δ(34)S values in recent sea sediments and their significance using several sediment profiles from the western Baltic Sea

The isotope ratios of various sulphur components (total sulphur content in the sediment, sulphate and H(2)S in the pore-water) were measured in a number of cores from recent marine sediments taken from the Kieler Bucht (Kiel Bay) region in the western Baltic Sea. Additionally, the quantitative contents of total sulphur, sulphate, sulphide, chloride, organic carbon, iron and water in the sediment and in the pore-water solutions, respectively, were determined. These investigations provided the following results: 1. The sulphur contained in the sediment (～ 0.3-2% of the dry sample) was for the most part introduced only after sedimentation. This confirms the deliberations of Kaplan et al. [The Distribution and Isotopic Abundance of Sulfur in Recent Marine Sediments off Southern California, Geochim. Cosmochim. Acta 27, 297 (1963)]. The organic substance contributes to the sulphur content of the sediment only to an insignificant degree (in our samples with ～5-10% of the total sulphur). 2. The sulphate in the pore-waters has been identified as a source for sulphur in the sediment. During normal sedimentation, the exchange of sulphate by diffusion significant for changes in the sulphur content goes down to a sediment depth of 4-6 cm. In this process, the sulphate consumed by reduction and formation of sulphide or pyrite is mostly replaced. The uppermost sediment layer thus represents a partially open system for the total sulphur. The diagenesis of the sulphur is allochemical. At depths below 4-6 cm, we are dealing with a closed system. The further diagenesis of sulphur here is isochemical. 3. The isotope values of the sediment sulphur are influenced primarily by sulphur which comes into the sediment by diffusion and which is bound by subsequent bacteriological reduction as either sulphide or pyrite. As a consequence of the prevailing reduction of (32)S and reverse-diffusion of sulphate into the open sea water, a (32)S enrichment takes place in the uppermost layer of the sediment. The δ(34)S values in the sediment range in general between-15 and-35‰, while seawater sulphate is+20‰. No relationship could be established between sedimentological or chemical changes and isotope ratios. In the cores, successive sandy and clayish layers showed no change in the δ(34)S values. However, the sedimentation rate seems to influence δ(34)S values. In one core with relatively low sedimentation rates, the δ(34)S values varied between-29 and-33‰, while cores with higher sedimentation rates showed values between-17 and-24‰. 4. As sediment depth increases, the pore-water sulphate shows, as expected, decreasing concentrations (in a depth of 30-40 cm, we found between 20 and 70% of the seawater values), and increasing δ(34)S values (in one case reaching more than+60‰). The concentration of sulphide in the pore-water increases, however, with sediment depth (to various extents, reaching 80 mg S per litre in one case). The δ(34)S values of the pore-water sulphide in all cores show increases paralleling the sulphate sulphur, with a nearly constant δ difference of 50-60‰ in all cores. This seems to confirm the genetic relationship between the two components.     

Experimental investigation of sulphur isotope partitioning during outgassing of hydrogen sulphide from diluted aqueous solutions and seawater

The diffusion of hydrogen sulphide across the sediment-water interface and subsequent liberation to the atmosphere may occur in iron-deficient coastal marine environments with enhanced microbial activity in surface sediments and corresponding accumulation of dissolved H2S in near-surface pore waters. The involvement of analogue processes in periods of global mass extinctions during Earth's history (e.g. at the Permian-Triassic boundary) is currently in discussion [L.R. Kump, A. Pavlov, and M. Arthur,Massive Release of Hydrogen Sulfide to the Surface Ocean and Atmosphere During Intervals of Oceanic Anoxia, Geology 33, 397 (2005)]. The outgassing of H?S is associated with a fractionation of the stable sulphur isotopes, which has so far only been investigated experimentally at selected acidic and neutral pH values, and no experiments with seawater had been carried out. In this communication, we report on sulphur isotope fractionation that takes place during the experimental degassing of H?S from aqueous solution by an inert gas (N?) at 21 °C. Experiments were conducted in the pH range between 2.6 and 10.8, corresponding to the dominance fields of dissolved hydrogen sulphide (H?S(aq)), bisulphide (HS-(aq)), and mixtures of both sulphide species. Overall isotope enrichment factors between -1.6 and +3.0‰ were observed, with the residual dissolved sulphide being enriched or depleted in 3?S compared to the liberated H?S at low and high pH values, respectively. The difference in the low and high pH isotope fractionation effects can be explained by isotope exchange between H?S(aq) and HS-(aq) [B. Fry, H. Gest, and J.M. Hayes, Sulfur Isotope Effects Associated with Protonation of HS- and Volatilization of H?S, Chem. Geol. (Isot. Geosci. Sec.) 58, 253 (1986); R. Ge?ler and K. von Gehlen, Investigation of Sulfur Isotope Fractionation Between H2S Gas and Aqueous Solutions, Fresenius J. Anal. Chem. 324, 130 (1986)] followed by the subsequent transfer of H?S(aq) to the gaseous phase. The assumption of pure physical outgassing of H?S(aq) at low pH values leads to an isotope enrichment factor of -0.9 ± 0.4‰ (n = 14) which is caused by the combined differences in dehydration and diffusion coefficients of H?32S(aq) and H?3?S(aq). In the pH range of natural surface and shallow pore waters, 3?S will be equal to or enriched in the gaseous phase compared to the aqueous solution, therefore creating no or a slight enrichment of 32S in the aqueous solution. Experiments in seawater solution showed no significant influence of increased ionic strength and changed corresponding aqueous speciation on sulphur isotope effects.     

Isotope fractionation in aqua-gas systems: Cl(2)-HCl-Cl(-), Br(2)-HBr-Br(-) and H(2)S-S(2-)

We report calculated values of isotope fractionation factors between chlorine, bromine and sulphide hydrated anions and respective gaseous compounds: hydrogen chloride, hydrogen bromide, molecular chlorine and bromine and hydrogen sulphide. For the calculation of the reduced partition function ratios (β-factors) of hydrated Cl(-), Br(-) and S(2-) anions, we used a model of a cluster composed of the considered ion surrounded by two shells of H(2)O molecules. Only the electrostatic interaction between ion and water molecules treated as electric dipoles was taken into account. The β-factors for the gaseous compounds (HCl, Cl(2), HBr, Br(2) and H(2)S) were calculated from vibrational frequencies reported by Urey and Greiff [Isotopic Exchange Equilibria, J. Am. Chem. Soc. 57, 321 (1935)] and Schauble et al. [Theoretical Estimates Equilibrium Chlorine-Isotope Fractionation, Geochim. Cosmochim. Acta 67, 3267 (2003)]. Low-temperature isotope fractionation between chlorine-hydrated anion and hydrogen chloride attains 1.55-1.68‰ (this work), which is in good agreement with experimental data (1.4-1.8‰) [Z.D. Sharp, J.D. Barnes, T.P. Fischer and M. Halick, An Experimental Determination of Chlorine Isotope Fractionation in Acid Systems and Applications to Volcanic Fumaroles, Geochim. Cosmochim. Acta 74, 264 (2010)]. The predicted isotope fractionations for hydrated bromine and HBr, Br(2) gases are very small, 1000?ln α, do not exceed 0.8‰; thus, the expected variations of bromine isotope composition in aqua-gas systems will require enhanced precision for their detection. In contrast, the sulphur isotope fractionation between H(2)S( gas ) and S(2-) attains 6.0‰ at room temperature and drops nearly linearly to 3.1‰ at 350°C.     

Measuring δ(13)C values of atmospheric acetaldehyde via sodium bisulfite adsorption and cysteamine derivatisation

δ(13)C values of gaseous acetaldehyde were measured by gas chromatograph-combustion-isotope ratio mass spectrometer (GC-C-IRMS) via sodium bisulfite (NaHSO(3)) adsorption and cysteamine derivatisation. Gaseous acetaldehyde was collected via NaHSO(3)-coated Sep-Pak(?) silica gel cartridge, then derivatised with cysteamine, and then the δ(13)C value of the acetaldehyde-cysteamine derivative was measured by GC-C-IRMS. Using two acetaldehydes with different δ(13)C values, derivatisation experiments were carried out to cover concentrations between 0.009×10(-3) and 1.96×10(-3)?mg·l(-1)) of atmospheric acetaldehyde, and then δ(13)C fractionation was evaluated in the derivatisation of acetaldehyde based on stoichiometric mass balance after measuring the δ(13)C values of acetaldehyde, cysteamine and the acetaldehyde-cysteamine derivative. δ(13)C measurements in the derivertisation process showed good reproducibility (<0.5?‰) for gaseous acetaldehyde. The differences between predicted and measured δ(13)C values were 0.04-0.31?‰ for acetaldehyde-cysteamine derivative, indicating that the derivatisation introduces no isotope fractionation for gaseous acetaldehyde, and obtained δ(13)C values of acetaldehyde in ambient air at the two sites were distinct (-34.00?‰ at an urban site versus-31.00?‰ at a forest site), implying potential application of the method to study atmospheric acetaldehyde.     

Sulphur stable isotope systematics in diagenetic pyrite from the North Sea hydrocarbon reservoirs revealed by laser combustion analysis

Our study focuses on pyrite nodules developed in the Brent Group sandstones, which host the Brent Oilfield, one of the North Sea's greatest oil and gas producers. Timing of nodule formation is equivocal, but due to the forceful, penetrative textures that abound, it is considered late. This pyrite offers a research opportunity because it records the development of the supply of H(2)S in a hydrocarbon reservoir and its sulphur isotopic composition. Laser-based analysis of δ(34)S reveals an extraordinary diversity in values and patterns. The values range from-27 to+72‰, covering half the terrestrial range, with large variations at the submillimetre scale. Isotopically heavy (δ(34)S ～+30‰ or higher) sulphide is endemic, but low δ(34)S pyrite is also present and appears to represent a temporally though not spatially (on the ～cm scale) distinct pyritisation event. The distribution of δ(34)S values within individual concretions can be normal (Gaussian), but in some cases may reflect progressive isotope fractionation process(es), conceivably of Rayleigh type. The source of the sulphur and the identity of the isotope fractionation process(es) remain enigmatic.     

Identifying sources and processes controlling the sulphur cycle in the Canyon Creek watershed, Alberta, Canada

Sources and processes affecting the sulphur cycle in the Canyon Creek watershed in Alberta (Canada) were investigated. The catchment is important for water supply and recreational activities and is also a source of oil and natural gas. Water was collected from 10 locations along an 8?km stretch of Canyon Creek including three so-called sulphur pools, followed by the chemical and isotopic analyses on water and its major dissolved species. The δ(2)H and δ(18)O values of the water plotted near the regional meteoric water line, indicating a meteoric origin of the water and no contribution from deeper formation waters. Calcium, magnesium and bicarbonate were the dominant ions in the upstream portion of the watershed, whereas sulphate was the dominant anion in the water from the three sulphur pools. The isotopic composition of sulphate (δ(34)S and δ(18)O) revealed three major sulphate sources with distinct isotopic compositions throughout the catchment: (1) a combination of sulphate from soils and sulphide oxidation in the bedrock in the upper reaches of Canyon Creek; (2) sulphide oxidation in pyrite-rich shales in the lower reaches of Canyon Creek and (3) dissolution of Devonian anhydrite constituting the major sulphate source for the three sulphur pools in the central portion of the watershed. The presence of H(2)S in the sulphur pools with δ(34)S values ～30?‰ lower than those of sulphate further indicated the occurrence of bacterial (dissimilatory) sulphate reduction. This case study reveals that δ(34)S values of surface water systems can vary by more than 20?‰ over short geographic distances and that isotope analyses are an effective tool to identify sources and processes that govern the sulphur cycle in watersheds.     

Origin and Distribution of Sulphate in Surface Waters of the Mansfeld Mining District (Central Germany)—A Sulphur Isotope Study

Abstract

In the Mansfeld region (Central Germany) copper mining contributed to an enormous pollution of the environment. Metal- and sulphate-bearing sediments and leachates emerge from the former copper smelters and mining waste heaps, spread along local rivers and finally reach the Saale river. A sulphur isotope study on water and stream sediments was performed along the River “Böse Sieben” and from its tributaries to determine the different sulphur sources. Four major sulphur sources exist in the area: metal sulphide mineralisations (Kupferschiefer), metalliferous sulphidic flue dust, slag, and anhydrite and gypsum of Permian and Triassic age. We obtained δ³⁴S(SO₄)-values in water samples varying from +4‰ to ?18‰ CDT, clearly reflecting the input of sulphate from different sources. Sulphate from the oxidation of sulphidic mining residues is restricted to the mining area and cannot be traced for more than 5 km downstream. The major source for sulphate is the dissolution of gypsum and anhydrite. The sulphur isotope composition in dissolved and sedimentary adsorbed sulphate differs only slightly from each other. Microbial dissimilatory sulphate reduction can not be excluded in the shallow sediment layers.     

Studies of the protein and the energy metabolism in man during a wintering in Antarctica

During the 29th Soviet Antarctic Expedition in Novolazarevskaya from March 1984 to March 1985, the protein and energy metabolisms were studied in six expeditioners from the German Democratic Republic. The investigations were carried out at the beginning of the expedition (May), during the polar night (July) and during the polar day (December). The effect of a special stress situation (sledge trek in April 1984) was investigated in one subject. The stable nitrogen isotope (15)N was used to study the protein metabolism. The assessment of the energy metabolism was based on the oxygen consumption, which was determined by means of a spirograph. In addition, the vital capacity, the breath minute volume, the blood pressure, etc. were measured. The following results were obtained: During the polar night, the utilisation of the dietary proteins and the whole body protein synthesis calculated by means of the (15)N excretion of the total nitrogen in urine were greater (73.6±0.9 % and 3.48±0.17?g protein d(-1)?kg(-1), n=3) than the respective values during the polar day (69.7±1.2, p<0.05, n=3 and 3.05±0.07, p<0.05, n=3) and at the beginning of the expedition (69.6±1.4, p<0.02, n=5 and 2.81±0.09, p<0.01, n=5). The lowest values (58.0 % and 2.43?g protein d(-1)?kg(-1)) were obtained in the subject after the trek. The resting metabolic rate (in kJ?d(-1)?m(-2)) was decreased during the polar night (45.6±5.0, n=4) in comparison with the polar day (61.5±11.3, n=3) and the beginning of the expedition (52.3±9.6, n=4) with p<0.01 in both cases.     

Comparison of sample preparation methods for stable isotope analysis of dissolved sulphate in forested watersheds

Pretreatment methods for measuring stable sulphur (δ(34)S) and oxygen (δ(18)O) isotope ratios of dissolved sulphate from watersheds have evolved throughout the last few decades. The current study evaluated if there are differences in the measured stable S and O isotope values of dissolved sulphate from forested watersheds when pretreated using three different methods: Method 1 (M1): adsorb sulphate on anion exchange resins and send directly to isotope facility; Method 2 (M2): adsorb sulphate on anion exchange resins, extract sulphate from anion exchange resins, and send the produced BaSO(4) to the isotope facility; and Method 3 (M3): directly precipitate BaSO(4) without anion exchange resins with the precipitates being sent to the isotope facility. We found an excellent agreement of the δ(34)S(sulphate) values among all the three methods. However, some differences were observed in the δ(18)O(sulphate) values (M1 versus M2:-1.5 ‰; M1 versus M3:-1.2 ‰) associated with possible O contamination before isotope measurement. Several approaches are recommended to improve the pretreatment procedures for δ(18)O(sulphate) analysis.     

Methane-derived carbonates in a native sulfur deposit: stable isotope and trace element discriminations related to the transformation of aragonite to calcite

Abstract Stable isotope ((13)C, (18)O, (34)S) and trace element (Sr(2+), Mg(2+), Mn(2+), Ba(2+), Na(+)) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ(13)C = -41 to -47‰ vs. PDB) associated with native sulfur (δ(34)S = + 10 to + 15‰ vs. V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ(18)O = -3.9 to -5.9‰ vs. PDB) and a secondary SrSO(4) (δ(18)O = + 20‰ vs. SMOW; δ(34)S = + 59‰ vs. V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ(34)S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species.     

Comparison of sample preparation methods for stable isotope analysis of dissolved sulphate in forested watersheds

Pretreatment methods for measuring stable sulphur (δ³⁴S) and oxygen (δ¹⁸O) isotope ratios of dissolved sulphate from watersheds have evolved throughout the last few decades. The current study evaluated if there are differences in the measured stable S and O isotope values of dissolved sulphate from forested watersheds when pretreated using three different methods: Method 1 (M1): adsorb sulphate on anion exchange resins and send directly to isotope facility; Method 2 (M2): adsorb sulphate on anion exchange resins, extract sulphate from anion exchange resins, and send the produced BaSO₄ to the isotope facility; and Method 3 (M3): directly precipitate BaSO₄ without anion exchange resins with the precipitates being sent to the isotope facility. We found an excellent agreement of the δ³⁴S_sulphate values among all the three methods. However, some differences were observed in the δ¹⁸O_sulphate values (M1 versus M2:?1.5 ‰; M1 versus M3:?1.2 ‰) associated with possible O contamination before isotope measurement. Several approaches are recommended to improve the pretreatment procedures for δ¹⁸O_sulphate analysis.     

Position-specific carbon isotope analysis of trichloroacetic acid by gas chromatography/isotope ratio mass spectrometry

Trichloroacetic acid (TCAA) is an important environmental contaminant present in soils, water and plants. A method for determining the carbon isotope signature of the trichloromethyl position in TCAA using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) was developed and tested with TCAA from different origins. Position-specific isotope analysis (PSIA) can provide direct information on the kinetic isotope effect for isotope substitution at a specific position in the molecule and/or help to distinguish different sources of a compound. The method is based on the degradation of TCAA into chloroform (CF) and CO? by thermal decarboxylation. Since thermal decarboxylation is associated with strong carbon isotope fractionation (ε = -34.6 ± 0.2‰) the reaction conditions were optimized to ensure full conversion. The combined isotope ratio of CF and CO? at the end of the reaction corresponded well to the isotope ratio of TCAA, confirming the reliability of the method. A method quantification limit (MQL) for TCAA of 18.6 μg/L was determined. Samples of TCAA produced by enzymatic and non-enzymatic chlorination of natural organic matter (NOM) and some industrially produced TCAA were used as exemplary sources. Significant different PSIA isotope ratios were observed between industrial TCAA and TCAA samples produced by chlorination of NOM. This highlights the potential of the method to study the origin and the fate of TCAA in the environment.     

Methane-Derived Carbonates in a Native Sulfur Deposit: Stable Isotope and Trace Element Discriminations Related to the Transformation of Aragonite to Calcite

Abstract

Stable isotope (¹³C, ¹⁸O, ³⁴S) and trace element (Sr²⁺, Mg²⁺, Mn²⁺, Ba²⁺, Na⁺) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ¹³C = ?41 to ?47‰ vs. PDB) associated with native sulfur (δ³⁴S = + 10 to + 15‰ vs. V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ¹⁸O = ?3.9 to ?5.9‰ vs. PDB) and a secondary SrSO₄ (δ¹⁸O = + 20‰ vs. SMOW; δ³⁴S = + 59‰ vs. V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ³⁴S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species.     

Concrete under sulphate attack: an isotope study on sulphur sources

The formation of secondary sulphate minerals such as thaumasite, ettringite and gypsum is a process causing severe damage to concrete constructions. A major key to understand the complex reactions, involving concrete deterioration is to decipher the cause of its appearance, including the sources of the involved elements. In the present study, sulphate attack on the concrete of two Austrian tunnels is investigated. The distribution of stable sulphur isotopes is successfully applied to decipher the source(s) of sulphur in the deteriorating sulphate-bearing minerals. Interestingly, δ(34)S values of sulphate in local groundwater and in the deteriorating minerals are mostly in the range from+14 to+27 ‰. These δ(34)S values match the isotope patterns of regional Permian and Triassic marine evaporites. Soot relicts from steam- and diesel-driven trains found in one of the tunnels show δ(34)S values from-3 to+5 ‰, and are therefore assumed to be of minor importance for sulphate attack on the concretes. In areas of pyrite-containing sedimentary rocks, the δ(34)S values of sulphate from damaged concrete range between-1 and+11 ‰. The latter range reflects the impact of sulphide oxidation on local groundwater sulphate.     

Sulfur Isotope Fractionation in the Biogeochemical Sulfur Cycle of Marine Sediments

Abstract

The sulfur isotopic record of sedimentary sulfides (mainly pyrite) and sulfates shows considerable variations in time and plays an important role in the biological and geochemical interpretation, e.g., of the evolution of life and the oxygen partial pressure of Earth's atmosphere (e.g. [1]). From a comparison of experimental results with Desulfovibrio spp. it can be inferred that the S isotope fractionation during reduction of sulfur compounds is controlled by the number of electrons transferred (Fig. 1). Sulfur isotope discrimination in the sulfur cycle of marine sediments is dominated by dissimilatory bacterial sulfate reduction (BSR), and [2] used laboratory experiments with mesophilic bacteria to postulate that high sulfate reduction rates with abundant sulfate at enhanced temperature dominated the Ocean water chemistry during early Archean time. Experiments with pure cultures of thermophilic sulfate reducers [3] and natural hydrothermally influenced communities [4], however, demonstrated that isotope discrimination is close to average fractionation by mesophiles and that temperature is not directly influencing isotope discrimination during BSR.     

Sulphur diagenesis in the sediments of the Kiel Bight, SW Baltic Sea, as reflected by multiple stable sulphur isotopes

In this work, the biogeochemistry of marine sediments from the Kiel Bight, coastal SW Baltic Sea, is studied based on the abundance and isotopic composition of organic carbon and different forms of sedimentary sulphur. Active bacterial sulphate reduction, partly under sulphate-limiting conditions, is evident from paired δ(34)S and δ(18)O values of pore water sulphate. The resulting pore water sulphide is partly precipitated as acid-volatile iron sulphide and subsequently forms sedimentary pyrite, partly serves in later diagenetic sulphurisation of organic matter, or remains dissolved in the pore water, all evident from the respective δ(34)S values. Microbial sulphate turnover is associated with an apparent isotopic fractionation between dissolved sulphate and dissolved sulphide (Δ(34)S) that varies between 46 and 66‰.     

Magnetic and magnetocaloric properties of the high-temperature modification of TbTiGe

The high-temperature form (HT) of the ternary germanide TbTiGe was prepared by melting. The investigation of HT-TbTiGe by x-ray and neutron powder diffractions shows that the compound crystallizes in the tetragonal CeScSi-type structure (space group I4/mmm; a?=?404.84(5) and c?=?1530.10(9)?pm as unit cell parameters). Magnetization and specific heat measurements as well as neutron powder diffraction performed on HT-TbTiGe reveal a ferromagnet having T(C)?=?300(1)?K as the Curie temperature; the Tb-moments are aligned along the c-axis. This magnetic ordering is associated with a modest magnetocaloric effect around room temperature. The isothermal magnetic entropy change ΔS(m) was determined from the magnetization data; ΔS(m) reaches, respectively, a maximum value of -?4.3 and -?2.0?J?K(-1)?kg(-1) for a magnetic field change of 5 and 2?T.     

Early Aptian carbon and sulphur isotope signatures at ODP site 765

Current carbon and sulphur isotope ratios (δ(13)C and δ(34)S) suggest there were major shifts in partitioning between reduced and oxidised reservoirs of carbon and sulphur during the Early Cretaceous. However, the δ(13)C and δ(34)S records are composed from different Ocean Drilling Program sites and are hard to correlate at high resolution. We present high-resolution Aptian δ(13)C(org) and δ(34)S(barite) values derived from the same set of samples, enabling a higher certainty correlation than previously possible. Two major hypotheses aim to explain the Early Aptian S-isotope excursion: increased volcanic degassing and/or fluctuations in the marine sulphate concentration. Our S-isotope data provide tight constraints on the timing and magnitude of volcanic flux required. We show that the observed S-isotope signature can be explained by a 2?Ma pulse of increased volcanic flux, injecting ～4.5×10(18)?mol C into the atmosphere. Further work is needed to evaluate whether these fluxes are compatible with the existing C-isotope record.     

Stable Sulfur Isotope Effects Related to Local Intense Sulfate Reduction in a Tidal Sandflat (Southern North Sea): Results from Loading Experiments

Abstract

Anoxic sediment surfaces coloured black by iron monosulfides (“black spots”) evolve in tidal sandflats of the Wadden Sea (southern North Sea) as a result of the degradation of buried organic matter. To follow the short- and long-term effects of organic matter burial on pore water and sediment isotopic biogeochemistry, formation of artificial black spots was initiated on the Groninger Plate (site RP63) in the backbarrier tidal flats of Spiekeroog island. Changes in concentrations (DOC, TA, TOC, sulfate, sulfide, TRS, Fe) and isotopic compositions (sulfate, sulfide, TRS, pyrite, TOC) were followed for up to 12 months and compared to reference areas. 13°C ratios of TOC clearly mirror the early diagenetic degradation of organic matter. At least temporarily closed system sulfate reduction is inferred for the artificial black spot from the variation of sulfate concentrations and stable sulfur isotope partitioning, In the interstitial waters of the black spot, 34S/32S values of coexisting dissolved sulfate and sulfide yield fractionation degrees between ?5 and ?25%. On the reference area, 34S/32S are fractionated by ?32 to ?42% as calculated from the isotope composition of solid phase reduced sulfur and pore water sulfate. Sulfur isotope fractionation seems to increase with decreasing sulfate reduction rate. Limiting factor seems to be the availability of DOC. Between the pyrite pool and the dissolved sulfide in the black spot, no significant isotope exchange is observed within 12 months.     

Origin and distribution of sulphate in surface waters of the Mansfeld mining district (Central Germany)--a sulphur isotope study.

In the Mansfeld region (Central Germany) copper mining contributed to an enormous pollution of the environment. Metal- and sulphate-bearing sediments and leachates emerge from the former copper smelters and mining waste heaps, spread along local rivers and finally reach the Saale river. A sulphur isotope study on water and stream sediments was performed along the River "B?se Sieben" and from its tributaries to determine the different sulphur sources. Four major sulphur sources exist in the area: metal sulphide mineralisations (Kupferschiefer), met alliferous sulphidic flue dust, slag, and anhydrite and gypsum of Permian and Triassic age. We obtained delta34S(SO4)-values in water samples varying from +4 per thousand to -18 per thousand CDT, clearly reflecting the input of sulphate from different sources. Sulphate from the oxidation of sulphidic mining residues is restricted to the mining area and cannot be traced for more than 5 km downstream. The major source for sulphate is the dissolution of gypsum and anhydrite. The sulphur isotope composition in dissolved and sedimentary adsorbed sulphate differs only slightly from each other. Microbial dissimilatory sulphate reduction can not be excluded in the shallow sediment layers.