Sulfur Abundance Research Articles

Sulphur in the Sculptor dwarf spheroidal galaxy

In Galactic halo stars, sulphur has been shown to behave like other $\alpha$-elements, but until now, no comprehensive studies have been done on this element in stars of other galaxies. Here, we use high-resolution ESO VLT/FLAMES/GIRAFFE spectra to determine sulphur abundances for 85 stars in the Sculptor dwarf spheroidal galaxy, covering the metallicity range $-2.5\leq \text{[Fe/H]} \leq-0.8$. The abundances are derived from the S~I triplet at 9213, 9228, and 9238~\AA. These lines have been shown to be sensitive to departure from local thermodynamic equilibrium, i.e. NLTE effects. Therefore, we present new NLTE corrections for a grid of stellar parameters covering those of the target stars. The NLTE-corrected sulphur abundances in Sculptor show the same behaviour as other $\alpha$-elements in that galaxy (such as Mg, Si, and Ca). At lower metallicities ($\text{[Fe/H]}\lesssim-2$) the abundances are consistent with a plateau at $\text{[S/Fe]}\approx+0.16$, similar to what is observed in the Galactic halo, $\text{[S/Fe]}\approx+0.2$. With increasing [Fe/H], the [S/Fe] ratio declines, reaching negative values at $\text{[Fe/H]}\gtrsim-1.5$. The sample also shows an increase in [S/Mg] with [Fe/H], most probably because of enrichment from Type Ia supernovae.

High Areal Capacity Sulfur Cathodes for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have practical energy densities of >500 Wh/kg, which are three times higher than the current Li-ion technology based on lithium metal oxide cathode and graphite anode (~150-200 Wh/kg). As such, they have the potential as a next generation energy storage for electric vehicles, portable devices and grid storage. Moreover, the abundance of sulfur and its high theoretical capacity of 1672 mAh/g suggest that costs of <$200 kWh can be met to significantly increase the rate of electric vehicle adoption. However, to realize the potential of Li-S batteries, the utilization of active material at cell level must be significantly improved. Today, most of the high specific capacity (900-1100 mAh/g) and/or long cycle life data in the literature have been recorded with low sulfur loading (~0.5-2 mg/cm2), translating to an areal capacity of <2 mAh/cm2 (Figure 1a). Another often-overlooked factor is the electrolyte-to-sulfur (E/S in ml/g) ratio. Usually, a high E/S ratio of 10-60 is used to compensate for the depletion of electrochemically active Li-ions and electrolyte solvent during Li stripping and plating due to the formation of solid-electrolyte-interface (SEI). The excessive passive weight accompanying high E/S ratio significantly reduces the energy density of the cell. Ideally, the E/S ratio of <3 is desired1. Analogous to techniques that were developed for thick transitional metal oxide electrodes by our group2, electrodes with low tortuosity pathways have been developed. Whereas a 250 µm thick sulfur/carbon nanotube (CNT) electrodes with density ~1.2 g/cm3 used as a reference electrode gives an initial capacity of ~300 mAh/g at C-rate of 1/30 h-1 and a corresponding current density of 0.67 mA/cm2 (Figure 1b), tuning of porosity and surface chemistry through a grafting technique produces in the same thickness and sulfur density an electrode with threefold higher specific capacity (867 mAh/g) and a high areal capacity of 10.5 mAh/cm2 (Figure 1c). A Coulombic efficiency of >93% was achieved for the developed high-areal-capacity Li-S battery, which retained about half of the initial capacity after 50 cycles at a C-rate of 1/15 h-1. Importantly, these results were achieved at a relatively low E/S ratio of 3. Acknowledgment This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. X. Chen acknowledges the financial support from the Agency for Science, Technology and Research (A*STAR), Singapore. Reference 1 M. Hagen, P. Fanz and J. Tübke, J. Power Sources, 2014, 264, 30–34. 2 C.-J. Bae, C. K. Erdonmez, J. W. Halloran and Y.-M. Chiang, Adv. Mater., 2013, 25, 1254–8. Figure 1: (a) The dependency of energy density of a Li-S battery on the areal capacity of the electrode. The calculated energy densities are on based on a cell level with a structure of “current collector-cathode-electrolyte-separator-protective layer-anode-current collector”. The pink area highlights the current status of Li-S and the red dot marks the highest achieved areal capacity in this work. An inset shows SEM micrograph of the cathode composite with a thickness of 250 µm. The S loading is ~12.1 mg/cm2. (b) Galvanostatic charge-discharge profiles of the Li-S showing the 2nd cycle of Li-S batteries comparing between our cathode vs a S/CNT cathode (electrode thickness of 250 µm) at a current density of 0.67 mA/cm2 (theoretical C-rate of 1/30 h-1). (c) Comparison of the energy density and areal capacity for different electrode thickness to highlight the improvement of our Li-S batteries over conventional Li-S batteries. Figure 1

High Conductive Carbon Nanofiber-Graphite Paper Electrodes with Ultrahigh Polysulfide-Loading for Advanced Lithium-Sulfur Batteries

Lithium sulfur (Li-S) battery has attracted much attention due to its high energy density and the abundance of sulfur on the Earth, but some major problems including short cycle life, low sulfur loading, and inferior sulfur utilization have impeded its practical applications. Here, wereport a rational combination of conductive carbon nanofiber-graphite paper (CNGP) with dissolved polysulfides to the formation of advanced sulfur cathode structures that can take full advantage of each building block. The hierarchical CNGP electrode has an ultrahigh sulfur loading of 6.7 mg cm-2, and a high electrical conductivity of 328 S cm-1. In the CNGP electrode, the integrated carbon nanofiber paper (~100 μm) with extremely low density (2.1 mg cm-2) is used as current collector and carrier for the dissolved Li2S6 species, while the densely tapped graphite film (~5 μm) on the top of CNF acts as a protection layer to prevent migration of the dissolved polysulfides from the cathode to the anode. The use of CNGP electrodes and dissolved Li2S6 species enables the fabrication of remarkably improved Li-S batteries with a reversible capacity of 750 mAhg-1 over 300 cycles at 1 C, and 80% of capacity retention from 720 to 580 mAhg-1 over 500 cycles at 1.5 C with an average Coulombic efficiency of 99.5%. The results provide important progress towards the fabrication of Li-S batteries with long cycle life and high rate capabilities.

A Hybrid Dual-Type Sulfur Cathode and a Lithiated Si/SiOx Nanosphere Anode for Li-Sulfur Full Cells

Lithium−sulfur batteries could become an excellent alternative to replace the currently used lithium-ion batteries. 1 The natural abundance and low cost of sulfur, coupled with the high theoretical energy density of sulfur-based cathodes, namely, 1675 mAh g-1 and 2600 Wh kg-1, are the major advantages of this sulfur battery.2 However, commercialization of lithium−sulfur batteries has so far been limited due to the cyclability problems associated with both the sulfur cathode and the lithium−metal anode.3 Herein, we demonstrate a highly reliable lithium−sulfur battery showing cycle performance comparable to that of lithium-ion batteries; our design uses a highly reversible hybrid dual-type sulfur cathode (solid sulfur electrode and polysulfide catholyte) and a lithiated Si/SiOx nanosphere anode. Our result shows superior battery performance in terms of high specific capacity, excellent charge−discharge efficiency, and notable cycle life, delivering a specific capacity of ∼750 mAh g−1 over 500 cycles (85% of the initial capacity). These promising behaviors may arise from a synergistic effect of the enhanced electrochemical performance of the newly designed anode and the optimized layout of the cathode.

Effect of Conductive Substrate Material on Li2S Electrodepositionkinetics in Li-S Batteries

Lithium-sulfur batteries are of interest because of their high theoretical energy density and the very low cost and high abundance of sulfur. As most of the theoretical capacity (~1670 mAh/g) of a lithium sulfur battery results from the electrodeposition of either Li2S (~1250 mAh/g) or sulfur (~210 mAh/g), it is critical to understand the kinetics of the nucleation and growth processes by which these insoluble species are formed. Moreover, the precipitation of these species is thought to have a negative impact on the cycle life of Li-S batteries due to the electronic isolation of some of the material.1We have previously demonstrated, through electrodeposition from polysulfide solutions, that Li2S forms via a 2-dimensional island nucleation and growth process, where reduction occurs at the interface of the electrolyte and conducting substrate due to the high electronic resistivity of Li2S.2 Furthermore, we quantified the nucleation and growth rates of the precipitate on graphite fiber surfaces (to represent the conductive carbon additive used in the majority of Li-S batteries), and found them to be highly dependent on electrolyte solvent. However, even in the best case, electrodeposition is slow on carbon surfaces due to the relatively low affinity of Li2S with nonpolar carbon. Alternative surfaces, such as conducting metal oxides and polymer-modified carbon, have been proposed to lower the energy of the sulfide-substrate interface and thereby improve the electrodeposition kinetics.3–5Here, we will discuss the effects of alternative surfaces, such as metal oxides, on the kinetics and morphology of Li2S precipitation in lithium-sulfur batteries. We will show that metal oxide surfaces such as Ti4O7 reduce the overpotential required (Figure 1) for nucleation by reducing the interface energy between nuclei and the substrate. We will also show that the enhancement in electrodeposition kinetics arises from this reduced barrier, rather than any increase in exchange current density for the reduction of polysulfides in solution. AcknowledgementsThis work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.References(1) Elazari, R.; Salitra, G.; Talyosef, Y.; Grinblat, J.; Scordilis-Kelley, C.; Xiao, A.; Affinito, J.; Aurbach, D. J. Electrochem. Soc. 2010, 157 (10), A1131.(2) Fan, F. Y.; Carter, W. C.; Chiang, Y.-M. Submitted 2015.(3) Pang, Q.; Kundu, D.; Cuisinier, M.; Nazar, L. F. Nat. Commun. 2014, 5 (May), 4759.(4) Yao, H.; Zheng, G.; Hsu, P.-C.; Kong, D.; Cha, J. J.; Li, W.; Seh, Z. W.; McDowell, M. T.; Yan, K.; Liang, Z.; Narasimhan, V. K.; Cui, Y. Nat. Commun. 2014, 5 (May), 3943.(5) Zheng, G.; Zhang, Q.; Cha, J. J.; Yang, Y.; Li, W.; Seh, Z. W.; Cui, Y. Nano Lett. 2013, 13 (3), 1265–1270. Figure Caption:Figure 1. Potentiostatic intermittent titration technique (PITT) curves for the reduction of polysulfide solution (2.5 mol S/L as Li2S8 in triglyme) on carbon felt/Ti4O7 nanoparticle composite. The first current peak results from precipitation on the oxide surface, while the second results from precipitation on the carbon surface, which occurs at a ~100mV lower potential. Figure 1

(Invited) A Mesoscale Approach Toward Elucidating Microstructure-Transport-Performance Interaction in Li-S Battery Electrodes

Lithium-sulfur (Li-S) battery is a promising energy storage technology, which offers improved performance in terms of higher energy density and material sustainability owing to the abundance of sulfur (S) as the active material. However, one of the key challenges centers on insoluble discharge product formation in the cathode and concomitant internal shuttle effect [1-5]. The polysulfide (such as Li2S) formation poses a deleterious consequence on the electrode microstructural change, thereby impacting the transport and electrochemical properties and ultimately resulting in capacity fade. In this regard, the cathode architecture plays an important role in determining the Li-S battery performance. A desirable electrode microstructure should effectively deter the dissolution of polysulfide, and facilitate lithium ion transport. This warrants a fundamental understanding of the physicochemical interplay resulting from the underlying microstructure-transport-performance interaction. In this work, a mesoscale computational model, shown schematically in Fig.1, will be presented in order to fundamentally investigate the morphology evolution due to Li2S precipitation and the resulting influence on the electrode microstructural and performance attributes. Acknowledgement: Financial support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, grant DE-EE0006832 (Program manager: Dr. Tien Duong) is gratefully acknowledged.

Linking mutagenic activity to micropollutant concentrations in wastewater samples by partial least square regression and subsequent identification of variables

We deployed multivariate regression to identify compounds co-varying with the mutagenic activity of complex environmental samples. Wastewater treatment plant (WWTP) effluents with a large share of industrial input of different sampling dates were evaluated for mutagenic activity by the Ames Fluctuation Test and chemically characterized by a screening for suspected pro-mutagens and non-targeted software-based peak detection in full scan data. Areas of automatically detected peaks were used as predictor matrix for partial least squares projections to latent structures (PLS) in combination with measured mutagenic activity. Detected peaks were successively reduced by the exclusion of all peaks with lowest variable importance until the best model (high R2 and Q2) was reached. Peaks in the best model co-varying with the observed mutagenicity showed increased chlorine, bromine, sulfur, and nitrogen abundance compared to original peak set indicating a preferential selection of anthropogenic compounds. The PLS regression revealed four tentatively identified compounds, newly identified 4-(dimethylamino)-pyridine, and three known micropollutants present in domestic wastewater as co-varying with the mutagenic activity. Co-variance between compounds stemming from industrial wastewater and mutagenic activity supported the application of “virtual” EDA as a statistical tool to separate toxicologically relevant from less relevant compounds.

THE SULPHUR ABUNDANCE BEHAVIOUR IN THE GALACTIC DISC STARS

The sulphur abundances in the atmospheres of the F-G-K-type dwarf stars that belong to the thin and thick disc populations (in the metallicity range – 1.0 < [Fe/H] < 0.3) were determined. The observations were conducted using the 1.93 m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle-type spectrograph ELODIE (R = 40 000). The abundances were derived under the LTE approximation; the synthetic spectrum for the sulphur lines in the region of 6743-6762 AA was computed accounting for the hyperfine structure. The correlation between the abundances of some elements and metallicity [Fe/H] in the Galactic thin and thick disc stars was analyzed. To discuss the sources of sulphur production, the comparison between the sulphur abundance trend and current theoretical computations of the Galactic chemical evolution was made.

Basalt volatile fluctuations during continental rifting: An example from the Rio Grande Rift, USA

AbstractHydration and metasomatism of the lithospheric mantle potentially influences both the magmatic and tectonic evolution of southwestern North America. Prior studies have suggested that volatile enrichments to the mantle underlying western North America resulted from shallow subduction of the Farallon Plate during the Laramide (∼74–40 Ma). This study examines temporal and spatial variations in volatile elements (H2O, Cl, F, and S) determined from olivine and orthopyroxene‐hosted melt inclusions along and across the Rio Grande Rift, the easternmost extent of Laramide shallow subduction. Maximum chlorine enrichments are observed in the southern rift with a Cl/Nb of ∼210 and reduce with time to MORB‐OIB levels (∼5–17). Measured water abundances are &lt;0.8 wt % in rehomogenized inclusions; however, calculated H2O, based on Cl/Nb systematics, primarily varies from 0.5 to 2 wt % H2O. Sulfur abundances (&lt;0.61 wt %), and calculated sulfide saturation, indicate magmas with high Cl/Nb also contain oxidized sulfur. The abundance of fluorine in melt inclusions (up to 0.2 wt %) is not correlated to other volatile elements. Temporal variations in melt inclusion volatile abundances coupled with varying isotopic (Sr‐Nd‐Pb) whole‐rock systematics suggest a transition from lithospheric to asthenospheric melt generation in the southern RGR and potential lithosphere‐asthenosphere melt mixing in the central RGR. East to west decrease in volatile enrichment likely reflects a combination of varying mantle sources and early removal of metasomatized lithospheric mantle underlying regional extension. Results indicate, from multiple causes, subduction‐related volatile enrichment to the lithospheric mantle is ephemeral, and strong enrichments in volatiles are not preserved in active magmatic‐tectonic provenances.

Galactic evolution of sulphur as traced by globular clusters

Context. Sulphur is an important volatile α element, but its role in the Galactic chemical evolution is still uncertain, and more observations constraining the sulphur abundance in stellar photospheres are required.

From lithium to sodium: cell chemistry of room temperature sodium-air and sodium-sulfur batteries.

Research devoted to room temperature lithium–sulfur (Li/S8) and lithium–oxygen (Li/O2) batteries has significantly increased over the past ten years. The race to develop such cell systems is mainly motivated by the very high theoretical energy density and the abundance of sulfur and oxygen. The cell chemistry, however, is complex, and progress toward practical device development remains hampered by some fundamental key issues, which are currently being tackled by numerous approaches. Quite surprisingly, not much is known about the analogous sodium-based battery systems, although the already commercialized, high-temperature Na/S8 and Na/NiCl2 batteries suggest that a rechargeable battery based on sodium is feasible on a large scale. Moreover, the natural abundance of sodium is an attractive benefit for the development of batteries based on low cost components. This review provides a summary of the state-of-the-art knowledge on lithium–sulfur and lithium–oxygen batteries and a direct comparison with the analogous sodium systems. The general properties, major benefits and challenges, recent strategies for performance improvements and general guidelines for further development are summarized and critically discussed. In general, the substitution of lithium for sodium has a strong impact on the overall properties of the cell reaction and differences in ion transport, phase stability, electrode potential, energy density, etc. can be thus expected. Whether these differences will benefit a more reversible cell chemistry is still an open question, but some of the first reports on room temperature Na/S8 and Na/O2 cells already show some exciting differences as compared to the established Li/S8 and Li/O2 systems.

Oxygen, α-element and iron abundance distributions in the inner part of the Galactic thin disc★†

We derived elemental abundances in 27 Cepheids, the great majority situated within a zone of Galactocentric distances ranging from 5 to 7 kpc. One star of our sample, SU Sct, has a Galactocentric distance of about 3 kpc, and thus falls in a poorly investigated region of the inner thin disc. Our new results, combined with data on abundances in the very central part of our Galaxy taken from the literature, show that iron, magnesium, silicon, sulphur, calcium and titanium local thermodynamic equilibrium abundance radial distributions, as well as non-local thermodynamic equilibrium distribution of oxygen reveal a plateau-like structure or even positive abundance gradient in the region extending from the Galactic Centre to about 5 kpc.

Multiple sulfur isotope composition of oxidized Samoan melts and the implications of a sulfur isotope ‘mantle array’ in chemical geodynamics

To better address how subducted protoliths drive the Earth's mantle sulfur isotope heterogeneity, we report new data for sulfur (S) and copper (Cu) abundances, S speciation and multiple S isotopic compositions (32S, 33S, 34S, 36S) in 15 fresh submarine basaltic glasses from the Samoan archipelago, which defines the enriched-mantle-2 (EM2) endmember.Bulk S abundances vary between 835 and 2279 ppm. About 17±11% of sulfur is oxidized (S6+) but displays no consistent trend with bulk S abundance or any other geochemical tracer. The S isotope composition of both dissolved sulfide and sulfate yield homogeneous Δ33S and Δ36S values, within error of Canyon Diablo Troilite (CDT). In contrast, δ34S values are variable, ranging between +0.11 and +2.79‰ (±0.12‰ 1σ) for reduced sulfur, whereas oxidized sulfur values vary between +4.19 and +9.71‰ (±0.80‰, 1σ). Importantly, δ34S of the reduced S pool correlates with the 87Sr/86Sr ratios of the glasses, in a manner similar to that previously reported for South-Atlantic MORB, extending the trend to δ34S values up to +2.79±0.04‰, the highest value reported for undegassed oceanic basalts.As for EM-1 basalts from the South Atlantic ridge, the linear δ34S–87Sr/86Sr trend requires the EM-2 endmember to be relatively S-rich, and only sediments can account for these isotopic characteristics. While many authors argue that both the EM-1 and EM-2 mantle components record subduction of various protoliths (e.g. upper or lower continental crust, lithospheric mantle versus intra-metasomatized mantle, or others), it is proposed here that they primarily reflect sediment recycling. Their distinct Pb isotope variation can be accounted for by varying the proportion of S-poor recycled oceanic crust in the source of mantle plumes.

Dual‐Confined Flexible Sulfur Cathodes Encapsulated in Nitrogen‐Doped Double‐Shelled Hollow Carbon Spheres and Wrapped with Graphene for Li–S Batteries

Batteries with high energy and power densities along with long cycle life and acceptable safety at an affordable cost are critical for large‐scale applications such as electric vehicles and smart grids, but is challenging. Lithium–sulfur (Li‐S) batteries are attractive in this regard due to their high energy density and the abundance of sulfur, but several hurdles such as poor cycle life and inferior sulfur utilization need to be overcome for them to be commercially viable. Li–S cells with high capacity and long cycle life with a dual‐confined flexible cathode configuration by encapsulating sulfur in nitrogen‐doped double‐shelled hollow carbon spheres followed by graphene wrapping are presented here. Sulfur/polysulfides are effectively immobilized in the cathode through physical confinement by the hollow spheres with porous shells and graphene wrapping as well as chemical binding between heteronitrogen atoms and polysulfides. This rationally designed free‐standing nanostructured sulfur cathode provides a well‐built 3D carbon conductive network without requiring binders, enabling a high initial discharge capacity of 1360 mA h g−1 at a current rate of C/5, excellent rate capability of 600 mA h g−1 at 2 C rate, and sustainable cycling stability for 200 cycles with nearly 100% Coulombic efficiency, suggesting its great promise for advanced Li–S batteries.

Characterization of PM2.5 Source Profiles for Traffic and Dust Sources in Raipur, India

This paper describes results from a detailed source profile characterization study conducted in Raipur, India to prepare source profiles for traffic and dust-related sources. A companion paper has been published with results for a range of other combustion sources. PM2.5 samples were analyzed for mass, elements (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, S, Sb, Se, V, Zn), ions (Na+, K+, Mg2+, Ca2+, NH4+, Cl–, F–, NO3–, SO42–) and carbonaceous fractions (OC and EC). All dust profiles were dominated by crustal elements (Al, Ca, Fe and Mg), while carbonaceous species (OC and EC) were most abundant in vehicular emission profiles. Trace element fraction was found to be significantly higher in vehicular exhaust compared to the resuspended dust. Remarkably, sulphur abundance was observed to be several-fold higher in vehicular emission profiles than resuspended dust profiles. Al and Ca were identified as reliable markers for resuspended dust while V, Pb and EC were identified as markers for vehicular exhaust.

Characterization of PM2.5 Source Profiles for Traffic and Dust Sources in Raipur, India

This paper describes results from a detailed source profile characterization study conducted in Raipur, India to prepare source profiles for traffic and dust-related sources. A companion paper has been published with results for a range of other combustion sources. PM2.5 samples were analyzed for mass, elements (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, S, Sb, Se, V, Zn), ions (Na+, K+, Mg2+, Ca2+, NH4+, Cl–, F–, NO3–, SO42–) and carbonaceous fractions (OC and EC). All dust profiles were dominated by crustal elements (Al, Ca, Fe and Mg), while carbonaceous species (OC and EC) were most abundant in vehicular emission profiles. Trace element fraction was found to be significantly higher in vehicular exhaust compared to the resuspended dust. Remarkably, sulphur abundance was observed to be several-fold higher in vehicular emission profiles than resuspended dust profiles. Al and Ca were identified as reliable markers for resuspended dust while V, Pb and EC were identified as markers for vehicular exhaust.

Sulfur@metal cotton with superior cycling stability as cathode materials for rechargeable lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have great potential for some high energy applications such as electric vehicles and smart grids due to the high capacity, natural abundance, low cost and environmental friendliness of sulfur. In this work, we use the metal cotton to absorb sulfur firmly as cathode material for Li–S batteries. The as-designed sulfur@metal cotton (S@MC) composite shows a good cycling stability and rate capability. The capacity is retained at 480mAhg−1 at 0.1C after 200 cycles. Furthermore, for higher rates, the S@MC cathode material also exhibits stable capacity during different periods.

Drilling Shallow-Water Massive Sulfides at the Palinuro Volcanic Complex, Aeolian Island Arc, Italy

A subseafloor replacement-style barite and sulfide occurrence was drilled in shallow waters at the Palinuro volcanic complex, the northernmost Aeolian arc volcano in the Tyrrhenian Sea, Italy. Using a lander-type drilling device, 11 successful drill holes yielded a total of 13.5 m of core from a sediment-filled depression located at a water depth of 630 to 650 m. The longest continuous drill core recovered consists of 4.84 m of massive to semimassive barite and sulfides with abundant late, native sulfur overprint. Seafloor observations suggest that the hydrothermal system associated with the formation of the subseafloor barite and sulfide ore zone is still active, although black smoker activity does not occur on the seafloor. The recovered drill core shows that the subseafloor deposit is zoned with depth. The top of the mineralized zone is comprised of a variably silicified vuggy barite-sulfide facies that shows notable polymetallic metal enrichment, while the deeper portion of the mineralized zone is dominated by massive pyrite having distinctly lower base and precious metal grades. Metal zonation of the barite and sulfide deposit is related to the evolution of the hydrothermal fluids in space and time. The barite cap and the massive pyrite present in the deeper portion of the mineralized zone appear to have formed early in the paragenesis. During the main stage of the mineralization, the barite cap was brecciated and cemented by a polymetallic assemblage of barite and pyrite with minor chalcopyrite and tetrahedrite, trace famatinite, and rare cinnabar. Lower temperature precipitates formed during the main stage of mineralization include sphalerite, galena, pyrite, opal-A, and barite, which are associated with traces of Pb-Sb-As sulfosalts such as bournonite-seligmannite, or semseyite. A distinct mineral assemblage of fine-grained anhedral enargite, hypogene covellite, chalcopyrite, and galena is commonly associated with colloform sphalerite, galena, and pyrite as a late phase of this main stage. Colloform pyrite and marcasite are the last sulfides formed in the paragenetic sequence. The deposit is interpreted to have formed from fluids having an intermediate-sulfidation state, although excursions to high- and very high sulfidation states are indicated by the presence of abundant enargite and hypogene covellite. Laser ablation and conventional sulfur isotope analyses show that pyrite formed close to the seafloor within the zone of polymetallic metal enrichment has a variable sulfur isotope composition (δ34S = −39 to +3‰), whereas a more narrow range is observed in the massive pyrite at depth (δ34S = −10 to 0‰). Similar variations were also documented for the late native sulfur overprint. Overall, the negative sulfur isotope ratios at depth, the intermediate- to very high sulfidation conditions during mineralization, and the abundance of native sulfur suggest contributions of magmatic volatiles to the mineralizing fluids from a degassing magma chamber at depth. Biological processes are interpreted to have played a major role during late stages of ore formation. The combination of a subseafloor replacement deposit with a massive to semimassive barite cap rock overlying massive pyrite, the intermediate- to high-sulfidation characteristics, and the strong biological influence on the late stages of mineralization are distinct from other modern seafloor massive sulfide deposits and represents a style of submarine mineralization not previously recognized in a modern volcanic arc environment. The barite and sulfide occurrence at Palinuro shares many characteristics with porphyry-related base metal veins and intermediate-sulfidation epithermal deposits, suggesting that metallogenic processes associated with arc-related magmatic-hydrothermal systems are not restricted to the subaerial environment.

PHOTON-DOMINATED REGION MODELING OF THE [C I], [C II], AND CO LINE EMISSION FROM A BOUNDARY IN THE TAURUS MOLECULAR CLOUD

We present [Ci] and [Cii] observations of a linear edge region in the Taurus molecular cloud, and model this region as a cylindrically symmetric PDR exposed to a low-intensity UV radiation field. The sharp, long profile of the linear edge makes it an ideal case to test PDR models and determine cloud parameters. We compare observations of the [C i], 3P1 -> 3P0 (492 GHz), [C i] 3P2 -> 3P1 (809 GHz), and [Cii] 2P3/2 -> 2P1/2 (1900 GHz) transitions, as well as the lowest rotational transitions of 12CO and 13CO, with line intensities produced by the RATRAN radiative transfer code from the results of the Meudon PDR code. We constrain the density structure of the cloud by fitting a cylindrical density function to visual extinction data. We study the effects of variation of the FUV field, 12C/13C isotopic abundance ratio, sulfur depletion, cosmic ray ionization rate, and inclination of the filament relative to the sky-plane on the chemical network of the PDR model and resulting line emission. We also consider the role of suprathermal chemistry and density inhomogeneities. We find good agreement between the model and observations, and that the integrated line intensities can be explained by a PDR model with an external FUV field of 0.05 G0, a low ratio of 12C to 13C ~ 43, a highly depleted sulfur abundance (by a factor of at least 50), a cosmic ray ionization rate (3 - 6) x 10-17 s^-1, and without significant effects from inclination, clumping or suprathermal chemistry.

Clues on the Galactic evolution of sulphur from star clusters

(Abridged) The abundances of alpha-elements are a powerful diagnostic of the star formation history and chemical evolution of a galaxy. Sulphur, being moderately volatile, can be reliably measured in the interstellar medium (ISM) of damped Ly-alpha galaxies and extragalactic HII regions. Measurements in stars of different metallicity in our Galaxy can then be readily compared to the abundances in external galaxies. Such a comparison is not possible for Si or Ca that suffer depletion onto dust in the ISM. Furthermore, studying sulphur is interesting because it probes nucleosynthetic conditions that are very different from those of O or Mg. The measurements in star clusters are a reliable tracers of the Galactic evolution of sulphur. We find <A(S)>NLTE=6.11+/-0.04 for M 4, <A(S)>NLTE=7.17+/-0.02 for NGC 2477, and <A(S)>NLTE=7.13+/-0.06 for NGC 5822. For the only star studied in Trumpler 5 we find A(S)NLTE=6.43+/-0.03 and A(S)LTE=6.94+/-0.05. Our measurements show that, by and large, the S abundances in Galactic clusters trace reliably those in field stars. The only possible exception is Trumpler 5, for which the NLTE sulphur abundance implies an [S/Fe] ratio lower by roughly 0.4 dex than observed in field stars of comparable metallicity, even though its LTE sulphur abundance is in line with abundances of field stars. Moreover the LTE sulphur abundance is consistent only with the abundance of another alpha-element, Mg, in the same star, while the low NLTE value is consistent with Si and Ca. The S abundances in our sample of stars in clusters imply that the clusters are chemically homogeneous for S within 0.05 dex.