The macrobenthic fauna of a former perennial and now episodically filled mexican saline lake

Totolcingo (El Carmen), a large and now episodically filled playa lake in the east-ernmost portion of the Mexican Plateau, filled with water in 1993. Water persisted for just one month (May). Alkaline (pH 10), saline (K₂₅ up to 30,000S/cm) waters, dominated by NaHCO₃ and Na₂CO₃, characterized the lake. The fauna was depauperate. The components of the fauna wereEphydra (Hydropyrus)hians Say (ephydrid),Limnodrilus hoffmeisteri Claparède (tubificid), andBerosus sp. (Coleoptera). The species in the lake were widely dispersed and typical inhabitants of saline lakes. Possible reasons for the depauperate fauna include (a) overall physical and chemical conditions, (b) unpredictable hydrology, and (c) the short (one month) inundation period prevented colonization.     

A unified hydrogeological conceptual model of the Milk River transboundary aquifer,traversing Alberta (Canada) and Montana (USA)

A conceptual model of the transboundary Milk River Aquifer (MRA), extending across the Canada–USA border, was developed based on literature, focused fieldwork and a three-dimensional geological model. The MRA corresponds to the Virgelle Member of the Milk River Formation (Eagle Formation in Montana, USA) and it is an important groundwater resource over a large area (25,000 km²). The Virgelle outcrops near the international border and along the Sweet Grass Arch in Montana. The down-gradient limit of the MRA is the unconformity separating the Virgelle from the gas-bearing sandy shale of the Alderson Member. The MRA is confined above by the Pakowki/Claggett Formations aquitards and below by the Colorado Group aquitard. The MRA contains higher transmissivity areas resulting in preferential flowpaths, confirmed by natural geochemical tracers. Tritium and ¹⁴C delineate restricted recharge areas along the outcrops on both sides of the international border. Drastic decreases in horizontal hydraulic gradients indicate that the Milk River intercepts a large proportion of groundwater flowing to the north from the recharge area. Downgradient of the Milk River, groundwater movement is slow, as shown by ³⁶Cl residence times exceeding 1 Ma. These slow velocities imply that groundwater discharge downgradient of the Milk River is via vertical leakage through the Colorado Group and upward along buried valleys, which act as drains and correspond to artesian areas. When confined, the MRA contains a fossil groundwater resource, not significantly renewed by modern recharge. Groundwater exploitation thus far exceeds recharge, a situation requiring properly managed MRA groundwater depletion.     

Mapping groundwater storage variations with GRACE: a case study in Alberta,Canada

The applicability of the Gravity Recovery and Climate Experiment (GRACE) to adequately represent broad-scale patterns of groundwater storage (GWS) variations and observed trends in groundwater-monitoring well levels (GWWL) is examined in the Canadian province of Alberta. GWS variations are derived over Alberta for the period 2002–2014 using the Release 05 (RL05) monthly GRACE gravity models and the Global Land Data Assimilation System (GLDAS) land-surface models. Twelve mean monthly GWS variation maps are generated from the 139 monthly GWS variation grids to characterize the annual GWS variation pattern. These maps show that, overall, GWS increases from February to June, and decreases from July to October, and slightly increases from November to December. For 2002–2014, the GWS showed a positive trend which increases from west to east with a mean value of 12 mm/year over the province. The resulting GWS variations are validated using GWWLs in the province. For the purpose of validation, a GRACE total water storage (TWS)-based correlation criterion is introduced to identify groundwater wells which adequately represent the regional GWS variations. GWWLs at 36 wells were found to correlate with both the GRACE TWS and GWS variations. A factor f is defined to up-scale the GWWL variations at the identified wells to the GRACE-scale GWS variations. It is concluded that the GWS variations can be mapped by GRACE and the GLDAS models in some situations, thus demonstrating the conditions where GWS variations can be detected by GRACE in Alberta.     

Nb-Ta-minerals from the cap de creus pegmatite field,eastern Pyrenees: distribution and geochemical trends

Summary Internal structure and mineralogy facilitate distinction of four main pegmatite types at the eastern end of the Pyrenees. Three main trends in compositional variations in Nb-Ta-Sn-REE-Ti minerals have been established: a regional trend, with Ta/(Ta + Nb) ratio increasing towards the more evolved pegmatites, Mn/(Mn + Fe) being relatively low and increasing only slightly; a single-body trend, with similar enrichment toward the late pegmatite units; a single-crystal trend, with zoning related to both Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios and a tendency toward Ta-enrichment in the late growth stages. The regional geochemical enrichment trends in the Mn/(Mn + Fe) ratios and Ta/(Ta + Nb) are those expected for a beryl-columbite pegmatite type. In a single pegmatite, the evolution depends on the simultaneous growth of other mineral species. Three factors seem to control the development of zoning in columbite-tantalite crystals: availability of Mn, Ta, Fe, Nb, significant differences in solubility between mineral group end members and re-equilibria with late pegmatite fluids.

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Nb-Ta-Minerale aus dem Pegmatit-Feld vom Cap de Creus, östliche Pyrenäen: Verteilung und geochemische Trends

Zusammenfassung Am Ostrand der Pyrenäen können anhand des inneren Aufbaus und der Mineralogie vier Haupttypen von Pegmatiten unterschieden werden. Die Zusammensetzungen von Nb-Ta-Sn-SEE-Ti-Mineralen folgen drei Haupttrends: einem regionalen Trend, bei dem das Verhältnis Ta/(Ta + Nb) zu den höher entwickelten Pegmatiten hin zunimmt, während Mn/(Mn + Fe) relativ niedrig ist und nur leicht zunimmt; einem lokalen (auf das jeweilige Vorkommen beschränkten) Trend mit einer ähnlichen Anreicherung zu den spätpegmatitischen Einheiten hin; einem auf Einzelkristalle bezogenen Trend mit Zonierung in bezug auf die Verhältnisse Ta/(Ta + Nb) und Mn/(Mn + Fe) und einer Tendenz zur T a-Anreicherung in den späten Wachstumsphasen. Die regionalen geochemischen Anreicherungstrends in den Mn/(Mn + Fe)- und Ta/(Ta + Nb)-Verhältnissen entsprechen jenen, wie sie für den Beryll-Columbit-Pegmatit-Typ erwartet werden. In einem einzelnen Pegmatit hängt die Entwicklung vom gleichzeitigen Wachstum anderer Mineral-Spezies ab. Drei Faktoren scheinen die Ausbildung einer Zonierung in Columbit-Tantalit-Kristallen zu kontrollieren: das Angebot an Mn, Ta, Fe und Nb, deutliche Unterschiede in der Löslichkeit der Endglieder von Mineralgruppen und die Iteequilibrierung mit spätpegmatitischen Lösungen.

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The solubility of calcite in seawater solutions of various magnesium concentration, It = 0.697 m at 25 °C and one atmosphere total pressure

Stoichiometric solubility constants of calcite in initially supersaturated solutions of various magnesium to calcium concentration ratios but identical ionic strength were determined at 25°C and one atmosphere total pressure.The thermodynamic solubility constant of calcite is used with ion pairing equations to interpret the data reported in this study. Results indicate that even though magnesian calcites, rather than pure calcite, precipitate from seawater solutions containing magnesium ions, the incorporation of MgCO₃ in the calcite crystal lattice does not extensively alter the equilibrium calcium carbonate activity product.The equilibrium activity of the ionic species in solution and the composition of magnesian calcite overgrowths precipitated from solutions of similar composition are used to calculate the solubility of magnesian calcites. The values for magnesian calcite solubilities obtained by this approach are lower than those obtained from the dissolution kinetics of biogenic carbonates.     

A Compatible Single-Phase/Two-Phase Numerical Model: 1. Modeling the Transient Salt-Water/Fresh-Water Interface Motion

Abstract A numerical model (NEWVAR) to simulate the transient movement of a discrete interface between salt water and fresh water has been developed. NEWVAR is designed to allow the analysis of a regional two-dimensional ground-water flow in coastal aquifers. The numerical solution permits the prediction of both regional fresh-water levels and two-dimensional fresh-water/salt-water interface by using nested square meshes.
The numerical solution is based on the finite-difference method; the Gauss-Jordan direct method is used for solving steady- and unsteady-state linear equations. Different procedures are used to avoid numerical difficulties in the transient position of the interface toe for two-dimensional areal flow.
The numerical solution was tested against the analytical ones for the cases of an advancing interface and of a floating fresh-water lens over sea water. These tests showed good agreement, thus verifying the finite-difference approximation. The results of an application of this model to a real aquifer are discussed in a companion paper entitled: "A Compatible Single-Phase/Two-Phase Numerical Model 2. Application to a Coastal Aquifer in Mexico."     

Pa andSa waves and the upper mantle

Summary This investigation is based on records of 96 earthquakes withPa andSa written by the Press-Ewing instruments at Uppsala in the interval June 1961–December 1962.Pa andSa waves are observed for all earthquake regions, irrespective of distance, focal depth or path properties. They have significantly higher velocities under continents than under oceans, which demonstrates corresponding differences in the upper mantle. Continental velocities are 8.35 km/sec (Pa) and 4.56 km/sec (Sa), oceanic velocities 8.01 km/sec (Pa) and 4.45 km/sec (Sa). The most frequent periods are 10 sec (Pa) and 20 sec (Sa). They are independent of distance forPa but increase with distance forSa. The best developedPa andSa are obtained for earthquakes at focal depths less than about 60 km. The particle motion ofSa may be anything from pureSV to pureSH motion and has high correlation to the particle motion ofS. The apparent angles of emergence (in average 51° forPa and 54° forSa) vary with distance. On the basis of our observations it is suggested thatPa andSa propagate by multiple reflections under grazing incidence under the Moho discontinuity.

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Zusammenfassung Die vorliegende Untersuchung gründet sich auf die Registrierungen von 96 Erdbeben mitPa- undSa-Wellen, die mit Hilfe der Press-Ewing Instrumente zu Uppsala im Zeitraum Juli 1961–Dezember 1962 aufgenommen wurden. DiePa- undSa-Wellen sind für alle seismischen Regionen beobachtet worden, unabhängig von Entfernung, Herdtiefe oder Wellenweg. Sie haben bedeutend höhere Geschwindigkeiten unter den Kontinenten als unter den Ozeanen, was einen entsprechenden Unterschied im oberen Erdmantel beweist. Die kontinentalen Geschwindigkeiten betragen 8.35 km/sec (Pa) und 4.56 km/sec (Sa), die ozeanischen Geschwindigkeiten 8.01 km/sec (Pa) und 4.45 km/sec (Sa). Die am häufigsten vorkommenden Perioden betragen 10 sec (Pa) und 20 sec (Sa). Sie sind unabhängig von der Entfernung fürPa aber wachsen mit der Entfernung fürSa. Die am besten entwickeltenPa- undSa-Wellen werden für Erdbeben mit kleinerer Herdtiefe als rund 60 km beobachtet. FürSa wird jede beliebige Orbitalbewegung zwischenSV undSH beobachtet. Sie hat eine hohe Korrelation mit der Orbitalbewegung vonS. Die scheinbaren Emergenzwinkel (durchschnittlich 51° fürPa und 54° fürSa) variieren mit der Entfernung. Auf Grund unserer Beobachtungen wird die Hypothese aufgestellt, dass sich diePa-undSa-Wellen durch Mehrfachreflexionen, bei tangentialem Einfall, unter der Moho-Diskontinuität ausbreiten.

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Resumen La presente investigación está basada en los sismogramas de 96 terremotos, que muestranPa ySa, registrados por los sismógrafos de Uppsala (Press-Ewing), durante el periodo Junio 1961 a Diciembre 1962. Las fasesPa ySa se observan en todas las regiones sismicas, independientemente de la distancia, de la profundidad focal ó de las propiedades de la trayectoria. Tienen velocidades significativamente mayores bajo continentes que bajo los océanos, lo que demuestra la existencia de diferencias en el manto superior. Las velocidades continentales son 8.35 km/seg (Pa) y 4.56 km/seg (Sa) y las oceánicas 8.01 km/seg (Pa) y 4.45 km/seg (Sa). Los periodos mas frecuentes son 10 segundos paraPa y 20 segundos paraSa. Tales periodos son independientes de la distancia en el caso dePa pero crecen con ella paraSa. Las fasesPa ySa mejor desarrolladas se obtienen para terremotos cuya profundidad focal es inferior a los 60 kilómetros. El movimiento de la particula del suelo debido aSa puede ser de cualquier tipo, desde puroSV a puroSH, y muestra gran correlación con el movimiento de la particula deS. Los ángulos de emergencia aparentes (de promedio 51° paraPa y 54° paraSa) varian con la distancia. Basándonos en nuestras observaciones sugerimos quePa ySa se propagan por reflexión múltiple, bajo incidencia rozante bajo la discontinuidad de Mohorovii.

     

Geant4 simulations of soft proton scattering in X-ray optics

Low energy protons (< 300 keV) can enter the field of view of X-ray telescopes, scatter on their mirror surfaces at small incident angles, and deposit energy on the detector. This phenomenon can cause intense background flares at the focal plane decreasing the mission observing time (e.g. the XMM-Newton mission) or in the most extreme cases, damaging the X-ray detector. A correct modelization of the physics process responsible for the grazing angle scattering processes is mandatory to evaluate the impact of such events on the performance (e.g. observation time, sensitivity) of future X-ray telescopes as the ESA ATHENA mission. The Remizovich model describes particles reflected by solids at glancing angles in terms of the Boltzmann transport equation using the diffuse approximation and the model of continuous slowing down in energy. For the first time this solution, in the approximation of no energy losses, is implemented, verified, and qualitatively validated on top of the Geant4 release 10.2, with the possibility to add a constant energy loss to each interaction. This implementation is verified by comparing the simulated proton distribution to both the theoretical probability distribution and with independent ray-tracing simulations. Both the new scattering physics and the Coulomb scattering already built in the official Geant4 distribution are used to reproduce the latest experimental results on grazing angle proton scattering. At 250 keV multiple scattering delivers large proton angles and it is not consistent with the observation. Among the tested models, the single scattering seems to better reproduce the scattering efficiency at the three energies but energy loss obtained at small scattering angles is significantly lower than the experimental values. In general, the energy losses obtained in the experiment are higher than what obtained by the simulation. The experimental data are not completely representative of the soft proton scattering experienced by current X-ray telescopes because of the lack of measurements at low energies (< 200 keV) and small reflection angles, so we are not able to address any of the tested models as the one that can certainly reproduce the scattering behavior of low energy protons expected for the ATHENA mission. We can, however, discard multiple scattering as the model able to reproduce soft proton funnelling, and affirm that Coulomb single scattering can represent, until further measurements at lower energies are available, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.     

High-resolution spectrometer for atmospheric studies

A high-resolution spectrometer (0.0014 nm at 313 nm) has been developed at the University of L’Aquila (Italy) for atmospheric spectroscopic studies. The layout, optics and software for the instrument control are described. Measurements of the mercury low-pressure lamp lines from 200 to 600 nm show the high performances of the spectrometer. Laboratory measurements of OH and NO₂ spectrums demonstrate that the system could be used for cross-section measurements and to detect these species in the atmosphere. The first atmospheric application of the system was the observation of direct solar and sky spectrums that shows a filling-in of the sky lines due to rotational Raman scattering. The measurements have been done with clear and cloudy sky and in both there was a strong dependence of the filling-in from the solar zenith angle whereas no dependence from the wavelengths was evident at low solar zenith angles (less than 85°).