Experimental determination of magnesia and silica solubilities in graphite-saturated and redox-buffered high-pressure COH fluids in equilibrium with forsterite + enstatite and magnesite + enstatite

We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids, synthesized using a rocking piston cylinder apparatus at pressures from 1.0 to 2.1 GPa and temperatures from 700 to 1200 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni–NiO–H₂O (ΔFMQ = ??0.21 to ??1.01), employing a double-capsule setting. Fluids, binary H₂O–CO₂ mixtures at the P, T, and fO₂ conditions investigated, were generated from graphite, oxalic acid anhydrous (H₂C₂O₄) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO₂-bearing fluids. The experimental data show that forsterite?+?enstatite solubility in H₂O–CO₂ fluids is higher compared to pure water, both in terms of dissolved silica (mSiO₂?=?1.24 mol/kg_H2O versus mSiO₂?=?0.22 mol/kg_H2O at P?=?1 GPa, T?=?800 °C) and magnesia (mMgO?=?1.08 mol/kg_H2O versus mMgO?=?0.28 mol/kg_H2O) probably due to the formation of organic C–Mg–Si complexes. Our experimental results show that at low temperature conditions, a graphite-saturated H₂O–CO₂ fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO₂ ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal, while at higher temperatures these fluid, characterized by MgO/SiO₂ ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to the carbon-free aqueous fluids. Therefore, the amount of fluid required to metasomatize the mantle decreases in the presence of carbon at high P–T conditions. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to the shallowest level of the upper mantle.     

Distribution of diatom assemblages and their relationship to environmental variables in the surface sediments of three northern Egyptian lakes

Surficial sediments of three northern Egyptian lakes (Manzala, Burullus and Edku) show differences in diatom assemblages deposited in different sites of these lakes. A total of 172 species and varieties belonging to 58 genera were identified and counted from 62 samples. Of these, 163 diatom taxa were recorded from Manzala Lake sediments, 147 taxa were found in Burullus Lake sediments, and 117 taxa were identified in Edku Lake sediments. The considerable variation in the composition and distribution of the diatom assemblages among these lakes was mainly related to differences in the water quality, salinity, the concentration of nutrients and climatic changes. The planktonic diatom Cyclotella meneghiniana was dominant in the majority of the samples from Manzala Lake, but dominant in only a few samples from the middle parts of Burullus and Edku lakes. The non-planktonic epiphytic taxa Cocconeis placentula and Epithemia sorex were the subdominant species in the surface sediments, especially in shallow and marginal parts of the lakes. Multivariate statistical techniques (hierarchical ascending clustering and canonical correspondence analysis) were used to identify ecological groups of diatoms and to investigate which environmental variables were important in explaining the variation between these groups. Eight ecological groups containing distinctive diatom assemblages reflect current environmental conditions; especially saltwater intrusion in the north and nutrient-rich freshwater in the south.     

Paleolimnological records reveal biotic homogenization driven by eutrophication in tropical reservoirs

Biodiversity changes in response to eutrophication, climate variability and species invasions. These pressures have been shown to reduce community heterogeneity at various scales; however, how productivity drives homogenization patterns in a community of primary producers, such as diatoms, has not been studied. Using a dataset with good temporal resolution, obtained from cores collected from seven tropical reservoirs, we evaluated patterns of spatial and temporal homogenization, i.e. the trends in temporal α-diversity and spatial β-diversity (change in community composition), of diatom assemblages over the past 60–100 years. The paleolimnological records allowed us to study biodiversity trends since the initial community (reservoir construction) in those systems with low anthropogenic impact and also those undergoing eutrophication. No clear trend of spatial β-diversity change over time was found when all reservoirs were analyzed together. However, when only eutrophic reservoirs were considered, a marked decrease in the spatial β-diversity occurred, suggesting that eutrophication leads to homogenization of the diatom assemblage. These findings were reinforced by the lack of change in β-diversity when the age of the reservoirs was standardized, indicating that the reservoirs’ ontogeny did not influence the spatial β-diversity trend and β-diversity did not increase even in the reservoirs with low anthropogenic impact. In addition, the results showed a decrease of α-diversity over time for almost all the eutrophic reservoirs, as well as a decrease in the total species pool for the reservoirs, although periphytic diatoms may be favored by the appearance and sometimes mass development of floating macrophytes in warm, shallow eutrophic reservoirs. This study supports the role of eutrophication as one of the main drivers of diatom assemblage homogenization in tropical reservoirs, with a significant loss of species over time.     

Mn-Cr systematics of carbonates in CM chondrites: Implications for the timing and duration of aqueous alteration

CM chondrites contain carbonates and other secondary minerals such as phyllosilicates, sulfides, sulfates, oxides and hydroxides that are believed to have formed by aqueous alteration reactions on their parent asteroid. We report in situ Mn-Cr isotope measurements in the highly aqueously altered CM2.1 chondrites QUE 93005 and ALH 83100 using secondary ion mass spectrometry (Cameca ims-1270 ion microprobe). The ⁵³Cr excesses are correlated with the ⁵³Mn/⁵⁵Mn ratio and result from the in situ decay of ⁵³Mn, a short-lived radioisotope with a half-life of 3.7 Ma. If we assume that carbonate grains in samples QUE 93005 and ALH 83100 are cogenetic, then the excesses define initial ⁵³Mn/⁵⁵Mn ratios ((⁵³Mn/⁵⁵Mn)₀) of (4.1 ± 1.2) × 10⁻⁶ and (5.1 ± 1.7) × 10⁻⁶, respectively. These values are comparable to those in carbonates from other CM chondrites as reported in the literature. Initial ⁵³Mn/⁵⁵Mn ratios for calculated model isochrones for individual carbonate grains range from (3.8 ± 1.4) × 10⁻⁶ to (4.8 ± 2.1) × 10⁻⁶ for QUE 93005 and from (3.1 ± 1.6) × 10⁻⁶ to (1.3 ± 0.5) × 10⁻⁵ for ALH 83100. A possible interpretation for the ranges in (⁵³Mn/⁵⁵Mn)₀ could be that alteration in individual CM chondrites was episodic and occurred over an extended period of time. However, isochrones based on the entire set of carbonate grains in each of the CM chondrites imply that the degree of aqueous alteration is roughly correlated with the age of carbonate formation in CM chondrites of different subtypes and that alteration on the CM parent asteroid started contemporaneously with or shortly after CAI formation and lasted at least 4 Ma.     

Early detection of volcanic hazard by lidar measurement of carbon dioxide

Volcanic gases give information on magmatic processes. In particular, anomalous releases of carbon dioxide precede volcanic eruptions. Up to now, this gas has been measured in volcanic plumes with conventional measurements that imply the severe risks of local sampling and can last many hours. For these reasons and for the great advantages of laser sensing, the thorough development of volcanic lidars has been undertaken at ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development). In fact, lidar profiling allows one to scan remotely volcanic plumes in a fast and continuous way, and with high spatial and temporal resolution. A differential absorption lidar instrument will be presented in this paper: BILLI (BrIdge voLcanic LIdar). It is based on injection-seeded Nd:YAG laser, double-grating dye laser, difference frequency mixing and optical parametric amplifier. BILLI is funded by the ERC (European Research Council) project BRIDGE (BRIDging the gap between Gas Emissions and geophysical observations at active volcanos). It scanned the gas emitted by Pozzuoli Solfatara (Naples, Italy) and Stromboli Volcano (Sicily, Italy) during field campaigns carried out from October 13 to 17, 2014, and from June 24 to 29, 2015, respectively. Carbon dioxide concentration maps were retrieved remotely in few minutes in the crater areas. To our knowledge, it is the first time that carbon dioxide in a volcanic plume is retrieved by lidar. This result represents the first direct measurement of this kind ever performed on active volcanos and shows the high potential of laser remote sensing in early detection of volcanic hazard.     

A modeling language to support the interoperability of global navigation satellite systems

The availability of multiple Global Navigation Satellite Systems (GNSS) will offer the opportunity to provide seamless navigation services and improved positioning performance. However, before this opportunity can be exploited, a number of issues need to be solved to ensure the compatibility and interoperability of existing GNSS. In particular, the GNSS interoperability can be technically defined as the capability of receivers to compute their global position using two or more GNSS signals. This capability can be more effectively achieved if Signal-In-Space interface specifications are available in a consistent, unambiguous, and possibly standard format, which can support engineers to design interoperable receivers. We aim to support the design of interoperable receivers with the introduction of the Interface Communication Modeling Language (ICML), a graphical language for the formal specification of Signal-In-Space interfaces. The ICML language enables receiver engineers to specify these interfaces at different levels of abstraction, such as analog signal or binary data. In addition, the ICML language also supports the specification of conversion routines between adjacent levels, for the representation of the dynamic aspects—e.g., convolution and encryption processes—of the interface specification. As such, the ICML language proposes an alternative format to textual-based interface specifications and can possibly integrate with the ongoing trend of the Model-based Systems Engineering approaches. We present the structure of the framework implementing the language and an example ICML-based specification for a simplified and reduced version of the Galileo Freely Accessible Navigation (F/NAV) message. The language metamodel is also attached for technical reference. An important caveat: no endorsement is made for the use of the ICML language for the official Galileo Signal-In-Space interface specification.     

Recent trends in seasonal and annual precipitation indices in Tuscany (Italy)

Global warming alters the hydrological cycle since a rise in temperature leads to an increase in the moisture-holding capacity of the atmosphere at a rate of about 7 %/°C. This fact can influence the global, but also local characteristics of precipitation, such as total amount and intensity. Therefore, it is important to study changes in rainfall regime in regions with complex orography, like Tuscany, where there are strong spatial gradients in precipitation amounts. The aim of this study is to look for temporal change in precipitation from 1955 to 2007 searching for spatial differences. Daily data of 21 meteorological stations were analyzed to identify trends in seasonal and annual precipitation indices. Cluster analysis applied to principal components was applied to identify homogeneous groups of stations. A decrease in precipitation was observed at annual time scale, during winter and spring, especially in northwestern areas. Wet days highlighted a decrease in all of Tuscany, due to the same seasons. In northern Tuscany, the decrease in rainfall amount was mainly determined by a lower frequency of rainy events which in turn caused a decrease in the occurrence of extreme daily precipitation events (75th, 90th, and 95th percentile). In central-southern Tuscany, no significant changes were observed except for an increase in precipitation fraction, due to extreme events and in mean daily total amount for wet days. These results are consistent with recent findings for the Mediterranean area and confirm the usefulness of cluster analysis for the analysis of the spatial distribution of precipitation.     

Rates of hydrothermal cooling of new oceanic upper crust derived from lithium-geospeedometry

Episodic emplacement and cooling of lavas and dikes at mid-ocean ridges leads to large fluctuations in hydrothermal fluxes and biological activity. However, the processes operating beneath the seafloor during these transient events such as permeability creation and dike cooling are poorly understood. We have developed a new approach to determine the cooling rate of the sheeted dike complex based on the extent of diffusion of lithium from plagioclase into clinopyroxene during cooling. We have calibrated this Li-geospeedometer using new high-temperature experiments to determine both the temperature dependence of the partitioning of Li between plagioclase and clinopyroxene and the diffusion coefficient for Li in clinopyroxene. Application of this method to lavas and dikes from ODP Hole 504B shows that cooling rates vary dramatically with depth in the upper oceanic crust. Extremely rapid cooling rates (> 450 °C hr^− 1) in the upper part of the sheeted dike complex are sufficient to power hydrothermal megaplume formation within the overlying water column.     

Isolation and characterization of crude-oil-degrading bacteria from the Persian Gulf and the Caspian Sea

Twenty-five crude-oil-degrading bacteria were isolated from oil-contaminated sites in the Persian Gulf and the Caspian Sea. Based on a high growth rate on crude oil and on hydrocarbon degradation ability, 11 strains were selected from the 25 isolated strains for further study. Determination of the nucleotide sequence of the 16S rRNA gene showed that these isolated strains belonged to genera Acinetobacter, Pseudomonas, Gordonia, Rhodococcus, Cobetia, Halomonas, Alcanivorax, Marinobacter and Microbacterium. Among the 11 isolates, strains BS (Acinetobacter calcoaceticus, 98%) and PG-12 (Alcanivorax dieselolei, 98%) were the most effective in degrading crude oil. Rate of crude-oil degradation of 82% (isolate BS) and 71% (isolate PG-12) were observed after 1 week of cultivation in mineral medium. These strains had high emulsification activity and biosurfactant production. GC-MS analysis showed that A. dieselolei PG-12 can degrade different alkanes in crude oil. Screening of the distribution of the alkane hydroxylase gene in 25 isolates in relation to the source of isolation indicated that the group (II) alkane hydroxylase is prevalent in the Caspian Sea, but in the Persian Gulf, the frequency of the group (III) alkane hydroxylase gene is greater than that of the group (II) alkane hydroxylase gene.