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All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Effects of atmospheric moisture on rock resistivity.

This study examines the changes in resistivity of rock samples as induced by atmospheric moisture. Experiments were performed on samples of hematitic sandstone, pyrite, and galena. The sandstone underwent a change in resistivity of four orders of magnitude when it was measured in a vacuum of 500 ntorr and in air of 37% relative humidity. Pyrite and galena showed no variations in resistivity when they were measured under the same conditions. These results, plus others obtained elsewhere, indicate that rocks of the resistive type are affected in their electrical properties by atmospheric moisture, whereas rocks of the conductive type are not. The experimental evidence obtained is difficult to reconcile with a model of aqueous electrolytic conduction on the sample surface. It is instead suggested that adsorbed water molecules alter the surface resistivity in a manner similar to that observed in semiconductors and insulators.

Alvarez, R.↗
NASA NTRS1976

Exploration for porphyry copper deposits in Pakistan using digital processing of Landsat-1 data

Rock-type classification by digital-computer processing of Landsat-1 multispectral scanner data has been used to select 23 prospecting targets in the Chagai District, Pakistan, five of which have proved to be large areas of hydrothermally altered porphyry containing pyrite. Empirical maximum and minimum apparent reflectance limits were selected for each multispectral scanner band in each rock type classified, and a relatively unrefined classification table was prepared. Where the values for all four bands fitted within the limits designated for a particular class, a symbol for the presumed rock type was printed by the computer at the appropriate location. Drainage channels, areas of mineralized quartz diorite, areas of pyrite-rich rock, and the approximate limit of propylitic alteration were very well delineated on the computer-generated map of the test area. The classification method was used to evaluate 2,100 sq km in the Mashki Chah region. The results of the experiment show that outcrops of hydrothermally altered and mineralized rock can be identified from Landsat-1 data under favorable conditions.

Schmidt, R. G.↗
NASA NTRS1992

Radar-anomalous, high-altitude features on Venus

Over nearly all of the surface of Venus the reflectivity and emissivity at centimeter wavelengths are about 0.15 and 0.85 respectively. These values are consistent with moderately dense soils and rock populations, but the mean reflectivity is about a factor of 2 greater than that for the Moon and other terrestrial planets. Pettingill and Ford, using Pioneer Venus reflectivities and emissivities, found a number of anomalous features on Venus that showed much higher reflectivities and much lower emissivities with both values approaching 0.5. These include Maxwell Montes, a number of high regions in Aphrodite Terra and Beta Regio, and several isolated mountain peaks. Most of the features are at altitudes above the mean radius by 2 to 3 km or more. However, such features have been found in the Magellan data at low altitudes and the anomalies do not exist on all high structures, Maat Mons being the most outstanding example. A number of papers have been written that attempt to explain the phenomena in terms of the geochemistry balance of weathering effects on likely surface minerals. The geochemists have shown that the fundamentally basaltic surface would be stable at the temperatures and pressures of the mean radius in the form of magnetite, but would evolve to pyrite and/or pyrrhotite in the presence of sulfur-bearing compounds such as SO2. Pyrite will be stable at altitudes above 4 or 5 km on Venus. Although the geochemical arguments are rather compelling, it is vitally important to rationally look at other explanations for radar and radio emission measurements such as that presented by Tryka and Muhleman. The radar reflectivity values are retrieved from the raw Magellan backscatter measurements by fitting the Hagfors' radar scattering model in which a surface roughness parameters and a normal incidence electrical reflectivity are estimated. The assumptions of the theory behind the model must be considered carefully before the results can be believed. These include that the surface roughness exists only at horizontal scales large compared to the wavelength, the vertical deviations are gaussianly distributed, there is no shadowing, and that the reflection occurs at the interface of two homogeneous dielectric half-spaces. Probably all these conditions are violated at the anomalous features under discussion. The most important of these is the homogeneity of the near surface of Venus, particularly in highlands. Under the assumptions of the theory, all of the radio energy is reflected by the impedance jump at the very boundary. However, in heterogeneous soil some fraction of the illuminating energy is propagated into the soil and then scattered back out by impedance discontinuities such as rock, voids, and cracks. In light soils, the latter effect can overwhelm the scattering effects of the true surface and greatly enhance the backscatter power, suggesting a much higher value of an effective dielectric constant that would be estimated from Hagfors' model.

Muhleman, Duane O.↗
NASA NTRS1992

Mineral equilibria and the high radar reflectivity of Venus mountaintops

The relationship between altitude and microwave emissivity in 10 highland regions of Venus is investigated on the basis of the Magellan data set. Highlands on Venus are found to display high radar reflectivity. The required change in surface electrical properties occurs abruptly at a 'critical altitude,' whose value varies from one highland area to another. Critical altitudes range from 4.75 km to 2.49 km. Differences in reflectivity are caused by differences in the surface mineral assemblage, which determines the dielectric constant of surface material. The mineral responsible for high radar reflectivity on mountaintops is pyrite, which occurs in weathered mineral assemblages at high altitudes. Conductive pyrite occurs dispersed in insulating materials, forming a loaded dielectric material.

Klose, K. B.↗
NASA NTRS1993

Rates of oxidative weathering on the surface of Mars

A model of acid weathering is proposed for the iron-rich basalts on Mars. Aqueous oxidation of iron sulfides released SO4(2-) and H(+) ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe(2+) ions. The Fe(2+) ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time-dependence of acid weathering reactions show that pyrrhotite is rapidly converted to pyrite plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. On Mars, oxidation rates of dissolved Fe(2+) ions in equatorial melt-waters in contact with the atmosphere are estimated to lie in the range 0.3-3.0 ppb Fe/yr over the pH range 2 to 6. Oxidation of Fe(2+) ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith.

Burns, Roger G.↗
NASA NTRS1994

Geochemical evidence for mixing of three components in martian orthopyroxenite ALH 84001

ALH 84001, a ferroan martian orthopyroxenite, originally consisted of three petrographically defined components: a cumulus assemblage of orthopyroxene + chromite, a trapped melt assemblage of orthopyroxene(?) + chromite + maskelynite + apatite + augite +/- pyrite, and a metasomatic assemblage of carbonate +/- pyrite. We present the results of Instrumental Neutron Activation Analysis (INAA) study of five bulk samples of ALH 84001, combined with Scanning Ion Mass Spectrometer (SIMS) data on the orthopyroxene, in order to attempt to set limits on the geochemical characteristics of the latter two components, and therefore on the petrogenesis of ALH 84001. The INAA data support the petrographic observations, suggesting that there are at least three components in ALH 84001. We will assume that each of the three geochemically required components can be equated with one of the petrographically observed components. Both trapped melt and metasomatic components in ALH 84001 have higher Na than orthopyroxene based on compositions of maskelynite, apatite, and carbonate. For the metasomatic component, we will assume its Na content is that of carbonate, while for a trapped melt component, we will use a typical Na content inferred for martian meteorite parent melts, approximately 1 wt% Na2O. Under these assumptions, we can set limits on the Light Rare Earth Elements/Heavy Rare Earth Elements (LREE/HREE) ratios of the components, and use this information to compare the petrogenesis of ALH 84001 with other martian meteorites. The above calculations assume that the bulk samples are representative of different portions of ALH 84001. We will also evaluate the possible heterogeneous distribution of mineral phases in the bulk samples as the cause of compositional heterogeneity in our samples.

Mittlefehldt, D. W.↗
NASA NTRS2002

Microfossils in the Murchison and Rainbow Carbonaceous Meteorites

Astrobiologists are working to develop methodologies for the recognition of bacterial microfossils, biominerals, and chemical biomarkers in terrestrial rocks, to provide a basis for the scientific assessment of possible microfossils in meteorites and other Astromaterials. During the past 5 years, we have conducted electron microscopy investigations to understand the morphology and chemical composition of microfossils in ancient terrestrial rocks and to search for microfossils presence in meteorites. We have detected evidence of indigenous microfossils and biominerals in-situ in every carbonaceous meteorite investigated but have found no evidence for microfossils in the nickel-iron and stony meteorites studied. In this paper, we provide a brief review of prior evidence for microfossils in meteorites and present Scanning and Environmental Scanning Electron Microscope (SEM and ESEM) and Field Emission Scanning Electron Microscope (FESEM) images of microfossils found in-situ in freshly fractured surfaces of the Murchison and Rainbow meteorites. We describe the techniques and methods used to protect the samples from contamination and for the discrimination of indigenous microfossils from recent terrestrial contaminants We provide data from Energy Dispersive Spectroscopy (EDS) and Link microprobe analysis of the chemical elements and 2D x-ray maps as strong evidence that these biogenic forms are indigenous to the meteorites and cannot logically be interpreted as recent bio-contaminants. We show evidence of framboidal magnetites and pyrites and compare them with framboidal magnetites and pyrites found in Cambrian richs from the Siberian Platform.

Hoover, Richard B.↗
NASA NTRS2010

Mud Volcanoes - Analogs to Martian Cones and Domes (by the Thousands!)

Mud volcanoes are mounds formed by low temperature slurries of gas, liquid, sediments and rock that erupt to the surface from depths of meters to kilometers. They are common on Earth, with estimates of thousands onshore and tens of thousands offshore. Mud volcanoes occur in basins with rapidly-deposited accumulations of fine-grained sediments. Such settings are ideal for concentration and preservation of organic materials, and mud volcanoes typically occur in sedimentary basins that are rich in organic biosignatures. Domes and cones, cited as possible mud volcanoes by previous authors, are common on the northern plains of Mars. Our analysis of selected regions in southern Acidalia Planitia has revealed over 18,000 such features, and we estimate that more than 40,000 occur across the area. These domes and cones strongly resemble terrestrial mud volcanoes in size, shape, morphology, associated flow structures and geologic setting. Geologic and mineralogic arguments rule out alternative formation mechanisms involving lava, ice and impacts. We are studying terrestrial mud volcanoes from onshore and submarine locations. The largest concentration of onshore features is in Azerbaijan, near the western edge of the Caspian Sea. These features are typically hundreds of meters to several kilometers in diameter, and tens to hundreds of meters in height. Satellite images show spatial densities of 20 to 40 eruptive centers per 1000 square km. Many of the features remain active, and fresh mud flows as long as several kilometers are common. A large field of submarine mud volcanoes is located in the Gulf of Cadiz, off the Atlantic coasts of Morocco and Spain. High-resolution sonar bathymetry reveals numerous km-scale mud volcanoes, hundreds of meters in height. Seismic profiles demonstrate that the mud erupts from depths of several hundred meters. These submarine mud volcanoes are the closest morphologic analogs yet found to the features in Acidalia Planitia. We are also conducting laboratory analyses of surface samples collected from mud volcanoes in Azerbaijan, Taiwan and Japan. X-ray diffraction, visible / near infrared reflectance spectroscopy and Raman spectroscopy show that the samples are dominated by mixed-layer smectite clays, along with quartz, calcite and pyrite. Thin section analysis by optical and scanning electron microscopy confirms the mineral identifications. These samples also contain chemical and morphological biosignatures, including common microfossils, with evidence of partial replacement by pyrite. The bulk samples contain approximately 1 wt% total organic carbon and 0.4 mg / gm volatile hydrocarbons. The thousands of features in Acidalia Planitia cited as analogous to terrestrial mud volcanoes clearly represent an important element in the sedimentary record of Mars. Their location, in the distal depocenter for massive Hesperian-age floods, suggests that they contain fine-grained sediments from a large catchment area in the martian highlands. We have proposed these features as a new class of exploration target that can provide access to minimally-altered material from significant depth. By analogy to terrestrial mud volcanoes, these features may also be excellent sites for the sampling martian organics and subsurface microbial life, if such exist or ever existed.

Allen, Carlton C.↗
NASA NTRS2004

Process for Making Single-Domain Magnetite Crystals

A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with deionized water.

Golden, D. C.↗
NASA NTRS2012

Paleo-Environment and C-14 Dating: The Key to the Depositional Age of the Tha Chang and Related Sand Pits, Northeastern Thailand

Tha Chang sand pits, Nakhon Ratchasima Province and many other sand pits in the area adjacent to the Mun River are characterized by their fluviatile environment in association with mass wasting deposits, along the paleo-river channel and the flood plain of the Mun River. Sediments of these deposits are characterized by clasts of various rock types especially the resistant ones with frequent big tree trunks, logs and wood fragments in different sizes and various stages of transformation from moldering stage to lignification and petrification. Widespread pyritization of the lower horizon suggests strongly reducing environment during burial. The Tha Chang deposits have been received much attention from geoscientists especially paleontologist communities, as they contain fragments of some distinct vertebrate species such as Stegadon sp., hominoid primate, rhinoceros Aceratherium and others. Based on the associated mammal fauna and hominoid fossils, the late Miocene ( 9 - 6 Ma) was given for the time of deposition of this sand and gravel unit. Some other reports believed that sediments and materials of these sand and gravel quarries (pits) were deposited by high-energy flood pulses contemporaneous with the tektites forming event during mid-Pleistocene at c. 0.8 Ma. Interpretation from Palynostratigraphical study suggested that the lower horizon of Tha Chang sand pit was deposited during Pliocene/Pleistocene period and the upper horizons are Pleistoncene/Holocene. It is crystal clear that all the fluviatile sediments including tektites and almost all fossil fragments being deposited in these sand pits were, likely a multiple times reworked materials. Only some old bamboo trees, some old crowling trees and fossils grasses observed on the old river bank are considered in situ. C-14 dating of 5 old wood specimens from Tha Chang Sand Pits, 15 old wood specimens from Chumpuang Sand Pits and one sample of old pottery from a Chumpuang Sand Pit were carried out in the NSF- Arizona AMS Laboratory. Although, there is no sharp boundary between the unconsolidated sedimentary horizons in the pits, C-14 ages obtained from the Tha Chang vary from 34,340 BP at the middle horizon (approx 10 m below ground zero) to >49,900 BP at the lower horizon with unknown basal formation (highly pyritized zone approx 20 - 25 m below ground zero). The ages for the Chumpuang vary from 41,700 BP, >45,900 BP and >49,900 BP from the upper most to the lower most of a broad horizon (approx 8 m to approx 12 m below ground zero). The C-14 age of the pottery collected from layer approximately 5 m below ground zero is 2,514 BP. The nature of fluviatile together with occasional mass wasting characteristics of all sand pits studies suggest the relatively faster depositional rate of the lower horizon which involved more flooding and mass wasting deposits than those of the upper horizons. The apparent of some mixing of the wood ages may indicate reworking and lag deposits nature of the area. The depositional rate of the upper most sand and soil horizon (5 m thick) is approximately 1 m per 500 years which mean both erosion and deposition had played a significant role during that time period. In term of the true age of the formation, we argue that since most of the materials deposited are reworked materials, all ages obtained from fossil fragments could not be the age of sand and gravel formation. Furthermore, the maximum age of all the tektite bearing horizons cannot be older than 0.8 Ma. The oldest C-14 age of 49,900 BP is interpreted as the minimum age of the Tha Chang and related sand pits formation when geomorphology of the area was a lot more hilly and much higher gradient than that of the present day.

Putthapiban, P.↗
DOE OSTI2025

Spatially resolved X-ray imaging and molecular characterisation of sulfur and iron in organic- and sulfur-rich hydrocarbon source mudstones

Sulfurisation of organic matter (OM) is a prominent preservation mechanism, however iron sulfide precipitation, particularly pyrite (FeS2), can counteract this mechanism. There is a dearth of high-resolution, spatially-resolved spectroscopic (redox) information on sulfur and iron inventories within organic-rich rocks that would improve our understanding of prevailing environmental conditions during deposition. Here, state-of-the-art synchrotron-based X-ray absorption and fluorescence analyses of key organic- and sulfur-rich mudstones demonstrate the potential of these techniques to non-destructively map and produce detailed spectroscopic information. Detailed high-resolution analyses (μm- to mm-scale) reveal the presence of widespread sulfurised OM in the Blackstone Band of the Kimmeridge Clay Formation, in line with a persistence of euxinia over a long temporal span and low reactive iron input, facilitating the preservation of OM through sulfurisation. In contrast, the presence of sulfurised OM was transitional in the Monterey Formation, consistent with fluctuating water column redox conditions, and is less significant in the Whitby Mudstone Formation, likely due to the high reactive iron concentrations outcompeting sulfurised OM formation. Analyses of sulfur species using model compounds further indicate that the Whitby Formation is strongly enriched in inorganic reduced sulfur minerals, while both the Kimmeridge Clay and Monterey Formations are dominated by organic sulfur species. These synchrotron-based observations improve our understanding of environmental conditions during the time of deposition of these mudstones and thus show great promise in the study of organic-rich sediments, especially in allowing their depositional settings to be more accurately reconstructed.

Kimmeridge Clay Formation↗
DOE OSTI2025

Biogeochemical controls on iron speciation and cycling across upland to shoreline gradients in freshwater and estuarine coastal soils (Lake Erie and Chesapeake Bay, United States)

Coastal environments are dynamic interfaces that mediate carbon and nutrient exchanges between terrestrial landscapes and open waters, and understanding the biogeochemical factors controlling these exchanges, particularly iron (Fe) redox transformations, is crucial for predicting coastal ecosystem functions. Here, we investigated the mechanisms controlling Fe speciation changes across upland-to-shoreline gradients in freshwater and estuarine soils using Fe K-edge X-ray absorption spectroscopy, solid and porewater composition analysis, and 16S rRNA sequencing analysis. We show that Fe transformations depend primarily on inundation patterns. In unsaturated uplands, Fe occurs as Fe(III) oxyhydroxides, mainly goethite (9–35 %), Fe(II,III)-phyllosilicates (39–89 %), and Fe(III)-organic species (0–61 %). Soils influenced by estuarine waters exhibit porewater sulfide concentrations reaching up to 221 μM, Fe- and S-cycling bacteria, and up to 81 % pyrite (FeS 2 ), indicating that sulfur-driven redox dynamics control Fe transformations. In lacustrine wetlands, Fe(III) reduction is indicated by porewater Fe(II) concentrations increasing to 1.0–2.1 mM, and ~10–15 % of Fe as Fe(II,III)-(hydr)oxides (green rust), vivianite (Fe 3 (PO 4 ) 2 ·8H 2 O), and/or adsorbed Fe(II) species. EXAFS data also indicate reduction of structural Fe(III) to Fe(II) in phyllosilicates. The presence of Fe- and S-cycling bacteria, as well as sulfide (0–10 μM), suggests that Fe-cycling is microbially driven and potentially coupled with cryptic S-cycling. Fe(II) oxidation was indicated above/near the water table by the presence of Fe(III) oxyhydroxides (ferrihydrite, lepidocrocite). Furthermore, negligible Fe(III) or sulfate reduction was observed at some water-saturated sites located at the upland-wetland transition, likely due to oxic (sub-)surface water inputs. Overall, our results highlight the importance of considering both Fe-speciation and hydro-biogeochemical dynamics when predicting Fe-cycling at coastal interfaces.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Inorganic Alterations in Unconventional Shale Reservoirs: Importance of Additive and Base Fluid Chemistry

The effective development of unconventional petroleum systems requires the use of significant water resources. In an effort to reduce the consumption of freshwater resources for hydraulic fracturing, highly saline produced waters are increasingly recycled for use as a base fluid. However, there are significant knowledge gaps regarding potential water–rock interactions resulting from the introduction of produced waters and associated additives into shale reservoirs such as formation and deposition of mineral scale, which can negatively affect hydrocarbon production through wellbore restriction and damage to hydraulically generated fractures. To assess the impacts of field stimulation practices in the subsurface, a series of laboratory experiments were completed using (a) three distinct sedimentary rock formations of the Midland Basin (Texas, USA) and (b) additives with two different base fluids: municipal fresh water and clean brine. The experimental approach used relevant injection sequences and mixing ratios in specialized reactors for 3 weeks. Static pressurized experiments and nonpressurized time-resolved experiments were undertaken. The resulting solids and liquids were analyzed by using a variety of laboratory- and synchrotron-based techniques. The use of an acid spearhead (15% HCl) resulted in texturing of both clay-rich and calcareous shales, which can temporarily enhance porosity but subsequently result in mineral scale deposition. The primary matrix scale was Fe(III)-bearing phases, which occurred in all experiments regardless of base fluid chemistry. Additionally, strontium sulfate (SrSO 4 ) precipitated on shale surfaces when clean brines were used. It was concluded that clean brine was the main source of Sr 2+ species, while persulfate breaker degradation and oxidation of pyrite were the sources of SO 4 2– . Sulfate scaling was more pronounced in clay-rich shales, suggesting that Sr sorption is important for promoting celestite formation. This work demonstrates that mineral scale deposition is a complex phenomenon, whereby the type and proportions of various mineral phases are determined from reservoir alteration processes and coprecipitation of constituents from injection fluids. In conclusion, the experimental results shown here should be considered when evaluating different base fluids and additives in order to mitigate mineral precipitation in unconventional shale reservoirs, which could result in reservoir degradation.

Jew, Adam D. [SLAC National Accelerator Laboratory↗
DOE OSTI2024

Oxidized Sulfur Species in Slab Fluids as a Source of Enriched Sulfur Isotope Signatures in Arcs

Recycling of oxidized sulfur from subducting slabs to the mantle wedge provides simultaneous explanations for the elevated oxygen fugacity (fO 2 ) in subduction zones, their high hydrothermal and magmatic sulfur outputs, and the enriched sulfur isotopic signatures (i.e., δ 34 S > 0‰) of these outputs. However, a quantitative understanding of the abundance and speciation of sulfur in slab fluids consistent with high pressure experiments is lacking. Here we analyze published experimental data for anhydrite solubility in H 2 O-NaCl solutions to calibrate a high-pressure aqueous speciation model of sulfur within the framework of the deep earth water model. We characterize aqueous complexes, required to account for the high experimental anhydrite solubilities. We then use this framework to predict the speciation and solubility of sulfur in chemically complex fluids in equilibrium with model subducting mafic and ultramafic lithologies, from 2 to 3 GPa and 400 to 800°C at log fO 2 from FMQ-2 to FMQ+4. We show that sulfate complexes of calcium and sodium markedly enhance the stability of sulfate in moderately oxidized fluids in equilibrium with pyrite at fO 2 conditions of FMQ+1 to +2, causing large sulfur isotope fractionations up to 10‰ in the fluid relative to the slab. Such fluids could impart oxidized, sulfur-rich and high δ 34 S signatures to the mantle wedge that are ultimately transferred to arc magmas, without the need to invoke 34 S-rich subducted lithologies.

58 GEOSCIENCES↗
DOE OSTI2024

Climate forcing controls on carbon terrestrial fluxes during shale weathering

Climate influences near-surface biogeochemical processes and thereby determines the partitioning of carbon dioxide (CO 2 ) in shale, and yet the controls on carbon (C) weathering fluxes remain poorly constrained. Using a dataset that characterizes biogeochemical responses to climate forcing in shale regolith, we implement a numerical model that describes the effects of water infiltration events, gas exchange, and temperature fluctuations on soil respiration and mineral weathering at a seasonal timescale. Our modeling approach allows us to quantitatively disentangle the controls of transient climate forcing and biogeochemical mechanisms on C partitioning. We find that ~3% of soil CO 2 (1.02 mol C/m 2 /y) is exported to the subsurface during large infiltration events. Here, net atmospheric CO 2 drawdown primarily occurs during spring snowmelt, governs the aqueous C exports (61%), and exceeds the CO 2 flux generated by pyrite and petrogenic organic matter oxidation (~0.2 mol C/m 2 /y). We show that shale CO 2 consumption results from the temporal coupling between soil microbial respiration and carbonate weathering. This coupling is driven by the impacts of hydrologic fluctuations on fresh organic matter availability and CO 2 transport to the weathering front. Diffusion-limited transport of gases under transient hydrological conditions exerts an important control on CO 2 (g) egress patterns and thus must be considered when inferring soil CO 2 drawdown from the gas phase composition. Our findings emphasize the importance of seasonal climate forcing in shaping the net contribution of shale weathering to terrestrial C fluxes and suggest that warmer conditions could reduce the potential for shale weathering to act as a CO 2 sink.

58 GEOSCIENCES↗
DOE OSTI2024

Republished: Colossal density-driven resistance response in the negative charge transfer insulator MnS 2

The Mn chalcogenides show a remarkable variation in structural and physical properties with density. In MnS 2 we observe a pronounced difference with the effects of varying hydrostaticity with pressure inducing a structural transition at 300 K. Within the pyrite phase, a colossal electrical resistance drop of 10 8 Ohms is observed by 12 GPa of nonhydrostatic compression at 300 K. DFT simulations reveal the metallization to be unexpectedly driven by previously unoccupied S$^{2-}_2$ σ$^*_{3p}$ antibonding states crossing the Fermi level. This is a seldom seen variant of the charge transfer insulator to metal transition for negative charge transfer insulators which have anions with an unsaturated valence. Finally, by 36 GPa of nonhydrostatic compression, the single presence of the low-spin insulating arsenopyrite (P2 1 /c) phase is confirmed, and the bulk metallicity is broken with the system returning to an insulative electronic state.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Impact of mineral and non-mineral sources of iron and sulfur on the metalloproteome of Methanosarcina barkeri

Methanogens often inhabit sulfidic environments that favor the precipitation of transition metals such as iron (Fe) as metal sulfides, including mackinawite (FeS) and pyrite (FeS 2 ). These metal sulfides have historically been considered biologically unavailable. Nonetheless, methanogens are commonly cultivated with sulfide (HS - ) as a sulfur source, a condition that would be expected to favor metal precipitation and thus limit metal availability. Recent studies have shown that methanogens can access Fe and sulfur (S) from FeS and FeS 2 to sustain growth. As such, medium supplied with FeS 2 should lead to higher availability of transition metals when compared to medium supplied with HS - . Here, we examined how transition metal availability under sulfidic (i.e., cells provided with HS - as sole S source) versus non-sulfidic (cells provided with FeS 2 as sole S source) conditions impact the metalloproteome of Methanosarcina barkeri Fusaro. To achieve this, we employed size exclusion chromatography coupled with inductively coupled plasma mass spectrometry and shotgun proteomics. Significant changes were observed in the composition and abundance of iron, cobalt, nickel, zinc, and molybdenum proteins. Among the differences were alterations in the stoichiometry and abundance of multisubunit protein complexes involved in methanogenesis and electron transport chains. Furthermore, our data suggest that M. barkeri utilizes the minimal iron-sulfur cluster complex and canonical cysteine biosynthesis proteins when grown on FeS 2 but uses the canonical Suf pathway in conjunction with the tRNA-Sep cysteine pathway for iron-sulfur cluster and cysteine biosynthesis under sulfidic growth conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Identifying microbial functional guilds performing cryptic organotrophic and lithotrophic redox cycles in anaerobic granular biofilms

Granular biofilms used in anaerobic digester systems contain diverse microbial populations that interact to hydrolyze organic matter and produce methane within controlled environments. Prior research investigated the feasibility of utilizing granular biofilms obtained from an anaerobic digester to remove nitrate without the addition of exogenous electron donors. These granules possessed a unique structure of alternating light and dark iron sulfide and pyrite rich layers that potentially served as both an electron source and sink, linking carbon, nitrogen, sulfur, and iron cycles. To characterize the functional roles of diverse microbial populations enriched within these layered biofilms, we analyzed metagenomes obtained from three different granules. Comparisons between the functional gene content of forty metagenome assembled genomes (MAGs) identified phylogenetically cohesive functional guilds. Each of these functional MAG clusters was assigned to specific steps in anaerobic digestion (hydrolysis, acidogenesis, acetogenesis, and methanogenesis) and anaerobic respiration (denitrification and sulfate reduction). Comparisons with metagenomes derived from a variety of natural and engineered ecosystems confirmed that the enriched denitrifying bacteria were similar to populations typically found in wetlands and biological nitrogen removal systems. Analysis of read alignments to individual genes within the forty MAGs identified conserved genomic features that were representative of the functions that distinguished functional guilds. Overall, this research illustrates the utility of functional based classification of microorganisms for characterizing ecosystem functions and highlights the potential application of engineered ecosystems to serve as experimental models for complex natural ecosystems.

Ecosystem engineering↗