Trace Oxygen Isotope Research Articles

Structures and contributions of active substances in the latent oxidation of coal based on the oxygen isotope tracer method

The oxygen isotope tracer method was used to determine the structures and contributions of the active substances that trigger coal spontaneous combustion (CSC). After artificially changing the oxygen isotope ratio, the coal samples were subjected to isothermal oxidation under different conditions (different temperatures, different oxidation times and different coal types) in an 18O2 atmosphere. First, the oxidation gases were obtained with cyclic oxidation experiments. The basic parameters were provided for tests of the gas isotopes. The oxidation products labeled with 18O were then analyzed with an isotope ratio mass spectrometer. The original active substances in the coal were determined. Evolution of the functional groups in the coal was determined by XPS. The transformation paths of the active substance were analyzed. The results showed that during the oxidation process, more than 70 % of the CO was generated from the original hydroxyl and aldehyde groups in the coal, and more than 99 % of the CO2 was generated from the original carboxyl groups in the coal. Inhibition of oxidative decomposition of hydroxyl, aldehyde and carboxyl groups can effectively control CSC and solve the problem of CO overflow caused by low-rank coal oxidation.

Oxygen tracer diffusion in amorphous hafnia films for resistive memory.

The oxygen diffusion rate in hafnia (HfO2)-based resistive memory plays a pivotal role in enabling nonvolatile data retention. However, the information retention times obtained in HfO2 resistive memory devices are many times higher than the expected values obtained from oxygen diffusion measurements in HfO2 materials. In this study, we resolve this discrepancy by conducting oxygen isotope tracer diffusion measurements in amorphous hafnia (a-HfO2) thin films. Our results show that the oxygen tracer diffusion in amorphous HfO2 films is orders of magnitude lower than that of previous measurements on monoclinic hafnia (m-HfO2) pellets. Moreover, oxygen tracer diffusion is much lower in denser a-HfO2 films deposited by atomic layer deposition (ALD) than in less dense a-HfO2 films deposited by sputtering. The ALD films yield similar oxygen diffusion times as experimentally measured device retention times, reconciling this discrepancy between oxygen diffusion and retention time measurements. More broadly, our work shows how processing conditions can be used to control oxygen transport characteristics in amorphous materials without long-range crystal order.

Temporal and Spatial Distribution Characteristics and Source Analysis of Nitrate in Surface Water of Wuding River Basin

The Wuding River Basin is a first-class tributary of the Yellow River, and the quality of its water ecological environment has a profound impact on the ecological protection and high-quality development of the Yellow River Basin. In order to identify the source of nitrate pollution in the Wuding River Basin, surface water samples of the Wuding River were collected from 2019 to 2021, and the temporal and spatial distribution characteristics and influencing factors of nitrate concentration in surface water in the basin were explored. Nitrogen and oxygen isotope tracer technology and the MixSIAR model were used to qualitatively and quantitatively determine the sources of surface water nitrate and their contribution rates. The results showed that there were significant spatial and temporal differences in nitrate concentrations in the Wuding River Basin. In terms of time, the mean concentration of NO-3-N in surface water in the wet season was higher than that in the flat-water period; spatially, the mean concentration of NO-3-N in the downstream surface water was higher than that in the upstream. The spatial and temporal differences in surface water nitrate concentrations were mainly affected by rainfall runoff, soil types, and land use types. The main sources of nitrates in the surface water of the Wuding River Basin during the wet season were domestic sewage, manure, chemical fertilizers, and soil organic nitrogen, whose contribution rates were 43.3%, 27.6%, and 22.1%, respectively, and the contribution rate of precipitation was only 7.0%. There were differences in the contribution rate of nitrate pollution sources in surface water of different river sections. The contribution rate of soil nitrogen in the upstream was significantly higher than that in the downstream, which was 26.5%. The contribution rate of domestic sewage and manure in the downstream was significantly higher than that in the upstream, which was 48.9%. To provide a basis for the analysis of nitrate sources and pollution control in Wuding River and even rivers in arid and semi-arid regions.

Paleoclimate Signals and Groundwater Age Distributions From 39 Public Water Works in the Netherlands; Insights From Noble Gases and Carbon, Hydrogen and Oxygen Isotope Tracers

AbstractKnowing the age distribution of water abstracted from public water supply wells helps to ensure customer trust in drinking water sources and underpin predictions of water quality evolution. We sampled the mixed water of 39 large public supply well fields for major ion chemistry, 3H, 3He, 18O, 2H, 14CDIC, 13CDIC and noble gases and determined the Noble Gas Temperature (NGT). We used a discrete travel time distribution model to quantify the age distributions using 3H, 4He, 14C apparent age and NGT as the 4 distinctive tracers. Helium‐4 and NGT provided information on the older part of the age distributions and showed that the 14C apparent ages are often the result of mixing of waters ranging between 2,000 and 35,000 years old, instead of being discrete ages with a limited variance as previously assumed. The results reveal a large range of age distributions, comprising vulnerable well fields with >60% young water (<100 years) and well fields with >30% paleo groundwater (>25,000 years) and all forms of intermediate distributions. The age distributions match the hydrogeological setting; well fields with age distributions skewed towards older ages appear in the Roer Valley Graben structure, where fluvial and marine aquitards and sealed faults provide protection from recent recharge. Waters from this graben exhibit paleoclimate signals, with a clear relation between NGT (range 3.2–9.3 °C), 4He (up to 3.3 × 10−6 ccSTP/g) and δ18O (range −8.5‰ to −5.9‰VSMOW). Moreover, 3He/4He ratios of these graben waters suggest a certain influx of He from mantle origin.

Effects of water and nitrogen stress on water utilization of dominant species in broadleaved Korean pine forest in Changbai Mountain, China

The aggravation of global nitrogen deposition may change plant water utilization and affect plant growth. Understanding the changes of vegetation water consumption under nitrogen deposition is of great significance for simulating and predicting the evolution of each component of forest hydrological cycle. We used the hydrogen and oxygen isotope tracer method to analyze water consumption source, quantity and law of Quercus mongolica (Qm), Fraxinus manshurica (Fm) and Tilia amurensis (Ta), the dominant species in broadleaved Korean pine forest of Changbai Mountain, under different add amounts of nitrogen [low nitrogen addition group (11.8 kg·hm-2·a-1), LN; high nitrogen addition group (23.6 kg·hm-2· a-1), HN] and different amounts of simulated precipitation (water addition amount were 0, 400, 800 and 1600 mL, equivalent to single rainfall amount were 0, 16, 32 and 64 mm, respectively). The results showed that under the condition of relative drought, soil water utilization ratio of Qm, Fm and Ta in the LN group were 26%, 12% and 20%, higher than that in HN group. When the amount of simulated precipitation was 16 mm, soil water utilization ratio of Qm, Fm and Ta in LN group reached the highest, being 73%, 70% and 43%, respectively. This ratio also reached a high value in HN group, but being less than the values in LN group. When the amount of simulated precipitation was 32 mm, soil water content approximated the average value in broadleaved Korean pine forest in the growing season in Changbai Mountain. The average soil water utilization ratio of test tree species in HN group was 39%, higher than that in LN group (16%). When the amount of simulated precipitation reached 64 mm, the soil water was saturation. Soil water utilization ratio of Qm, Fm and Ta in LN group was 14%, 5% and 1%, which was lower than that in HN group, the corresponding ratio were 64%, 13% and 10%, respectively. In conclusion, under the condition of less precipitation and relatively dry soil, the soil water utilization ratio of those three tree species were lower, and the increases of nitrogen availability further reduced the ratio. When the amount of precipitation was high and soil moisture was higher than the average value of the growing season, soil water utilization ratio of those tree species was higher. With the increases of soil nitrogen availability, this ratio was further increased.

Oxygen and Triple Oxygen Isotope Measurements Provide Different Insights into Gross Oxygen Production in a Shallow Salt Marsh Pond

The metabolism of estuarine environments is often estimated by measuring changes in dissolved oxygen concentrations. A central assumption of common oxygen-based approaches is that oxygen consumption rates (primarily respiration) are similar under light and dark conditions. Evaluating this assumption is critical, especially in benthic-dominated systems, because differences between daytime and nighttime respiration could result in underestimation or overestimation of ecosystem productivity. We evaluated rates of gross oxygen production over hourly to seasonal time scales in a shallow, temperate salt marsh pond. To assess whether a dissolved oxygen diel mass balance underestimated gross oxygen productivity, we compared rates using this traditional approach and using the triple oxygen isotope tracer of photosynthesis. This is a powerful combination because the triple oxygen isotope approach is theoretically insensitive to respiration. The methods agreed well over daily to seasonal time scales. However, during midday periods of peak light and productivity, the triple oxygen isotope approach resulted in higher hourly scale gross oxygen production rates. The timing and magnitude of this short-term difference is consistent with light-dependent oxygen uptake fluxes including photoreduction and/or light-stimulated community respiration. Finally, aquatic vegetation was associated with variability in productivity across the pond. Such small-scale environmental heterogeneity is evidence that this shallow pond was not laterally well mixed, and likely contributes to the dynamism of these common estuarine environments.

Recognizing the role of plant species composition in the modification of soil nutrients and water in rubber agroforestry systems

Reliable guidance for crop selection and related management to achieve sustainable soil resource use in rubber agroforestry systems is limited. One important reason for this limited guidance is that our understanding of the effects of different plant functional groups on soil resources is still insufficient. Here, to examine the effects of the species composition of trees, shrubs and herbs on soil nutrients and soil water with increases in the complexity of the plant community structure, we measured the soil nutrient concentrations (i.e., C, N, P, K, Ca and Mg), soil water content and soil water residence time (with stable hydrogen and oxygen isotope tracers) at six soil depths in a monoculture rubber plantation, four multi-species rubber agroforestry systems, and a tropical rainforest. As the plant species composition increased, the soil C and N increased. The soil water content also increased with increases in soil C and N. However, the effects of plant species composition on the soil water content gradually changed from positive to negative, especially under the effects of herb species, which could accelerate soil water drainage and hence shorten the soil water residence time. Therefore, the faster water infiltration and potentially higher flow of soil water in complex plant communities increased the risk and magnitude of mineral nutrient leaching. In addition, as the plant composition increased, plant competition decreased the concentration of soil nutrients, especially soil P, K and Ca. In general, plant interspecific interactions definitively decreased soil mineral nutrients as the plant composition increased, and the effects of tree, shrub and herb species on soil nutrients and soil water differed and sometimes appeared contradictory. However, the effects of plant species composition on soil gradually weakened with increases in soil depth.

黄土区小流域植被类型对沟坡地土壤水分循环的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土区小流域植被类型对沟坡地土壤水分循环的影响 DOI: 10.5846/stxb201902120248 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 基金面上项目（41771311）；国家自然科学基金国际（地区）合作与交流项目（41561144011）；国家自然科学基金（41807066） Effects of vegetation types in small watershed on soil water cycle in gully-slope land of loess region Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:沟坡作为黄土丘陵区小流域水土流失最为活跃的区域，探究不同下垫面植被类型下的土壤水分循环特征对于沟坡地植被恢复具有重要意义。基于氢氧同位素示踪技术，通过野外水样采集和室内同位素分析旨在揭示植被类型对沟坡地土壤水分循环的影响机制。结果表明：（1）各水体氢氧同位素均遵循：降水 > 刺槐林地土壤水 > 草地土壤水 > 地表水 > 地下水，降水的变异系数最大，地表水和地下水的变异系数较小。（2）草地土壤水主要以降水补给为主，所占比例为59.12%，刺槐林地土壤水则以深层土壤水的上升补给为主，所占比例为60.97%。短阵性暴雨条件下，草地土壤水运移速率较刺槐林地高约1 cm/d，且主要发生在0-50 cm土层。（3）土壤水的垂向运移为地下水的主要补给形式，草地土壤水对地下水的补给比例为51.64%，约比刺槐林地高0.52%。表明植被类型对土壤水分循环特征具有一定的影响，刺槐林对深层土壤水分利用强度较大，可能加剧深层土壤干层化，而草地更有利于降水入渗以及地下水补给，该研究可为小流域沟坡的生态修复和综合治理提供科学依据。 Abstract:The gully-slope land is the most active area of soil erosion in small watershed of loess hilly region. It is of great significance to explore the characteristics of soil water cycle under different underlying vegetation types for vegetation restoration on gully-slope land. Based on the hydrogen and oxygen isotope tracer technique, the mechanism of vegetation types affecting soil water cycle in gully-slope land was revealed through field water sample collection and indoor isotope analysis. The results were: (1) The hydrogen and oxygen isotope concentration in the five water bodies decreased in an orderly way, with precipitation being observed to have the greatest amount, followed by soil water of black locust forest, then soil water of grassland, then surface water, finally groundwater. The coefficient of variation of precipitation was the largest, and the coefficient of variation of surface water and groundwater was smaller. (2) Soil water in grassland was mainly recharged by precipitation, accounting for 59.12%. Soil water in black locust forest was mainly recharged by the rising of deep soil water, accounting for 60.97%. Under the condition of short-burst rainstorm, the water transport rate of grassland soil was about 1 cm/d higher than that of black locust forest. And the main transport ranges of soil water in two vegetation types were 0-50 cm. (3) The vertical migration of soil water was the main form of groundwater recharge. The groundwater recharge ratio by soil water of grassland was 51.64%, which was about 0.52% higher than that of black locust forest. It indicated that the vegetation type had certain influence on the characteristic of soil water cycle. Black locust forest had a strong utilization of deep soil water, which might aggravate the dried soil layer of deep soil. And the grassland was more conducive to precipitation infiltration and groundwater recharge. This study can provide a scientific basis for ecological restoration and comprehensive management of gully-slope land in small watershed. 参考文献 相似文献 引证文献

(Invited) Liquid Electrolyte Contacts to Semiconductor Nanostructures: Probing and Programming Local Defect Behavior

Replacing the metal top electrode of a metal-insulator-semiconductor (MIS) or –metal (MIM) junction with a liquid electrolyte contact can be used 1) to study the capacitance and conductance response of semiconductor nanostructures with a conformal liquid contact, and 2) to program, at higher voltages, populations of point defects in an insulator layer, as a means of investigating local resistance switching. This presentation will summarize recent results on both of these topics, beginning with a discussion of electrochemical spectroscopy (EIS) applied to semiconductor-liquid junctions as a means of performing quantitative interface state characterization on micro- and nano-structured samples. Using aqueous KCl solution as a blocking contact to a semiconductor electrode, electrochemical impedance spectroscopy measures the multifrequency capacitance-voltage and conductance-voltage characteristics of planar p-Si (100), planar p-Si0.55Ge0.45 (100), and p-Si crystals with surfaces that are textured to create nanoscale features.1 These substrates are coated with thin atomic layer deposited Al2O3 dielectrics. Analysis of impedance data obtained from the planar samples produces results that are in good agreement with solid-state multi-frequency C-V and g-V data from the same sample, including similar extracted values for density of interface states. Impedance data and the extracted interface trap properties of ALD-Al2O3 passivated silicon microwire arrays for application in solar cells will also be described. Liquid electrolyte contacts have also been used to study resistance switching and its relation to local oxygen deficiency in an initially insulating metal oxide layer.2 Local variations in electrical conductivity in amorphous TiO2 films prepared by atomic layer deposition (ALD) are examined using conductive atomic force microscopy. The local TiO2 conductivity is correlated with changes in oxygen stoichiometry revealed by electron energy loss spectroscopy performed in the electron microscope and by oxygen isotope tracer exchange. Both highly resistive ionic liquids and highly conductive electrolyte solutions are used as liquid top contacts to the TiO2 layers. In this way, the effects of field-driven migration of oxygen ions in and out of the TiO2 film can be distinguished from local accumulation of oxygen vacancies via Joule heating at high programming currents. We find that gating using a resistive ionic liquid contact at room temperature and positive gate bias produces an oxygen deficient ALD-TiO2 film with enhanced electronic conductivity, demonstrating the ease with which field-driven oxygen vacancy formation occurs at low temperature in these thin amorphous layers. However, conductive filaments were formed only when the TiO2 is programmed using a lower-resistivity electrolyte top contact. This indicates the decisive importance of programming current in localization of the point defects required for filamentary conduction. C. Meng, K. Tang, M. Braun, L. Zhang, and P.C. McIntyre, “Electrochemical Impedance Spectroscopy for Quantitative Interface State Characterization of Planar and Nanostructured Semiconductor-Dielectric Interfaces,” Nanotechnol. 28, 415704 (2017). Tang, A.C. Meng, F. Hui, Y. Shi, T. Petach, C. Hitzman, A.L. Koh, D. Goldhaber-Gordon, M. Lanza, and P.C. McIntyre, “Distinguishing Oxygen Vacancy Electromigration and Conductive Filament Formation in TiO2 Resistance Switching Using Liquid Electrolyte Contacts,” Nano Lett. 17, 4390–99 (2017).

Influence of trace O<inf>2</inf> on SF<inf>6</inf> decomposition characteristics under partial discharge based on oxygen isotope tracer

As an excellent electrical insulation and arc-interruption medium, sulfur hexafluoride (SF 6 ) has been widely used in gas-insulated switchgear (GIS). Insulation failures in GIS are usually evolved from the partial discharges which are induced by hidden defects, such as metal protrusions, free conducting particles, floating components. In the presence of discharges, SF 6 decomposes into various by-products. Accordingly, these decomposition by-products are often used to detect and identify partial discharges in GIS based on SF 6 decomposition characteristics. Oxygen (O 2 ) as an impurity plays an important role in the formation of SF 6 decomposition by-products. In this paper, the influence of O 2 on SF 6 decomposition characteristics under partial discharge has been investigated based on oxygen isotope tracer 18O 2 and 16O 2 . In our experiments, SF 6 isotopic decomposition by-products were induced, as severity degree of partial discharge or ratio of 18O 2 to 16O 2 varied. The isotopic decomposition by-products were measured by gas chromatograph mass spectrometer. Based on the results, the sequences of reactions that lead to SO 2 F 2 and SO 2 were described. It is shown that the formation of SO 2 F 2 depends not only on O 2 but also H 2 O, whereas the formation of SO 2 has little dependence on O 2 .

Applying Environmental Isotope Theory to Groundwater Recharge in the Jiaozuo Mining Area, China

This study establishes the surface water evaporation line in theory and numerically simulates the δD and δ18O value distribution interval of the recharge source of deep groundwater in the Jiaozuo mining area. The recharge elevation is calculated based on hydrogen and oxygen isotope tracer theory. Theoretical calculation and experimental data indicate that the surface water evaporation line in the study area in theory is almost the same as the measured surface data-fitting line. A significant linear relationship is identified between δ18O and the elevation of spring outcrop. The topography increases per 100 m, and the δ18O value reduces by 0.23‰ on average. The δ18O value is converted into formula to calculate the groundwater recharge elevation, which is approximately from 400 to 800 m. The measured tritium values of karst groundwater are greater than 3 TU. The second factor score is a fraction distribution in shallow groundwater and negative fraction distribution in spring and deep groundwater, which indicates that the Northern Taihang Mountain is the main recharge area, where carbonate-exposed areas exist. The research conclusion holds a certain value for the flood evaluation of local coal mines.

Characterization of Mixing Processes in the Confluence Zone between the Three Gorges Reservoir Mainstream and the Daning River Using Stable Isotope Analysis.

Understanding the interaction processes between the mainstream and its tributaries and detailing the rates of contribution of water and nutrients from two different waterbodies in the confluence zone are essential for water management in the Three Gorges Reservoir (TGR). The stable isotope ratios of hydrogen (δD) and oxygen (δ(18)O) were applied to explore the interactions between the TGR mainstream and a typical tributary, the Daning River. The results of the model calculations showed that approximately 78.9% of the water and 88% of the nitrate in the confluence zone were from the TGR mainstream. The dynamic vertical distributions of the mixing ratios, major ion contributions, and flow velocities indicated that the water mass from the Yangtze River mainstream flowed backward from the confluence zone up to the tributary along the surface and upper-middle layers, whereas water from the tributary flowed into the mainstream through the lower-middle and bottom layers. This study demonstrates the value of hydrogen and oxygen isotope tracers in accurately describing water mass mixing processes and estimating the rates of contribution of different nutrient sources in the confluence zone, which will provide valuable information for controlling algal blooms in the future.

Microscopic and Isotope Tracer Study on the Growth of Spherical ZnO Particles in Water–Ethylene Glycol Solvent

ZnO spherical powder with hierarchical structure was synthesized from zinc acetate anhydride and hexamethylenetetramine in a solvent of water and ethylene glycol (EG), and its time evolution was investigated by microscopic and isotope tracer studies. Initially, spherical ZnO particles made of nanocrystallites were precipitated. From the early growth stage, crystallites were radially aligned along the c-axis. With aging, the nanoparticles transformed into hexagonal prism-like particles with pyramidal tops, which showed clear radial alignment. Subsequently, the ZnO spheres became cracked and broke into wedge-shaped pieces of the pyramid-like particles. The microscopic studies suggested that the spherical particles grew through oriented attachment of small particles during the early growth stage, while Ostwald ripening through dissolution–recrystallization changed the component particles to a pyramidal shape in the later stage. In order to investigate the growth process, we attempted a novel isotope tracer study, where H218O was used for the solvent and the distribution of 18O in the spherical particles was analyzed by a secondary ion mass spectrometer. The concentric 18O distribution in the ZnO spherical powder aided the mechanism of continuous concentric-oriented attachment of nanoparticles to form spherical ZnO particles. The difference in the 18O distribution before and after transformation into the pyramid shape was small, which implies that this change was a local reaction. The oxygen isotope tracer study in water–EG solvent was proven effective in determining the history of the particles and the development of their inner structures.

The mechanism of borosilicate glass corrosion revisited

Currently accepted mechanistic models describing aqueous corrosion of borosilicate glasses are based on diffusion-controlled hydrolysis, hydration, ion exchange reactions, and subsequent re-condensation of the hydrolyzed glass network, leaving behind a residual hydrated glass or gel layer. Here, we report results of novel oxygen and silicon isotope tracer experiments with ternary Na borosilicate glasses that can be better explained by a process that involves the congruent dissolution of the glass, which is spatially and temporally coupled to the precipitation and growth of an amorphous silica layer at an inwardly moving reaction interface. Such a process is thermodynamically driven by the solubility difference between the glass and amorphous silica, and kinetically controlled by glass dissolution reactions at the reaction front, which, in turn, are controlled by the transport of water and solute elements through the growing corrosion zone. Understanding the coupling of these reactions is the key to understand the formation of laminar or more complex structural and chemical patterns observed in natural corrosion zones of ancient glasses. We suggest that these coupled processes also have to be considered to realistically model the long-term performance of silicate glasses in aqueous environments.

The triple oxygen isotope tracer of primary productivity in a dynamic ocean model

AbstractThe triple oxygen isotopic composition of dissolved oxygen (17Δdis) was added to the ocean ecosystem and biogeochemistry component of the Community Earth System Model, version 1.1.1. Model simulations were used to investigate the biological and physical dynamics of 17Δdis and assess its application as a tracer of gross photosynthetic production (gross oxygen production (GOP)) of O2 in the ocean mixed layer. The model reproduced large‐scale patterns of 17Δdis found in observational data across diverse biogeographical provinces. Mixed layer model performance was best in the Pacific and had a negative bias in the North Atlantic and a positive bias in the Southern Ocean. Based on model results, the steady state equation commonly used to calculate GOP from tracer values overestimated the globally averaged model GOP by 29%. Vertical entrainment/mixing and the time rate of change of 17Δdis were the two largest sources of bias when applying the steady state method to calculate GOP. Entrainment/mixing resulted in the largest overestimation in midlatitudes and during summer and fall and almost never caused an underestimation of GOP. The tracer time rate of change bias resulted both in underestimation of GOP (e.g., during spring blooms at high latitudes) and overestimation (e.g., during the summer following a bloom). Seasonally, bias was highest in the fall (September‐October‐November in the Northern Hemisphere, March‐April‐May in the Southern), overestimating GOP by 62%, globally averaged. Overall, the steady state method was most accurate in equatorial and low‐latitude regions where it estimated GOP to within ±10%. Field applicable correction terms are derived for entrainment and mixing that capture 86% of model vertical bias and require only mixed layer depth history and triple oxygen isotope measurements from two depths.

Andean-scale highlands in the Late Cretaceous Cordillera of the North American western margin

From the Late Jurassic through the Cretaceous, collision between the North American and Farallon plates drove extensive thin-skinned thrusting and crustal shortening that resulted in substantial relief in the North American Cordillera. The elevation history of this region is tightly linked to the tectonic, climatic and landscape evolution of western North America but is not well constrained. Here we use an atmospheric general circulation model with integrated oxygen isotope tracers (isoCAM3) to predict how isotope ratios of precipitation would change along the North American Cordillera as the mean elevation of orogenic highlands increased from 1200m to 3975m. With increases in mean elevation, highland temperatures fall, monsoonal circulation along the eastern front of the Cordillera is enhanced, and wet season (generally spring and summer) precipitation increases. Simulated oxygen isotopic ratios in that precipitation are compared to those obtained from geologic materials (e.g. fossil bivalves, authigenic minerals). Quantification of match between model and data-derived δ18O values suggests that during the Late Cretaceous, the best approximation of regional paleoelevation in western North America is a large orogen on the scale of the modern Andes Mountains with a mean elevation approaching 4000m and a north-south extent of at least 15° of latitude.

Distributions of runoff, sea-ice melt and brine using δ 18O and salinity data — A new view on freshwater cycling in Hudson Bay

Distributions of sea-ice melt (SIM) and runoff (RW) were determined in Hudson Bay (Canada) using salinity and oxygen isotope (δ 18O) tracers. In late summer/early fall, stations throughout the Bay exhibited a summer surface mixed layer (SSML) 30–60 m deep, which contained the seasonal freshwater inputs. The SSML overlies a cold subsurface water, extending up to 125 m deep in the water column, indicative of the previous winter's surface mixed layer (WSML). Our data show that most of the RW remains in a nearshore coastal regime in summer, with limited exchange into the interior of the Bay. At depth, brine (negative SIM) accumulation is closely associated with excess RW, implying that deep water formation occurs when sufficient brine is rejected from the growing ice to overcome RW buoyancy in surface water. The inventory of RW at depths below the WSML is equivalent to almost one year's runoff inputs which, given a residence time of deep water of 4–14 years, implies that 6–16% of the annual river discharge is shunted into deeper waters each winter. The balance between the RW buoyancy in surface waters and densification due to ice formation appears to control where and when deep-water formation can occur. Although not directly measured, regions forming deep water are likely small (< 10% of the Bay area) and associated with flaw leads extending around the perimeter of the landfast ice edge in the Bay. The processes evident in δ 18O and salinity data must be incorporated into ocean models to obtain a realistic view of freshwater cycling and its sensitivity to climate perturbations.

Oxygen isotope composition of evapotranspiration and its relation to C4photosynthetic discrimination

[1] The oxygen isotope of water (18O-H2O) and carbon dioxide (18O-CO2) is an important signal of global change and can provide constraints on the coupled carbon-water cycle. Here, simultaneous observations of 18O-H2O (liquid and vapor phases) and 18O-CO2 were used to investigate the relation between canopy leaf water 18O enrichment, 18O-CO2 photosynthetic discrimination (18Δ), isotope disequilibrium (Deq), and the biophysical factors that control their temporal variability in a C4 (Zea mays L.) ecosystem. Data and analyses are presented from a 74 day experiment conducted in Minnesota during summer 2009. Eddy covariance observations indicate that the oxygen isotope composition of C4 evapotranspiration (δE) ranged from about −20‰ (VSMOW scale) in the early morning to −5‰ after midday. These values were used to estimate the isotope composition at the sites of leaf water evaporation (δL,e) assuming non-steady-state conditions and revealed a strong diurnal pattern ranging from about −5‰ in the early morning to +10‰ after midday. With the addition of net ecosystem CO2 exchange measurements and carbonic anhydrase (CA) assays, we derived canopy-scale 18Δ. These estimates typically varied from 11.3 to 27.5‰ (VPDB scale) and were shown to vary significantly depending on the steady state or non-steady-state assumptions related to leaf water enrichment. We demonstrate that the impact of turbulence on kinetic fractionation and steady state assumptions result in larger estimates of 18Δ and Deq. Further, the results indicate that both leaf-scale and canopy-scale CO2 hydration efficiency may be substantially lower than that previously reported for laboratory conditions. These results may have important implications for interpreting variations in atmospheric 18O-CO2 and constraining regional carbon budgets based on the oxygen isotope tracer approach.

Oxidation kinetics of Y‐doped FeCrAl‐alloys in low and high pO2 gases

AbstractA model Fe‐20Cr‐5Al‐0.05Y alloy was oxidized in Ar‐20%O2 and Ar‐4%H2‐7%H2O at 1200–1300 °C. Two‐stage oxidation experiments using oxygen isotope tracers showed that inward oxygen diffusion was predominant in both gases, but more isotope exchange was observed in the H2/H2O gas reaction. The alumina scales formed in both gases were composed of columnar grains, the lateral size of which increased linearly with depth beneath the scale surface. Thermogravimetric measurement of oxygen uptake revealed kinetics which were intermediate to parabolic and cubic kinetic rate laws. A model based on grain boundary diffusion control coupled with competitive oxide grain growth accounts satisfactorily for the results when the requirement for a divergence‐free flux within the scale is imposed. This treatment shows that the oxide grain boundary diffusion coefficient is lower when H2O is the oxidant. It is concluded that hydrogen slows the grain boundary diffusion process by altering the nature of the diffusing species.

Global application of stable hydrogen and oxygen isotopes to wildlife forensics

Stable isotopes are being increasingly used in wildlife forensics as means of determining the origin and movement of animals. The heavy isotope content of precipitated water and snow (deltaD(p), delta(18)O(p)) varies widely and systematically across the globe, providing a label that is incorporated through diet into animal tissue. As a result, these isotopes are potentially ideal tracers of geographic origin. The hydrogen and oxygen isotope tracer method has excellent potential where (1) spatial variation of precipitation isotopes exist, and (2) strong, mechanistic relationships link precipitation and isotope ratios in biological tissue. Here, we present a method for interpolation of precipitation isotope values and use it to create global basemaps of growing-season (GS) and mean annual (MA) deltaD(p) and delta(18)O(p). The use of these maps for forensic application is demonstrated using previously published isotope data for bird feathers (deltaD(f)) in North America and Europe. The precipitation maps show that the greatest potential for applying hydrogen and oxygen isotope forensics exists in mid- to high-latitude continental regions, where strong spatial isotope gradients exist. We demonstrate that deltaD(f)/deltaD(p) relationships have significant predictive power both in North America and Europe, and show how zones of confidence for the assignment of origin can be described using these predictive relationships. Our analysis focuses on wildlife forensics, but the maps and approaches presented here will be equally applicable to criminal forensic studies involving biological materials. These maps are available in GIS format at http://www.waterisotopes.org.