Boron isotopic fractionation between minerals and fluids: New insights from in situ high pressure-high temperature vibrational spectroscopic data     

Carmen Sanchez-Valle  Bruno Reynard  Christophe Lecuyer  Jean-Claude Chervin 《Geochimica et cosmochimica acta》2005,69(17):4301-4313

Equilibrium boron isotopic fractionations between trigonal B(OH)₃ and tetragonal B(OH)₄⁻ aqueous species have been calculated at high P-T conditions using measured vibrational spectra (Raman and IR) and force-field modeling to compute reduced partition function ratios for B-isotopic exchange following Urey’s theory. The calculated isotopic fractionation factor at 300 K, α_3/4 = 1.0176(2), is slightly lower than the formerly calculated value of α_3/4 = 1.0193 (Kakihana and Kotaka, 1977), due to differences in the determined vibrational frequencies. The effect of pressure on α_3/4 up to 10 GPa and 723 K is shown to be negligible relative to temperature or speciation (pH) effects. Implications for the interpretation of boron fractionation in experimental and natural systems are discussed. We also show that the relationship between seawater-mineral B isotope fractionation and pH can be expressed using two variables, α_3/4 on one hand, and the pK_a of the boric acid-borate equilibrium on the other hand. This latter value is given by the equilibrium of boron species in water for the carbonate-water exchange, but could be governed by mineral surface properties in the case of clays. This may allow defining intrinsic paleo-pHmeters from B isotope fractionation between carbonate and authigenic minerals. Finally, it is shown that fractionation of boron isotopes can be rationalized in terms of the changes in 1) coordination of B from trigonal to tetrahedral in both fluids and minerals; and 2) the ligand nature around B from OH⁻ in the fluid and some hydrous minerals to non-hydrogenated O in many minerals. Relationships are established that allow predicting the isotopic fractionation factor of B between minerals and fluid.  相似文献   

Heavy metal contamination in the Arieş river catchment, western Romania: Implications for development of the Roşia Montană gold deposit     

Graham Bird  Paul A. Brewer  Mark G. Macklin  Mihaela Serban  Dan Balteanu  Basarab Driga 《Journal of Geochemical Exploration》2005,86(1):26-48

The Abrud–Arieş river system, western Romania, is subject to ongoing mining activity associated with Cu, Pb and Zn ore extraction. The catchment contains what is believed to be Europe's largest unutilized Au deposit at Roşia Montană that is planned to be exploited by open-cast mining techniques. The magnitude and environmental significance of metal (Cd, Cu, Pb, and Zn) concentrations in surface water and river channel sediment have been investigated along a 140 km reach of the Rivers Abrud and Arieş and 9 tributaries affected by mining. The speciation of sediment-bound metals was established using a 4-stage sequential extraction procedure (SEP) that identified four chemical phases: (1) exchangeable, (2) Fe/Mn oxides, (3) organic matter/sulphides and (4) residual. Peak solute and sediment-bound metal concentrations were found to occur in the River Abrud downstream of the EM Bucium mine and in mining-affected tributaries, with up to 71% of sites containing sediment metal concentrations in excess of Dutch intervention values. The River Arieş was found to be much less polluted than the River Abrud, with only Cu showing concentrations above guideline values, as a consequence of porphyry Cu mineralization in the catchment. The magnitude and spatial extent of metal pollution is influenced by local physico-chemical conditions and hydrological linkages between mining and local river systems. Sediment-bound Cd and Zn were found to be predominantly associated with the exchangeable phase of the sediment (9–74% and 6–65%, respectively), whilst Fe/Mn oxides (5–76%) and organic matter/sulphides (1–45%) generally accounted for a majority of Pb and Cu partitioning, respectively. Sites of environmentally significant sediment-metal pollution were identified in the Rivers Abrud and Arieş where exchangeable metal concentrations exceeded Dutch intervention values. The implications of metal contamination in the Arieş river basin to the proposed mining development at Roşia Montana are discussed in relation to other contaminated Romanian catchments and with the EU Water Framework Directive.  相似文献   

In Situ Biotransformation of BTEX Compounds Under Methanogenic Conditions   总被引：3，自引：0，他引：3  

Martin Reinhard  Gary D. Hopkins  Eva Steinle-Darling  Carmen A. LeBron 《Ground Water Monitoring & Remediation》2005,25(4):50-59

  相似文献   

The Morphological and Optical Properties of Volcanic Glass: A Tool to Assess Density-induced Vertical Migration of Tephra in Sediment Cores     

Mihaela D. Enache  Brian F. Cumming 《Journal of Paleolimnology》2006,35(3):661-667

Volcanic ash layers in sediment cores are valuable geochronological markers in paleolimnological research. The composition of volcanic glass is related to identifiable, chronologically distinctive volcanic eruptions. Consequently, tephra layers provide time horizons allowing regional-scale correlations for lake sediments. Volcanic glass is often present in samples routinely prepared by paleolimnologists such as diatom slides and thin sections. Knowledge of the morphological and optical properties of volcanic glass allows for its identification. This is essential for the identification of ash layers that are not macroscopically visible or to track their vertical migration in soft organic sediments. The purposes of this note are to: (1) describe how the morphological (i.e., shape, vesicularity) and optical (i.e., refractive index and birefringence) properties can be used to identify volcanic glass in preparations from lake sediments; and (2) show how the quantification of volcanic glass from diatom slides is used to quantify the density-induced displacement of a 4.5 cm-thick Mazama ash-layer through organic sediments and to approximate its timing of initial deposition.  相似文献   

EURD Data Processing     

José F. Gómez  Joaquín Trapero  Carmen Morales  Verónica Orozco  Jerry Edelstein  Eric Korpela  Michael Lampton 《Astrophysics and Space Science》2001,276(1):233-238

EURD (EspectrógrafoUltravioleta extremo para la Radiación Difusa) is one of thescientific instruments on board MINISAT 01. EURD is a spectrograph withvery high sensitivity and spectral resolution ( 5 Å), designed to obtain extremeultraviolet ( 350-1100 Å) spectra of diffuse radiation.We outline the processing of EURD data, and how we obtain informationfrom these data on the scientific goals of the mission: hot interstellarmedium, neutrino decay line, nightglow emission, and early-type stars.  相似文献   

Physically based evaluation of climate models over the Iberian Peninsula     

Carmen Sánchez de Cos  Jose M. Sánchez-Laulhé  Carlos Jiménez-Alonso  Juan M. Sancho-Avila  Ernesto Rodriguez-Camino 《Climate Dynamics》2013,40(7-8):1969-1984

A novel approach is proposed for evaluating regional climate models based on the comparison of empirical relationships among model outcome variables. The approach is actually a quantitative adaptation of the method for evaluating global climate models proposed by Betts (Bull Am Meteorol Soc 85:1673–1688, 2004). Three selected relationships among different magnitudes involved in water and energy land surface budgets are firstly established using daily re-analysis data. The selected relationships are obtained for an area encompassing two river basins in the southern Iberian Peninsula corresponding to 2 months, representative of dry and wet seasons. The same corresponding relations are also computed for each of the thirteen regional simulations of the ENSEMBLES project over the same area. The usage of a metric based on the Hellinger coefficient allows a quantitative estimation of how well models are performing in simulating the relations among surface magnitudes. Finally, a series of six rankings of the thirteen regional climate models participating in the ENSEMBLES project is obtained based on their ability to simulate such surface processes.  相似文献   

Simulation of glacial-interglacial cycles by simple relaxation models: consistency with observational results   总被引：1，自引：0，他引：1  

Antonio García-Olivares  Carmen Herrero 《Climate Dynamics》2013,41(5-6):1307-1331

The model of Paillard and Parrenin (Earth Planet Sci Lett 227:263–271, 2004) was modified to obtain a closer fit to δ¹⁸O and CO₂ time series for the last 800 kyr. The model performance can be improved if its CO₂ sensitivity to I₆₅ insolation is eliminated and if different response times are assumed for ablation/accumulation of ice. Correlations between simulated and experimental time series for CO₂ and ice volume V increase from 0.59 and 0.63 to 0.79 and 0.88, respectively. According to these models, terminations are produced by I₆₅ amplification through CO₂-T and T-CO₂ feedbacks, in synergy with an extra CO₂ contribution from the deep ocean. This contribution is strongly dependent on ice-sheet extent and ice volume (or alternatively, CO₂ concentration, which is a good proxy of Antarctic temperature) but is insensitive to Southern Ocean (SO) insolation on 21 February (I₆₀). Change of deep SO state may be the “order parameter” for nonlinear deglacial changes. According to these models, 100 kyr periodicity of glacial cycles arises from the characteristic time of Antarctic ice sheet advance to the continental slope.  相似文献   

Rainfall spatial organization and areal reduction factors in the metropolitan area of Barcelona (Spain)     

Raul Rodríguez  Xavier Navarro  M. Carmen Casas  Angel Redaño 《Theoretical and Applied Climatology》2013,114(1-2):1-8

The rainfall spatial organization in the metropolitan area of Barcelona (Spain) has been studied from records of an urban rain gauge network in the period 1994–2009. Using statistical and regional analysis techniques, correlation between data recorded by the different rain gauges has been calculated, and the effective number of independent stations (n _eq) equivalent to the used network has been determined. It has been found out that for durations longer than 20 min, the areal rainfall return period observed for a storm registered by the network approximately decreases by a factor of 1/n _eq in relation to the current point rainfall intensity–duration–frequency relationships for the metropolitan area of Barcelona. Using objective analysis techniques, continuous precipitation fields have been generated on a regular grid with a spatial resolution of 300?×?300 m for the storms registered by the rain gauges from 1994 to 2009, for durations from 10 min to 24 h. The precipitation fields obtained have been useful to estimate the characteristic areal reduction factors in the metropolitan area of Barcelona. A direct relationship has been found between the areal reduction factor for all the area corresponding to the urban rainfall network of Barcelona and the effective number of n _eq for every duration considered.  相似文献   

Towards a better understanding of the evolution of the flood risk in Mediterranean urban areas: the case of Barcelona     

Cort&#;s  Maria  Llasat  Maria Carmen  Gilabert  Joan  Llasat-Botija  Montserrat  Turco  Marco  Marcos  Ra&#;l  Mart&#;n Vide  Juan Pedro  Falc&#;n  Llu&#;s 《Natural Hazards》2017,85(1):39-57

Dam failure constitutes a grave threat to human life. However, there is still a lack of systematic and comprehensive research on the loss of life (L) caused by dam break in China. From the perspective of protecting human life, a new calculation method for L occurred in dam break floods is put forward. Fourteen dam failure cases in China are selected as the basic data by three-dimensional stratified sampling, balancing spatial, vertical elevation and temporal representations, as well as considering various conditions of the dam collapse. The method includes three progressive steps: Firstly, some impact factors of loss of life (IFL) are selected by literature survey, i.e., severity of dam break flood (S _F), population at risk (P _R), understanding of dam break (U _B), warning time (T _W) and evacuation condition (E _C). And the other IFL of weather during dam break (W _B), dam break mode (M _B), water storage (S _W), building vulnerability (V _B), dam break time (T _B) and average distance from affected area to dam (D _D) are also taken into account to get a more comprehensive consideration. According to disaster system and disaster risk, these eleven IFL are divided into four categories. Through the improved entropy method, eight key IFL are further selected out of the eleven. Secondly, four L modules are built based on four categories, which are L-causing factor module (M ₁), L-prone environment module (M ₂), affected body module (M ₃) and rescue condition module (M ₄). Eventually, by using two methods of multivariate nonlinear regression and leave-one-out cross-validation in combination with coupled four modules, the calculation method for L is established. Compared with the results of Graham method and D&M method, the result of the proposed one is much closer to the actual value and performs better in fitting effect and regional applicability. In the application, L calculation and consequence assessment are carried out in the example of Hengjiang reservoir that has already broken down. At the same time, L calculation and risk prediction are used in the analysis of Yunshan reservoir, which is under planning. The proposed method can not only be applied to estimate L and its rate (f _L ) under various types of dam break conditions in China, but also provide a reliable consequence assessment and prediction approach to reduce the risk of L.  相似文献   

Air–Water CO<Subscript>2</Subscript> Fluxes and Net Ecosystem Production Changes in a Baja California Coastal Lagoon During the Anomalous North Pacific Warm Condition     

Ma Carmen Ávila-López  J. Martín Hernández-Ayón  Víctor F. Camacho-Ibar  Armando Félix Bermúdez  Adan Mejía-Trejo  Isaí Pacheco-Ruiz  Jose M. Sandoval-Gil 《Estuaries and Coasts》2017,40(3):792-806

The present study examines the temporal variability of air–water CO₂ fluxes (FCO₂) and seawater carbonate chemistry in a Baja California coastal lagoon during an exceptionally warm anomaly that was developed in Northeast Pacific coasts during 2014. This oceanographic condition led to a summer-like season (weak upwelling condition) during the study period, which reached a maximum surface temperature anomaly of 2 °C in September 2014. San Quintín Bay acts as a source of CO₂ to the atmosphere in 2014 (3.3 ± 4.8 mmol C m^?2 day^?1) with the higher positive fluxes mainly observed in summer months (9.0 ± 5.3 mmol C m^?2 day^?1). Net ecosystem production (NEP) switched seasonally between net heterotrophy and net autotrophy during the study period, with an annual average of 2.2 ± 7.1 mmol C m^?2 day^?1, which indicates that San Quintín Bay was a net autotrophic system during the atypical warm oceanographic condition in 2014. This pattern of seasonal variations in the carbon balance at San Quintín Bay appears to be linked to the life cycle of benthic communities, which play an important role in the whole-ecosystem metabolism. Under the limited input from external sources coupled with an increase in seawater temperatures, the recycled benthic carbon and nutrient fluxes play a major role to sustain water-column processes within the bay. Since the upwelling condition may influence the magnitude of the air–water CO₂ fluxes, our results clearly indicated that San Quintín Bay is a net source of carbon to the atmosphere regardless of the adjacent oceanic conditions. Our study sheds light on the carbon dynamics and its metabolic implications in a shallow coastal ecosystem under a regional warm anomaly and contributes potentially relevant information in view of the likely future scenario of global climate change.  相似文献