Inorganic synthesis of Fe–Ca–Mg carbonates at low temperature

A set of free-drift experiments was undertaken to synthesize carbonates of mixed cation content (Fe, Ca, Mg) from solution at 25 and 70 °C to better understand the relationship between the mineralogy and composition of these phases and the solutions from which they precipitate. Metastable solid solutions formed at 25 °C which are not predicted from the extrapolation of higher temperature equilibrium assemblages; instead, solids formed that were intermediary in chemical composition to known magnesite–siderite and dolomite solid solutions. A calcite–siderite solid solution precipitated at 25 °C, with the percentage of CaCO₃ in the solid being proportional to the aqueous Ca/Fe ratio of the solution, while Mg was excluded from the crystal structure except at relatively high aqueous Mg/Ca and Mg/Fe ratios and a low Ca content. Alternatively, at 70 °C Mg was the predominant cation of the solid solutions. These results are compatible with the hypothesis that the relative dehydration energies of Fe, Ca and Mg play an important role in the formation of mixed cation carbonates in nature.     

Economic risk assessment of Cotopaxi volcano,Ecuador, in case of a future lahar emplacement

Natural Hazards - The Cotopaxi volcano in north-central Ecuador is one of the most dangerous volcanoes of the world due to its ability to generate far-reaching lahars, which are able to destroy...     

Adaptation of <Emphasis Type="Italic">Shigella flexneri</Emphasis> to starvation: morphology,outer membrane proteins and lipopolysaccharide changes

Lack of nutrients is a common challenge for enteric pathogens, like Shigella, when discharged in waters and soils by infected persons. These bacteria must evolve protective mechanisms to survive nutrient changing conditions. Many studies have demonstrated that bacterial starvation can affect cell morphology and surface properties such as lipopolysaccharide content. This study focuses on the morphological and physiological alterations of Shigella flexneri, a human pathogen, under nutrient starvation during 30 days. Our results showed that S. flexneri can survive under nutrient deficiency during 4 weeks. However, starved cells revealed several morphological changes indicating decrease of the size and change of the cell shape as observed by transmission electron microscopy. Furthermore, the outer membrane proteins and lipopolysaccharide profiles of starved cells revealed the disappearance, the appearance, and changes of the protein band levels. The survival and physiological adaptation of S. flexneri under nutrient limitation during 30 days may increase the risk of human and animal infections.     

Evolution of fluid geochemistry at the Turrialba volcano (Costa Rica) from 1998 to 2008

Turrialba (10°02′N, 83°45′W) is a 3,349-m high stratovolcano belonging to the Holocene “Cordillera Central” volcanic belt of Costa Rica. The summit consists of three EW-oriented craters (East, Central, and West). Since its last eruptive phase (1864–1866), the Central and West craters have displayed modest fumarolic activity, with outlet temperatures clustering around 90°C. In 2001, seismic swarms, ground deformation, and increasing fumarolic activity occurred. From 2005 to 2008, new fumarolic vents opened between and within the Central and West craters, and along the western and southwestern outer flanks of the volcanic edifice. These physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages: (1) hydrothermal (from 1998 to autumn 2001), characterized by the presence of H₂O, CO₂, H₂S, and, to a very minor extent, HCl and HF; (2) hydrothermal/magmatic (autumn 2001–2007), with the appearance of SO₂ and a significant increase of HCl and HF; and (3) magmatic-dominated (2007–2008), characterized by increased SO₂ content, SO₂/H₂S > 100, and temperatures up to 282°C. Accordingly, gas equilibrium in the CO₂-CH₄-H₂ system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions. The chemical–physical modifications of Turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems. Nevertheless, the risk of rejuvenation of the volcanic activity cannot be excluded, and an appropriate seismic, ground deformation, and geochemical monitoring program is highly recommended. Turrialba lies at a distance of 35 and 15 km from San José and Cartago, respectively, the two largest cities in Costa Rica.     

Space- and Time-Dependent Probabilities for Earthquake Fault Systems from Numerical Simulations: Feasibility Study and First Results

In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed “model steering”. Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California.     

Trends in total ozone and the effect of the equatorial zonal wind QBO

Trends in total column ozone have been analyzed in terms of the equatorial zonal wind. We used zonal monthly mean total ozone from Total Ozone Mapping Spectrometer (TOMS) and monthly mean zonal wind in the equatorial stratosphere at 30 hPa to define the phases of the quasi-biennial oscillation (QBO). Total column ozone trends have been assessed during the period 1979–2004, for both Hemispheres, and for each month, under three conditions considering, all the ozone dataset, ozone values during easterly phase and ozone values during westerly phase of the QBO. When the whole dataset is considered, negative trends are observed. From low to midlatitudes a zonal pattern is noticed with increasing negative values toward higher latitudes. When the data is filtered according to the QBO phase, statistically significant positive trends appear in the westerly case during January to May at low latitudes .The trend pattern in the case of the easterly phase presents more negative values.     

Delineation of regional arid karstic aquifers: an integrative data approach

This research integrates data procedures for the delineation of regional ground water flow systems in arid karstic basins with sparse hydrogeologic data using surface topography data, geologic mapping, permeability data, chloride concentrations of ground water and precipitation, and measured discharge data. This integrative data analysis framework can be applied to evaluate arid karstic aquifer systems globally. The accurate delineation of ground water recharge areas in developing aquifer systems with sparse hydrogeologic data is essential for their effective long-term development and management. We illustrate the use of this approach in the Cuatrociénegas Basin (CCB) of Mexico. Aquifers are characterized using geographic information systems for ground water catchment delineation, an analytical model for interbasin flow evaluation, a chloride balance approach for recharge estimation, and a water budget for mapping contributing catchments over a large region. The test study area includes the CCB of Coahuila, Mexico, a UNESCO World Biosphere Reserve containing more than 500 springs that support ground water-dependent ecosystems with more than 70 endemic organisms and irrigated agriculture. We define recharge areas that contribute local and regional ground water discharge to springs and the regional flow system. Results show that the regional aquifer system follows a topographic gradient that during past pluvial periods may have linked the Río Nazas and the Río Aguanaval of the Sierra Madre Occidental to the Río Grande via the CCB and other large, currently dry, upgradient lakes.     

(137)Cs baseline levels in the Mediterranean and Black Sea: a cross-basin survey of the CIESM Mediterranean Mussel Watch programme

The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify (137)Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured (137)Cs levels were found to be very low (usually < 1 Bq kg(-1) wet wt) (137)Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.