¹⁷O_pvalues in the central Andes and set the foundation for future paleoclimate and paleoaltimetry studies in the region. This study highlights the hydrologic understanding that comes from a combination of δ¹⁸O_p, d‐excess_p, and ∆′¹⁷O_pdata and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes.

    

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4. Determination of KGa‐1b and SHCa‐1 Δ′ 17 O and δ 18 O via Laser Fluorination of Lithium Fluoride Clay Pellets

   https://doi.org/10.1002/rcm.10021  

   Gagnon, Catherine A. ; Havel, Riley ; Chen, Jiquan ; Piccione, Gavin ; Ibarra, Daniel E. ( March 2025 , Rapid Communications in Mass Spectrometry)

   Stable oxygen isotope measurements in silicate clays, such as smectite and kaolinite, provide crucial information for understanding Earth's climate history and environmental changes. Despite a growing interest in the oxygen isotope analysis of silicate clays and clay‐rich sediments, there lacks a consensus on the preparation and standardization of clay mineral samples. To improve the accuracy and interlaboratory comparisons of clay isotope measurements, especially those involving laser fluorination techniques, newly established kaolinite and smectite oxygen isotope standards are much needed.

   We employed conventional nickel bomb fluorination combined with dual‐inlet isotope ratio mass spectrometry to establish precise δ¹⁸O and Δ′¹⁷O values for leached clay reference materials KGa‐1b and SHCa‐1, a kaolinite and a hectorite/smectite, respectively. We further measured leached KGa‐1b and SHCa‐1 pressed into pellets with a lithium fluoride as a binding agent for the laser fluorination method, allowing us to test the reproducibility between methods and utilize a standard laser chamber drift correction scheme.

   The laser fluorination technique yielded highly precise and reproducible δ¹⁸O and Δ′¹⁷O measurements for the KGa‐1b and SHCa‐1, aligning with bomb values of δ¹⁸O. This confirms the method's reliability and comparability to conventional isotope measurement techniques while also stressing the importance of proper sample preparation and laser chamber drift corrections.

   This study demonstrates that laser fluorination is an effective method for accurately measuring the stable oxygen isotope composition of silicate clays or clay‐rich sediments when corrected with known silicate clay standards. These methods offer a valuable methodology for future research and applications that will significantly improve our understanding of past climate and environmental conditions.

    

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5. Seasonal SIMS δ18O record in Astarte borealis from the Baltic Sea tracks a modern regime shift in the NAO

   https://doi.org/10.3389/fmars.2023.1293823  

   Hughes, Hunter P ; Surge, Donna ; Orland, Ian J ; Zettler, Michael L ; Moss, David K ( December 2023 , Frontiers in Marine Science)

   Astarte borealisholds great potential as an archive of seasonal paleoclimate, especially due to its long lifespan (several decades to more than a century) and ubiquitous distribution across high northern latitudes. Furthermore, recent work demonstrates that the isotope geochemistry of the aragonite shell is a faithful proxy of environmental conditions. However, the exceedingly slow growth rates ofA. borealisin some locations (<0.2mm/year) make it difficult to achieve seasonal resolution using standard micromilling techniques for conventional stable isotope analysis. Moreover, oxygen isotope (δ¹⁸O) records from species inhabiting brackish environments are notoriously difficult to use as paleoclimate archives because of the simultaneous variation in temperature and δ¹⁸O_watervalues.

   Here we use secondary ion mass spectrometry (SIMS) to microsample anA. borealisspecimen from the southern Baltic Sea, yielding 451 SIMS δ¹⁸O_shellvalues at sub-monthly resolution.

   SIMS δ¹⁸O_shellvalues exhibit a quasi-sinusoidal pattern with 24 local maxima and minima coinciding with 24 annual growth increments between March 1977 and the month before specimen collection in May 2001.

   Age-modeled SIMS δ¹⁸O_shellvalues correlate significantly with bothin situtemperature measured from shipborne CTD casts (r² = 0.52, p<0.001) and sea surface temperature from the ORAS5-SST global reanalysis product for the Baltic Sea region (r² = 0.42, p<0.001). We observe the strongest correlation between SIMS δ¹⁸O_shellvalues and salinity when both datasets are run through a 36-month LOWESS function (r² = 0.71, p < 0.001). Similarly, we find that LOWESS-smoothed SIMS δ¹⁸O_shellvalues exhibit a moderate correlation with the LOWESS-smoothed North Atlantic Oscillation (NAO) Index (r² = 0.46, p<0.001). Change point analysis supports that SIMS δ¹⁸O_shellvalues capture a well-documented regime shift in the NAO circa 1989. We hypothesize that the correlation between the SIMS δ¹⁸O_shelltime series and the NAO is enhanced by the latter’s influence on the regional covariance of water temperature and δ¹⁸O_watervalues on interannual and longer timescales in the Baltic Sea. These results showcase the potential for SIMS δ¹⁸O_shellvalues inA. borealisshells to provide robust paleoclimate information regarding hydroclimate variability from seasonal to decadal timescales.

    

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