Decomposition of oxalic acid in the presence of water was examined in a hydrothermal diamond-anvil cell up to 800 degrees C and 970-1480 MPa as a function of oxygen fugacity to assess its usefulness as a C-O-H fluid source in petrologic experiments. Fluid, vapor, and solid species were identified in situ at elevated temperature and pressure with Raman spectroscopy and optical microscopy. Under oxidizing conditions (buffered by the reaction NiO <-> Ni+1/2O(2)), oxalic acid decomposes to carbon dioxide and water. Under reducing conditions (buffered by the reaction Mo+O-2 <-> MoO2), oxalic acid decomposes to methane and hydrogen. Under unbuffered conditions, at intermediate oxygen fugacity (similar to O to 1 log units below the fayalite-quartz-magnetite buffer), oxalic acid disproportionates to graphite and minor methane and carbon dioxide. The results from the Ni-NiO-buffered and Mo-MoO2-buffered experiments result in observed fluid species that are similar to those predicted by previous investigations. However, there are substantial differences between our results and previous studies of oxalic acid decomposition in the unbuffered experiment that was within a log unit of the fayalite-magnetite-quartz (FMQ) buffer. These include the detection of aqueous C-H species at temperatures as low as 400 degrees C and a solid graphite-like phase at 800 degrees C. These differences can be explained if we consider that aqueous H-2 in our experiment reacted to form the C-H species, instead of being lost via diffusion through the H-2-permeable capsules used in previous studies. Consequently, for experiments within about 1 log unit of the FMQ buffer curve, oxalic acid is likely a poor choice for a C-O-H fluid source because the formation of graphitic carbon would result in significant deviations from the expected C-O-H fluid composition and concentration (i.e., CO2+H2O). At oxygen fugacities outside a log unit of FMQ, the observed fluid species are similar to those predicted by previous investigations and the use of oxalic acid as a C-O-H fluid source is permissible from the perspective of oxygen fugacity, although other system parameters (e.g., sample geometries, capsule thickness, capsule materials, gasket materials, wall thickness) must still be considered.

Motivation: This article presents Thresher, an improved technique for finding peak height thresholds for automated rRNA intergenic spacer analysis (ARISA) profiles. We argue that thresholds must be sample dependent, taking community richness into account. In most previous fragment analyses, a common threshold is applied to all samples simultaneously, ignoring richness variations among samples and thereby compromising cross-sample comparison. Our technique solves this problem, and at the same time provides a robust method for outlier rejection, selecting for removal any replicate pairs that are not valid replicates.

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An interesting characteristic of the pyroclastic glass bead deposits, select impact produced lithologies such as the "rusty rock" 66095, and unique lunar soils from the Apollo 16 landing site, is their unusual enrichments in Pb-204, Cd, Bi, Br, I, Ge, Sb, Tl, Zn, and Cl which indicates that portions of these sample contain a substantial volatile component. Sample 66095, a fine-grained, subophitic to ophitic polymict melt breccia, also hosts a pervasive low-temperature, volatile-rich, oxy-hydrated mineral assemblage. The volatile element enrichments in these assorted lunar lithologies have been attributed to a variety of extra-lunar and lunar processes, whereas the oxyhydration in 66095 has long been thought to represent either terrestrial alteration of lunar chlorides and Fe-Ni metal to beta FeO(OH,Cl) or indigenous lunar processes. In 66095, Cl is accommodated in FeO(OH,Cl), phosphates, and chlorides and is heterogeneously distributed. The low-temperature alteration occurs as rims around Fe-Ni metal and sulfide grains, and as dispersed grains in the adjacent matrix. Micro-Raman and transmission electron microscope (TEM) imaging indicate that akaganeite (beta FeO(OH,Cl)) is the dominant Fe0(OH) polymorph and is intergrown with goethite (alpha FeO(OH)) and hematite (alpha Fe2O3). TEM observations indicate a well-defined "nanometer-scale" stratigraphy" to the alteration. For example, kamacite (body centered cubic) --> face-centered cubic (fcc) Fe-Ni alloy --> lawrencite (FeCl2) --> akaganeite. The lunar lawrencite (Fe,Ni)Cl-2 in 66095 does not react directly to akaganeite on Earth. Rather, lawrencite exposed to terrestrial conditions reacts to form an amorphous Fe- and Cl-bearing phase, nano-crystalline goethite, and hematite. The morphology of these terrestrial alteration products is significantly different than that of the akaganeite occurring in 66095. The chlorine isotopic compositions of these volatile-rich samples are enriched in heavy Cl. For 66095, the delta Cl-32 ranges from +14.0 parts per thousand to +15.6 parts per thousand, whereas the delta Cl-32 for the volatile-rich A16 soils ranges from +5.6 parts per thousand to +15.7 parts per thousand. Based on these data it appears likely that the volatile element enrichments and the Cl isotopic fractionation observed in 66095 and the Apollo 16 soils did not result from extra-lunar additions, but are most likely indigenous to the Moon. Lawrencite was deposited on mineral surfaces at approximately 650 degrees C to 570 degrees C from a metal-chloride-bearing, H-poor gas phase. This gas phase was also responsible for the transport of other metals (e.g. Zn, Cu, Pb, Fe). The fractionation of Cl isotopes in the rusty rock can be attributed to fumarole processes in a low-H system. The origin and formation of the akaganeite is more enigmatic. The Cl-isotopes are consistent with it replacing lawrencite. However, numerous nanometer-scale observations are not consistent with a terrestrial origin and indicate multiple episodes of oxyhydration. (C) 2014 Elsevier Ltd. All rights reserved.

The Cometary Sampling and Composition (COSAC) experiment onboard the Philae lander is a combined Gas Chromatograph-Mass Spectrometer targeted to determine the organic composition of the nucleus of comet 67P/Churyumov-Gerasimenko. The COSAC flight-model mass spectrometer (FM-MS) was scheduled to sample volatile organic species from 67P's coma prior to Philae's detachment from the Rosetta orbiter in November 2014. It was again scheduled to sample subsequent to Philae's touchdown but prior to drilling operations, thereby retrieving measurements of volatiles from the surface of an unperturbed nucleus. This article evaluates the competence of COSAC mass spectrometers in identifying volatile organic species in both cometary and laboratory-simulated environments. The evaluation was conducted on an operationally optimized COSAC flight spare model mass spectrometer (FS-MS) maintained in ultra-high vacuum. The FS-MS obtained analytical measurements by "sniffing" several organic molecule mixtures of diverse chemical functional groups and molecules with broader molecular masses introduced into the vacuum vessel housing the instrument. The results demonstrate that COSAC produces mass fragmentation patterns of organic species similar to those in calibration standard mass spectra; it is able to identify various organic species within mixtures present at low concentrations (100 ppm); and it can identify fragmentation patterns of non-introduced unknown species and those with high molecular masses within organic mixtures. These observations successfully substantiate the potential of the FM-MS to make qualitative measurements of organic species both in the rarefied environment of the coma and in the relatively enriched nucleus surface. (C) 2014 Elsevier Ltd. All rights reserved.

The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150-300 parts per billion by weight (ppbw)) and C-2 to C-4 dichloroalkanes (up to 70ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles.

Comets harbor the most pristine material in our solar system in the form of ice, dust, silicates, and refractory organic material with some interstellar heritage. The evolved gas analyzer Cometary Sampling and Composition (COSAC) experiment aboard Rosetta's Philae lander was designed for in situ analysis of organic molecules on comet 67P/Churyumov-Gerasimenko. Twenty-five minutes after Philae's initial comet touchdown, the COSAC mass spectrometer took a spectrum in sniffing mode, which displayed a suite of 16 organic compounds, including many nitrogen-bearing species but no sulfur-bearing species, and four compounds-methyl isocyanate, acetone, propionaldehyde, and acetamide-that had not previously been reported in comets.

Changes in composition during the transition from sediment to rock are usually attributed to long, complicated histories and atmospheric influences, while the contribution of benthic mat-building cyanobacteria is not typically considered. Here the goal is to understand the influence of cyanobacterial mats on mineral weathering in postdepositional settings of sandy, shallow subaquatic environments. Laboratory incubation experiments were done using ilmenite sands and ilmenite-enriched quartz sands colonized by cyanobacterial mats for five months at three temperatures: 25 degrees C and 37 degrees C, representative of postdepositional weathering regimes, and 70 degrees C corresponding to early diagenesis. As a comparative control to represent abiotic processes, ilmenite sands and ilmenite-enriched quartz sands were also subjected to the same conditions without cyanobacterial colonization. The precipitation of minerals on cyanobacterial cells and extracellular polymeric substances (EPS) as well as the phase changes in natural ilmenites (FeTiO3) were documented to determine if cyanobacteria influence mineral reaction pathways. The precipitates, ilmenite grains, and permineralized cells were analyzed using complementary techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD), and micro-Raman spectroscopy. The results of this study show that a variety of pure and mixed mineral phases precipitate under postdepositional conditions (T <= 70 degrees C) in wet, sandy environments with or without cyanobacteria. Akaganeite, anatase, ankerite, lepidocrocite, gibbsite, kaolinite, and natrojarosite formed exclusively in the samples incubated with cyanobacteria. In the samples incubated with cyanobacteria, more mineral phases formed at 37 degrees C, suggesting that cyanobacteria play a greater role in weathering than in early diagenesis. Sulfate phases that formed in the presence of cyanobacteria differed in chemical composition from the abiotic precipitates as Na, Al, Mg, and Si were incorporated into the structures of newly formed biotic phases. Understanding the possible fate of these precursor mineral phases will help redefine geochemical biosignatures that can be used for the detection of ancient microbial life in sedimentary rocks on Earth as well as for future missions exploring life on other planets.