Optical scattering processes observed at the Moon: Predictions for the LADEE Ultraviolet Spectrometer

The Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft will orbit the Moon at an altitude of ≈50 km with a payload that includes the Ultraviolet Spectrometer (UVS) instrument, which will obtain high spectral resolution measurements at near-ultraviolet and visible wavelengths (≈231-826 nm). When LADEE/UVS observes the lunar limb from within the shadow of the Moon it is anticipated that it will detect a lunar horizon glow (LHG) due to sunlight scattered from submicron exospheric dust, as well as emission lines from exospheric gases (particularly sodium), in the presence of the bright coronal and zodiacal light (CZL) background. A modularized code has been developed at NMSU for simulations of scattered light sources as observed by orbiting instruments in lunar shadow. Predictions for the LADEE UVS and star tracker cameras indicate that LHG, sodium (Na) emission lines, and CZL can be distinguished based on spatial morphology and spectral characteristics, with LHG dominant at blue wavelengths (∼250-450 nm) and small tangent heights. If present, LHG should be readily detected by LADEE/UVS and distinguishable from other sources of optical scattering. Observations from UVS and the other instruments aboard LADEE will significantly advance our understanding of how the Moon interacts with the surrounding space environment; these new insights will be applicable to the many other airless bodies in the solar system.     

Acid drainage generation and associated Ca-Fe-SO4 minerals in a periglacial environment, Eagle Plains, Northern Yukon, Canada: A potential analogue for low-temperature sulfate formation on Mars

Near Eagle Plains, northern Yukon, Canada, acidic Ca-Fe-Mg sulfate waters are discharging year-long from disturbed permafrosted sandstone bedrock overlying pyritiferous black shales. These acidic waters are precipitating gypsum with minor amounts of jarosite-K (Na), schwertmannite and hematite. This mineral assemblage is similar to that observed at Meridiani Planum (and other location on Mars), making this site a valuable analogue for low-temperature sulfate geochemistry and mineral formation on Mars. Stable O-S isotope analysis of the acidic waters near Eagle Plains revealed that the oxygen in the dissolved sulfate is mostly derived from water (ca. 70%), suggesting that the sulfide oxidation process could be in part biomediated (i.e., accelerated by acidophilic Fe-oxidizing bacteria). However, unlike the dissolved sulfate in the waters, the formation of the Ca-Fe-SO₄ minerals appears to be purely abiotic. The stable O-S isotope composition of the sulfate minerals is well within the predicted equilibrium range at low temperature, suggesting that they formed through physico-chemical processes (i.e., evaporation or freezing). Low-temperature geochemical modeling with FREZCHEM and PHREEQC suggests that the mineral assemblage at Eagle Plains precipitated mainly through the freezing of Ca-Fe-Mg-SO₄ acidic waters, rather than through evaporation during the dry summer season, although the latter is still possible. This suggests that the sulfate mineral assemblage observed on Mars could have also formed under a periglacial-type climate. Considering that the active layer in the zone affected by acid drainage does not freeze-over during winter, the residual talik offers a localized niche environment to support acidophilic microorganisms. Overall, the fact that acid drainage is presently active near Eagle Plains allows the direct observation of the low-temperature geochemical processes responsible for generating acid drainage conditions and precipitation of gypsum, schwertmannite, jarosite-K, jarosite-Na, goethite and hematite.     

NanoSr – A New Carbonate Microanalytical Reference Material for In Situ Strontium Isotope Analysis

The in situ measurement of Sr isotopes in carbonates by MC‐ICP‐MS is limited by the availability of suitable microanalytical reference materials (RMs), which match the samples of interest. Whereas several well‐characterised carbonate reference materials for Sr mass fractions > 1000 µg g^?1 are available, there is a lack of well‐characterised carbonate microanalytical RMs with lower Sr mass fractions. Here, we present a new synthetic carbonate nanopowder RM with a Sr mass fraction of ca. 500 µg g^?1 suitable for microanalytical Sr isotope research (‘NanoSr’). NanoSr was analysed by both solution‐based and in situ techniques. Element mass fractions were determined using EPMA (Ca mass fraction), as well as laser ablation and solution ICP‐MS in different laboratories. The ⁸⁷Sr/⁸⁶Sr ratio was determined by well‐established bulk methods for Sr isotope measurements and is 0.70756 ± 0.00003 (2s). The Sr isotope microhomogeneity of the material was determined by LA‐MC‐ICP‐MS, which resulted in ⁸⁷Sr/⁸⁶Sr ratios of 0.70753 ± 0.00007 (2s) and 0.70757 ± 0.00006 (2s), respectively, in agreement with the solution data within uncertainties. Thus, this new reference material is well suited to monitor and correct microanalytical Sr isotope measurements of low‐Sr, low‐REE carbonate samples. NanoSr is available from the corresponding author.     

Geochemical signal of seasonality in annually laminated organic- carbonate sediments in Shira lake(Khakasia)

正1 Introduction The most valuable for the task of climate reconstruction are the time series with an annual resolution,which allows to reveal natural periodicity and pass to the search for mechanisms of regional and global climatic changes.Bottom sediments of lakes are one of the best climate archives in addition to tree ring series,ice cores etc.     

Iron solid-phase differentiation along a redox gradient in basaltic soils

Iron compounds in soil are multifunctional, providing physical structure, ion sorption sites, catalytic reaction-centers, and a sink for respiratory electrons. Basaltic soils contain large quantities of iron that reside in different mineral and organic phases depending on their age and redox status. We investigated changes in soil iron concentration and its solid-phase speciation across a single-aged (400 ky) lava flow subjected to a gradient in precipitation (2200-4200 mm yr⁻¹) and hence redox history. With increasing rainfall and decreasing Eh, total Fe decreased from about 25% to <1% of the soil mass. Quantitative speciation of soil solid-phase iron was constrained by combining ⁵⁷Fe Mössbauer spectroscopy (MBS) at 295 and 4.2 K with powder X-ray diffraction, selective chemical extractions, and magnetic susceptibility measurements. This approach allowed us to partition iron into (1) nanoparticulate and microcrystalline Fe^III-(oxy)hydroxides, (2) microcrystalline and bulk Fe^III-oxides, (3) organic/silicate bound Fe^III, and (4) ferrous iron. The Fe^III-(oxy)hydroxide fraction dominated solid-phase Fe, exhibiting a crystallinity continuum based on magnetic ordering temperature. The continuum extended from well-ordered microcrystalline goethite through nanocrystalline Fe^III-(oxy)hydroxides to a nano Fe^III-(oxy)hydroxide phase of extremely low crystallinity. Magnetic susceptibility was correlated (R² = 0.77) with Fe^III-oxide concentration, consistent with a contribution of maghemite to the otherwise hematite dominated Fe-oxide fraction. The Fe^III-(oxy)hydroxide fraction of total Fe decreased with increasing rainfall and was replaced by corresponding increase in the organic/silicate Fe^III fraction. The crystallinity of the Fe^III-(oxy)hydroxides also decreased with increasing rainfall and leaching, with the most disordered members of the crystallinity continuum, the nano Fe^III-(oxy)hydroxides, gaining proportional abundance in the wetter sites. This finding runs counter to the conventional kinetic expectation of preferential removal of the most disordered minerals in a reductive dissolution-dominated environment. We suggest the persistence of highly disordered Fe phases reflects the dynamic redox conditions of these upland soils in which periods of anoxia are marked by high water-throughput and Fe²⁺(aq) removal, while periodic Fe oxidation events occur in the presence of high concentrations of organic matter. Our ⁵⁷Fe Mössbauer study shows basalt-derived nano-scale Fe^III phases are more disordered than current synthetic analogs and have nano-structural characteristics that are linked to their formation environment.     

Results of a microearthquake study,one year before the El Asnam earthquake of October 10, 1980

In November 1979, five portable instruments were installed in the El Asnam area. During a ten-day recording period, nine events of magnitude 0.5 to 1.9 were located in the focal region of the 1980 earthquake. All but one of the events occurred in the north western block defined by the main fault. A composite fault-plane solution agrees with the mechanism of the main shock. No abnormal behaviour of the $\text{V}{}_{\mathrm{p}}\text{V}{}_{\mathrm{s}}$ ratio was observed.     

Means and Covariance Functions for Geostatistical Compositional Data: an Axiomatic Approach

This work focuses on the characterization of the central tendency of a sample of compositional data. It provides new results about theoretical properties of means and covariance functions for compositional data, with an axiomatic perspective. Original results that shed new light on geostatistical modeling of compositional data are presented. As a first result, it is shown that the weighted arithmetic mean is the only central tendency characteristic satisfying a small set of axioms, namely continuity, reflexivity, and marginal stability. Moreover, this set of axioms also implies that the weights must be identical for all parts of the composition. This result has deep consequences for spatial multivariate covariance modeling of compositional data. In a geostatistical setting, it is shown as a second result that the proportional model of covariance functions (i.e., the product of a covariance matrix and a single correlation function) is the only model that provides identical kriging weights for all components of the compositional data. As a consequence of these two results, the proportional model of covariance function is the only covariance model compatible with reflexivity and marginal stability.     

Geophysical characterization of the lithological control on the kinematic pattern in a large clayey landslide (Avignonet,French Alps)

Lithology variation is known to have a major control on landslide kinematics, but this effect may remain unnoticed due to low spatial coverage during investigation. The large clayey Avignonet landslide (French Alps) has been widely studied for more than 35 years. Displacement measurements at 38 geodetic stations over the landslide showed that the slide surface velocity dramatically increases below an elevation of about 700 m and that the more active zones are located at the bottom and the south of the landslide. Most of the geotechnical investigation was carried out in the southern part of the landslide where housing development occurred on lacustrine clay layers. In this study, new electrical prospecting all across the unstable area revealed the unexpected presence of a thick resistive layer covering the more elevated area and overlying the laminated clays, which is interpreted as the lower part of moraine deposits. The downslope lithological boundary of this layer was found at around 700 m asl. This boundary coincides with the observed changes in slide velocity and in surface roughness values computed from a LiDAR DTM acquired in 2006. This thick permeable upper layer constitutes a water reservoir, which is likely to influence the hydromechanical mechanism of the landslide. The study suggests a major control of vertical lithological variations on the landslide kinematics, which is highlighted by the relation between slide velocity and electrical resistivity.