Carbon Abundances Research Articles

A new pyrope-based mineralogical-petrological method for identifying the diamond potential of kimberlite/lamproite deposits

• Fluid compositions can be additional indicator of the carbon formation in petrology. • Optimum conditions for diamond growth and preservation correspond to water-rich fluid. • Estimated fluid of the main part of the high diamond grade pipes corresponds to water-rich fluid. • Calculated fluid compositions from EMP pyrope analyses can be used in the prospecting of diamond deposits. P-T- Oxygen fugacity (fO 2 ) conditions and fluid compositions were estimated for the formation conditions of pyrope garnet inclusions in diamonds and xenocrysts from diamond-bearing and diamond-free kimberlites using their total chemical analyses and single oxythermobarometry. Our data indicate that optimal conditions for diamond growth and preservation occur in the presumed water-rich mantle fluids containing the lowest abundance of free atomic carbon. The majority of the calculated C-H-O fluid compositions for diamond formation in peridotite xenoliths from high diamond grade kimberlites correspond to a high hydrogen and low carbon and oxygen atomic fluid percents, while those from the majority of peridotite xenoliths in the low grade diamond kimberlites corresponds to the low hydrogen, high carbon and oxygen atomic percent fluids. This new approach defines the conditions of diamond formation for kimberlitic deposits. It better characterizes diamond grades in kimberlites in comparison to the previous empirical mineralogical Ca-Cr methods and can be used as a more precise mineralogical-petrological method for prospecting for kimberlitic diamond deposits.

Immiscible metallic melts in the upper mantle beneath Mount Carmel, Israel: Silicides, phosphides, and carbides

Abstract Xenolithic corundum aggregates in Cretaceous mafic pyroclastics from Mount Carmel contain pockets of silicate melts with mineral assemblages [SiC (moissanite), TiC, Ti2O3 (tistarite), Fe-Ti-Zr silicides/phosphides] indicative of magmatic temperatures and oxygen fugacity (fO2) at least 6 log units below the iron-wüstite buffer (ΔIW ≤ –6). Microstructural evidence indicates that immiscible, carbon-rich metallic (Fe-Ti-Zr-Si-P) melts separated during the crystallization of the silicate melts. The further evolution of these metallic melts was driven by the crystallization of two main ternary phases (FeTiSi and FeTiSi2) and several near-binary phases, as well as the separation of more evolved immiscible melts. Reconstructed melt compositions fall close to cotectic curves in the Fe-Ti-Si system, consistent with trapping as metallic liquids. Temperatures estimated from comparisons with experimental work range from ≥1500 °C to ca. 1150 °C; these probably are maximum values due to the solution of C, H, P, and Zr. With decreasing temperature (T), the Si, Fe, and P contents of the Fe-Ti-Si melts increased, while contents of Ti and C decreased. The increase in Si with declining T implies a corresponding decrease in fO2, probably to ca. ΔIW-9. The solubility of P in the metallic melts declined with T and fO2, leading to immiscibility between Fe-Ti-Si melts and (Ti,Zr)-(P,Si) melts. Decreasing T and fO2 also reduced the solubility of C in the liquid metal, driving the continuous crystallization of TiC and SiC during cooling. The lower-T metallic melts are richer in Cr, and to some extent V, as predicted by experimental studies showing that Cr and V become more siderophile with decreasing fO2. These observations emphasize the importance of melt-melt immiscibility for the evolution of magmas under reducing conditions. The low fO2 and the abundance of carbon in the Mt. Carmel system are consistent with a model in which differentiating melts were fluxed by fluids that were dominated by CH4+H2, probably derived from a metal-saturated sublithospheric mantle. A compilation of other occur-rences suggests that these phenomena may commonly accompany several types of explosive volcanism.

UV Extinction as a More Fundamental Measure of Dust than E(B − V) or A V

Abstract The gas-to-dust ratio of reddened stars in the Milky Way (MW), the Magellanic Clouds, and in general, is usually expressed as a linear relation between the hydrogen column density, N(H), and the reddening, E(B − V), or extinction in the V-band (A V ). If the extinction curve were truly universal, the strength of the relationship and the linearity would naturally be maintained for extinction at any wavelength, as well as for N(H) versus E(B − V). However, extinction curves vary within the MW, and there is no reason, except by chance, why either E(B − V) or A V would be the most physical measure of dust column density. In this paper, we utilize for the first time full extinction curves to 41 MW sightlines, finding that the scatter between N(H) and extinction is minimized—and the relation becomes linear—for extinction at 2900 ± 160 Å. Scatter and nonlinearity increase at longer wavelengths, and are especially large for near-IR extinction. We conclude that near-UV extinction is a superior measure of the dust column density for MW dust. We provide new, nonlinear gas-to-dust relations for various dust tracers. We also find that the very large discrepancy between MW and SMC gas-to-dust ratios of 0.9 dex in N(H)/E(B − V) is reduced to 0.7 dex for far-UV extinction, which matches the difference in cosmic abundances of carbon between the two galaxies, and therefore confirms that N(C) is the preferred measure for gas in the gas-to-dust ratio, even though it may not be a convenient one.

The intermediate neutron capture process

Context. Results from observations report a growing number of metal-poor stars showing an abundance pattern midway between the s- and r-processes. These so-called r/s-stars raise the need for an intermediate neutron capture process (i-process), which is thought to result from the ingestion of protons in a convective helium-burning region, but whose astrophysical site is still largely debated. Aims. We investigate whether an i-process during the asymptotic giant branch (AGB) phase of low-metallicity low-mass stars can develop and whether it can explain the abundances of observed r/s-stars. Methods. We computed a 1 M⊙ model at [Fe/H] = −2.5 with the stellar evolution code STAREVOL, using a nuclear network of 1091 species (at maximum) coupled to the transport processes. The impact of the temporal and spatial resolutions on the resulting abundances was assessed. We also identified key elements and isotopic ratios that are specific to i-process nucleosynthesis and carried out a detailed comparison between our model and a sample of r/s-stars. Results. At the beginning of the AGB phase, during the third thermal pulse, the helium driven convection zone is able to penetrate the hydrogen-rich layers. The subsequent proton ingestion leads to a strong neutron burst with neutron densities of ∼4.3 × 1014 cm−3 at the origin of the synthesis of i-process elements. The nuclear energy released by proton burning in the helium-burning convective shell strongly affects the internal structure: the thermal pulse splits and after approximately ten years the upper part of the convection zone merges with the convective envelope. The surface carbon abundance is enhanced by more than 3 dex. This leads to an increase in the opacity, which triggers a strong mass loss and prevents any further thermal pulse. Our numerical tests indicate that the i-process elemental distribution is not strongly affected by the temporal and spatial resolution used to compute the stellar models, but typical uncertainties of ±0.3 dex on individual abundances are found. We show that specific isotopic ratios of Ba, Nd, Sm, and Eu can represent good tracers of i-process nucleosynthesis. Finally, an extended comparison with 14 selected r/s-stars show that the observed composition patterns can be well reproduced by our i-process AGB model. Conclusions. A rich i-process nucleosynthesis can take place during the early AGB phase of low-metallicity low-mass stars and explain the elemental distribution of most of the r/s-stars, but cannot account for the high level of enrichment of the giant stars in a scenario involving pollution by a former AGB companion.

Interaction between edaphic mesofauna and organic carbon within water-stable aggregates in forestry systems: A case study in northeastern Brazil

Soil mesofauna plays an important role in soil aggregation, which conditions the physical protection of soil organic carbon (SOC). Thus, our study associates the evaluation of mesofauna and SOC quantification to generate relevant information on the influencing level of these organisms on organic matter dynamics in aggregates. It is even more important investigating these indicators in places where decomposition processes are more intense, such as forest systems under tropical soils, where little is known about the interaction between these variables. In this context, the present study aimed to evaluate: (1) the influence of homogeneous Pterogyne nitens and Pinus caribaea plantations on the edaphic mesofauna community and on SOC stocks and carbon in soil aggregate classes using a native forest as a reference; and (2) the interaction between edaphic mesofauna, SOC and aggregate carbon. This study was performed on Oxisol soil areas located in the municipality of Vitória da Conquista, Bahia, Brazil. The edaphic mesofauna was evaluated using the modified Berlese-Tullgren funnel method. Physical soil fractionation was carried out by wet sieving. The organic carbon contents of the soil and aggregates were determined by wet oxidation. Implantation of homogeneous Pterogyne nitens and Pinus caribaea stands causes a reduction in the edaphic mesofauna (abundance and average richness) and in the amount of soil macroaggregates. The differences between the forest systems are largely explained by the abundance of fauna, SOC and carbon of the macroaggregates, microaggregates and silt + clay. The edaphic mesofauna has a direct and positive influence on the SOC, which highlights its important role in regulating the soil carbon dynamics in the soil.

Iron colloids dominate sedimentary supply to the ocean interior

Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a "rusty source") that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.

Amorphous Se species anchored into enclosed carbon skeleton bridged by chemical bonding toward advanced K-Se batteries

Potassium-selenium (K-Se) batteries have attracted significant attention as one of the most promising alternatives of lithium-ion storage systems owing to high energy density and low cost. In the design of Se-based cathode materials, however, the low utilization rate of active Se and the rapid dissolution of polyselenides seriously weaken the capacity and cycle stability. Therefore, how to make full use of Se species without loss during the charge and discharge process is the key to design high-performance Se-based cathode. In this paper, a 3D “water cube”-like Se/C hybrid (denoted as Se−O−PCS) is constructed with the assistance of Na2CO3 templates. Thanks to the abundant carbonate groups (CO32−) originated from the Na2CO3 templates, the molten Se species are firmly anchored into the pore of carbon skeleton by strong C−O−Se bonding. Thus, this unique Se−O−PCS model not only improves the utilization of active Se species, but also can reduce the contact with the electrolyte to inhibit the shuttle effect of polyselenides. Moreover, flexible carbon skeleton gives Se-O-PCS hybrid a good electrical conductivity and excellent structural robustness. Consequently, the resultant Se−O−PCS hybrid is endowed with an obviously enhanced K-ions storage property.

Winter Carnivory and Diapause Counteract the Reliance on Ice Algae by Barents Sea Zooplankton

The Barents Sea is a hotspot for environmental change due to its rapid warming, and information on dietary preferences of zooplankton is crucial to better understand the impacts of these changes on food-web dynamics. We combined lipid-based trophic marker approaches, namely analysis of fatty acids (FAs), highly branched isoprenoids (HBIs) and sterols, to compare late summer (August) and early winter (November/December) feeding of key Barents Sea zooplankters; the copepods Calanus glacialis, C. hyperboreus and C. finmarchicus and the amphipods Themisto libellula and T. abyssorum. Based on FAs, copepods showed a stronger reliance on a diatom-based diet. Phytosterols, produced mainly by diatoms, declined from summer to winter in C. glacialis and C. hyperboreus, indicating the strong direct linkage of their feeding to primary production. By contrast, C. finmarchicus showed evidence of year-round feeding, indicated by the higher winter carnivory FA ratios of 18:1(n-9)/18:1(n-7) than its larger congeners. This, plus differences in seasonal lipid dynamics, suggests varied overwintering strategies among the copepods; namely diapause in C. glacialis and C. hyperboreus and continued feeding activity in C. finmarchicus. Based on the absence of sea ice algae-associated HBIs (IP25 and IPSO25) in the three copepod species during both seasons, their carbon sources were likely primarily of pelagic origin. In both amphipods, increased FA carnivory ratios during winter indicated that they relied strongly on heterotrophic prey during the polar night. Both amphipod species contained sea ice algae-derived HBIs, present in broadly similar concentrations between species and seasons. Our results indicate that sea ice-derived carbon forms a supplementary food rather than a crucial dietary component for these two amphipod species in summer and winter, with carnivory potentially providing them with a degree of resilience to the rapid decline in Barents Sea (winter) sea-ice extent and thickness. The weak trophic link of both zooplankton taxa to sea ice-derived carbon in our study likely reflects the low abundance and quality of ice-associated carbon during late summer and the inaccessibility of algae trapped inside the ice during winter.

Differences in the isotopic signature of activated sludge in four types of advanced treatment processes at a municipal wastewater treatment plant

The natural abundance of stable isotopes is a powerful tool for evaluating biological reactions and process conditions. However, there are few stable isotope studies on the wastewater treatment process. This study carried out the first investigation on variations in natural abundance of carbon and nitrogen stable isotope ratios (δ13C and δ15N) of activated sludge in four types of advanced treatment process (extended aeration activated sludge (EAAS), aerobic-anoxic-aerobic (A2O), recycled nitrification-denitrification (RND), and modified Bardenpho (MB)) at a municipal wastewater treatment plant. The δ13C and δ15N values of influent suspended solids settled in the primary sedimentation tank (i.e., primary sludge) ranged from −25.4‰ to −24.6‰ and 0.5‰–2.9‰, respectively, during monitoring periods. The δ13C values of the activated sludge were −24.6‰ to −23.6‰ (EAAS), −25.4‰ to −24.3‰ (A2O), −25.7‰ to −24.9‰ (RND), and −25.7‰ to −24.3‰ (MB). The δ13C values of the activated sludge were similar to those of influent suspended solids. However, the δ13C values of activated sludge in EAAS was significantly higher than in A2O, RND, and MB. Meanwhile, the δ15N values of activated sludge were obviously higher than influent suspended solids; 5.8‰–7.5‰ (EAAS), 6.6‰–8.1‰ (A2O), 5.5‰–7.5‰ (RND), and 5.3‰–7.6‰ (MB). Changes in δ13C and δ15N values of the activated sludge within the treatment system were also found. These findings indicate that changes in δ13C and δ15N values of the activated sludge rely on important function for biological wastewater treatment such as nitrification, denitrification, and methane oxidation through wastewater treatment over time.

Fault-controlled carbonate cementation: A case study from Eocene turbidite-delta sandstones (Dongying Depression) and implication for hydrocarbon migration

The subsurface distribution of carbonate cements in sandstones is cornerstone in understanding the fluid regime and origin of cements to shed the light on hydrocarbon migration. Petrography, cuttings, cores, well logs, and seismic data were integrated to better understand the distribution of carbonate cements in the Eocene turbidite-delta sandstones of the Dongying Depression. Petrographic examinations (including cathodoluminescence, CL) reveal that the carbonate cements are mainly calcite with minor ankerite that precipitated in deep burial settings. The significant abundance of carbonate cements near fault zones implies migration of fluids from deep settings through late fractures developed by compaction under deep burial conditions. The extent of carbonate-cemented zones may reach hundreds of meters away from the faults, while scatter carbonate cements are much more extensive. The relationship of pervasive and scattered calcites with oil-bearing sandstones suggests that the pervasive calcite cementation started as soon as the hydrocarbon and brine mixed fluid were displaced while the scatter calcite cements came after. The occurrence of abundant carbonate-cemented zones in the delta front oil-free sandstone intervals suggests possible hydrocarbon migration to the overlying sandstone units.

Diagenesis and fluid evolution in the third member of the Eocene Shahejie Formation, Bonan Sag, Bohai Bay Basin, China

Diagenesis significantly influences sandstone reservoir quality, so that a detailed understanding of diagenesis is essential for the identification and prediction of favorable reservoirs. Several studies have been conducted on individual sandstone reservoirs in the Bonan Sag, a typical half-graben, oil-producing sag in eastern China, but few have explicitly considered the potential impact of the asymmetric shape of the sag, which is steep in the north and gentle in the south. This research takes full consideration of the tectonic setting and distribution of source rocks in the sag to compare the style, magnitude and timing of diagenesis in the northern Steep Slope and Sag Zone (SSSZ) and the southern Gentle Slope Zone (GSZ) by means of drill core observations, thin section petrography, high resolution scanning electron microscopy, fluid inclusion microthermometry, as well as cathodoluminescence and carbonate stable isotope analysis. Petrographic observations identify the wide-spread occurrence of authigenic quartz and clay minerals in association with dissolved feldspar, as well as abundant carbonate cements occurring as several distinct generations due to evolving pore fluid composition. The SSSZ has variable carbonate mineralogy while ankerite dominates in the GSZ. The homogenization temperature of fluid inclusions in authigenic quartz in the SSSZ has a wider range (93°C–157.9 °C) and lower starting temperature (93 °C) compared with the GSZ (106.2 °C) and is characterized by more lighter carbonate δ13C and δ18O values (δ18O: −14.8‰~-11.3‰, δ13C: 1.1‰–2.7‰ for the SSSZ; δ18O: −11.9‰~-5.8‰, δ13C: 2.9‰–5.5‰ for the GSZ). The results indicate that (1) Diagenetic conditions in the Bonan Sag evolved from alkaline to acidic to alkaline in general, but with distinct late stage carbonate cementation in SSSZ vs GSZ; (2) the diagenetic processes as well as the nature of pore waters varied across different zones and also temporally. Acidic conditions in the SSSZ started earlier and persisted for longer than in the GSZ. (3) The regional differentiation of the diagenetic processes and pore fluid evolution result from the source rock distribution and burial histories which differ across the Bonan Sag because of the asymmetric shape of the half-graben. We propose a model of fluid evolution over space and time which may provide a new framework for understanding the diagenetic processes and the fluid evolution of oil-producing sags and also contribute to the prediction of favorable reservoirs.

Did life originate from low-temperature areas of the Universe?

The biological molecules delivered to Earth on the board of meteorites and comets were called one of the possible causes of the origin of life. Therefore, our understanding of the routes of formation of biomolecules in space should shed a light on the possibility of the existence of habitable extrasolar planets. The large abundance of organic molecules is found in the space regions with the lowest temperature. Different routes of the organics formation in these areas were suggested. In this article, we demonstrate that complex organic molecules (COMs) as well as important biological molecules can be formed due to the reaction of C atoms with the mantels of molecular ices covering refractory dust grains present in the interstellar medium (ISM). Having four valence electrons, C atoms act as glue joining simple non-organic molecules and converting them into organic matter. The formation of many molecules is barrierless and thus can happen at low temperature. The barrierless reaction C + NH3 + CO → NH2CHCO attracts particular interest. The product of this reaction is an isomer of the glycine residue of a polypeptide and expected to be efficiently formed in the translucent molecular clouds. The polymerization of these molecules leads to the formation of proteins that according to some theories are life’s first molecules. Considering a high abundance of atomic carbon in the ISM, we expect a high efficiency of the formation of a large variety of different organic molecules, and show why the amount of organic material formed by condensation of atomic carbon can be underestimated.

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH–NH Photometry. VI. M3 (NGC 5272) Is Not a Prototypical Normal Globular Cluster* †

Abstract We present Ca–CN–CH–NH photometry for the well-known globular cluster (GC) M3 (NGC 5272). We show new evidence for two M3 populations with distinctly different carbon and nitrogen abundances, seen in a sharp division between CN-weak and CN-strong red-giant branches (RGBs) in M3. The CN-strong population shows a C–N anticorrelation that is a natural consequence of the CN cycle, while the CN-weak population shows at most a very weak C–N anticorrelation. Additionally, the CN-weak population exhibits an elongated spatial distribution that is likely linked to its fast rotation. Our derived metallicities reveal bimodal distributions in both populations, with 〈[Fe/H]〉 ≈ −1.60 and −1.45, which appear to be responsible for the discrete double RGB bumps in the CN-weak population and the large range. From this discovery, we propose that M3 consists of two GCs, namely C1 (23%, 〈[Fe/H]〉 ≈ −1.60) and C2 (77%, 〈[Fe/H]〉 ≈ −1.45), each of which has its own C–N anticorrelation and structural and kinematical properties, which are strong indications of independent systems in M3. The fractions of the CN-weak population for both C1 and C2 are high compared to Galactic GCs but they are in good agreement with GCs in the Magellanic Clouds. We suggest that M3 is a merger remnant of two GCs, most likely in a dwarf galaxy environment, and accreted to our Galaxy later in time. This is consistent with recent proposals of an ex situ origin for M3.

Carbon cycle evolution before and after the Great Oxidation of the atmosphere

The rock record of organic carbon abundance and its isotopic composition is consistent with the evolution of life more than 3800 million years ago (Ma). Despite this, there are very few insights as to the ecology of this ancient biosphere or to its level of activity. One possible insight, however, comes from the isotopic composition of inorganic and organic carbon in ancient rocks. This isotope record can be used, in principle, to determine the proportion of inorganic carbon entering the oceans that was buried in sediments as organic matter, and thus it helps constrain the activity level of the ancient biosphere. A quantitative analysis of this isotope record, however, requires that we understand how the Earth-surface carbon reservoir has evolved over time, as burial rates of organic matter in marine sediments depend on the input rates of carbon to the oceans. We must also know how organic matter is weathered as a function of atmospheric oxygen concentrations, thus indicating how much of the organic matter in sediments is newly formed or recycled. To explore these issues, a carbon cycle model is developed here that includes an evolving Earth-surface carbon reservoir as well as the oxygen dependency of the organic matter weathering in rocks. The model also allows for the release of CO₂ from organic matter during metamorphism and it contains a rock cycle with young and old reservoirs with appropriate transfer fluxes between them. The model shows that before the Great Oxidation Event (GOE) about 2400 Ma, only about 5 percent to 10 percent as much organic matter was buried into marine sediments as compared with today. Such low rates of organic matter burial would be consistent with a subdued marine biosphere. Such a subdued biosphere could possibly be consistent with primary production driven by anoxygenic photosynthesis coupled to an iron cycle. In association with, and in the aftermath of, the GOE, the biosphere likely increased its activity level by an order of magnitude. This large increase would have completely transformed the biology of the Earth and could have resulted from either the evolution and/or expansion of oxygen-producing cyanobacteria or a dramatic increase in the availability of nutrients to fuel oxygenic phototrophs.

Calcium Stable Isotopes of Tonga and Mariana Arc Lavas: Implications for Slab Fluid‐Mediated Carbonate Transfer in Cold Subduction Zones

AbstractCarbonation of oceanic lithosphere occurs widely during seawater alteration, and subducted carbonated oceanic lithosphere may play a key role in carbon recycling in subduction zones. Here we investigate the Ca isotopic composition of arc lavas from the Tonga rear arc and Mariana arc, western Pacific, to explore the effect of fluid‐mediated carbonate transfer in subduction zones. Fresh basalts (0.84 ± 0.01‰, 2sd, n = 3) and dacites (0.84 ± 0.10‰, 2sd, n = 9) from the Tonga rear arc show indistinguishable δ44/40Ca, reflecting negligible Ca isotopic fractionation during differentiation of hydrous arc magmas. More importantly, arc lavas from both the Tonga rear arc (0.84 ± 0.09‰, 2sd, n = 12) and Mariana arc (0.79 ± 0.12‰, 2sd, n = 9) display MORB‐like δ44/40Ca values. The MORB‐like δ44/40Ca of arc lavas indicates that the carbonates released from altered oceanic lithosphere (AOL) do not significantly modify the Ca isotopic composition of the mantle wedge, although extensive volcanic CO2 degassing at both arcs suggests that slab fluids might introduce abundant carbonate into the depleted mantle wedge. These results could be attributed to a limited Ca budget in the slab fluids added to the mantle wedge and/or homogenization effect of variable δ44/40Ca for the slab fluids. At cold subduction zones, a fraction of carbonates from the AOL may survive during slab dehydration and recycle into the deep mantle.

Lithogeochemical and Hyperspectral Halos to Ag-Zn-Au Mineralization at Nimbus in the Eastern Goldfields Superterrane, Western Australia

With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle halos surrounding orebodies at minimal expense. The Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity, and tectonic setting, it is interpreted to represent a shallow water (~650 mbsl) and low-temperature (<250 °C) volcanogenic massive sulfide (VMS) deposit with epithermal characteristics (i.e., a hybrid bimodal felsic deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization to aid exploration. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic sulfides that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb ± Pb ± As ± (Cu)-bearing sulfosalts, minor pyrrhotite, arsenopyrite, and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite, and bournonite. Zones of sulfide mineralization in quartz-sericite(±carbonate)-altered dacite are marked by significant mass gains in Fe, S, Zn, Pb, Sb, Ag, As, Cd, Ni, Cu, Ba, Co, Cr, Tl, Bi, and Au. Basaltic rocks show reduced mass gains in most elements, with zones of intense quartz-chlorite-carbonate±fuchsite alteration restricted to thick sequences of hyaloclastite, and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, and are marked by high Alteration Index and Chlorite-Carbonate-Pyrite Index (CCPI) values, strong Na-Ca depletion, and an absence of feldspar (albite) in thermal infrared (TIR) data. White mica compositions are predominantly muscovitic in weakly altered sections of the dacitic footwall sequence. More paragonitic compositions are associated with zones of increased sericitization and high-grade polymetallic sulfide mineralization. Chlorite in dacitic rocks often occurs adjacent to zones of sulfide mineralization and is restricted to narrow intervals. Carbonate abundance is sporadic in dacite, but is most abundant outside the main zones of Na-Ca depletion. Basaltic rocks are characterized by strongly paragonitic white mica compositions, and abundant chlorite and carbonate. Shifts from Ca carbonates and Fe-rich chlorites to more Mg-rich compositions of both minerals occur in more intensely hydrothermally altered basaltic hyaloclastite, and near contacts with dacitic rocks. Hanging-wall polymict conglomerates are characterized by minor amounts of muscovitic to phengitic white mica (2205–2220 nm), and an absence of chlorite and carbonate alteration.

Tillage-induced effects on organic carbon in earthworm casts through changes in their physical and structural stability parameters

Earthworm casts have been recognized as contributing to long-term carbon protection, but few studies have focused on the mechanism by which this is achieved. Most of the literature documenting earthworm casts revolves around the difference between the earthworm cast and natural soil, whereas little attention has been given to deciphering the effects of different tillage systems on earthworm casts. Further, whether or not an earthworm cast, like soil, affects its own organic carbon content through physical structure stability is still somewhat vague, and very little is known. The objective for this study was to determine the effect of tillage on organic carbon and physical structure stability parameters in earthworm casts. Undisturbed soil columns were collected from a 17-year tillage experiment including no tillage (NT), ridge tillage (RT) and mouldboard ploughing (MP) in Northeast China. Each column was seeded with ten earthworms (Eisenia foetida), incubated at 18 °C for 120 days and casts were collected and analysed. Both NT and RT led to significantly greater organic carbon (20.5% and 14.4%), total pore volume (54.6% and 75.6%), total pore area (45.4% and 60.4%), permeability (21.8% and 66.4%), fluid conductivity (26.2% and 31.1%), tensile strength (34.1% and 51.2%) and water resistance index (16.7% and 22.3%) in the casts compared to MP (P < 0.05), whereas water repellency showed a significant decrease (42.9% and 52.4%) (P < 0.05). Correlation analysis showed that total pore area, tensile strength and water repellency were the three most critical factors affecting organic carbon in earthworm casts (r = 0.943, 0.742, 0.762 and 0.715, 0.758, 0.743 for NT and RT, respectively). The results of tillage effects on organic carbon and physical structure stability parameters combined with Structural Equation Modelling analysis identified that NT and RT could increase organic carbon by increasing total pore area, tensile strength and water repellency in earthworm casts. These results demonstrate that tillage through physical structure stability (total pore area, tensile strength and water repellency) changes affect organic carbon in earthworm cast which are major new findings. This signifies similarity in the underlying processes by which tillage affects organic carbon and physical structure stability parameters in earthworm casts and the surrounding bulk soil. Moreover, the increased abundance of earthworms and greater organic carbon in earthworm casts under conservation tillage, suggest that earthworms enhance the conversion of residue into organic carbon and therefore enhance the long-term soil organic carbon sequestration.

Identification of Host Bloodmeal Source in Ornithodoros turicata Dugès (Ixodida: Argasidae) Using DNA-Based and Stable Isotope-Based Techniques.

The ecology and host feeding patterns of many soft ticks (Ixodida: Argasidae) remain poorly understood. To address soft tick–host feeding associations, we fed Ornithodoros turicata Dugès on multiple host species and evaluated quantitative PCR (qPCR) and stable isotope analyses to identify the vertebrate species used for the bloodmeal. The results showed that a qPCR with host-specific probes for the cytochrome b gene successfully identified bloodmeals from chicken (Gallus gallus L.), goat (Capra aegagrus hircus L), and swine (Sus scrofa domesticus) beyond 330 days post-feeding and through multiple molting. Also, qPCR-based bloodmeal analyses could detect multiple host species within individual ticks that fed upon more than one species. The stable isotope bloodmeal analyses were based on variation in the natural abundance of carbon (13C/12C) and nitrogen (15N/14N) isotopes in ticks fed on different hosts. When compared to reference isotope signatures, this method discerned unique δ13C and δ15N signatures in the ticks fed on each host taxa yet could not discern multiple host species from O. turicata that fed on more than one host species. Given the significance of soft tick-borne zoonoses and animal diseases, elucidating host feeding patterns from field-collected ticks using these methods may provide insight for an ecological basis to disease management.

Fundamental parameters and non‐local thermodynamic equilibrium abundances of key light elements for nine bright and nearby K giants

AbstractFor nine bright K giants within 100 pc of the sun, the fundamental parameters and the non‐local thermodynamic equilibrium (LTE) abundances of three key light elements (Li, C, and O) are accurately determined. These stars are of special interest due to the planets detected around them. Their fundamental parameters are found to be typical for K giants; in particular, these stars have effective temperatures Teff = 3,920–4,830 K, surface gravities log g = 1.20–2.85, masses M = 1.2–2.8 M⊙, and ages t = 0.4–5.4 Gyr (the pronounced anticorrelation between ages t and masses M exists). The microturbulent parameter Vt derived from Fe I lines varies between 1.2 and 1.9 km s−1; the metallicity index [Fe/H] forfive stars is close to the normal (zero) value, for other four stars it varies between −0.3 and −0.4 dex. All the giants are on the red giant branch stage and passed the first‐dredge‐up (FDU) phase. This conclusion is confirmed by the published low isotope ratios 12C/13C and 16O/17O. Basing on the non‐LTE analysis of Li I, C I, and O I lines, we determined abundances of lithium, carbon, and oxygen, three tracers of stellar evolution. The carbon deficiency −0.3 dex is found for the giants, which is quite expectable for these post‐FDU objects. The oxygen abundance is likely to be unchanged, whereas for the C/O ratio we obtained (after correction due to galactic chemical evolution) the mean value [C/O]cor = −0.22 ± 0.10 that is in very good agreement with the theory. The lithium abundance is not detected for seven of nine program giants; this result is quite expectable for the post‐FDU stars. We determined the Li abundance with the confidence only for two giants, namely, log ϵ(Li) = 0.92 for β Gem and log ϵ(Li) = 0.45 for μ Leo; this result contradicts the standard theory. Hypothetical engulfment by a star of a giant planet could solve the problem.

Acidification alters the functionality of metal polluted soils

Acidification can alter soil ecosystem functioning, thus jeopardizing the provision of valuable ecosystem services. Moreover, soil acidification can be accompanied by other soil threats, such as, for instance, metal pollution. The aim of this work was to assess to what extent acidification affects the functionality of metal polluted soils. To this aim, the pH of two soils (a highly metal polluted and a moderately metal polluted soil) was lowered by adding elemental sulphur at different doses, resulting in the following pH gradient in both soils: 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0 and 3.5. A variety of microbial indicators of soil health were measured in the treated soils: enzyme activities, substrate-induced respiration, microbial biomass carbon, bacterial and fungal abundances by qPCR, and bacterial and fungal richness by DGGE. Metal (Cd, Cu, Pb, Zn) bioavailability increased at decreasing pH values. The values of enzyme activities were strongly affected by acidification in both soils, followed by the values of soluble organic carbon in the highly polluted soil and bioavailable metal concentrations in the moderately polluted soil. These results improve our understanding of the role of microorganisms in the biogeochemical cycles of metal polluted acidic soils.