A predictive numerical model for potential mapping of the gas hydrate stability zone in the Gulf of Cadiz

This paper presents a computational model for mapping the regional 3D distribution in which seafloor gas hydrates would be stable, that is carried out in a Geographical Information System (GIS) environment. The construction of the model is comprised of three primary steps, namely: (1) the construction of surfaces for the various variables based on available 3D data (seafloor temperature, geothermal gradient and depth-pressure); (2) the calculation of the gas function equilibrium functions for the various hydrocarbon compositions reported from hydrate and sediment samples; and (3) the calculation of the thickness of the hydrate stability zone. The solution is based on a transcendental function, which is solved iteratively in a GIS environment.The model has been applied in the northernmost continental slope of the Gulf of Cadiz, an area where an abundant supply for hydrate formation, such as extensive hydrocarbon seeps, diapirs and fault structures, is combined with deep undercurrents and a complex seafloor morphology. In the Gulf of Cadiz, the model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic gas compositions, and explains the geometry and distribution of geological structures derived from gas venting in the Tasyo Field (Gulf of Cadiz) and the generation of BSR levels on the upper continental slope.     

Magnetic Lasso: A New Kinematic Solar Wind Propagation Method

Solar wind propagation from the point of measurement to an arbitrary target in the heliosphere is an important input for heliospheric, planetary and cometary studies. In this paper a new kinematic propagation method, the magnetic lasso method is presented. Compared to the simple ballistic approach our method is based on reconstructing the ideal Parker spiral connecting the target with the Sun by testing a previously defined range of heliographic longitudes. The model takes into account the eventual evolution of stream–stream interactions and handles these with a simple model based on the dynamic pressure difference between the two streams. Special emphasis is given to input data cleaning by handling interplanetary coronal mass ejection events as data gaps due to their different propagation characteristics. The solar wind bulk velocity is considered radial and constant. Density and radial magnetic field are propagated by correcting with the inverse square of the radial distance. The model has the advantage that it can be coded easily and fitted to the problem; it is flexible in selecting and handling input data and requires little running time.     

On the use of logistic regression for stellar classification

We are totally immersed in the Big Data era and reliable algorithms and methods for data classification are instrumental for astronomical research. Random Forest and Support Vector Machines algorithms have become popular over the last few years and they are widely used for different stellar classification problems. In this article, we explore an alternative supervised classification method scarcely exploited in astronomy, Logistic Regression, that has been applied successfully in other scientific areas, particularly biostatistics. We have applied this method in order to derive membership probabilities for potential T Tauri star candidates from ultraviolet-infrared colour-colour diagrams.     

Comparative Study of the Three-Dimensional Thermodynamical Structure of the Inner Corona of Solar Minimum Carrington Rotations 1915 and 2081

Using differential emission measure tomography (DEMT) based on time series of EUV images, we carry out a quantitative comparative analysis of the three-dimensional (3D) structure of the electron density and temperature of the inner corona (\(r<1.25\,\mathrm{R}_{\odot}\)) between two specific rotations selected from the last two solar minima, namely Carrington Rotations (CR)1915 and CR-2081. The analysis places error bars on the results because of the systematic uncertainty of the sources. While the results for CR-2081 are characterized by a remarkable north–south symmetry, the southern hemisphere for CR-1915 exhibits higher densities and temperatures than the northern hemisphere. The core region of the streamer belt in both rotations is found to be populated by structures whose temperature decreases with height (called “down loops” in our previous articles). They are characterized by plasma \(\beta\gtrsim1\), and may be the result of the efficient dissipation of Alfvén waves at low coronal heights. The comparative analysis reveals that the low latitudes of the equatorial streamer belt of CR-1915 exhibit higher densities than for CR-2081. This cannot be explained by the systematic uncertainties. In addition, the southern hemisphere of the streamer belt of CR-1915 is characterized by higher temperatures and density scale heights than for CR-2081. On the other hand, the coronal hole region of CR-1915 shows lower temperatures than for CR-2081. The reported differences are in the range \({\approx}\,10\,\mbox{--}\,25\%\), depending on the specific physical quantity and region that is compared, as fully detailed in the analysis. For other regions and/or physical quantities, the uncertainties do not allow assessing the thermodynamical differences between the two rotations. Future investigation will involve a DEMT analysis of other Carrington rotations selected from both epochs, and also a comparison of their tomographic reconstructions with magnetohydrodynamical simulations of the inner corona.     

The impact of extreme turbidity events on the nursery function of a temperate European estuary with regulated freshwater inflow

Estuaries are used as nursery grounds by numerous marine species despite being usually subject to strong anthropogenic disturbances. Abundances of marine recruits (fish and crustacean decapods) and their main prey (mysids) were monitored by monthly sampling, from June 1997 to February 2009, in the lower reaches of the Guadalquivir estuary (SW Spain). During that period, unusually high and persistent turbidity events (HPTEs) were observed twice. Both HPTEs started with strong and sudden freshwater discharges after relatively long periods of very low freshwater inflow. Data from this time-series were used to test the hypothesis that HPTEs may negatively impact the nursery function of estuaries either by decreasing prey availability or by decreasing survival/arrival of marine recruits. During HPTEs, the commonest mysid (Mesopodopsis slabberi), a key species in the estuarine food web, showed a significant decrease in abundance. Likewise, some marine recruits that prey on M. slabberi and whose peaks of abundance within the estuary occur in summer–autumn (Engraulis encrasicolus and Pomadasys incisus) were less abundant during HPTEs. It is also suggested that HPTEs might have triggered a shift in the distribution of the most euryhaline prey (Neomysis integer) and predator (Dicentrarchus punctatus and Crangon crangon) species, towards more saline waters. This could have contributed to an increase in the inter-specific competition (for food/habitat) within the estuarine nursery area. The results discussed in this study call attention to the need to reduce as much as possible the anthropogenic pressures that may stimulate the occurrence of high and persistent turbidity events (HPTEs) in order to preserve the nursery function of temperate estuaries.     

Dichte und Lichtbrechung der Moldavite von Něchov

In this experimental work I studied the correlation of the specific gravity and index of refraction at 19 moldavites from a finding place in Nchov. This place is in the south of Bohemia, in a district of eské Budjovice (Budweis). The reason for this work was the extraordinary declaration of the correlation of the specific gravity and index of refraction at one moldavite from Nchov that is: d=2,395 and n _D =1,5033.These declarations were settled by Nováek. The results of these measurings have shown that the linear correlation of the specific gravity and index of refraction of the moldavites from other finding places are characteristic also for these ones. The definition of this correlation at 19 pieces of moldavites from Nchov shows also this linear character in the measuring of values d=2,355–2,395 and n _D =1,4870–1,4950.In this work there were settled also some other dates of unity (so-called in couple-moldavites). But we must not oversee certain vaccilations of the declaration at the moldavites from Nchov, as at those from other finding places. The secularity of these declarations about the moldavites of Nchov lies also therein, that the avarage value of the correlation of specific gravity and index of refraction of this finding place is higher than those of other places.

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Herrn Dr. Walter Weiskirchner, Dozent an der Universität Tübingen, danke ich herzlich für die freundliche Durchsicht der Arbeit.     

Electron-probe check of fe-distribution in sphalerite grains of the Nagybörzsöny hydrothermal ore deposits,Hungary

Micron-scale iron-distribution patterns in sphalerite grains derived from two contrasting mineral assemblages of the Nagybörzsöny hydrothermal ore deposits (high temperature stockwork and low temperature veins), were determined with electron microprobe, pointcounter and continuous chart-recorder measurements along radial profiles. A significant oscillation of iron-content ranging from 8.1 to 18 per cent for stockwork and 4.3 to 15.8 per cent for veins took place during crystal growth. Homogeneous crystal cores are characteristic for vein-filling, while replacement occurring in deeper levels of the stockwork results in mosaic cores. Frequent oscillation of iron content is relevant to top-sections of the ore bodies, copious supply being recorded in recurring shells, whereas scanty, unilateral ones produce crescents arranged in onion-like structure.

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Zusammenfassung Bestimmungen der Eisenverteilung wurden an Zinkblendekörnern aus zwei verschiedenen Mineralparagenesen (Hochtemperatur-Stockwerk und Gangfüllungen niederiger Bildungstemperatur) der hydrothermalen Erzlagerstätte Nagybörzsöny im Mikronbereich durch Elektronen-Mikrosonde-Messungen (Punktzählung und kontinuierliche Band-Registrierung) entlang radialer Profile vorgenommen. Bedeutende Schwankungen des Eisengehaltes (8,1–18% für das Stockwerk und 4,3–15,8% für die Gänge) wurden registriert. Homogene Kristallkerne kennzeichnen die Gangfüllungen, wogegen in tieferen Horizonten des Stockwerks Verdrängungen zur Bildung von Kristallen mit Mosaik-Kernen führen. Allgemein ist in den Gipfel-Partien der Erzkörper Fluktuation des Eisengehaltes häufig. Gleichmäßiger Nachschub während des Kristallwachstums führte zu ringförmigen Zonen gleicher Eisengehalte, spärlicher oder einseitiger dagegen zu halbmondförmigen Hüllen mit Zwiebelstruktur.

     

Determination par activation neutronique des rapports Cl/Br des inclusions fluides de divers gypses. Correlation avec les donnees de la microcryoscopie et interpretations genetiques

Gypsum contains liquid inclusions which fill mainly primary cavities. Analysis of inclusions may give some information about the mineral formation process. In places, diagenetic solutions have filled secondary cavities along cleavage planes or replaced initial liquid inclusions in primary cavities; the presence of such secondary inclusions must, therefore, be taken into consideration. This study presents our results on the Cl/Br ratio of liquid inclusions in gypsum. The Cl/Br ratio is practically constant in present sea water, and has been measured in many different types of waters. The Br content of halite has also been extensively studied to trace the compositional changes of a salt-depositing brine. In gypsum Br is present only in microscopic fluid inclusions. For this reason we used the neutron-activation method. We adopted the technique in order to prevent any contamination and obtain directly Cl/Br ratio within 10% accuracy. In order to ascertain that liquid inclusions reside mainly in primary cavities of gypsum, we selected our samples only after microscopic observation. Fifty-eight samples from different types of gypsum were analysed. The salinities of the inclusions, obtained through the data on freezing, and the Cl/Br ratio, obtained through activation-analysis, give us clues as to the nature of the fluids depositing the gypsum. Recent gypsum deposits from French salt-pans of Mediterranean and Atlantic coasts were sampled. The latter has apparently been diagenetically altered by meteoric water; the salinity of many inclusions having been changed while the Cl/Br ratio (315 and 350) in both remains close to the value of present sea water (#300). Liquid inclusions of Recent crystals from New Caledonia, deposited in mangrove swamps are enriched in Br (Cl/Br = 150 and 200). The enrichment might be related to the presence of abundant organic materials. Inclusions in crystals from Sebkha el Melah (Tunisia) also show high Br content (Cl/Br = 194). In this case, the brine was highly concentrated and was saturated with NaCl. The Upper Miocene gypsum from Sicily was studied to test the various models for the genesis of this important evaporite formation of the Mediterranean. Freezing data show some decrease of salinities, probably by groundwater diagenesis, but the Br content is high. The Cl/Br ratio is 175, and this value is similar to that of Sebkha el Melah. Samples from three thick Eocene and Oligocene sequences near Paris and in the South of France were studied. Freezing data and Cl/Br ratio of their inclusions indicate that those gypsum deposits have crystallized in marine environments receiving considerable influx of river-waters.     

Kanonaite, (Mn 0.76 3+ Al0.23Fe 0.02 3+ )[6]Al[5][O¦SiO4], a new mineral isotypic with andalusite

Kanonaite forms rare porphyroblasts up to 12mm long in a gahnite— Mg-chlorite — coronadite — quartz schist occurring near Kanona, Zambia. The composition is (microprobe analysis): SiO₂ 32.2, Al₂O₃ 33.9, Mn as Mn₂O₃ 32.2, Fe₂O₃ 0.66, ZnO 0.13, MgO 0.04, BaO 0.04, TiO₂ 0.01, CaO 0.01, PbO 0.01, CuO 0.01, total 99.21, corresponding to $$\left( {{\text{Mn}}_{{\text{0}}{\text{.76}}}^{{\text{3 + }}} {\text{Al}}_{{\text{0}}{\text{.23}}} {\text{Fe}}_{{\text{0}}{\text{.015}}}^{{\text{3 + }}} } \right)_{1.005}^{\left[ 6 \right]} {\text{AL}}_{1.00}^{\left[ 5 \right]} \left[ {{\text{O}}_{{\text{1}}{\text{.00}}} |{\text{Si}}_{{\text{0}}{\text{.99}}} {\text{O}}_{{\text{4}}{\text{.00}}} } \right]$$ The mineral is greenish black, strongly pleochroic with X(∥a) yellow green, Y(∥b) bluish green, Z(∥c) deep golden yellow, biaxial positive, with 2V = 53°(3°), α = 1.702, β = 1.730, γ = 1.823. Vickers microhardness (100 gram load) ranges between 906 and 1017kp/mm². The structure is orthorhombic, isotypic with andalusite, space group Pnnm, a = 0.7953(2), b = 0.8038(2), c = 0.5619(2) nm, V = 0.3592(1) nm³, a/b = 0.9895(3), c/b = 0.6990(3), S.G.(_x) = 3.395 g/cm³, Z = 4. The strongest X-ray powder lines are (d in nm, I, hkl):0.5669, 100, 110; 0.4590, 75, 011 and 101; 0.3577, 90, 120 and 210; 0.2827, 94, 220; 0.2517, 90, 310 and 112; 0.2212, 83, 320, 122 and 212. Comparison of the intensities of 373 observed X-ray reflections with those calculated for several models of Mn³⁺-distribution indicates octahedral coordination of all or most of the manganese present. Interpretation of magnetic measurements (μ_eff = 3.15B.M. per Mn atom at 25 ° C) indirectly supports octahedral coordination of Mn³⁺. The name of the mineral is for Kanona, a town near the type locality. The name is proposed for the end member Mn^{3+ [6]}Al^[5][O¦SiO₄] and for members of the solid-solution series towards andalusite with octahedral Mn³⁺>Al. The presently described mineral may be referred to as aluminian kanonaite.