The Local Interstellar Medium in the Direction of the Galactic Anticentre     

Ricardo Génova  John E. Beckman 《Astrophysics and Space Science》2001,276(1):187-195

High resolution observations of interstellar Na Iabsorptions in the spectra of early-type stars in the second Galacticquadrant have been used to derive the spatial distribution of thenearby interstellar gas in the Galactic anticentre hemisphere. The datashow the presence, within the region explored and within the nearest150 pc, of eight diffuse interstellar clouds with LSR velocities in therange 15–55 km s^-1. Molecular gas previously identified close tothe Sun by Trapero et al. (1995) and Trapero et al. (1996) is embeddedin one of the clouds. The motion of these clouds does not reflect anymotion of the gas away from the Scorpio-Centaurus association, showingthat the kinematics observed in the neighbourhood of the Sun byLallement and Bertin (1992) is restricted, in the second Galactic quadrant,to the nearest 50 pc.  相似文献   

Reply to comments on “book review:An Introduction to Applied Geostatistics”     

Ricardo A. Olea 《Mathematical Geosciences》1991,23(4):683-685

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Phase and point defect equilibria in the titanomagnetite solid solution     

Aragón  Ricardo  McCallister  Robert H. 《Physics and Chemistry of Minerals》1982,8(3):112-120

The position of the titanomagnetite subsolidus stability field boundaries, within the Fe-Ti-O ternary, above 1,000° C, has been calculated from chemical equilibrium considerations, using experimental data for the calibrated buffers of end member compositions. The relationship between chemical composition and intrinsic oxygen fugacity, within the single phase spinel field, has been investigated with a Frenkel cation point defect model. With this calculation scheme, conditions for departure from strict metal-oxygen stoichiometry to stable cation rich or deficient phases can be predicted.

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Ion association of chloride and sulphate with sodium,potassium, magnesium and calcium in seawater at 25°C     

Kenneth S Johnson  Ricardo M Pytkowicz 《Marine Chemistry》1979,8(1):87-93

Stoichiometric association constants, which have been measured for the ion pairs of Cl^? and SO₄^?2 with Na⁺, K⁺, Mg²⁺, and Ca²⁺, were used to determine the speciation in an artificial sea water containing only these ions. The resulting distribution is quite different to that found in earlier models in which chloride ion association was ignored. The concentrations of chloride ion pairs with the cations are 4 to 5 times larger than the concentrations of the sulphate ion pairs with the same cations. The total activity coefficients of the neutral salts in sea water calculated from the model are in good agreement with the experimentally measured values. The concentration of MgSO₄⁰ calculated to be present agrees with the amount determined from ultrasonic absorption data. The calculated solubility of gypsum is also in good agreement with the measured values.  相似文献   

Large-Scale Temperature Changes across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years   总被引：4，自引：0，他引：4  

Ricardo Villalba  Antonio Lara  José A. Boninsegna  Mariano Masiokas  Silvia Delgado  Juan C. Aravena  Fidel A. Roig  Andrea Schmelter  Alexia Wolodarsky  Alberto Ripalta 《Climatic change》2003,59(1-2):177-232

Long-term trends of temperature variations across the southern Andes (37–55° S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930–1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43° S are characterized by negative trends in mean annual temperature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46°S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45° S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes.Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% ofthe temperature variance over the interval 1930–1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930–1989, indicates that most of the explained varianceis at periods >10 years in length. At periods >15 years, the squaredcoherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi-decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20thcentury have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900–1990 are 0.53 °C and 0.86 °C above the1640–1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.Local temperature regimes are affected by changes in planetary circulation, with in turn are linked to global sea surface temperature (SST) anomalies. Therefore, we explored how temperature variations in the southern Andes since 1856 are related to large-scale SSTs on the South Pacific and South Atlantic Oceans. Spatial correlation patterns between the reconstructions and SSTs show that temperature variations in the northern sector of the southern Andes are strongly connected with SST anomalies in the tropical and subtropical Pacific. This spatial correlation pattern resembles the spatial signature of the PDO mode of SST variability over the South Pacific and is connected with the Pacific-South American (PSA) atmospheric pattern in the Southern Hemisphere. In contrast, temperature variations in the southern sector of the southern Andes are significantly correlated with SST anomalies over most of the South Atlantic, and in less degree, over the subtropical Pacific. This spatial correlation field regressed against SST resembles the `Global Warming' mode of SST variability, which in turn, is linked to the leading mode of circulation in the Southern Hemisphere. Certainly, part of the temperature signal present in the reconstructions can be expressed as a linear combination of four orthogonal modes of SST variability. Rotated empirical orthogonal function analysis, performed on SST across the South Pacific and South Atlantic Oceans, indicate that four discrete modes of SST variability explain a third, approximately, of total variance in temperature fluctuations across the southern Andes.  相似文献   

Off-Line and On-Line Determination of Eleven Rare Earth Elements in Silicate Rocks by ICP-AES Using Dowex Minicolumns for Separation of Interfering Elements in Continuous Flow Systems   总被引：1，自引：0，他引：1  

Geraldo R. Boaventura  Robson C. De  Oliveira Ricardo E. Santelli 《Geostandards and Geoanalytical Research》2002,26(1):63-73

The methodologies developed in this work comprise ion-exchange separation of interfering elements from rare earth elements (Fe, Al and Ca), by using resin minicolumns (Dowex-50W-X8 200-400 mesh) for the determination of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb and Lu by inductively coupled plasma-atomic emission spectrometry, using both off-line and on-line continuous flow systems. These methods can be used to determine rare earth elements in common silicate rocks, such as granite, basalt, rhyolite and andesite. Thirteen geochemical reference materials were used to evaluate the accuracy and precision of the off-line and on-line methods. Chondrite-normalized diagrams were obtained and compared to values reported in the literature. When compared to conventional procedures, the proposed methods provide fast and low cost rare earth elements determinations in the analysis of silicate rocks. Eighteen samples per hour could be analysed by the proposed method using the automated procedure for the determination of the eleven rare earth elements.  相似文献   

Early Records of Icebergs in the South Atlantic Ocean from Spanish Documentary Sources     

A. Maria del Rosario Prieto  B. Ricardo García-Herrera  Emiliano Hernández Martin 《Climatic change》2004,66(1-2):29-48

The use of documentary sources has proven useful to identify extremeclimatic events and their variability during the pre-instrumental period. Theaim of this paper is to describe iceberg sightings in the Western SouthAtlantic during the second half of the 18th century, as recorded from Spanishlogbooks. A total of five sightings have been found, two corresponding toisolated bergs and three to outbreaks. The relevance of these results istwofold: they are the first documented iceberg sightings to date and, aboveall, they correspond to very unusual episodes, characterized by a high numberof high-sized bergs and by the relatively low latitude of their location. Itis suggested that they could be associated to cold episodes in Antarctica.  相似文献   

Boron isotope composition of geothermal fluids and borate minerals from salar deposits (central Andes/NW Argentina)     

Simone A. Kasemann  Anette Meixner  Jrg Erzinger  Jos G. Viramonte  Ricardo N. Alonso  Gerhard Franz 《Journal of South American Earth Sciences》2004,16(8):2562

We have measured the boron concentration and isotope composition of regionally expansive borate deposits and geothermal fluids from the Cenozoic geothermal system of the Argentine Puna Plateau in the central Andes. The borate minerals borax, colemanite, hydroboracite, inderite, inyoite, kernite, teruggite, tincalconite, and ulexite span a wide range of δ¹¹B values from −29.5 to −0.3‰, whereas fluids cover a range from −18.3 to 0.7‰. The data from recent coexisting borate minerals and fluids allow for the calculation of the isotope composition of the ancient mineralizing fluids and thus for the constraint of the isotope composition of the source rocks sampled by the fluids. The boron isotope composition of ancient mineralizing fluids appears uniform throughout the section of precipitates at a given locality and similar to values obtained from recent thermal fluids. These findings support models that suggest uniform and stable climatic, magmatic, and tectonic conditions during the past 8 million years in this part of the central Andes. Boron in fluids is derived from different sources, depending on the drainage system and local country rocks. One significant boron source is the Paleozoic basement, which has a whole-rock isotopic composition of δ¹¹B=−8.9±2.2‰ (1 SD); another important boron contribution comes from Neogene-Pleistocene ignimbrites (δ¹¹B=−3.8±2.8‰, 1 SD). Cenozoic andesites and Mesozoic limestones (δ¹¹B≤+8‰) provide a potential third boron source.  相似文献   

A new look for the Southern Hemisphere jet stream     

David Gallego  Pedro Ribera  Ricardo Garcia-Herrera  Emiliano Hernandez  Luis Gimeno 《Climate Dynamics》2005,24(6):607-621

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The use of vein fluorite as probe for paleofluid REE and Sr-Nd isotope geochemistry: The Santa Catarina Fluorite District, Southern Brazil   总被引：1，自引：0，他引：1  

Ricardo Sallet  Robert Moritz 《Chemical Geology》2005,223(4):227-248

Fluorite can be used as a probe for the source of Sr and REE, as well as for the Sr and Nd isotope systematics of mineralizing solutions, allowing characterization of the composition, oxidation state and sources of the fluids. The ⁸⁷Sr / ⁸⁶Sr ratios in vein fluorite from the Santa Catarina Fluorite District, southern Brazil, are low (0.720 to 0.745) relative to those of the majority of host granites at the time of mineralization (90 Ma), but are similar to those of less abundant and less evolved Sr- and Ca-rich granites and plagioclases of the heterogeneous Pedras Grandes granite association. Major contributions of Sr from the unradiogenic Parana Basin rocks (⁸⁷Sr / ⁸⁶Sr_{90 Ma} = 0.705 to 0.718) are unlikely, considering the radiogenic character of the lower ⁸⁷Sr / ⁸⁶Sr end-member in fluorite mixing lines. Estimated fluorite fluid partition coefficients (K_d^Sr-Ca = 0.019 and D^Sr ≈ 600) indicate a Sr / Ca ratio in the fluorite-forming solution of 0.012, and Sr contents of 0.05 to 0.25 ppm, which are similar to those of present-day granitic geothermal waters. Initial Nd isotopic compositions of the vein fluorites (0.5120 to 0.512) are similar to those of the Pedras Grandes granites. The ¹⁴³Nd / ¹⁴⁴Nd_{90 Ma} of the evolved granites of the Tabuleiro granite association, their accessory fluorites and the Parana Basin rocks are considerably more radiogenic (0.5120 to 0.5127) and these are thus considered to be unlikely sources of the fluids. The REE patterns of vein fluorites, normalized to upper continental crust, show a range of LREE-depleted patterns, with highly variable positive and negative Eu anomalies. The host Pedras Grandes granites show flat to slightly depleted UCC normalized LREE patterns with strong negative Eu anomalies. Depletion of the LREE in fluorites resulted from the mobility of HREE fluoride complexes during fluid migration. A REE fractionation model based on ionic potential ratios indicates that Eu³⁺ was stable during fluid migration and fluorite precipitation. The coexistence of pyrite and Eu³⁺ in the mineralizing fluids is consistent with low pH and oxygen fugacities near the hematite-magnetite buffer.  相似文献