Intramolecular fractionation of hydrogen isotopes in silicate quenched melts

Losq, Charles Le; Mysen, B. O.; Cody, George D.

doi:10.7185/geochemlet.1609

Cited by 12 publications

(4 citation statements)

References 16 publications

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“…To be able to compare any discrepancies in the results, we solved Equation using δ 2 H and δ 18 O independently. Rarely considered in plant source water identification studies, it has been shown that some trees in certain environments (Ellsworth & Williams, ; Lin & da Sternberg, ) do fractionate hydrogen isotopes (“ 2 H/ 1 H fractionation”) during uptake (Note: For consistency with terminology across multiple disciplines, here we use “ 2 H/ 1 H fractionation” to refer to fractionation between the deuterium and protium isotopes of hydrogen; Horita, ; Le Losq, Mysen, & Cody, ; Sachs & Kawka, ; Wang, Sessions, Nielsen, & Goddard, ). When the soil as a source can be modelled as a single compartment (i.e., minimal to nil isotopic variability with depth), the possible effect of 2 H/ 1 H fractionation can be calculated as the magnitude of isotopic separation (Ellsworth & Williams, ):

Δ^{2} normalH = δ^{2} H_{soil} - δ^{2} H_{xyl}

…”

Section: Methodsmentioning

confidence: 99%

Plant source water apportionment using stable isotopes: A comparison of simple linear, two‐compartment mixing model approaches

Evaristo

McDonnell

Clemens³

2017

Hydrological Processes

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Plant source water identification using stable isotopes is now a common practice in ecohydrological process investigations. Notwithstanding, little critical evaluation of the approaches for source apportionment have been conducted. Here, we present a critical evaluation of the main methods used for source apportionment between vadose and saturated zone water: simple mass balance and Bayesian mixing models. We leverage new isotope stem water samples from a diverse set of tree species in a strikingly uniform terrain and soil conditions at the Christchurch Botanic Garden, New Zealand. Our results show that using δ2H alone in a simple, two‐source mass balance approach leads to erroneous results, particularly an apparent overestimation of groundwater contribution to xylem. Alternatively, using both δ2H and δ18O in a Bayesian inference framework improves the source water estimates and is more useful than the simple mass balance approach, particularly when soil and groundwater contributions are relatively disproportionate. We suggest that plant source water quantification methods should take into consideration the possible effects of 2H/1H fractionation. The Bayesian inference approach used here may be less sensitive to 2H/1H fractionation effects than simple mass balance methods.

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Δ^{2} normalH = δ^{2} H_{soil} - δ^{2} H_{xyl}

…”

Section: Methodsmentioning

confidence: 99%

Plant source water apportionment using stable isotopes: A comparison of simple linear, two‐compartment mixing model approaches

Evaristo

McDonnell

Clemens³

2017

Hydrological Processes

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“…In general, however, this assumption is not valid for silicate melts because strong intermolecular bonds influence isotopic exchanges, thereby leading to a significant underestimation of the isotopic fractionation between distinct phases (e.g., refs. 59, 67, 72, and 73). However, this calculation shows that larger N-isotopic fractionations between the metal and silicate phases are produced depending on whether N is dissolved as N – H complexes or as molecular N 2 .…”

Section: The Effects Of Fo2 and N Speciation On ∆15nmetal-silicatementioning

confidence: 99%

Redox control on nitrogen isotope fractionation during planetary core formation

Dalou

Füri

Deligny

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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The present-day nitrogen isotopic compositions of Earth’s surficial (15N-enriched) and deep reservoirs (15N-depleted) differ significantly. This distribution can neither be explained by modern mantle degassing nor recycling via subduction zones. As the effect of planetary differentiation on the behavior of N isotopes is poorly understood, we experimentally determined N-isotopic fractionations during metal–silicate partitioning (analogous to planetary core formation) over a large range of oxygen fugacities (ΔIW −3.1 < logfO2 < ΔIW −0.5, where ΔIW is the logarithmic difference between experimental oxygen fugacity [fO2] conditions and that imposed by the coexistence of iron and wüstite) at 1 GPa and 1,400 °C. We developed an in situ analytical method to measure the N-elemental and -isotopic compositions of experimental run products composed of Fe–C–N metal alloys and basaltic melts. Our results show substantial N-isotopic fractionations between metal alloys and silicate glasses, i.e., from −257 ± 22‰ to −49 ± 1‰ over 3 log units of fO2. These large fractionations under reduced conditions can be explained by the large difference between N bonding in metal alloys (Fe–N) and in silicate glasses (as molecular N2 and NH complexes). We show that the δ15N value of the silicate mantle could have increased by ∼20‰ during core formation due to N segregation into the core.

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“…This complex environment of protons in silicate melts results in interesting effects such as, for instance, the intramolecular fractionation of the hydrogen isotopes between different structural positions [ Wang et al ., ; Le Losq et al ., ]. This latter effect reflects a complex hydrogen partition function in silicate melts, which influences the fractionation of hydrogen isotopes between silicate melts and minerals or fluids as isotopic partition functions drive partitioning of isotopes between materials [ Bigeleisen and Mayer , ; Urey , ; Richet et al ., ].…”

Section: Introductionmentioning

confidence: 98%

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

2017

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The bonding and speciation of water dissolved in Na silicate and Na and Ca aluminosilicate melts were inferred from in situ Raman spectroscopy of the samples, in hydrothermal diamond anvil cells, while at crustal temperature and pressure conditions. Raman data were also acquired on Na silicate and Na and Ca aluminosilicate glasses, quenched from hydrous melts equilibrated at high temperature and pressure in a piston cylinder apparatus. In the hydrous melts, temperature strongly influences O‐H stretching ν(O‐H) signals, reflecting its control on the bonding of protons between different molecular complexes. Pressure and melt composition effects are much smaller and difficult to discriminate with the present data. However, the chemical composition of the melt + fluid system influences the differences between the ν(O‐H) signals from the melts and the fluids and, hence, between their hydrogen partition functions. Quenching modifies the O‐H stretching signals: strong hydrogen bonds form in the glasses below the glass transition temperature Tg, and this phenomenon depends on glass composition. Therefore, glasses do not necessarily record the O‐H stretching signal shape in melts near Tg. The melt hydrogen partition function thus cannot be assessed with certainty using O‐H stretching vibration data from glasses. From the present results, the ratio of the hydrogen partition functions of hydrous silicate melts and aqueous fluids mostly depends on temperature and the bulk melt + fluid system chemical composition. This implies that the fractionation of hydrogen isotopes between magmas and aqueous fluids in water‐saturated magmatic systems with differences in temperature and bulk chemical composition will be different.

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Intramolecular fractionation of hydrogen isotopes in silicate quenched melts

Cited by 12 publications

References 16 publications

Plant source water apportionment using stable isotopes: A comparison of simple linear, two‐compartment mixing model approaches

Plant source water apportionment using stable isotopes: A comparison of simple linear, two‐compartment mixing model approaches

Redox control on nitrogen isotope fractionation during planetary core formation

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

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