A Multi-Sims Investigation of Water Content and D/H Ratios in Roberts Massif 04262 with Insight to Sources of Hydrogen in Maskelynite

We want to define the H2O content ([H2O]) and hydrogen (H) isotope composition of meteoritic material from Mars [1-3] with motivation to understand Mars volatile history, constrain geochemical signatures of interior water reservoirs (i.e. the Martian mantle) and explore effects of planetary (e.g. planet formation, magma ocean degassing) and local (e.g. volcanic degassing, impact melting and degassing) processes on H incorporated in minerals. Secondary ion mass spectrometry (SIMS) allows multiple avenues to address these questions. However, application to (1) precious astromaterials and (2) low level H measurements, pose specific challenges that are further complicated when combined. We present preliminary data of a multi-approach (SIMS vs. NanoSIMS) study of H in Roberts Massif 04262 (RBT 04262), an enriched lherzolitic shergottite with nonpoikilitic (NP) and poikilitic (P) lithologies [4]. We analyze olivine, pyrox-ene, and melt inclusions to compare indigenous mantle water, with impact-generated maskelynite to investigate H signatures due to shock

Fractionation of MG Isotopes between the Sun’s Photosphere and the Solar Wind

The Genesis mission goal is to precisely determine the elemental and isotopic composition of the solar photosphere through measurements of solar wind; the photospheric composition being a proxy for the early solar nebula. So, how elements and isotopes are fractionated (or not) when accelerated out of the photosphere is fundamental to interpreting Genesis data

Determining the Elemental and Isotopic Composition of the preSolar Nebula from Genesis Data Analysis: The Case of Oxygen

We compare element and isotopic fractionations measured in solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are consistent with the process of solar wind fractionation. Based on bulk wind measurements, we also consider in more detail the isotopic and elemental abundances of O. We find mild support for an O abundance in the range 8.75 - 8.83, with a value as low as 8.69 disfavored. A stronger conclusion must await solar wind regime specific measurements from the Genesis samples.Comment: 6 pages, accepted by Astrophysical Journal Letter

Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica

International audienceContinental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4 kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer)

D/H Isotope Fractionation During H Diffusion Loss from Clinopyroxene Evidenced in Martian Nakhlites

Knowing the distribution and origin of water in terrestrial planets is crucial to understand their formation, evolution and the source of their atmospheres and surface water. Mantle D/H ratios may be used to determine what type of material contributed water to the terrestrial planets [1]. However, other processes, magmatic or surface alteration processes, can also modify D/H ratios, and for Mars, we only have samples from the crust, as meteorites. The D/H ratio of igneous phases of Martian meteorites is generally explained in terms of the mixing contributions of two reservoirs: surficial with high D/H (dD > 700 ) related to interaction with the martian atmosphere (dD ~ 5000), and mantle-derived with lower D/H (dD < 500 but the exact value is still debated)[2]. However, our present study evidences that H loss in clinopyroxene during degassing can significantly fractionate H isotopes and increase their D/H ratios. In situ analyses of H isotopes, and of water, major and trace element contents were performed on the pyroxenes of 5 nakhlites. Nakhlites are clinopyroxenites that likely originated from the same lava flow or shallow magma chamber. Water contents decrease (380 to <5 ppm H2O) with increasing dD (-268 to 4860 ). Significant influence from spallation, exchange with the martian atmosphere, shock, surface alteration, and hydrothermal processes is ruled out. Together with the evidence of less water at the edge of individual pyroxene grains compared to their interior, we interpret this correlation as the result of preferential diffusive loss of H relative to D from the already crystallized pyroxenes during ascent of the partially-crystallized magma. Similar H isotope fractionations have been observed in another nominally anhydrous mineral, garnet, during experimental dehydration [3]. These results emphasize that caution is warranted when interpreting H isotope analyses of igneous, nominally anhydrous minerals in terms of planetary processes

An Analysis of Tropical Transport: Influence of the Quasi-biennial Oscillation

An analysis of over 4 years of Upper Atmosphere Research Satellite (UARS) measurements of CH4, HF, O3, and zonal wind are used to study the influence of the quasi-biennial oscillation (QBO) on constituent transport in the tropics. At the equator, spectral analysis of the Halogen Occultation Experiment (HALOE) and Microwave Limb Sounder (MLS) observations reveals QBO signals in constituent and temperature fields at altitudes between 20 and 45 km. Between these altitudes, the location of the maximum QBO amplitude roughly corresponds with the location of the largest vertical gradient in the constituent field. Thus, at 40 km where CH4 and HF have strong vertical gradients, QBO signals are correspondingly large, while at lower altitudes where the vertical gradients are weak, so are the QBO variations. Similarly, ozone, which is largely under dynamical control below 30 km in the tropics, has a strong QBO signal in the region of sharp vertical gradients (∼28 km) below the ozone peak. Above 35 km, annual and semi-annual variations are also found to be important components of the variability of long-lived tracers. Therefore, above 30 km, the variability in CH4 and HF at the equator is represented by a combination of semiannual, annual, and QBO timescales. A one-dimensional vertical transport model is used to further investigate the influence of annual and QBO variations on tropical constituent fields. QBO-induced vertical motions are calculated from observed high resolution Doppler imager (HRDI) zonal winds at the equator, while the mean annually varying tropical ascent rate is obtained from the Goddard two-dimensional model. Model simulations of tropical CH4 confirm the importance of both the annual cycle and the QBO in describing the HALOE CH4 observations above 30 km. Estimates of the tropical ascent rate and the variation due to the annual cycle and QBO are also discussed

Magnesium isotopes of the bulk solar wind from Genesis diamond‐like carbon films

NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are “ground truth” for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in the DLC. The resulting SW Mg fractionation relative to the DSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (total) error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. (2011)

Implications of extinction due to meteoritic smoke in the upper stratosphere

Recent optical observations of aerosols in the upper stratosphere and mesosphere show significant amounts of extinction at altitudes above about 40 km where the stratospheric sulfate aerosol layer ends. Recent modeling of this region reveals that meteoritic smoke settling from the mesosphere and its interaction with the upper part of the sulfate aerosol layer is the origin of the observed extinction. Extinction in this region has major implications for the interpretation and analysis of several kinds of aerosol data (satellite and lidar). We compare observations from the SAGE II satellite and from NOAA's lidar located at Mauna Loa, Hawaii to extinction profiles derived from the Whole Atmosphere Community Climate Model (WACCM) coupled with the Community Aerosol and Radiation Model for Atmospheres (CARMA). Our results show that a major source of extinction exists in the region above about 30 km that must be addressed by all remote sensing instruments that have traditionally used the stratosphere above about 30 km as an aerosol free region to estimate the molecular component of their total extinction. It is also shown that meteoritic smoke not only contributes to but also becomes the dominant source of aerosol extinction above 35 km and poleward of 30 degrees in latitude, as well as above 40 km in the tropics. After addressing the concerns described here, current and past observations of this region could be reanalyzed to further our understanding of meteoritic dust in the upper stratosphere

The role of recent admixture in forming the contemporary West Eurasian genomic landscape

Over the past few years, studies of DNA isolated from human fossils and archaeological remains have generated considerable novel insight into the history of our species. Several landmark papers have described the genomes of ancient humans across West Eurasia, demonstrating the presence of large-scale, dynamic population movements over the last 10,000 years, such that ancestry across present-day populations is likely to be a mixture of several ancient groups [1-7]. While these efforts are bringing the details of West Eurasian prehistory into increasing focus, studies aimed at understanding the processes behind the generation of the current West Eurasian genetic landscape have been limited by the number of populations sampled or have been either too regional or global in their outlook [8-11]. Here, using recently described haplotype-based techniques [11], we present the results of a systematic survey of recent admixture history across Western Eurasia and show that admixture is a universal property across almost all groups. Admixture in all regions except North Western Europe involved the influx of genetic material from outside of West Eurasia, which we date to specific time periods. Within Northern, Western, and Central Europe, admixture tended to occur between local groups during the period 300 to 1200 CE. Comparisons of the genetic profiles of West Eurasians before and after admixture show that population movements within the last 1,500 years are likely to have maintained differentiation among groups. Our analysis provides a timeline of the gene flow events that have generated the contemporary genetic landscape of West Eurasia