Hydrogen Isotope Fractionation Research Articles

Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

Hydrogen and carbon isotope systematics of H2O–H2–CO2–CH4 in hydrogenotrophic methanogenesis and their relation to H2 availability were investigated. Two H2-syntrophic cocultures of fermentatively hydrogenogenic bacteria and hydrogenotrophic methanogens under conditions of <102 Pa-H2 and two pure cultures of hydrogenotrophic methanogens under conditions of ~105 Pa-H2 were tested. Carbon isotope fractionation between CH4 and CO2 during hydrogenotrophic methanogenesis was correlated with pH2, as indicated in previous studies. The hydrogen isotope ratio of CH4 produced during rapid growth of the thermophilic methanogen Methanothermococcus okinawensis under high pH2 conditions (~105 Pa) was affected by the isotopic composition of H2, as concluded in a previous study of Methanothermobacter thermautotrophicus. This “ $$ {\updelta \mathrm{D}}_{{\mathrm{H}}_2} $$ effect” is a possible cause of the diversity of previously reported values for hydrogen isotope fractionation between CH4 and H2O examined in H2-enriched culture experiments. Hydrogen isotope fractionation between CH4 and H2O, defined by (1000 + $$ {\updelta \mathrm{D}}_{{\mathrm{CH}}_4} $$ )/(1000 + $$ {\updelta \mathrm{D}}_{{\mathrm{H}}_2\mathrm{O}} $$ ), during hydrogenotrophic methanogenesis of the H2-syntrophic cocultures was in the range 0.67–0.69. The hydrogen isotope fractionation of our H2-syntrophic dataset overlaps with those obtained not only from low-pH2 experiments reported so far but also from natural samples of “young” methane reservoirs (0.66–0.74). Conversely, such hydrogen isotope fractionation is not consistent with that of “aged” methane in geological samples (≥0.79), which has been regarded as methane produced via hydrogenotrophic methanogenesis from the carbon isotope fractionation. As a possible process inducing the inconsistency in hydrogen isotope signatures between experiments and geological samples, we hypothesize that the hydrogen isotope signature of CH4 imprinted at the time of methanogenesis, as in the experiments and natural young methane, may be altered by diagenetic hydrogen isotope exchange between extracellular CH4 and H2O through reversible reactions of the microbial methanogenic pathway in methanogenic region and/or geological methane reservoirs.

Carbon and hydrogen isotope fractionation during methanogenesis: A laboratory study using coal and formation water

Carbon and hydrogen isotope compositions of CH4 generated via methanogenesis in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation waters grown on coal, acetate and H2+CO2 were investigated. CH4 production and molecular analysis confirmed the presence of active microbial communities that are able to convert coal into CH4 using both acetoclastic and hydrogenotrophic pathways. The representative bacterial sequences were dominated by Bacteroidetes, Firmicutes and Deltaproteobacteria, while Methanosaeta and Methanosarcina were the most prevalent archaeal methanogens present in the cultures.CH4 produced in this study's culturing experiments has δ13C values in the range of −50 ‰ to −20 ‰, with most values falling outside the current understanding of the carbon isotopic boundaries for biogenic CH4 (−110 ‰ to −30 ‰). However, the corresponding apparent carbon isotopic α factor (αc=1.02±0.006), and isotopic effect (εc=−20.1 ‰±15.3) showed that CH4 in SSB cultures was predominantly produced by acetoclastic methanogenesis, which is consistent with the results of molecular DNA analysis. In addition, the calculated contribution of CO2 reduction from the δ13C values of coal-treated cultures was overall <50 %, further confirming the high contribution of the acetoclastic pathway to CH4 production in the SSB cultures. The outcome of this experimental study also suggests that δ2H-CH4 values may not provide a reliable basis for distinguishing methanogenic pathways, while apparent carbon isotopic fractionation factor (αc) and isotope effect (εc) are considered more useful indicators of the methanogenic pathway.The high δ13C-CH4 values (≥30 ‰) and the dominance of Methanosaeta over Methanosarcina indicate that methanogens within the SSB cultures were operating at low substrate concentrations. An unusually positive δ13C-CH4 suggests a substrate depletion effect, which is thought to be related to a decrease in the relative abundance of key bacterial coal degraders with formation water inoculum storage time. Closer observation of δ13C-CH4 values during the growth of cultures within a single experiment also showed a 13C-enrichment trend over time. At log phase of growth, the CH4 produced was 13C-depleted when compared to the stationary phase that also indicates substrate depletion effects. Finally, the δ13C-CH4 values encountered in this study (as high as −20 ‰) highlight the possible positive extension of δ13C-CH4 values of acetoclastic methanogenesis from those currently reported in the literature for natural and experimental samples (as high as −30 ‰).

Measurements of hydrogen, oxygen and carbon isotope variability inSphagnummoss along a micro‐topographical gradient in a southern Patagonian peatland

ABSTRACTPeat archives offer a diverse range of physical and chemical proxies from which it is possible to study past environmental and ecological changes. Direct numerical calibration and verification is difficult so process‐based and mechanistic studies are therefore required to establish and quantify links between environmental changes and their associated proxy‐responses. Traditional ‘space‐for‐time’ calibrations provide a solution to this calibration problem, but are often unable to isolate a single environmental variable from other potentially confounding variables. In this study, we explored the potential of a site‐specific ‘space‐for‐time’ approach applied to a hummock‐hollow transect on an ombrotrophic raised bog in Patagonia, southern Chile. Coupled stable carbon, oxygen and hydrogen isotopic measurements were made on individual samples ofSphagnummoss cellulose and compared with plant‐associated waters, local hydrology, temperature and relative humidity, sampled at the same points along the study transect. Results reveal a range of environmental responses, which were supported by plant‐physiological models in the case of carbon and oxygen isotopes. For hydrogen isotopes, the results obtained from cellulose indicated a need for further research into hydrogen isotope fractionation inSphagnum. We recommend conducting site‐specific characterization of plant response to support the development of peat‐based isotope records for palaeoenvironmental research, and where logistically possible, that monitoring is conducted over timescales appropriate to the time‐integrative nature of theSphagnumrecord.

Temporal variations in the δD of leaf n-alkanes from four riparian plant species

The hydrogen isotopic composition of terrestrial plant leaf waxes is widely used as a proxy for the isotopic composition of ambient water at the time of plant growth, yet there is considerable uncertainty about how environmental or plant-specific factors impact apparent hydrogen isotope fractionation. We sampled leaves from four riparian plant species (Pinus strobus, Tsuga canadensis, Phalaris arundinacea and Corylus americana) during the 2013 growing season (April to October) to evaluate the controls of hydrogen isotope fractionation in plant-derived n-alkanes. Our data show that plants from different taxonomic classes produce distinct seasonal patterns of isotopic change that could reflect differences in stomatal regulation, soil versus groundwater uptake and timescales of wax synthesis. These patterns are distinct even for plants from the same functional group (i.e. angiosperms versus gymnosperms). P. strobus (gymnosperm tree) and P. arundinacea (angiosperm grass) are characterized by a significant increase in apparent fractionation during the growing season (>50‰ change). In contrast, n-alkanes from C. americana (angiosperm) show a decrease in ε value from −145±8‰ during early season growth to −111±6‰ late in the season. T. canadensis (gymnosperm) exhibits a constant ε of −123±10‰ throughout the growing season with minimal temporal change. Sedimentary n-alkanes collected from the stream channel adjacent to our plant sample locality show minor changes over the sampling period with a mean ε value of −130±6‰. Apparent fractionation differences between plant species greatly exceed variations in stream composition throughout the growing season, indicating that differences in the timing of wax production or groundwater δD cannot alone explain the variation in ε between different plant types. In contrast to individual plant leaves, fluvial sediments represent a time-integrated ecosystem average of n-alkane δD that yields a more consistent isotopic record of changes in ambient ecosystem water than individual plants.

Water concentrations and hydrogen isotope compositions of alkaline basalt-hosted clinopyroxene megacrysts and amphibole clinopyroxenites: the role of structural hydroxyl groups and molecular water

The aim of this study was to determine both ‘water’ contents (as OH− and H2O) and δD values of several clinopyroxene samples from alkaline basalts. These parameters were first obtained from five clinopyroxene samples using both the classical ‘off-line’ vacuum extraction technique and the ‘on-line’ high-temperature pyrolysis technique. Blanks measured with the ‘on-line’ gas extraction techniques were low enough to prevent any contamination by atmospheric water vapour. The comparison of data has revealed that our ‘on-line’ procedure is more effective for the extraction of ‘water’ from clinopyroxenes and, consequently, this ‘on-line’ technique was applied to ten additional clinopyroxene samples. Sample δD values cover a similar range from −95 to −45 ‰ (VSMOW) regardless of the studied locations, whereas the total ‘water’ content varies from ~115 to ~2570 ppm. The structural hydroxyl content of clinopyroxene samples measured by micro-FTIR spectrometry varies from ~0 to 476 ppm expressed in molecular water equivalent. The total ‘water’ concentrations determined by mass spectrometry differ considerably from structural hydroxyl contents constrained by micro-FTIR, thus indicating that considerable proportion of the ‘water’ may be present in (nano)-inclusions. The structural hydroxyl concentration—apart from clinopyroxenes separated from amphibole clinopyroxenite xenoliths—correlates positively with the δD values of clinopyroxene megacrysts for each locality, indicating that structurally bond hydrogen in clinopyroxenes may have δD values higher than molecular water in inclusions. This implies that there may be a significant hydrogen isotope fractionation for structural hydroxyl during crystallization of clinopyroxene, while for molecular water there may be no or only negligible isotope fractionation.

Near-constant apparent hydrogen isotope fractionation between leaf wax n-alkanes and precipitation in tropical regions: Evidence from a marine sediment transect off SW Africa

A transect of marine surface sediment samples from 1°N to 28°S off southwest Africa was analysed to verify the application of hydrogen isotope compositions of terrestrial plant-wax n-alkanes preserved in ocean sediments as a proxy for continental hydrological conditions. Conditions on the adjacent continent range from humid evergreen forests to deciduous forests, wood- and shrub land and further to arid grasslands and deserts. The hydrogen isotope values for the dominant n-alkane homologues (C29, C31 and C33) vary from −123‰ to −141‰ VSMOW and correlate with the modelled hydrogen isotope composition of mean annual and growing season precipitation of postulated continental source areas (r up to 0.8, p<0.01). The apparent hydrogen isotope fractionation between alkanes and mean annual precipitation is remarkably uniform (−109‰ on average, σ⩽5‰, n=27). Potentially, effects of aridity on the apparent hydrogen isotope fractionation are concealed by the contribution of different plants (C3 dicotyledons vs C4 grasses). Thus, isotope ratios of leaf wax n-alkanes preserved in ocean margin sediments in these and similar tropical regions may be directly converted to δD ratios of ancient precipitation by employing a constant hydrogen isotope fractionation.

Hydrogen Isotope Fractionation As a Tool to Identify Aerobic and Anaerobic PAH Biodegradation.

Aerobic and anaerobic polycyclic aromatic hydrocarbon (PAH) biodegradation was characterized by compound specific stable isotope analysis (CSIA) of the carbon and hydrogen isotope effects of the enzymatic reactions initiating specific degradation pathways, using naphthalene and 2-methylnaphtalene as model compounds. Aerobic activation of naphthalene and 2-methylnaphthalene by Pseudomonas putida NCIB 9816 and Pseudomonas fluorescens ATCC 17483 containing naphthalene dioxygenases was associated with moderate carbon isotope fractionation (εC = -0.8 ± 0.1‰ to -1.6 ± 0.2‰). In contrast, anaerobic activation of naphthalene by a carboxylation-like mechanism by strain NaphS6 was linked to negligible carbon isotope fractionation (εC = -0.2 ± 0.2‰ to -0.4 ± 0.3‰). Notably, anaerobic activation of naphthalene by strain NaphS6 exhibited a normal hydrogen isotope fractionation (εH = -11 ± 2‰ to -47 ± 4‰), whereas an inverse hydrogen isotope fractionation was observed for the aerobic strains (εH = +15 ± 2‰ to +71 ± 6‰). Additionally, isotope fractionation of NaphS6 was determined in an overlaying hydrophobic carrier phase, resulting in more reliable enrichment factors compared to immobilizing the PAHs on the bottle walls without carrier phase. The observed differences especially in hydrogen fractionation might be used to differentiate between aerobic and anaerobic naphthalene and 2-methylnaphthalene biodegradation pathways at PAH-contaminated field sites.

New Bio-Indicators for Long Term Natural Attenuation of Monoaromatic Compounds in Deep Terrestrial Aquifers.

Deep subsurface aquifers despite difficult access, represent important water resources and, at the same time, are key locations for subsurface engineering activities for the oil and gas industries, geothermal energy, and CO2 or energy storage. Formation water originating from a 760 m-deep geological gas storage aquifer was sampled and microcosms were set up to test the biodegradation potential of BTEX by indigenous microorganisms. The microbial community diversity was studied using molecular approaches based on 16S rRNA genes. After a long incubation period, with several subcultures, a sulfate-reducing consortium composed of only two Desulfotomaculum populations was observed able to degrade benzene, toluene, and ethylbenzene, extending the number of hydrocarbonoclastic–related species among the Desulfotomaculum genus. Furthermore, we were able to couple specific carbon and hydrogen isotopic fractionation during benzene removal and the results obtained by dual compound specific isotope analysis (𝜀C = -2.4‰ ± 0.3‰; 𝜀H = -57‰ ± 0.98‰; AKIEC: 1.0146 ± 0.0009, and AKIEH: 1.5184 ± 0.0283) were close to those obtained previously in sulfate-reducing conditions: this finding could confirm the existence of a common enzymatic reaction involving sulfate-reducers to activate benzene anaerobically. Although we cannot assign the role of each population of Desulfotomaculum in the mono-aromatic hydrocarbon degradation, this study suggests an important role of the genus Desulfotomaculum as potential biodegrader among indigenous populations in subsurface habitats. This community represents the simplest model of benzene-degrading anaerobes originating from the deepest subterranean settings ever described. As Desulfotomaculum species are often encountered in subsurface environments, this study provides some interesting results for assessing the natural response of these specific hydrologic systems in response to BTEX contamination during remediation projects.

Different hydrogen isotope fractionations during lipid formation in higher plants: Implications for paleohydrology reconstruction at a global scale.

Leaf wax δDn-alkane values have shown to differ significantly among plant life forms (e.g., among grasses, shrubs, and trees) in higher plants. However, the underlying causes for the differences in leaf wax δDn-alkane values among different plant life forms remain poorly understood. In this study, we observed that leaf wax δDn-alkane values between major high plant lineages (eudicots versus monocots) differed significantly under the same environmental conditions. Such a difference primarily inherited from different hydrogen biosynthetic fractionations (εwax-lw). Based upon a reanalysis of the available leaf wax δDn-alkane dataset from modern plants in the Northern Hemisphere, we discovered that the apparent hydrogen fractionation factor (εwax-p) between leaf wax δDn-alkane values of major angiosperm lineages and precipitation δD values exhibited distinguishable distribution patterns at a global scale, with an average of −140‰ for monocotyledonous species, −107‰ for dicotyledonous species. Additionally, variations of leaf wax δDn-alkane values and the εwax-p values in gymnosperms are similar to those of dicotyledonous species. Therefore, the data let us believe that biological factors inherited from plant taxonomies have a significant effect on controlling leaf wax δDn-alkane values in higher plants.

Intramolecular fractionation of hydrogen isotopes in silicate quenched melts

Intramolecular fractionation of hydrogen isotopes in silicate quenched melts

Hydrogen isotopes in palmitic and stearic acids in suspended particles from the Changjiang River Estuary

Hydrogen isotopes in lipid biomarkers can trace past changes in the hydrologic cycle. Recent studies have revealed the potential of hydrogen isotopes in microalgal lipids for quantitatively reconstructing water δ2H (δD) values and salinity. In this study we collected suspended particles along a salinity gradient from the Changjiang River Estuary (CRE), and measured δD values in fatty acids in these particles. The results indicated that δD values of water were correlated highly with salinity from the CRE, in agreement with the results from other estuaries. δD values in palmitic acid and stearic acid had a positive correlation with δD values of water from the CRE. Nevertheless, in the CRE, hydrogen isotope fractionation in fatty acids relative to water increased as salinity increased, opposite the trend in hydrogen isotope fractionation with salinity found in microalgal culture and field studies. We attribute the increase in hydrogen isotope fractionation as salinity increased to light availability, which was likely lower in the particle rich mixing zone at the end of the estuary, and potentially as well to multiple sources of fatty acids in the CRE.

Analyzing sites of OH radical attack (ring vs. side chain) in oxidation of substituted benzenes via dual stable isotope analysis (δ13C and δ2H)

OH radicals generated by the photolysis of H2O2 can degrade aromatic contaminants by either attacking the aromatic ring to form phenolic products or oxidizing the substituent. We characterized these competing pathways by analyzing the carbon and hydrogen isotope fractionation (εC and εH) of various substituted benzenes. For benzene and halobenzenes that only undergo ring addition, low values of εC (−0.7‰ to −1.0‰) were observed compared with theoretical values (−7.2‰ to −8‰), possibly owing to masking effect caused by pre-equilibrium between the substrate and OH radical preceding the rate-limiting step. In contrast, the addition of OH radicals to nitrobenzene ring showed a higher εC (−3.9‰), probably due to the lower reactivity. Xylene isomers, anisole, aniline, N,N-dimethylaniline, and benzonitrile yielded normal εH values (−2.8‰ to −29‰) indicating the occurrence of side-chain reactions, in contrast to the inverse εH (11.7‰ to 30‰) observed for ring addition due to an sp2 to sp3 hybridization change at the reacting carbon. Inverse εH values for toluene (14‰) and ethylbenzene (30‰) were observed despite the formation of side-chain oxidation products, suggesting that ring addition has a larger contribution to isotope fractionation. Dual element isotope slopes (∆δ2H/∆δ13C) therefore allow identification of significant degradation pathways of aromatic compounds by photochemically induced OH radicals. Issues that should be addressed in future studies include quantitative determination of the contribution of each competing pathway to the observed isotope fractionation and characterization of physical processes preceding the reaction that could affect isotope fractionation.

Hydrogen isotope fractionation and redox‐controlled solution mechanisms in silicate‐COH melt + fluid systems

AbstractThe behavior of volatiles in silicate‐COH melts and fluids and hydrogen isotope fractionation between melt and fluid were determined experimentally to advance our understanding of the role of volatiles in magmatic processes. Experiments were conducted in situ while the samples were at the desired temperature and pressure to 825°C and ~1.6 GPa and with variable redox conditions. Under oxidizing conditions, melt and fluid comprised CO2, CO3, HCO3, OH, H2O, and silicate components, whereas under reducing conditions, the species were CH4, H2, H2O, and silicate components. Temperature‐dependent hydrogen isotope exchange among structural entities within coexisting fluids and melts yields ΔH values near 14 and 24 kJ/mol and −5 and −1 kJ/mol under oxidizing and reducing conditions, respectively. This temperature (and probably pressure)‐dependent D/H fractionation is because of interaction between D and H and silicate and C‐bearing species in silicate‐saturated fluids and in COH fluid‐saturated melts. The temperature‐ and pressure‐dependent D/H fractionation factors suggest that partial melts in the presence of COH volatiles in the upper mantle can have δD values 100% or more lighter relative to coexisting silicate‐saturated fluid. This effect is greater under oxidizing than under reducing conditions. It is suggested that δD variations of upper mantle mid‐ocean ridge basalt (MORB) sources, inferred from the δD of MORB magmatic rocks, can be explained by variations in redox conditions during melting. Lower δD values of the MORB magma reflect more reducing conditions in the mantle source.

Non-linear dynamics of stable carbon and hydrogen isotope signatures based on a biological kinetic model of aerobic enzymatic methane oxidation

The non-linear dynamics of stable carbon and hydrogen isotope signatures during methane oxidation by the methanotrophic bacteria Methylosinus sporium strain 5 (NCIMB 11126) and Methylocaldum gracile strain 14 L (NCIMB 11912) under copper-rich (8.9 µM Cu2+), copper-limited (0.3 µM Cu2+) or copper-regular (1.1 µM Cu2+) conditions has been described mathematically. The model was calibrated by experimental data of methane quantities and carbon and hydrogen isotope signatures of methane measured previously in laboratory microcosms reported by Feisthauer et al. [1] M. gracile initially oxidizes methane by a particulate methane monooxygenase and assimilates formaldehyde via the ribulose monophosphate pathway, whereas M. sporium expresses a soluble methane monooxygenase under copper-limited conditions and uses the serine pathway for carbon assimilation. The model shows that during methane solubilization dominant carbon and hydrogen isotope fractionation occurs. An increase of biomass due to growth of methanotrophs causes an increase of particulate or soluble monooxygenase that, in turn, decreases soluble methane concentration intensifying methane solubilization. The specific maximum rate of methane oxidation υm was proved to be equal to 4.0 and 1.3 mM mM−1 h−1 for M. sporium under copper-rich and copper-limited conditions, respectively, and 0.5 mM mM−1 h−1 for M. gracile. The model shows that methane oxidation cannot be described by traditional first-order kinetics. The kinetic isotope fractionation ceases when methane concentrations decrease close to the threshold value. Applicability of the non-linear model was confirmed by dynamics of carbon isotope signature for carbon dioxide that was depleted and later enriched in 13C. Contrasting to the common Rayleigh linear graph, the dynamic curves allow identifying inappropriate isotope data due to inaccurate substrate concentration analyses. The non-linear model pretty adequately described experimental data presented in the two-dimensional plot of hydrogen versus carbon stable isotope signatures.

A hot and high Eocene Sierra Nevada

Research Article| March 01, 2016 A hot and high Eocene Sierra Nevada Hari T. Mix; Hari T. Mix † 1Department of Environmental Studies and Sciences, Santa Clara University, Santa Clara, California 95053, USA2Department of Earth System Science, Stanford University, Stanford, California 94305, USA †hmix@scu.edu Search for other works by this author on: GSW Google Scholar Daniel E. Ibarra; Daniel E. Ibarra 2Department of Earth System Science, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Andreas Mulch; Andreas Mulch 3Senckenberg Biodiversity and Climate Research Centre (BiK-F), 60325 Frankfurt/Main, Germany4Institut für Geowissenschaften, Goethe Universität Frankfurt, 60438 Frankfurt/Main, Germany5Senckenberg Research Institutes and Natural History Museums, Senckenberganlage 25, 60325 Frankfurt/Main, Germany Search for other works by this author on: GSW Google Scholar Stephan A. Graham; Stephan A. Graham 6Department of Geological Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar C. Page Chamberlain C. Page Chamberlain 2Department of Earth System Science, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Hari T. Mix † 1Department of Environmental Studies and Sciences, Santa Clara University, Santa Clara, California 95053, USA2Department of Earth System Science, Stanford University, Stanford, California 94305, USA Daniel E. Ibarra 2Department of Earth System Science, Stanford University, Stanford, California 94305, USA Andreas Mulch 3Senckenberg Biodiversity and Climate Research Centre (BiK-F), 60325 Frankfurt/Main, Germany4Institut für Geowissenschaften, Goethe Universität Frankfurt, 60438 Frankfurt/Main, Germany5Senckenberg Research Institutes and Natural History Museums, Senckenberganlage 25, 60325 Frankfurt/Main, Germany Stephan A. Graham 6Department of Geological Sciences, Stanford University, Stanford, California 94305, USA C. Page Chamberlain 2Department of Earth System Science, Stanford University, Stanford, California 94305, USA †hmix@scu.edu Publisher: Geological Society of America Received: 03 Feb 2015 Revision Received: 14 Jul 2015 Accepted: 09 Sep 2015 First Online: 09 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2015 Geological Society of America GSA Bulletin (2016) 128 (3-4): 531–542. https://doi.org/10.1130/B31294.1 Article history Received: 03 Feb 2015 Revision Received: 14 Jul 2015 Accepted: 09 Sep 2015 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hari T. Mix, Daniel E. Ibarra, Andreas Mulch, Stephan A. Graham, C. Page Chamberlain; A hot and high Eocene Sierra Nevada. GSA Bulletin 2016;; 128 (3-4): 531–542. doi: https://doi.org/10.1130/B31294.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Despite broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California’s Sierra Nevada remains actively debated. Prior stable isotope–based studies of the Sierra Nevada have relied primarily on hydrogen isotopes in kaolinite, hydrated volcanic glass, and leaf n-alkanes. Here, we reconstruct the temperature and elevation of the early Eocene Sierra Nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral Yuba and American Rivers that drained the windward (Pacific) flank of the Sierra Nevada. First, we evaluated the possible contributions of hydrogen isotope exchange in kaolinite by direct comparison with oxygen isotope measurements. Next, we utilized differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain early Eocene midlatitude weathering temperatures. Oxygen isotope geochemistry of in situ kaolinites indicates upstream (eastward) depletion of 18O in the northern Sierra Nevada. The δ18O values, ranging from 11.4‰ to 14.4‰ at the easternmost localities, correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a Pacific source using Eocene boundary conditions. This result is consistent with prior hydrogen isotope studies of the northern Sierra, but oxygen isotope–based paleoelevation estimates are systematically ∼500–1000 m higher than those from hydrogen-based estimates from the same samples. Kaolinite geothermometry from 16 samples produced early Eocene weathering temperatures of 13.0–36.7 °C, with an average of 23.2 ± 6.4 °C (1σ). These kaolinite temperature reconstructions are in general agreement with paleofloral and geochemical constraints from Eocene California localities and climate model simulations. Our results confirm prior hydrogen isotope–based paleoelevation estimates and further substantiate the existence of a hot and high Eocene Sierra Nevada. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

&amp;lt;italic&amp;gt;n&amp;lt;/italic&amp;gt;-Alkanes and hydrogen isotope fractionations of aquatic plants in lakes on the Changbai Mountains-Lake Baikal transect

With the advance of gas chromatography/thermal conversion isotope ration mass spectrometry (GC/TC/IRMS), compound-specific hydrogen isotope composition ( d D) of molecular organic markers is increasingly used as a palaeoclimate proxy. To explore the hydrogen isotopic fractionation relationships between the alkanes derived from aquatic plants in lakes and the lake waters, we have investigated n -alkane distributions and their d D values of the aquatic plants collected from 5 typical lakes on the Changbai Mountains-Lake Baikal transect in the northern East Asian monsoon regime. The n -C23 and/or n -C25 alkanes are the dominant compounds in submerged aquatic plants. The average chain length (ACL) and the P aq values range from 22.7-26.3 and 0.5-0.99, respectively. d D values of different n -alkanes from a single plant are similar, especially for the n -C21, n -C23 and n -C25. The mean apparent hydrogen isotope fractionation between the lacustrine aquatic plant alkanes and lake waters is -159‰ for the study area, consistent with the conclusion obtained from a European transect (-160‰). We suggest that n -alkanes from aquatic plants can be used to trace the hydrogen isotope composition of the environmental water. On a global scaled basis, the average d D values of n -C23 and n -C25 alkanes might be an optimized proxy with great potential in paleoenvironmental study.

Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia

Hydrogen isotope ratios (2H/1H or δ2H) of plant leaf waxes typically covary with those of precipitation, and are therefore used as a proxy for past hydrologic variability. Mangroves present an important exception to this relationship, as salinity can strongly influence 2H fractionation in leaf lipids. To better understand and calibrate this effect, δ2H values of taraxerol and n-alkanes were measured in the leaves of Rhizophora spp. (red mangroves) from three estuaries and four brackish lakes on the Micronesian islands of Pohnpei and Palau, and compared to the δ2H and δ18O values of leaf water, xylem water and surface water. Net 2H discrimination between surface water and taraxerol increased by 0.9±0.2‰ per part per thousand (ppt−1) over a salinity range of 1–34ppt. Xylem water was always depleted in 2H relative to surface water, and the magnitude of this depletion increased with salinity, which is most likely due to a combination of greater 2H discrimination by roots during water uptake and opportunistic use of freshwater. Changes in the 2H content of xylem water can account for up to 43% of the change in net taraxerol fractionation with salinity. Leaf water isotopes were minimally enriched relative to xylem water and there was not significant variability in leaf water enrichment with salinity, which is consistent with a Péclet-modified Craig–Gordon model of leaf water enrichment. As leaf water enrichment is therefore unlikely to be responsible for increased 2H/1H fractionation in mangrove leaf lipids at elevated salinities, the majority of this signal is most likely explained either by changes in biosynthetic fractionation in response to salt stress or by salinity influenced changes in the timing of water uptake and lipid synthesis.

In situ study of the fractionation of hydrogen isotopes between aluminosilicate melts and coexisting aqueous fluids at high pressure and high temperature – Implications for the δD in magmatic processes

The hydrogen isotopic composition of melt inclusions trapped in phenocrysts during their crystallization and growth in a magma may contribute to a better understanding of the water cycle between the atmosphere, the hydrosphere and the lithosphere. Such understanding relies on the knowledge of the hydrogen isotopic fractionation factors between aqueous fluids, silicate melts, and minerals at temperature and pressure conditions relevant to the Earth's interior. Significant D/H fractionation between silicate melts and aqueous fluids was reported at hundreds of MPa and °C by using in situ measurements in hydrothermal diamond anvil cell (HDAC) experiments (Mysen, 2013a, 2013b, Am. Mineral. 98, 376–386 and 1754–1764). However, the available dataset is focused on fluids and melts with D/H ratios close to unity. The relevance of such data for natural processes that involve per mil variations of δD-values may not always be clear. To address such concerns, the effect of the bulk D/H ratio on hydrogen isotope partitioning between water-saturated silicate melts and coexisting silicate-saturated aqueous fluids has been determined in the Na2O–Al2O3–SiO2–H2O–D2O system. To this end, in situ Raman spectroscopic measurements were performed on fluids and melts with bulk D/H ratios from 0.05 to 2.67 by using an externally-heated diamond anvil cell in the 300–800 °C and 200–1500 MPa temperature and pressure range, respectively.In these pressure/temperature ranges, the D/H ratios of fluids in equilibrium with melt barely change with temperature (in average ΔHfluid=0.47±1.15 kJ/mol). In contrast, the D/H ratios of coexisting melts display strong dependence on temperature (average ΔHmelt=7.18±1.27 kJ/mol). The temperature-dependence of the D/H fractionation factor between melt and fluid (αfluid-melt=D/Hfluid/D/Hmelt) is comparable in all the experiments and can be written: 1000⋅ln⁡(αfluid-melt)=263(±26)⋅T−2–126(±48). Therefore, the αfluid-melt is independent of the bulk D/H ratio of the melt + fluid system.Experimentally determined αfluid-melt using D-enriched fluids, therefore, can be applied to natural systems. It follows that for water-saturated magma strong isotopic fractionation of D and H between water dissolved in magmas and deep aqueous fluids may occur. The δD-values in melt inclusions in phenocrysts in such water-saturated magma will reflect such fluid/melt fractionation effects. A likely result is underestimation of the δD isotopic composition of slab fluids based on δD-values in melt inclusions. The temperature-dependent hydrogen isotope fractionation must be taken into account in the modeling of slab fluid–magma interaction in the mantle wedge.

N-Alkane biosynthetic hydrogen isotope fractionation is not constant throughout the growing season in the riparian tree Salix viminalis

Compound-specific δ2H values of leaf wax n-alkanes have emerged as a potentially powerful paleohydrological proxy. Research suggests terrestrial plant n-alkane δ2H values are strongly correlated with meteoric water δ2H values, and may provide information on temperature, relative humidity, evaporation, and precipitation. This is based upon several assumptions, including that biosynthetic fractionation of n-alkanes during synthesis is constant within a single species. Here we present a multi-isotope study of the n-alkanes of riparian Salix viminalis growing in Norwich, UK. We measured n-alkane δ2H, leaf water δ2H, xylem water δ2H, and bulk foliar δ13C and evaluated the variability of n-alkane δ2H values and net biosynthetic fractionation (εlw-wax) over a whole growing season. S. viminalis n-alkane δ2H values decreased by 40‰ between the start of the growing season in April and the time when they stabilized in July. Variation in leaf and xylem water δ2H did not explain this variability. εlw-wax varied from −116‰ during leaf expansion in April to −156‰ during the stable phase. This suggests that differential biosynthetic fractionation was responsible for the strong seasonal trends in S. viminalis n-alkane δ2H values. We suggest that variability in εlw-wax is driven by seasonal differences in the carbohydrate source and thus the NADPH used in n-alkane biosynthesis, with stored carbohydrates utilized during spring and recent occurring growing season assimilates used later in the season. This is further supported by bulk foliar δ13C values, which are 13C-enriched during the period of leaf flush, relative to the end of the growing season. Our results challenge the assumption that biosynthetic fractionation is constant for a given species, and suggest that 2H-enriched stored assimilates are an important source for n-alkane biosynthesis early in the growing season. These findings have implications for the interpretation of sedimentary n-alkanes and call for a careful design of calibration studies using contemporary samples.

Hydrogen and oxygen stable isotope fractionation in body fluid compartments of dairy cattle according to season, farm, breed, and reproductive stage.

Environmental temperature affects water turnover and isotope fractionation by causing water evaporation from the body in mammals. This may lead to rearrangement of the water stable isotope equilibrium in body fluids. We propose an approach to detect possible variations in the isotope ratio in different body fluids on the basis of different homoeothermic adaptations in varying reproductive stages. Three different reproductive stages (pregnant heifer, primiparous lactating cow, and pluriparous lactating cow) of two dairy cattle breeds (Italian Friesian and Modenese) were studied in winter and summer. Blood plasma, urine, faecal water, and milk were sampled and the isotope ratios of H (2H/1H) and O (18O/16O) were determined. Deuterium excess and isotope-fractionation factors were calculated for each passage from plasma to faeces, urine and milk. The effects of the season, reproductive stages and breed on δ 2H and δ 18O were significant in all the fluids, with few exceptions. Deuterium excess was affected by season in all the analysed fluids. The correlations between water isotope measurements in bovine body fluids ranged between 0.6936 (urine-milk) and 0.7848 (urine-plasma) for δ 2H, and between 0.8705 (urine-milk) and 0.9602 (plasma-milk) for δ 18O. The increase in both isotopic δ values in all body fluids during summer is representative of a condition in which fractionation took place as a consequence of a different ratio between ingested and excreted water, which leads to an increased presence of the heavy isotopes. The different body water turnover between adult lactating cattle and non-lactating heifers was confirmed by the higher isotopic δ for the latter, with a shift in the isotopic equilibrium towards values more distant from those of drinking water.