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At least 577 records · Page 32Linked to original sources

USGS2026

Interplanetary electric fields for extreme magnetic storms

Using a list of sudden-commencement storms, the ring-current index, and 1-h near-Earth solar-wind measurements from solar cycles 20–25, we develop extreme-value statistical models relating storm intensity 𝐷 =max⁡{−𝐷⁢𝑠⁢𝑡} to the storm main-phase maximum duskward interplanetary electric field 𝐸 . The conditional relationship 𝐷|𝐸 is demonstrably sublinear—linear models are confidently rejected—indicating saturation of magnetospheric response under extreme solar-wind forcing. An event like that of July 2012 ( 𝐸 =69.6 mV/m), if Earth-directed, would be associated with a median storm intensity of 𝐷 =49⁢5 648 378 nT. Storms comparable to March 1989 ( 𝐷 =594 nT) correspond to electric fields of 𝐸 =5⁢4 76 39 mV/m, while Carrington-class storms ( 𝐷 =964 nT) correspond to 𝐸 =9⁢5 133 68 mV/m—substantially lower than several previous estimates. These results indicate that solar-wind conditions capable of driving extremely intense magnetic storms are less exceptional, and potentially more frequent, than previously thought.

Geophysical Research Letters↗

USGS2026

Stream temperature variability in headwater beaver dam complexes in relation to hydrologic and environmental factors

Beaver modify hydrological regimes and have the ability to both increase water storage and alter stream temperatures. For these reasons, beaver translocation and the construction of human engineered beaver-dam analogs (BDAs) have become popular tools for climate-change adaptation. However, there is a lack of understanding about how beaver engineering affects stream temperature. The results from previous studies vary considerably and the drivers of the discrepancies remain unclear. We investigated the longitudinal and vertical variation of stream temperature in and around 24 sites consisting of one or more beaver ponds across 17 headwater streams around the Methow and Okanogan river valleys of Washington State (USA). We then explored possible hydrologic and environmental drivers of observed thermal patterns. Despite considerable variation, we found that beaver ponds were often associated with an increase in downstream temperatures. The magnitude of this effect increased with total pond hydraulic height, which was directly related to the number and size of ponds per site. We also found that pond bottoms were cooler than upstream inflow sites for a period of time in the afternoon. Thus, although beaver dam complexes in the Methow River watershed do not consistently cool streams—and in fact often increase downstream temperatures—the bottoms of beaver ponds can create relatively cool water areas during the hottest part of the day. Furthermore, if managers choose to use beaver translocation or BDAs, locations with topography that would result in deeper ponds with more canopy cover may limit negative temperature effects on coldwater aquatic biota.

Washington↗

USGS2026

Conservation enhances resilience of the United States Duck Factory as environmental shifts may diminish landscape-scale waterfowl breeding capacity

Wetlands in the U.S. Prairie Pothole Region (USPPR) provide habitat for an estimated 5 million breeding ducks and remain a focal point for North American waterfowl conservation. After decades of investment, almost 20% of the USPPR is protected by some form of wetland or grassland conservation. We synthesized four decades of modeling studies aimed at understanding how environmental change may impact duck populations. We built upon past modeling efforts by applying an integrated scenario-based approach to inform wetland-waterfowl conservation planning. By century’s end, all scenarios projected declines (27%–53%) in breeding duck abundance in the USPPR. Despite these declines, areas in the USPPR with higher rates of protection and wetland density will likely continue to support the most breeding ducks, indicating resilient conservation planning. Our findings underscore the benefits of interdisciplinary efforts that can inform complex conservation decision-making in the face of environmental uncertainty.

Iowa, Minnesota, Montana, North Dakota, South Dako↗

USGS2026

Pliocene (Piacenzian) planktic foraminiferal biogeography: Insights into how planktic biogeography is linked to climate and socioeconomic impacts on marine ecosystems

The Piacenzian Age (3.60–2.58 Ma) of the Pliocene Epoch was characterized by globally warmer climates, higher sea levels, and atmospheric CO 2 similar to present. Utilizing a robust dataset of 2,101 samples and over 637,000 foraminifer specimens from 77 deep-sea core sites worldwide, we document planktic foraminifer biogeography and biodiversity during the mid-Piacenzian Warm Period (mPWP). Cluster analysis and multidimensional scaling reveal five major bioregions: tropical, warm subtropical, transitional, polar, and a distinct North Atlantic polar bioregion. Each bioregion was dominated by characteristic species with well-established temperature preferences. Analyses demonstrate higher species richness and evenness in low and mid-latitudes, with increased diversity associated with periods of climatic warming and poleward expansion of warm water assemblages. The long-term stability of biogeographic patterns underscores ecological conservatism but also highlights potential vulnerability to rapid anthropogenic climate change. Our findings emphasize the critical role of planktic foraminifers in reconstructing past ocean conditions and offer valuable insights into links between planktic biogeography, climate, and socioeconomic impacts on marine ecosystems. This work advances our understanding of marine ecosystem responses to climate extremes and provides a foundation for future regional and temporal analyses of planktic foraminifer biogeography under global change scenarios.

Frontiers in Earth Science↗

USGS2026

The geologic history of the Chehalis Forearc Basin, Washington State, USA

The Chehalis basin is located between the Cascade arc and the Coast Range in southwest Washington State. It consists of sedimentary and volcanic rocks deposited throughout the Cenozoic and is underlain by the Siletzia terrane, a thick, large igneous province accreted in the Eocene. Here, we constrain evolution of the Chehalis basin depocenter using isochore maps derived from isostatic gravity anomalies, borehole data, and stratigraphy for several time periods: the Eocene (47.6–36.8 Ma), the Oligocene (36.8–20 Ma), and the Neogene (20–0 Ma). Our results suggest that local subsidence is driven by deformation on faults that bound and intersect the basin. We see northward depocenter migration, interpreted as a shift in deformation from the northwest striking Cedar Creek fault to the west striking Doty fault. We interpret these data in terms of the long-term north-south shortening and clockwise rotation of the Cascadia forearc. During the Eocene, the Cedar Creek fault was preferentially aligned with north-south shortening, but became less active when clockwise rotation brought the Doty fault into east-west alignment with the stress field. Sediment accumulation rates decreased from 196 m/Myr in the Paleogene (∼40–20 Ma) to 27 m/Myr in the Neogene (∼20–0 Ma) as Miocene uplift of the Coast Range limited accommodation space and shifted the depositional environment from marine to fluvial. Our results are consistent with the geologic evolution of the Portland and Tualatin basins to the south and reveal a depositional and structural history uniquely shaped by clockwise rotation of the Cascadia forearc.

Washington↗

USGS2026

Conflicts and collisions with an endangered carnivore: Landscape drivers and spatial risk pattern

Human–wildlife conflicts and anthropogenic mortality are expected to increase with the continuous encroachment on natural habitats within and around protected areas, yet the processes governing these risks remain poorly understood. We investigated the spatiotemporal dynamics and drivers of two distinct processes involving the endangered Florida panther ( Puma concolor coryi ; hereafter, panther): (1) direct human–panther interactions and livestock depredation (hereafter, conflicts), and (2) vehicle collisions (hereafter, collisions). Using long-term data collected between 2006 and 2022 within the panther's breeding range in Southwest Florida, USA, we applied dynamic occupancy models to estimate probabilities of occurrence, colonization, and extinction of conflicts and collisions while accounting for imperfect detection. A total of 277 conflicts and 239 collisions were recorded during the study period. Occurrence probabilities for both conflicts and collisions increased during the early years of the study and subsequently stabilized. Landscape configuration consistently showed strong associations with both processes. Conflicts were more likely in areas with fragmented but closely spaced habitat patches, whereas collisions were more likely along road segments characterized by connected landscapes with low resistance to panther movement. In contrast, areas that showed greater distances between habitat patches and increased proportions of protected area were associated with lower probabilities of conflict or collision persistence over time. A predictive map was created to highlight areas with high probability of conflict and road segments with high probability of collision in Southwest Florida, USA. Identifying areas with elevated risk can inform targeted mitigation strategies, including habitat management, wildlife crossings, and outreach efforts, and further support long-term coexistence between humans and large carnivore populations.

Florida↗

USGS2026

Ecogeomorphologic response of a tidally restricted salt marsh to tidal restoration and sea-level rise

Diked marshes with decades of restricted tidal flow exhibit fundamentally altered hydrologic and ecologic dynamics that result in limited vertical accretion, land subsidence, and underdeveloped tidal channels. These changes complicate marsh restoration efforts and constrain the marsh's ability to build elevation in response to future sea levels. In this study, we developed an integrated hydrodynamic and marsh accretion model to conduct the first assessment of the restoration potential of a diked marsh in response to reintroduction of tidal flow and sea-level rise (SLR). We applied our model to evaluate changes in biomass production in the Herring River estuary, Cape Cod, MA, USA—which has experienced significant ecological shifts due to more than a century of tidal restriction—in response to a range of SLR scenarios, tidal flow conditions, management interventions, and biomass production rates through 2100. We found that with restoration of tidal flow, the simulated marsh extent expanded in areas with efficient drainage, increasing biomass production by up to 4.4 times. However, when SLR was imposed, parts of the marsh gradually transitioned to open water, leading to a decline in marsh coverage from 19% to as low as 12%. Management interventions aimed at enhancing marsh elevation and improving the drainage capacity of tidal channels slowed marsh loss, supporting marsh area through 2100. Our findings provide insight into the key drivers of marsh resilience and loss, and our approach can be applied across tidally restricted and restored systems to develop targeted, adaptive restoration strategies that achieve desired ecological outcomes.

Massachusetts↗

USGS2026

Restoration is a partial but not complete solution for long-term declines in oyster populations—A case history from the northeastern Gulf of America

Objective We sought to evaluate whether oyster reef restoration is associated with sustained increases in intertidal eastern oyster Crassostrea virginica density in Suwannee Sound, Florida, and to examine how commercial fishing activity and freshwater discharge may modify those patterns. Methods We monitored intertidal oyster reefs for 14 years, including 9 years prior to large-scale restoration (completed in 2018) and 5 years of standardized postrestoration monitoring beginning in 2019 at Lone Cabbage Reef, an offshore intertidal reef complex that was rebuilt to target elevation using dolomite limestone. A Bayesian negative-binomial generalized linear mixed model framework estimated oyster densities while accounting for spatial differences among inshore, nearshore, and offshore reefs; variation in transect length; and temporal variability. We assessed restoration effectiveness via repeated-measures monitoring of fixed restored sites and landscape-scale comparisons of restored versus unrestored reefs. We evaluated covariates of management interest—commercial fishing activity and river discharge—using model comparison and posterior predictions of oyster density at observed covariate values. Results Restoration produced large per-area gains in live-oyster density on offshore reefs. At four fixed restored offshore stations, mean densities rose from near 0 to 91 oysters/m 2 (95% credible interval [CrI] = 43–185) within 6 months and reached 244 oysters/m 2 (95% CrI = 134–433) by year 5 at fixed restoration stations. At the broader landscape scale, restored offshore reefs averaged about 83 oysters/m 2 (95% CrI = 26–157) across sites and postrestoration periods, whereas model-based estimates for restored offshore reefs reached 218 oysters/m 2 (95% CrI = 128–366) in the final sampling period. Conclusions Restoring reef substrate rebuilt the physical capacity for oysters to persist and grow at Lone Cabbage Reef, yielding sustained density gains that degraded sites did not achieve on their own. Harvest status and river discharge showed weak, inconsistent associations once restoration was included, consistent with the interpretation that oyster cultch provides structural capacity, while environmental and fishing conditions modulate around it. Rebuilding and conserving oyster cultch constitute the essential first step to repair and sustain degraded oyster reefs; fishing regulations or favorable environmental conditions alone are unlikely to replace the need for reef structure.

Florida↗

USGS2026

Across-track tilt concept for sun glint mitigation in future Earth-observing missions

Sun glint is a major limitation for spaceborne optical remote sensing of aquatic environments, particularly in tropical and subtropical regions. By dominating the at-sensor radiance, sun glint complicates atmospheric correction and reduces the quality of aquatic reflectance products derived across Earth observation missions. This study presents a machine learning framework to quantify sun glint probability and evaluates the across-track tilt observational concept as a potential sun glint mitigation approach for satellite remote sensing missions. More than 14,000 cloud-free Landsat 8 and 9 scenes were analyzed to quantify glint occurrence as a function of sun-sensor geometry, latitude, and season. Logistic regression and machine learning models identified solar zenith angle (SZA), wind speed, and viewing zenith angle (VZA) as the primary predictors of sun glint probability, achieving >98% classification accuracy. Sun glint contamination was found to be negligible for SZA > 40° but frequent at SZA <35°, particularly in forward-scattering geometries. Introducing a 3° across-track westward tilt reduces the proportion of glint-contaminated pixels by ~21% in tropical and subtropical regions, while larger tilts of 6°, 9°, and 12° yield reductions of 43%, 59%, and 74%, respectively. These findings underscore the value of incorporating glint mitigation strategies in future Earth observing mission designs. A modest across-track tilt, combined with post-acquisition glint detection and correction, offers a practical pathway to increasing the availability of high-quality aquatic observations for monitoring inland and coastal water quality and ecosystems.

IEEE Transactions on Geoscience and Remote Sensing↗

USGS2026

Long-term aridity shapes grassland drought resistance and modulates the roles of plant diversity and functional composition

Understanding the drivers of plant community stability is crucial for predicting ecosystem responses to extreme drought events. In grasslands, drought resistance supports the maintenance of key functions such as above-ground primary productivity, making the identification of resistance drivers essential to guide management under climate change. Proposed factors contributing to grassland stability include multiple diversity facets, functional traits and long-term climate, but most assessments focus on temporal invariability under historical disturbance regimes, leaving mechanisms of extreme drought resistance and their variation across climatic contexts relatively underexplored. Here, we analysed data from 54 grassland sites of the International Drought Experiment to examine the resistance of above-ground net primary productivity to a short-term (i.e. 1 year) extreme drought. We investigated the relative importance and joint influence of functional composition (i.e. community-weighted means of leaf and root traits), plant diversity facets (taxonomic, functional and phylogenetic) and climate (aridity and rainfall variability) on drought resistance. We used structural equation models to disentangle direct, indirect, and moderating pathways linking these drivers to drought resistance. Long-term aridity appeared as one of the most important drivers of grassland resistance to drought, with more arid sites showing lower resistance. Moreover, aridity impacted resistance through indirect effects by shaping functional composition and plant diversity, and by moderating the influence of plant diversity and functional composition. Functional composition related to dehydration avoidance and dehydration tolerance was also positively associated with resistance, while diversity had a weaker relationship with resistance, mostly through functional and phylogenetic facets. Interannual rainfall variability also influenced resistance, with different effects in more arid versus humid and less arid sites. Synthesis . Widely studied stability drivers such as plant diversity and functional composition have only partial explanatory power for short-term drought resistance of above-ground productivity in grasslands at a global scale. The abiotic context, particularly long-term aridity, is crucial for understanding ecosystem responses to rainfall variation and can improve predictive models for advancing the study of ecosystem resistance to drought. Along with management practices that target high species diversity or specific traits, restoration and conservation practices should support vulnerable sites experiencing high aridity

Journal of Ecology↗

USGS2026

Computing flow-field distortion coefficients from well-construction and formation properties

Direct measurements of groundwater velocity made with borehole flowmeters in screened wells must be compensated for the effects of flow-field distortion (also known as borehole acceleration). A theoretical equation developed by Drost et al. (1968) and simple inputs describing hydraulic properties of well construction and geologic formation were programmed into an Excel workbook to facilitate computation by groundwater-flowmeter users. Tables describing the physical and hydraulic properties for well constructions and gravel pack media are provided with an example to facilitate use of the workbook. Groundwater flowlines converge or diverge as they pass from a geologic formation, through a gravel pack and well screen. The extent of flowline convergence or divergence and the value of the flow-field distortion coefficient is related to the relative changes in hydraulic conductivity of the well screen, gravel pack, and geologic formation. Convergence or divergence is accompanied by acceleration or deceleration of groundwater. Direct measurements of groundwater velocity at the center of the monitoring well can be adjusted to provide a more accurate estimate of velocity in the formation by applying a correction for flow-field distortion. Variables required to compute the flow-field distortion coefficient include the hydraulic conductivity of the gravel pack, well screen, and the geologic formation surrounding the well screen; the borehole radius, and the inside radius and outside radius of the well screen.

Groundwater↗

USGS2026

Lunar-VISE landing site selection and characterization at Mons Gruithuisen Gamma

The Lunar Vulkan Imaging and Spectroscopy Explorer (Lunar-VISE) was selected for a Commercial Lunar Payload Services (CLPS) delivery to the Gruithuisen domes region of the Moon as part of NASA’s Payloads and Research Investigation on the Surface of the Moon (PRISM) program. The Gruithuisen domes are chemically and morphologically distinct from their surroundings with a thorium-rich, silicic composition. The Lunar-VISE instrument payload is designed to investigate the compositional and thermophysical properties of dome materials in order to understand how late-stage silicic volcanism occurred on the Moon. Selection of a landing site required balancing science and exploration goals with the safety requirements for landing and rover trafficability. Science required access to boulders, potential exposures of bedrock, and if possible, rover access to the dome edge to enable observations of the surrounding maria. Safety considerations included landing hazards, maintenance of line-of-sight communications between the lander and rover, and any early morning or late afternoon shadows that would limit the mission duration. After consideration of several candidate landing sites, a 100-meter diameter landing ellipse centered on 36.45715° N, 319.20398° E, was selected near the edge of a topographic step and blocky ejecta crater (recently named Mareta) near the summit of Mons Gruithuisen Gamma. This location enables access to a field of boulders excavated by a relatively fresh impact providing a diversity of boulders for investigations, as well as views to the surrounding mare and Mons Gruithuisen Delta dome off of the dome edge via only a short rover traverse outside the landing ellipse (traverse < 100 m) while meeting safety requirements in accord with the CLPS risk posture.

Planetary Science Journal↗

USGS2026

A cross-site comparison of ecosystem- and plot-scale methane fluxes across multiple sites

Wetland and upland ecosystems play significant but opposing roles in the global methane (CH 4 ) budget, acting as natural sources and sinks, respectively. Two of the most common approaches for measuring CH 4 fluxes (FCH 4 ) are chambers, which measure fluxes at fine spatial scales (ca. 1 m 2 ), and eddy covariance (EC) towers, which integrate fluxes across larger footprints (ca. 100–10 000 m 2 ). Although chamber and EC observations have been combined in various syntheses and databases to estimate CH 4 budgets, a unified cross-site evaluation of FCH 4 estimates at plot and ecosystem scales is lacking. As a first step toward a systematic spatiotemporal scaling of EC tower and chamber footprints, we quantified differences in site-level aggregate FCH 4 between EC and chamber measurements ( Δ FCH 4 ) across ten wetland and upland sites at half-hourly, hourly, daily, weekly, monthly, and annual timescales. We found that ecosystem-scale median FCH 4 was consistently higher than plot-scale FCH 4 at all temporal scales, with the smallest difference at the daily timescale (multi-site median Δ FCH 4 : 1.36 nmol m −2 s −1 ; median ecosystem-scale FCH 4 = 1.56 nmol m −2 s −1 , median plot-scale FCH 4 = 0.06 nmol m −2 s −1 ) and the largest at annual scales (2.58 nmol m −2 s −1 ; median ecosystem-scale FCH 4 = 25.91 nmol m −2 s −1 , median plot-scale FCH 4 = 6.55 nmol m −2 s −1 ). In general, the agreement between ecosystem- and plot-scale FCH 4 decreased with finer temporal resolution (from Spearman ρ = 0.95 at the annual scale to ρ = 0.65 at the half-hourly scale), while Δ FCH 4 variation was greatest at daily-to-annual scales. Key environmental predictors of Δ FCH 4 across the ten sites included plot-scale spatial heterogeneity, dominant vegetation type, vapor pressure deficit, atmospheric pressure, and friction velocity at the daily and monthly scales. Wind direction was a significant predictor only at the monthly scale, suggesting EC footprint effects at these sites. These findings suggest that accounting for variability in EC footprint extent, chamber measurement placement, and measurement artifacts is key to reconciling multi-scale FCH 4 observations across diverse ecosystems and refining CH 4 budgets.

Biogeosciences↗

USGS2026

Fipronil baits as emerging tools for flea control and plague mitigation: Experiments with cricetid mice on prairie dog colonies

Plague is a zoonotic disease of mammalian hosts and flea vectors. Wildlife biologists most commonly mitigate plague by controlling flea populations. We evaluated the efficacy of edible baits for systemic flea control with two cricetid species on colonies of black-tailed prairie dogs ( Cynomys ludovicianus ): the western deer mouse ( Peromyscus sonoriensis ) and the northern grasshopper mouse ( Onychomys leucogaster ). We tested grain bait with 0.005% fipronil by weight and “FipBit” pellets with 0.46–1.52 mg of fipronil/pellet. Flea prevalence was assessed via combing of live-trapped mice. In one experiment with fipronil grain bait and FipBits ( n =564 combings), flea prevalence declined from 74% (grain) and 45% (FipBits) before treatments to 0% for both treatments from 30–44 d and from 324–413 d after treatments. During a second experiment with FipBits ( n =299 combings), flea prevalence declined from 13% to 32% before treatments to 0% from 11–15 d after treatments, but increased to 29–56% from 349–378 d after treatments. Results herein suggest annual fipronil bait treatments may be most effective for flea control.

Journal of Wildlife Diseases↗

USGS2026

Non-destructive sampling of larval amphibians shows tail tissues reflect whole-body methylmercury concentrations and trophic-related differences in bioaccumulation

Mercury (Hg), and specifically methylmercury (MeHg), is a contaminant of global concern to humans and wildlife, but there is still limited understanding of its effects on many taxa. Amphibians are closely associated with water, where Hg is converted to MeHg, and high concentrations of MeHg can reduce survival of amphibians in the wild. However, limited non-lethal proxies exist for estimating MeHg bioaccumulation in amphibian larvae, which could be used to reduce destructive sampling and allow sampling of imperiled species. We evaluated whether tail clips were indicative of whole-body MeHg concentrations of larval amphibians, whether dragonflies were an effective bioindicator of Hg concentrations of larval amphibians, and compared MeHg bioaccumulation in predatory caudate (salamanders, newts) and non-predatory anuran (frogs, toads) larvae. Tail-clip and whole-body MeHg concentrations were strongly correlated, especially for caudates. There was high variability among sites and species, but caudates had higher MeHg than anurans, and MeHg concentrations of caudates and anurans were strongly correlated. Dragonflies were a weak indicator of MeHg for anurans but strong indicators for larval caudates, likely because caudates and dragonflies are carnivorous and occupy similar trophic positions. Our study revealed that sampling tails can be an effective non-destructive index of whole-body MeHg for larval amphibians and demonstrates differences in MeHg bioaccumulation related to trophic position in larval amphibians and dragonflies. All post-embryo life stages for a broad suite of amphibian species can now be sampled non-lethally for MeHg, allowing for a broader examination of population-level effects and focus on imperiled species that cannot be sampled destructively.

conterminous United States↗

USGS2026

A scanning electron microscope-energy dispersive spectrometry (SEM-EDS) method for the quantitative analysis of common volcanic phases

In situ microanalysis by X-ray spectrometry is a fundamental geochemical technique for volcanology and the geosciences generally and typically performed using an electron microprobe (EPMA) equipped with wavelength dispersive spectrometers (WDS). The related technique of energy dispersive spectrometry (EDS), implemented using either EPMA or a scanning electron microscope (SEM), offers advantages in throughput, simplicity, and cost, yet has historically been relegated to qualitative tasks. We present a quantitative EDS procedure implemented using a W-source SEM and a moderate size silicon drift EDS detector applied to common volcanic materials. Glass and mineral standard data demonstrate that the accuracy and precision of this method is comparable to EPMA–WDS. We show that electron beam damage can be mitigated in volcanic glass through sample-specific optimizations without the need for a time-dependent intensity correction. Our implementation using a relatively inexpensive instrument can potentially increase the accessibility of high-quality, quantitative X-ray microanalysis of major and minor elements.

Volcanica↗

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↗