USGS44, a new high purity calcium carbonate reference material for δ13 C measurements

RATIONALE: The stable carbon isotopic (δ13 C) reference material (RM) LSVEC Li2 CO3 has been found to be unsuitable for δ13 C standardization work because its δ13 C value increases with exposure to atmospheric CO2 . A new CaCO3 RM, USGS44, has been prepared to alleviate this situation. METHODS: USGS44 was prepared from 8 kg of Merck high purity CaCO3 . Two sets of δ13 C values of USGS44 were determined. The first set of values was determined by on-line combustion, continuous-flow (CF) isotope-ratio mass spectrometry (IRMS) of NBS 19 CaCO3 (δ13 CVPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1 ‰), and LSVEC Li2 CO3 (δ13 CVPDB = -46.6 mUr exactly), and normalized to the two-anchor δ13 CVPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI) IRMS of CO2 evolved by reaction of H3 PO4 with carbonates, corrected for cross contamination, and normalized to the single anchor δ13 CVPDB scale. RESULTS: USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-μg amounts. It has a δ13 CVPDB-LSVEC value of -42.21 ± 0.05 mUr. Single-anchor δ13 CVPDB 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 δ13 CVPDB-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 δ13 CVPDB-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 δ18 O reference material. A δ13 CVPDB-LSVEC value of -29.99 ± 0.05 mUr was determined for NBS 22 oil

A 50-year record of NOx and SO2 sources in precipitation in the Northern Rocky Mountains, USA

Ice-core samples from Upper Fremont Glacier (UFG), Wyoming, were used as proxy records for the chemical composition of atmospheric deposition. Results of analysis of the ice-core samples for stable isotopes of nitrogen (δ15N, ) and sulfur (δ34S, ), as well as and deposition rates from the late-1940s thru the early-1990s, were used to enhance and extend existing National Atmospheric Deposition Program/National Trends Network (NADP/NTN) data in western Wyoming. The most enriched δ34S value in the UFG ice-core samples coincided with snow deposited during the 1980 eruption of Mt. St. Helens, Washington. The remaining δ34S values were similar to the isotopic composition of coal from southern Wyoming. The δ15N values in ice-core samples representing a similar period of snow deposition were negative, ranging from -5.9 to -3.2 ‰ and all fall within the δ15N values expected from vehicle emissions. Ice-core nitrate and sulfate deposition data reflect the sharply increasing U.S. emissions data from 1950 to the mid-1970s

Sources of Nonnative Centrarchids in the Upper Colorado River Revealed by Stable Isotope and Microchemical Analyses of Otoliths

Nonnative fishes represent a significant impediment to the recovery of imperiled fishes, including those endemic to the Colorado River in the southwestern United States. Efforts to control nonindigenous fish abundance in the upper Colorado River basin have been unsuccessful owing in part to lack of knowledge regarding nonnative fish recruitment sources. We determined the source habitat (floodplain pond versus riverine habitats) for nonnative centrarchid fishes (largemouth bass Micropterus salmoides, green sunfish Lepomis cyanellus, bluegill L. macrochirus, and black crappie Pomoxis nigromaculatus) in the upper Colorado River using stable hydrogen isotopic composition (δD) and strontium:calcium (Sr:Ca) ratios in fish otoliths as natural markers of environmental history. Stable hydrogen isotope analysis revealed that 59% of centrarchids exhibited the otolith core signatures expected for riverine-origin fish, while 22% had emigrated from floodplain ponds and 19% were of uncertain origin. Strontium:calcium ratio data were consistent with the δD assays and indicated that relatively few fish immigrated to the river from high-salinity habitats. Black crappie was the only species that originated primarily from floodplain ponds. Efforts to control the abundance of most of the fishes included in this study should be concentrated in riverine habitats given the hydrologic conditions (below-average river discharge) present during our study. However, the proportion of pond-origin fish increased with fish age, which, coupled with historical river discharge data, suggested that floodplain pond contributions to riverine nonnative fish populations fluctuate with the interannual variations in flow regime and river–pond connectivity. Our results are the first to demonstrate the utility of δD as a natural marker of fish environmental history that will probably provide valuable insights into the management of fish in other environments

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^2H_(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 ^2H-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 δ2H 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 ^2H-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies

Low-Temperature Polymorphic Phase Transition in a Crystalline Tripeptide L-Ala-L-Pro-Gly·H2O Revealed by Adiabatic Calorimetry

We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide l-alanyl-l-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide.National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-003151)National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-001960)National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-002026

Onset of the aerobic nitrogen cycle during the Great Oxidation Event

The rise of oxygen on the early Earth (about 2.4 billion years ago)1 caused a reorganization of marine nutrient cycles2, 3, including that of nitrogen, which is important for controlling global primary productivity. However, current geochemical records4 lack the temporal resolution to address the nature and timing of the biogeochemical response to oxygenation directly. Here we couple records of ocean redox chemistry with nitrogen isotope (15N/14N) values from approximately 2.31-billion-year-old shales5 of the Rooihoogte and Timeball Hill formations in South Africa, deposited during the early stages of the first rise in atmospheric oxygen on the Earth (the Great Oxidation Event)6. Our data fill a gap of about 400 million years in the temporal 15N/14N record4 and provide evidence for the emergence of a pervasive aerobic marine nitrogen cycle. The interpretation of our nitrogen isotope data in the context of iron speciation and carbon isotope data suggests biogeochemical cycling across a dynamic redox boundary, with primary productivity fuelled by chemoautotrophic production and a nitrogen cycle dominated by nitrogen loss processes using newly available marine oxidants. This chemostratigraphic trend constrains the onset of widespread nitrate availability associated with ocean oxygenation. The rise of marine nitrate could have allowed for the rapid diversification and proliferation of nitrate-using cyanobacteria and, potentially, eukaryotic phytoplankton

A 300-year record of sedimentation in a small tilled catena in Hungary based on δ13C, δ15N, and C/N distribution

Purpose Soil erosion is one of the most serious hazards that endanger sustainable food production. Moreover, it has marked effects on soil organic carbon (SOC) with direct links to global warming. At the same time, soil organic matter (SOM) changes in composition and space could influence these processes. The aim of this study was to predict soil erosion and sedimentation volume and dynamics on a typical hilly cropland area of Hungary due to forest clearance in the early eighteenth century. Materials and methods Horizontal soil samples were taken along two parallel intensively cultivated complex convex-concave slopes from the eroded upper parts at mid-slope positions and from sedimentation in toe-slopes. Samples were measured for SOC, total nitrogen (TN) content, and SOMcompounds (δ13C, δ15N, and photometric indexes). They were compared to the horizons of an in situ non-eroded profile under continuous forest. On the depositional profile cores, soil depth prior to sedimentation was calculated by the determination of sediment thickness. Results and discussion Peaks of SOC in the sedimentation profiles indicated thicker initial profiles, while peaks in C/N ratio and δ13C distribution showed the original surface to be ~ 20 cm lower. Peaks of SOC were presumed to be the results of deposition of SOC-enriched soil from the upper slope transported by selective erosion of finer particles (silts and clays). Therefore, changes in δ13C values due to tillage and delivery would fingerprint the original surface much better under the sedimentation scenario than SOC content. Distribution of δ13C also suggests that the main sedimentation phase occurred immediately after forest clearance and before the start of intense cultivation with maize. Conclusions This highlights the role of relief in sheet erosion intensity compared to intensive cultivation. Patterns of δ13C indicate the original soil surface, even in profiles deposited as sediment centuries ago. The δ13C and C/N decrease in buried in situ profiles had the same tendency as recent forest soil, indicating constant SOM quality distribution after burial. Accordingly, microbiological activity, root uptake, and metabolism have not been effective enough to modify initial soil properties

Biogenic Volatile Organic Compound and Respiratory CO2 Emissions after 13C-Labeling: Online Tracing of C Translocation Dynamics in Poplar Plants

Globally plants are the primary sink of atmospheric CO(2), but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important.We combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either (13)CO(2) to leaves or (13)C-glucose to shoots via xylem uptake. The translocation of (13)CO(2) from the source to other plant parts could be traced by (13)C-labeled isoprene and respiratory (13)CO(2) emission.In intact plants, assimilated (13)CO(2) was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h(-1). (13)C label was stored in the roots and partially reallocated to the plants' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76-78%) from recently fixed CO(2), to a minor extent from xylem-transported sugars (7-11%) and from photosynthetic intermediates with slower turnover rates (8-11%).We quantified the plants' C loss as respiratory CO(2) and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux