Measurements of PM<Subscript>10</Subscript> ions and trace gases with the online system MARGA at the research station Melpitz in Germany – A five-year study

An hourly quantification of inorganic water-soluble PM₁₀ ions and corresponding trace gases was performed using the Monitor for AeRosols and Gases in ambient Air (MARGA) at the TROPOS research site in Melpitz, Germany. The data availability amounts to over 80% for the five-year measurement period from 2010 to 2014. Comparisons were performed for the evaluation of the MARGA, resulting in coefficients of determinations (slopes) of 0.91 (0.90) for the measurements against the SO₂ gas monitor, 0.84 (0.88), 0.79 (1.39), 0.85 (1.20) for the ACSM NO₃ ^?, SO₄ ^2? and NH₄ ⁺ measurements, respectively, and 0.85 (0.65), 0.88 (0.68), 0.91 (0.83), 0.86 (0.82) for the filter measurements of Cl^?, NO₃ ^?, SO₄ ^2? and NH₄ ⁺, respectively. A HONO comparison with a batch denuder shows large scatter (R² = 0.41). The MARGA HNO₃ is underestimated compared to a batch and coated denuder with shorter inlets (slopes of 0.16 and 0.08, respectively). Less NH₃ was observed in coated denuders for high ambient concentrations. Long-time measurements show clear daily and seasonal variabilities. Potential Source Contribution Function (PSCF) analysis indicates the emission area of particulate ions Cl^?, NO₃ ^?, SO₄ ^2?, NH₄ ⁺, K⁺ and gaseous SO₂ to lie in eastern European countries, predominantly in wintertime. Coarse mode sea salt particles are transported from the North Sea to Melpitz. The particles at Melpitz are nearly neutralised with a mean molar ratio of 0.90 for the five-year study. A slight increase of the neutralization ratio over the last three years indicates a stronger decrease of the anthropogenically emitted NO₃ ^? and SO₄ ^2? compared to NH₄ ⁺.     

The Intertidal Burrowing Crab <Emphasis Type="Italic">Neohelice</Emphasis> (=<Emphasis Type="Italic">Chasmagnathus</Emphasis>) <Emphasis Type="Italic">granulata</Emphasis> Positively Affects Foraging of Rodents in South Western Atlantic Salt Marshes

The role of positive and indirect interactions is often crucial in communities with intense abiotic stress such as salt marshes. The burrowing crab, Neohelice (=Chasmagnathus) granulata, is the dominant benthic macroinvertebrate of southwest Atlantic marshes (southern Brazil to Northern Argentinean Patagonia), having strong direct and indirect effects on marsh soil and, in consequence, on marsh vegetation and primary consumers. In this work, we investigate if this crab indirectly modifies habitat use by the granivorous rodents, Akodon azarae and Oligoryzomys flavescens, by increasing nutrient availability and thus enhancing seed production by the marsh plant Spartina densiflora. The study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°32′ S). Rodent frequencies in S. densiflora were positively correlated with crab densities throughout the low and middle marsh. Additionally, the highest quality of S. densiflora and inflorescence density was recorded at the highest crab densities. Experimental manipulation of crab densities shows that N. granulata indirectly enhances the performance of S. densiflora (e.g., decreased fiber content and C/N ratios) and increases density of seeds. Moreover, N. granulata also facilitates S. densiflora seed availability to rodents by concentrating them in sediment mound at their burrows entrances. Experimental rodent exclusions showed that rodent species used S. densiflora seeds, a variable positively related to crab burrow density. Thus, our results show that N. granulata drives the granivorous rodent distribution and the intensity of seeds–rodent interaction trough facilitative and indirect interactions in marsh community.     

Analysis of coupled Sr/Ca and Sr/Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS

We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and ⁸⁷Sr/⁸⁶Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST “SRM1400 Bone Ash” with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and ⁸⁷Sr/⁸⁶Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas ⁸⁷Sr/⁸⁶Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the ⁸⁷Sr/⁸⁶Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.     

Prograde garnet growth along complex <Emphasis Type="Italic">P–T–t</Emphasis> paths: results from numerical experiments on polyphase garnet from the Wölz Complex (Austroalpine basement)

Garnet in metapelites from the Wölz Complex of the Austroalpine crystalline basement east of the Tauern Window characteristically consists of two growth phases, which preserve a comprehensive record of the geothermal history during polymetamorphism. From numerical modelling of garnet formation, detailed information on the pressure–temperature–time (P–T–t) evolution during prograde metamorphism is obtained. In that respect, the combined influences of chemical fractionation associated with garnet growth, modification of the original growth zoning through intragranular diffusion and the nucleation history on the chemical zoning of garnet as P and T change during growth are considered. The concentric chemical zoning observed in garnet and the homogenous rock matrix, which is devoid of chemical segregation, render the simulation of garnet growth through successive equilibrium states reliable. Whereas the first growth phase of garnet was formed at isobaric conditions of ～3.8 kbar at low heating/cooling rates, the second growth phase grew along a Barrovian P–T path marked with a thermal peak of ～625°C at ～10 kbar and a maximum in P of ～10.4 kbar at ～610°C. For the heating rate during the growth of the second phase of garnet, average rates faster than 50°C Ma^?1 are obtained. From geochronological investigations the first growth phase of garnet from the Wölz Complex pertains to the Permian metamorphic event. The second growth phase grew in the course of Eo-Alpine metamorphism during the Cretaceous.     

Metalliferous paragenesis of the San José mine, Oruro, Bolivia

The San José silver–tin deposit, Oruro, is located in the Cordillera Oriental, which contains most of the metalliferous mineralizations of Bolivia and is related to a quartz-latite dome of Miocene age. The mineral paragenesis encountered in this study is composed of cassiterite, stannite, miargyrite, pyrargyrite, andorite and Bi-rich andorite, jamesonite, pavonite/benjaminite, boulangerite, owyheeite, ramdohrite and Bi-rich ramdohrite, bismuthinite, besides pyrite, chalcopyrite, Ag-rich tetrahedrite, galena and sphalerite, all of which are analyzed by electron microprobe analysis. With semi-quantitative SEM/EDS and XRD analyses, rhodostannite and kësterite/ferrokësterite were found in association with andorite, and chalcostibite was determined by XRD, in association with zinkenite, tetrahedrite and pyrite.     

Garnet growth at high- and ultra-high pressure conditions and the effect of element fractionation on mineral modes and composition

In this paper we show that thermodynamic forward modelling, using Gibbs energy minimisation with consideration of element fractionation into refractory phases and/or liberated fluids, is able to extract information about the complex physical and chemical evolution of a deeply subducted rock volume. By comparing complex compositional growth zonations in garnets from high-and ultra-high pressure samples with those derived from thermodynamic forward modelling, we yield an insight into the effects of element fractionation on composition and modes of the co-genetic metamorphic phase assemblage. Our results demonstrate that fractionation effects cause discontinuous growth and re-crystallisation of metamorphic minerals in high pressure rocks. Reduced or hindered mineral growth at UHP conditions can control the inclusion and preservation of minerals indicative for UHP metamorphism, such as coesite, thus masking peak pressure conditions reached in subducted rocks.Further, our results demonstrate that fractional garnet crystallisation leads to strong compositional gradients and step-like zonation patterns in garnet, a feature often observed in high-and ultra-high pressure rocks. Thermodynamic forward modelling allows the interpretation of commonly observed garnet growth zonation patterns in terms of garnet forming reactions and the relative timing of garnet growth with respect to the rock's pressure–temperature path. Such a correlation is essential for the determination of tectonic and metamorphic rates in subduction zones as well as for the understanding of trace element signatures in subduction related rocks. It therefore should be commonplace in the investigation of metamorphic processes in subduction zones.