The molar abundance ratio of H2Om/OH of rhyolitic porous pyroclasts, obsidian pyroclasts, and flow obsidians from the 1060CE Glass Mountain eruption at Medicine Lake Volcano (USA) were obtained by Diffuse Reflectance Infrared Fourier Transform spectroscopy. Samples were also analyzed for their total water content, [H2Ot], and isotopic composition, delta D, via Temperature Conversion Elemental Analysis (TC/EA). Porous clasts exhibit a H2Om/OH ratio of 0-4.63 (and a [H2Ot] measured by Giachetti et al. (2020) of 0.34-1.2 wt%) that is positively correlated with their porosity and [H2Ot], contrary to the low [H2Ot] and low H2Om/OH ratios of both obsidian pyroclasts (0.32-0.72 wt.%, 0.14-0.63) and flow obsidians (0.04-0.07 wt.%, 0.24-0.28). These results confirm the interpretations of Giachetti et al. (2020) that porous clasts were rehydrated for about 1000 years after the eruption via diffusion of overwhelmingly molecular, meteoric water in the matrix-glass, whereas obsidian pyroclasts and flow obsidians are essentially dense and thus rehydrate poorly. Analyses were also conducted on two size fractions of flow obsidian (<= 63 mu m and 63-250 mu m) that were ground either (1) immediately before analysis or, (2) about nine years prior to analysis and kept in closed containers ever since. Results show that the <= 63 mu m ground samples gained 0.06-0.24 wt% of meteoric water in just nine years, with a H2Om/OH ratio increasing from 0.32-0.54 when measured immediately after crushing, to 3.35-4.64 when measured nine years later. For these smaller particles, even 24 h of heating at 130 degrees C under vacuum before analysis is insufficient to remove all the water gained by rehydration. We thus recommend the use of coarser powders (>= 63 mu m) and longer pre-analysis heating time under vacuum (>= 2 days) for more reliable [H2Ot], H2Om/OH, and delta D measurements on obsidian samples. Given the thinness of the glass in between vesicles in porous pyroclasts and thus their ability to quickly rehydrate, total water content obtained via analysis of the bulk material (e.g., by TC/EA, Loss on Ignition, Karl Fischer titration) must be interpreted together with delta D and/or H2Om/OH data to evaluate the extent of rehydration, even for relatively young samples.

Volcanic lightning during explosive eruptions has been suggested has a key process in the abiotic nitrogen fixation in the early Earth. Although laboratory experiences and thermodynamic models convincingly suggest that volcanic lightning can fix atmospheric nitrogen (e.g. Navarro-Gonzalez et al., 1998, Martin et al., 2007). No geological archives of N-fixed by volcanic lightning have been found yet. Recently, high nitrate concentrations in volcanic deposits from large Neogene explosive eruptions (VEI>7; Aroskay et al. 2023) have been discovered. It is tempting to infer that these nitrates correspond to the end-product of N-fixation by volcanic lightning. However long-term atmospheric deposition of nitrate is suggested to be responsible of nitrate deposits in arid environment (e.g. Atacama Desert and Mojave Desert – Michalski et al. 2004, Lybrand et al. 2013). Therefore, the long-term atmospheric deposition could contribute to nitrates preserved in volcanic deposits. Our study aims to distinguish the origin of nitrates in volcanic deposits: end-product of volcanic lightning or long term atmospheric deposition? To answer this question, volcanic samples from super-eruptions as well as sediments have been collected in the Tecopa Basin – California, USA. The whole sedimentary column (sediments interspersed with volcanic deposits) has been preserved in the same arid conditions for the last 2Ma. The multi-isotopic composition of nitrate has been measured (δ18O, δ15N and Δ17O) and shows clear distinction between nitrate from volcanic deposits and those from sediments. It appears that while nitrate from sediments result from a mix between atmospheric nitrate and biogenic nitrate, in volcanic deposit the nitrate are most likely the end product of volcanic lightning. As a conclusion, we demonstrate that volcanic deposits can be an archive of N-fixation by volcanic lightning. This is an open window on the direct quantification of N-fixation by large explosive volcanic eruptions and their role on the development of life on the early Earth.

Most of the nitrogen (N) accessible for life is trapped in dinitrogen (N2), the most stable atmospheric molecule. In order to be metabolized by living organisms, N2 has to be converted into biologically assimilable forms, so-called fixed N. Nowadays, nearly all the N-fixation is achieved through biological and anthropogenic processes. However, in early prebiotic environments of the Earth, N-fixation must have occurred via natural abiotic processes. One of the most invoked processes is electrical discharges, including from thunderstorms and lightning associated with volcanic eruptions. Despite the frequent occurrence of volcanic lightning during explosive eruptions and convincing laboratory experimentation, no evidence of substantial N-fixation has been found in any geological archive. Here, we report on the discovery of a significant amount of nitrate in volcanic deposits from Neogene caldera-forming eruptions, which are well correlated with the concentrations of species directly emitted by volcanoes (sulfur, chlorine). The multi-isotopic composition (δ18O, Δ17O) of the nitrates reveals that they originate from the atmospheric oxidation of nitrogen oxides formed by volcanic lightning. According to these first geological volcanic nitrate archive, we estimate that, on average, about 60 Tg of N can be fixed during a large explosive event. Our findings hint at a unique role potentially played by subaerial explosive eruptions in supplying essential ingredients for the emergence of life on Earth.

On Earth, most of the nitrogen (N) accessible for life is trapped in dinitrogen (N2), which is the most stable atmospheric molecule. In order to be metabolised by living organisms, N2 has to be converted into assimilable forms, also called fixed N. Nowadays, nearly all the N-fixation is achieved through biological and anthropogenic processes. However, in early environments of the Earth, before the emergence of life, N-fixation must have occurred via natural abiotic processes. Electrical discharges, including from thunderstorms and also lightning associated with volcanic eruptions is one of the most invoked processes. The occurence of volcanic lightning during explosive eruptions is frequent, and convincing laboratory experimentations support the role of this phenomenon, however no evidence of substantial N-fixation has been found in volcanic records. Here we report on the discovery of large amounts of nitrates in volcanic deposits from Neogene caldera-forming eruptions, which are well correlated with the concentrations of species directly emitted by volcanoes such as sulphur and chlorine. The multi-isotopic composition (δ18O, Δ17O) of the nitrates reveals that they originate from the atmospheric oxidation of nitrogen oxides formed by volcanic lightning that occur during the eruption. According to these volcanic nitrate records, our first estimates suggest that about 60 Tg of N can be fixed during a large explosive event. Our findings hint at a unique role potentially played by subaerial explosive eruptions in supplying essential ingredients for the emergence of life on Earth.

The dovecote is one of the last two witnesses of the medieval history of the city of Créteil (11 km SE of Paris). Classified as a historical monument by the French Ministry of Culture in 1972, it was moved away from its original location the same year and restored between 1980 and 1987. Fifty years after its displacement, the dovecote still shows salt efflorescence on the inner and outer wall surface. The aim of this study is to determine the composition and the ancient or modern source of these salts and whether their presence is harmful to the preservation of the dovecote. A combination of low- to non-invasive methods associating microclimatic measurements, mineralogical, petrophysical, chemical and isotopic analyses on micro-samples with historical documentation are used to find the causes of salt enrichment and migration throughout and after the service life of this monument.

This study reports on measurements of Δ17O (derived from the triple oxygen isotopes) in sulphate from black crust sampled in Sicily. Atmospheric oxidants, such as O3, H2O2, OH and O2 carry specific 17O-anomalies, which are partly transferred to the sulphate during sulphur gas (e.g. SO2) oxidation. Hence, the Δ17O in sulphate can be used as a tracer of sulphur oxidation pathways. So far, this method has been mostly applied on sulphate from aerosols, rainwaters, volcanic deposits and ice cores. Here we propose a new approach, that aims to investigate the dominant oxidants of gaseous sulphur precursors into sulphate extracted from black crust material. Black crusts are mostly found on building/monument/sculpture and are the result of the reaction between sulphur compounds (SO2, H2SO4) and carbonate (CaCO3) from the substrate, which leads to the formation of gypsum (CaSO4, 2H2O). Sicilian black crust from sites under different emission influences (anthropogenic, marine and volcanic) were collected. Multi oxygen and sulphur isotope analyses were performed to better assess the origins of black crust sulphate in these different environments. This is crucial for both a better understanding of the sulphur cycle and the preservation of historical monument. Multi sulphur isotopes show mostly negative values ranging from -0.4 ‰ to 0.02 ‰ ± 0.01 and from -0.59 ‰ to 0.41‰ ± 0.3 for Δ33S and Δ36S respectively. This is unique for natural samples and different from sulphate aerosols measured around the world (Δ33S > 0‰). This tends to indicate that sulphate from black crust is not generated by the same processes as sulphate aerosols in the atmosphere. Instead of SO2 oxidation in the atmosphere, dry deposition of SO2 and its oxidation on the substratum is preferred. The multi oxygen isotopes show a clear dependence with the geographical repartition of the samples. Indeed, black crusts from Palermo (the biggest Sicilian city) show small 17O-anomalies ranging between -0.16 ‰ to 1.02 ‰ with an average value of 0.45 ‰ ± 0.26 (n=12; 2σ). This is consistent with Δ17O values measured in black crust from the Parisian Basin (Genot et al., 2020), which are also formed in an environment influenced by anthropogenic and marine emissions. On the other hand, samples from the eastern part of the Mount Etna region, which are downwind of the volcanic emissions, show the highest 17O-anomalies ranging from 0.48 ‰ to 3.87 ‰ with an average value of 2.7 ‰ ± 0.6 (n=11; 2σ). These results indicate that volcanic emissions influence the oxygen isotopic signature of black crust sulphate. In standard urban areas, SO2 deposited on the substratum is mostly oxidised by O2-TMI and H2O2 to generate the black crust. Yet, under the influence of volcanic emissions, O3 may play the main role in the SO2 oxidation.

To better understand the formation and the oxidation pathways leading to gypsum-forming “black crusts” and investigate their bearing on the whole atmospheric SO2 cycle, we measured the oxygen (δ17O, δ18O, and Δ17O) and sulfur (δ33S, δ34S, δ36S, Δ33S, and Δ36S) isotopic compositions of black crust sulfates sampled on carbonate building stones along a NW–SE cross section in the Parisian basin. The δ18O and δ34S values, ranging between 7.5 ‰ and 16.7±0.5 ‰ (n=27, 2σ) and between −2.66 ‰ and 13.99±0.20 ‰, respectively, show anthropogenic SO2 as the main sulfur source (from ∼2 % to 81 %, average ∼30 %) with host-rock sulfates making the complement. This is supported by Δ17O values (up to 2.6 ‰, on average ∼0.86 ‰), requiring > 60 % of atmospheric sulfates in black crusts. Negative Δ33S and Δ36S values between −0.34 ‰ and 0.00±0.01 ‰ and between −0.76 ‰ and -0.22±0.20 ‰, respectively, were measured in black crust sulfates, which is typical of a magnetic isotope effect that would occur during the SO2 oxidation on the building stone, leading to 33S depletion in black crust sulfates and subsequent 33S enrichment in residual SO2. Except for a few samples, sulfate aerosols mostly have Δ33S values > 0 ‰, and no processes can yet explain this enrichment, resulting in an inconsistent S budget: black crust sulfates could well represent the complementary negative Δ33S reservoir of the sulfate aerosols, thus solving the atmospheric SO2 budget.

Volcanic emissions are an important source of atmospheric pollutants. Notably, sulfate aerosols formation from volcanic sulfur emissions induce regional climatic impacts, such as: "vog" production, acid deposition, and hazardous effects on health. Large uncertainties are still pertaining to tropospheric volcanic sulfate production, as active sulfur oxidation pathways within a plume are still uncertain. Recent observations indicate that volcanic emissions are characterized also by large concentrations of reactive halogens. Notably, halogens affect atmospheric oxidants budget via ozone depletion events (ODEs), thus influencing potentially sulfur oxidation in a volcanic plume. A photochemical box-model CiTTyCAT is used to simulate sulfur oxidation within the core of volcanic plumes, and resulting sulfate oxygen isotopic composition. The model accounts for SO2 oxidation by OH in the gas phase, and by H2O2, O3, O2/TMI, and HOX (HOX = HOBr + HOCl) in the liquid phase of: either water droplets and water on ash (referred as condensing plume), or sulfate aerosols in absence of ash (referred as non-condensing plume). It also describes transfer of oxygen mass-independent anomalies (O-MIF) from oxidants to produced sulfate. For condensing plumes, ODEs may also occur in presence of water droplets, while not affecting the hierarchy of oxidation pathways. Sulfur oxidation by O2/TMI remains dominant even for low TMI concentrations, reproducing most isotopic measurements of tropospheric sulfates extracted from volcanic ash, whose O-MIFs equal to 0 ‰. For non-condensing plumes ODEs occur even at very low halogens loading (ca. 50 ppbv). Sulfur oxidation rate is much lower than for condensing plumes, while being driven by H2O2 on sulphate aerosols, and by OH in the gas phase. Sulfate production and relative H2O2 and OH contributions to oxidation depend on halogen loading: larger halogens concentrations induce higher H2O2 contribution, resulting in lower sulfur oxidation. For non-condensing plumes sulfate O-MIF is between 0.8 and 1.4 ‰, in contrast to O-MIF absence in tropospheric sulfates extracted from volcanic ash. These results suggest that sulfate found on tropospheric volcanic ash-deposits is likely formed via sulfur oxidation in water-rich phases, and not via oxidation in the gas-phase or within sulfate aerosols.

At Lake Tecopa, in California, white play-of-color opals are found in vesicles of a volcanic ash layer from the Huckleberry Ridge Tuff super-eruption (2.1 Ma). They show characteristic traits of opal-AG by X-ray diffraction and scanning electron microscopy (silica spheres of similar to 330 nm). These properties are not typical for volcanic opals, and are usually associated with opals formed in a sedimentary environment, such as opal- AG from Australia. The conditions under which opal was formed at Lake Tecopa were determined by oxygen and hydrogen isotopic analyses and give a better understanding of the formation of opal in general. Tecopa opal's delta O-18 is similar to 30%, which leads to a formation temperature between 5 and 10 degrees C from water composition similar to the present spring water composition (delta O-18 = - 12%), or between 15 and 30 degrees C (the present day spring water temperatures) in water having a delta O-18 between -9.5 and -5.5%. As a result, opal experienced 25- 50% evaporation at the Tecopa basin. Contrary to long- held views, the formation of opal-AG vs. opal-CT (or opal-C) is not determined by the type of deposits, i.e., respectively sedimentary vs. volcanic, but mostly by the temperature of formation, low (<= 45 degrees C for opal- AG) vs. high (>= 160 degrees C for opal-CT) as suggested in most recent papers. The isotopic composition of water contained in Tecopa opals is assessed and results show that water in opal records different stages of opal formation from groundwater. Opal seems to precipitate from groundwater that is undertaking isotopic distillation during its circulation, most likely due to 15% up to 80-95% evaporation. Hydrogen isotopes are poorly documented in opal and require more systematic work, but this study reveals that, in Tecopa opals, molecular water (H2Om) is isotopically heavier than structural water (OH), a phenomena already well known in amorphous volcanic glass. Overall, opal isotopic composition reflects the composition of the water from which it precipitated and for that reason could be (as established for amorphous silicic glass) a useful tool for paleoenvironments, and paleoclimatic reconstitutions on Earth and on other terrestrial planets.

The photochemical box model CiTTyCAT is used to analyse the absence of oxygen mass-independent anomalies (O-MIF) in volcanic sulfates produced in the troposphere. An aqueous sulfur oxidation module is implemented in the model and coupled to an oxygen isotopic scheme describing the transfer of O-MIF during the oxidation of SO2 by OH in the gas-phase, and by H2O2, O3 and O2 catalysed by TMI in the liquid phase. Multiple model simulations are performed in order to explore the relative importance of the various oxidation pathways for a range of plausible conditions in volcanic plumes. Note that the chemical conditions prevailing in dense volcanic plumes are radically different from those prevailing in the surrounding background air. The first salient finding is that, according to model calculations, OH is expected to carry a very significant O-MIF in sulfur-rich volcanic plumes and, hence, that the volcanic sulfate produced in the gas phase would have a very significant positive isotopic enrichment. The second finding is that, although H2O2 is a major oxidant of SO2 throughout the troposphere, it is very rapidly consumed in sulfur-rich volcanic plumes. As a result, H2O2 is found to be a minor oxidant for volcanic SO2. According to the simulations, oxidation of SO2 by O3 is negligible because volcanic aqueous phases are too acidic. The model predictions of minor or negligible sulfur oxidation by H2O2 and O3, two oxidants carrying large O-MIF, are consistent with the absence of O-MIF seen in most isotopic measurements of volcanic tropospheric sulfate. The third finding is that oxidation by O2∕TMI in volcanic plumes could be very substantial and, in some cases, dominant, notably because the rates of SO2 oxidation by OH, H2O2 and O3 are vastly reduced in a volcanic plume compared to the background air. Only cases where sulfur oxidation by O2∕TMI is very dominant can explain the isotopic composition of volcanic tropospheric sulfate.

We report for the first time the petro-geochemical study and the emplacement age of the Flamanville granitoid pluton, which is one of the most pedagogical and frequently visited granitoid in France. This study shows that it consists of a potassic alkaline to calc-alkaline and metaluminous granodiorite with biotite, hornblende and pluri-centimetric potassic feldspar megacrysts. In situ U-Pb dating on zircon crystals established that this pluton was formed at 318.1 ± 1.5 Ma, which is older than previously obtained by Rb-Sr and K-Ar methods on biotite (between 299 and 316 Ma). We also report the oldest age measured in France, 2043 ± 4 Ma from in situ U-Pb dating on zircon crystals from the Anse du Cul-Rond gneiss, which could be representative of the Paleoproterozoic crust in which the Flamanville pluton emplaced. These zircons also record an age of 547 ± 15 Ma corresponding to metamorphism during the Cadomian orogeny.

Volcanic emissions are among the major natural sources of sulfur and SO2 in the atmosphere. However, there are still significant uncertainties pertaining to atmospheric oxidation pathways of SO2 and its implications on the budget of atmospheric sulfate particles. Mass- independent fractionations (MIF) can be used as quantitative markers to detect atmospheric pathways of reaction. The majority of the oxygen isotopic anomalies observed in sulfates originate from ozone and it is transferred during tropospheric oxidation of SO2. An oxygen isotopic chemistry scheme for sulfate is implemented into a photochemical box- model (CiTTyCAT) that contains a detailed description of tropospheric chemistry. The chemical scheme has been extended with heterogeneous chemistry of S(IV) and S(VI) species. The mass transfer and oxidation in liquid phases are explicitly treated with no assumptions regarding phase equilibria of soluble gases, and the acid-base equilibrium. The oxygen isotopes MIF scheme has been implemented to simulate the evolution of O-MIF of tropospheric sulfate. The model is used to determine pathways of sulfate formation during the oxidation of volcanic SO2. Comparisons within isotopic compositions of sulfate from volcanic deposits and modeled O-MIF suggest that SO2 is oxidized by O2/TMI in the liquid phase within the volcanic plume.

The use of volcanic glass as recorder of paleoenvironmental conditions has existed for 30 years. In this paper we investigate the methodological aspects of the determination of water content, isotopic composition, and water speciation in volcanic glass using the High Temperature Conversion/Elemental Analyzer (TCEA) mass spectrometer system on milligram quantities of glass concentrates. It is shown here that the precision and the reproducibility of this method is comparable to off-line conventional methods that require 100 times greater amount of material (delta D +/- 3 parts per thousand; H2O](tot) +/- 10relative% if <1 wt% and +/- 5 relative% if >1 wt%) but is quicker and permits easy replication. This method extracts 100% of the water as verified by FTIR measurements. Finally, this study confirms the interest of DRIFT spectroscopy in the NIR range for the study of porous samples such as volcanic pumices and tephra, to determine the water speciation (H2O/OH). It may complement conventional FTIR transmission measurements in the MIR or NIR range that usually require homogeneous transparent sections or high degree of sample dilution in a non-absorbing matrix. Using these methods, we attempt to discriminate residual magmatic from secondary meteoric water in volcanic glass. Using mafic to differentiated samples from different geological settings and different climatic conditions, we show that the H-isotope composition and water content of volcanic glass alone are not always sufficient to provide clear distinction between magmatic and meteoric origin. However if the magma is known to have a delta D between -90 parts per thousand and -40 parts per thousand (-60 parts per thousand. for MORB mantle source), it is quite easy to resolve the delta D evolution during magmatic degassing from post-depositional rehydration by meteoric water with delta D < -50 parts per thousand or delta D > -20 parts per thousand. Water speciation measurements may provide additional information. In most cases, isotopic and total water measurements should be complemented by characterization of water speciation. During magmatic degassing (from 6 wt% to similar to 0.1 wt% water) the H2O/OH is expected to decrease from 2 to close to 0. However, our dataset suggests that during secondary glass hydration (from 0.1 wt% to 6 wt% water) the H2O/OH ratio decreases from similar to 5 to 2, which is the complete opposite. Overall our results support the use of H-isotopes of volcanic glass to discuss the composition of meteoric waters and paleo-climate within a specific region. To this purpose, the volcanic glass has to be almost fully rehydrated in order to fingerprint the isotopic composition of the ambient environmental water. As rehydration is exponentially faster with increasing temperature, efficient rehydration taking months to years, may occur in a cooling volcanic deposits that are meters-thick and thus can remain at a few hundred degrees C for a years to hundreds of years after the eruption. Such deposits could then provide a snap-shot view of climatic conditions at the time of the studied eruption. (C) 2017 Elsevier B.V. All rights reserved.

RATIONALE:The O- and S-isotope compositions of sulfates can be used as key tracers of the fate and sink of sulfate in both terrestrial and extra-terrestrial environments. However, their application remains limited in those geological systems where sulfate occurs in low concentrations. Here we present a simple and reliable method to extract, purify and concentrate sulfate from natural samples. The method allows us to take into account the separation of nitrate, which is known to be an issue in O-isotope analysis.METHODS:The separation and concentration of sulfate from other anions in any aqueous solution are performed within a few hours via anion-exchange resin. The possible O- (δ18 O and Δ17 O) and S- (δ34 S, Δ33 S and Δ36 S) isotope exchanges, fractionations and/or contaminations are for the first time monitored during the whole procedure using initial O- and S-mass-dependent and mass-independent sulfate solutions.RESULTS:After elution in HCl, pure sulfate is fully retrieved and precipitated into BaSO4 , which is suitable for O- and S-isotopic measurements using established techniques. The analysis of retrieved barite presents no variation within 2σ uncertainties: ±0.5‰ and ±0.1‰ in O- (δ18 O, Δ17 O) and ±0.2‰, ±0.02‰ and ±0.09‰ in S- (δ34 S, Δ33 S and Δ36 S) isotope ratios, respectively.CONCLUSIONS:This study shows that the resin method for sulfate extraction and purification, in addition to being cheap, simple and quick, is applicable for the measurements of all O- and S-isotopic ratios in sulfates (including the Δ17 O, Δ33 S and Δ36 S values). Therefore, this method can be easily used for a high range of natural samples in which sulfate occurs in low concentration including aerosols, ice cores, sediments, volcanic deposits, (paleo)soils and rainwater, and thus it can be a key to our understanding of the sulfur cycle on Earth. Copyright © 2016 John Wiley & Sons, Ltd.

Atmospheric sulfates play an important role in the Earth’s radiative balance [IPPC report, 2013]. Volcanoes are among the main natural sources of sulfur in the atmosphere. Once injected in the atmosphere, volcanic sulfur is oxidized and converted to sulfate particles. There are still significant uncertainties pertaining to the atmospheric sulfur oxidation in different regions. Mass-independent isotopic fractionations (MIF) of sulfur oxidized species can be used as quantitative markers of oxidation pathways in the atmosphere and to constrain the sulfur cycle. The majority of the oxygen-MIF anomalies observed in sulfur species originate from the ozone anomaly transferred during oxidation, while the majority of the sulfur-MIF anomalies come from the photochemistry of atmospheric sulfur species. The isotopic composition of sulfate in volcanic deposits has been measured in different regions of the world. We present here the analysis of the isotopic data using a photochemical box-model (CiTTyCAT) that contains a detailed description of tropospheric chemistry. The box-model can be further coupled to a Lagrangian model (FLEXPART) to simulate the transport of chemically evolving air masses. We have added a detailed sulfur chemistry scheme which includes its heterogeneous chemistry in the aqueous phase. Moreover, we have implemented and linked to it an isotope sulfur oxygen scheme, which allows to model the time evolution of the oxygen-MIF in volcanic sulfates during the oxidation of volcanic sulfur. The MIF anomalies modeled in volcanic sulfate are finally compared to the isotopic measurements made on sulfates collected in different regions.