Noble gases and stable isotopes track the origin and early evolution of the Venus atmosphere

The composition the atmosphere of Venus results from the integration of many processes entering into play over the entire geological history of the planet. Determining the elemental abundances and isotopic ratios of noble gases (He, Ne, Ar, Kr, Xe) and stable isotopes (H, C, N, O, S) in the Venus atmosphere is a high priority scientific target since it could open a window on the origin and early evolution of the entire planet. This chapter provides an overview of the existing dataset on noble gases and stable isotopes in the Venus atmosphere. The current state of knowledge on the origin and early and long-term evolution of the Venus atmosphere deduced from this dataset is summarized. A list of persistent and new unsolved scientific questions stemming from recent studies of planetary atmospheres (Venus, Earth and Mars) are described. Important mission requirements pertaining to the measurement of volatile elements in the atmosphere of Venus as well as potential technical difficulties are outlined.Comment: 40 pages, 10 figures, 1 tabl

Isotopic Evidence for Multiple Recycled Sulfur Reservoirs in the Mangaia Mantle Plume

This document is the Accepted Version of Record for "Isotopic Evidence for Multiple Recycled Sulfur Reservoirs in the Mangaia Mantle Plume"Mangaia, an ocean island in the Cook-Austral volcanic chain, is the type locality for the HIMU mantle reservoir and has also been shown to exhibit evidence for recycled sulfur with anomalous δ34S and Δ33S that has been attributed an Archean origin. Here we report bulk S-isotope data from sulfide inclusions in olivine and pyroxene phenocrysts from one of the previously analyzed and four additional Mangaia basalts to further test for the prevalence of anomalous S in the HIMU mantle source feeding Mangaia. We document compositions that range from −5.13‰ to +0.21‰ (±0.3 2σ), +0.006‰ to +0.049‰ (±0.016 2σ), −0.81‰ to +0.69‰ (±0.3 2σ) for δ34S, Δ33S, and Δ36S, respectively. These data extend the range of measured compositions and suggest S-isotope heterogeneity in the HIMU mantle source at Mangaia. We show that S-isotope compositions of bulk sulfide in olivine is not in isotopic equilibrium with bulk sulfide in pyroxene from the same samples and that samples from a confined area (M4, M10, M12, and M13) in the northern central part of the island show a distinct covariation for δ34S and Δ33S. This isotopic variation (forming an array) suggests mixing of sulfur from two sources that were captured at different stages of crystallization by phenocrysts in the Mangaia HIMU sulfur endmember

Professional Culture: Let’s Talk Tackling of Inequity, Injustice, and Absent Talent

Progressive reforms and community kindness are encouraged; terminology common among DEI discussions is explored here

Ideas and Perspectives: A Strategic Assessment of Methane and Nitrous Oxide Measurements In the Marine Environment

In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics-namely production, consumption, and net emissions-is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climateactive trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to these efforts is ensuring that the datasets produced by independent scientists are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment

The origin of nitrogen in Earth's mantle: constraints from basalts 15 N/ 14 N and N2/ 3 He ratios

International audiencePlate tectonics is thought to be a major driver of volatile redistribution on Earth. The budget of nitrogen in Earth's mantle has been suggested to be almost entirely surfacederived. Recycling would contribute nitrogen with relatively heavy 15 N/ 14 N isotope ratios to Earth's mantle. This could explain why the Earth's mantle 15 N/ 14 N isotope ratio is substantially higher than both solar gases and chondritic parent bodies akin to enstatite chondrites. Here, published nitrogen isotope data of mid-ocean ridge and ocean island basalts are compiled and used to evaluate the nitrogen subduction hypothesis. Nitrogen isotope ratios are used in conjunction with published N2/ 3 He and K2O/TiO2 ratios on the same basalts. Assuming that 3 He is not recycled, N2/ 3 He ratios are argued to trace nitrogen addition to mantle sources via subduction. Various mantle source enrichments for basalts are tracked with K2O/TiO2 ratios: elevated K2O/TiO2 ratios are assumed to primarily reflect the contributions of recycled components in the basalts mantle sources. The main result of our data compilation is that for most basalts, d 15 N and N2/ 3 He remain constant across a vast range of K2O/TiO2 ratios. Mid-ocean ridge basalts have d 15 N signatures that are lower than air by ~ 4‰ and an average N2/ 3 He ratio of 3.7 (±1.2) x10 6 (95% confidence, n= 30). Published d 15 N and N2/ 3 He are invariant across K2O/TiO2 ratios that vary over a factor of ~ 20. Using estimates of slab K2O/TiO2 and [TiO2], the observed invariant d 15 N and N2/ 3 He ma

Methane thermometry in deep-sea hydrothermal systems: Evidence for re-ordering of doubly-substituted isotopologues during fluid cooling

International audienceDeep-sea hydrothermal fluids are often enriched in carbon dioxide, methane, and hydrogen. Methane effuses from metal-rich black smokers such as the Rainbow hydrothermal field, at temperatures higher than 200 °C. At the Lost City field, CH4 emanates from alkaline fluids at < 100 °C. The abundance of the rare, mass-18 CH4 isotopologues, 13 CH3D and 12 CH2D2, can mitigate degeneracies in the conventional isotopic signatures of methane. We studied the isotopologue compositions of methane from the Rainbow, Lucky Strike, Von Damm, and Lost City hydrothermal fields. At Rainbow, where the vented fluids are at ~360°C, our coupled D 12 CH2D2-D 13 CH3D data establish that methane is in internal equilibrium at 343 #$% &'(°C. This may track the formation temperature of abiotic methane, or it may be the result of equilibration of methane isotopologues within the carrier fluid. Lucky Strike and Von Damm have fluid temperatures < 300°C and although D 13 CH3D values are indistinguishable from those at Rainbow, 12 CH2D2 abundances are marginally higher. At Lost City, D 13 CH3D data show a range of values, which at face value correspond to apparent temperatures of between 265 #,' &,-°C an

Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen

International audienc

Origine, dynamique et multi-compositions isotopiques du soufre dans le manteau terrestre

La teneur et composition isotopique du soufre du manteau terrestre peut apporter des contraintes majeures sur la dynamique interne de cet élément ainsi que sur la nature des hétérogénéités mantelliques. La composition isotopique moyenne de ce réservoir en S peut également renseigner sur le potentiel équilibre entre manteau et noyau et donc sur l'origine du soufre sur Terre. Dans cette étude, nous rapportons les teneurs en S et les abondances relatives du 32S, 33S, 34S et 36S dans plus de 120 verres basaltiques provenant de 3 rides océaniques et d'une faille transformante. Nous proposons un nouveau protocole d'extraction du soufre de verres silicaté basé sur l'utilisation d'acide fluorhydrique. A cette occasion, nous mettons en évidence un biais analytique affectant les données précédemment publiées, lié à l'utilisation du réactif dit de "Kiba". Les 34S re-mesurés sur des échantillons précédemment analysés sont en moyenne 1 plus bas. Nous fournissons également les premièresdonnées de 33S et 36S de basaltes de dorsales. Ces données sont, dans l'erreur, indistinguables du standard international CDT, confirmant l'idée que le manteau a des 33S et 36S proches de 0.000 . Le 34S moyen des MORB est de -0,80 +- 0,38 , significativement inférieur à la valeur chondritique de 0,04 +- 0,31 , et montre une gamme de variation de près de 3 . Celui-ci présente des corrélations avec les isotopes radiogéniques, faisant du 34S un traceur de source. Les covariations entre 34S et isotopes du Plomb dans des basaltes de la ride Pacifique-Antarctique suggèrent le recyclage de croûte océanique portant un 34S positif au sein d'un manteau appauvri significativement négatif, que nous proposons à -1,40 +- 0,20 . Dans les basaltes de la ride Atlantique-Sud, le 34S est corrélé avec le rapport isotopique du Sr et les tendances isotopiques mettent en évidence le recyclage de sédiments dans le manteau source des basaltes étudiés. Dans l'ensemble, la variabilité du 34S associée à l'absence de variabilité du 33S et 36S montre que les composants recyclés sont d'âge post-archéens, en accord avec l'estimation de leur âge classiquement faite via les rapports isotopique du Pb. Enfin, le 34S négatif du manteau source des MORB peut être réconcilié avec un équilibre manteau-noyau, impliquant une origine interne du soufre par opposition à une origine tardive.Sulfur content and isotope composition of the terrestrial mantle can provide major constraints on the internal dynamic of this element and on nature of mantle heterogeneities. The mean S isotope composition of this reservoir can also characterize the potentiel mantle-core equilibrium and hence help to decipher the question of sulfur origin on Earth. In this study, we report S content and relative abundances of 32S, 33S, 34S and 36S in more than 120 glassy basalts coming from 3 ocean ridges and a transform fault. We propose a new sulfur extraction protocol for silicate glasses based on hydrofluoric acid. We evidenced an analytical bias affecting the previously published dataset, probably due to the use of the e"Kiba reagent". The redetermined 34S are approximately 1 lower than the previously published data. We also provide the first 33S and 36S data for ocean ridge basalts. These date are, within uncertainty, indistinguishable from our CDT estimate, confirming the idea that terrestrial mantle has a 33S and 36S close to 0.000 with respect to this international standard. The 34S variability encompasses a 3 range in ocean ridge basalts and correlations between O34S and radiogenic isotopes demonstrate that S isotopes are tracers of mantle heterogeneities. On the other hand, the mean 34S of MORB mantle is -0,80 +- 0,38 , significantly lower than the chondritic value of 0,04 +- 0,31 . The Pb-S isotope systematic in Pacific Antarctic basalts indicates that recycled oceanic crust bears a positive 34S. As a corrollary, this result implies that the depleted part of the mantle is even more negative thant the mean MORB value. We propose a 34S value of -1,40 +- 0,20 for this reservoir. In South Atlantic basalts, the 34S are correlated with Sr isotopes, trends being consistent with recycled sediment feeding the mantle source of these basalts. Taken together, the 34S variability associated to the 33S and 36S constancy indicates that the recycled components are a post-archean age, in agreement with independant estimation of their mean age using Pb isotopes. Finally, the negative 34S of MORB mantle can be reconcilied only with a mantle-core equilibrium, implying an internal origin of sulfur as opposed to a late origin.PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

The origin and dynamics of nitrogen in the Earth's mantle constrained by 15N15N in hydrothermal gases

International audienceThe development of high-resolution gas source mass spectrometry has permitted entirely new types of measurements of multiply-substituted isotopologues in gas species of geochemical significance. Here, we present recent advances afforded by measurements of 15 N 15 N in natural samples, together with 14 N 14 N and 15 N 14 N. We show that the abundance of the doubly-substituted 15 N 15 N isotopologue in hydrothermal gases, often mixtures of volatiles of widely different origins, allows tracing the provenance of nitrogen. The approach is based on the recent finding that atmospheric N2 has a substantial enrichment in 15 N 15 N of nearly 20‰ relative to any other source of N2. This is particularly useful for the study of hydrothermal gases, where characterizing the isotopic composition and provenance of volcanic N2 is important for a wide range of applications in high-temperature geochemistry, but where air-derived N2 is unavoidable. In this review, we summarize the evidence that 15 N 15 N is an unambiguous tracer of ai