Search

For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20 % gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for δ18O and δ2H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to −108.4 ‰ for δ2H and +11.8 to −14.9 ‰ for δ18O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.

International audience; Concern exists about the suitability of laser spectroscopic instruments for the measurement of the O-18/O-16 and H-2/H-1 values of liquid samples other than pure water. It is possible to derive erroneous isotope values due to optical interference by certain organic compounds, including some commonly present in ecosystem-derived samples such as leaf or soil waters. Here we investigated the reliability of wavelength-scanned cavity ring-down spectroscopy (CRDS) O-18/O-16 and H-2/H-1 measurements from a range of ecosystem-derived waters, through comparison with isotope ratio mass spectrometry (IRMS). We tested the residual of the spectral fit S-r calculated by the CRDS instrument as a means to quantify the difference between the CRDS and IRMS delta-values. There was very good overall agreement between the CRDS and IRMS values for both isotopes, but differences of up to 2.3 parts per thousand (delta O-18 values) and 23 parts per thousand (delta H-2 values) were observed in leaf water extracts from Citrus limon and Alnus cordata. The S-r statistic successfully detected contaminated samples. Treatment of Citrus leaf water with activated charcoal reduced, but did not eliminate, delta H-2(CRDS)-delta H-2(IRMS) linearly for the tested range of 0-20 % charcoal. The effect of distillation temperature on the degree of contamination was large, particularly for delta H-2 values but variable, resulting in positive, negative or no correlation with distillation temperature. S-r and delta(CRDS) - delta(IRMS) were highly correlated, in particular for delta H-2 values, across the range of samples that we tested, indicating the potential to use this relationship to correct the delta-values of contaminated plant water extracts. We also examined the sensitivity of the CRDS system to changes in the temperature of its operating environment. We found that temperature changes >= 4 degrees C for delta O-18 values and >= 10 degrees C for delta H-2 values resulted in errors larger than the CRDS precision for the respective isotopes and advise the use of such instruments only in sufficiently temperature-stabilised environments. Copyright (C) 2011 John Wiley & Sons, Ltd.

Conference: 6th Congress of the French-Society-of-Stables-Isotopes Location: ENSAT Sch, Ecolab Lab, Toulouse, FRANCE Date: OCT 26-29, 2010; International audience; We have used a high-precision, easy, low-cost and rapid method of oxygen isotope analysis applied to various O-bearing matrices, organic and inorganic (sulfates, nitrates and phosphates), whose (18)O/(16)O ratios had already been measured. It was first successfully applied to (18)O analyses of natural and synthetic phosphate samples. The technique uses high-temperature elemental analysis-pyrolysis (EA-pyrolysis) interfaced in continuous-flow mode to an isotope ratio mass spectrometry (IRMS) system. Using the same pyrolysis method we have been able to generate a single calibration curve for all those samples showing pyrolysis efficiencies independent of the type of matrix pyrolysed. We have also investigated this matrix-dependent pyrolysis issue using a newly developed pyrolysis technique involving 'purge-and-trap' chromatography. As previously stated, silver phosphate being a very stable material, weakly hygroscopic and easily synthesized with predictable (18)O/(16)O values, could be considered as a good candidate to become a reference material for the determination of (18)O/(16)O ratios by EA-pyrolysis-IRMS.

International audience; Water vapor isotopes represent an innovative and excellent tool for understanding complex mechanisms in the atmospheric water cycle over different time scales, and they can be used for a variety of applications in the fields of paleoclimatology, hydrology, oceanography, and ecology. We use an ultrasensitive near‐infrared spectrometer, originally designed for use on airborne platforms in the upper troposphere and lower stratosphere, to measure the water deuterium and oxygen‐18 isotope ratios in situ, in ground‐level tropospheric moisture, with a high temporal resolution (from 300 s down to less than 1 s). We present some examples of continuous monitoring of near‐surface atmospheric moisture, demonstrating that our infrared laser spectrometer could be used successfully to record high‐concentration atmospheric water vapor mixing ratios in continuous time series, with a data coverage of ∼90%, interrupted only for daily calibration to two isotope ratio mass spectrometry–calibrated local water standards. The atmospheric data show that the water vapor isotopic composition exhibits a high variability that can be related to weather conditions, especially to changes in relative humidity. Besides, the results suggest that observed spatial and temporal variations of the stable isotope content of atmospheric water vapor are strongly related to water vapor transport in the atmosphere.

International audience; Due to its resistance to oxidation, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this study we report on the properties of TaSiN thin films deposited by reactive magnetron sputtering of a TaSi2 target in an Ar/N-2 atmosphere. We especially focus on the influence of deposition parameters (pressure and power density) on TaSiN film properties. To study oxidation resistance, films are processed by rapid thermal annealing in O-18(2) at 650 degrees C. The concentration depth profiles of O-18 were measured via the narrow resonance of O-18(p,alpha)N-15 at 151 keV (FWHM = 100 eV). Whatever the power density, films deposited above 2 Pa are porous and exhibit high resistivity. Ta26Si47N27 deposited at 0.5 Pa with a power density of 2.65 W/cm(2) exhibits high density, low resistivity, and good oxidation resistance. (c) 2006 Elsevier B.V. All rights reserved.