A correlated shortening of the North and South American monsoon seasons in the past few decades   总被引：1，自引：1，他引：0  

Paola A. Arias  Rong Fu  Carolina Vera  Maisa Rojas 《Climate Dynamics》2015,45(11-12):3183-3203

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Stability analysis and morphometric characterization of palaeo-lakes of the Benjamin Matienzo basin, Las Cuevas River, Argentina     

Stella Moreiras  Carolina Lauro  Leandro Mastrantonio 《Natural Hazards》2012,62(2):593-611

Natural dams are caused by the blockage of streams as a result of the sudden arrival of detritus material during a glacial surge advance or fast slope collapse threatening downstream populations. Nevertheless, origin, morphological characteristics and stability of dammed lakes are frequently ignored. Six impounded palaeo-lakes were geomorphologically studied in the Benjamin Matienzo gully (32°14′ S–70°02′ W), denominated, from north to south: Goyete, Negro, Casa de Piedra, Lagunita, Susanita and Matienzo. We determined the origin, morphometric parameters, stability index and rate of streamflow rupture for these dammed ancient lakes in order to shed light on the potential outburst flood hazard in this Andean mountain region. According to our findings, we concluded that palaeo-lakes would have had a short life as they turned out to be unstable, except for the Goyete Lake, matching with the lack of fine lacustrine sediments in all river blockages. We also estimated the maximum peak discharge of a probable outburst flow generated during a drastic collapse of these dams. Obtained values range between 22 and 151 m³/s being notably higher than the average annual streamflow of Las Cuevas River (6.6 m³/s), but similar to the instantaneous streamflow of this river (157 m³/s, 2-year recurrence time).  相似文献   

Galaxy clusters in the line of sight to background quasars – II. Environmental effects on the sizes of baryonic halo sizes     

Nelson Padilla  Ivan Lacerna  Sebastián Lopez  L. Felipe Barrientos  Paulina Lira  Heather Andrews  Nicolás Tejos 《Monthly notices of the Royal Astronomical Society》2009,395(2):1135-1145

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The Collapse of Gran Dolina cave,Sierra de Atapuerca,Spain: Site formation processes of layer TD10‐1     

Carolina Mallol  Eudald Carbonell i Roura 《Geoarchaeology》2008,23(1):13-41

The last hominin occupations of Gran Dolina cave at Atapuerca are represented by layer TD10‐1. This layer has yielded high densities of anthropogenic bone and lithic remains that suggest the existence of a referential hominin campsite. Micromorphological analysis was carried out in order to reconstruct site formation processes and to find traces of hominin activity in the sediments. Results show that TD10‐1 is an autochthonous deposit whose components are derived from a local, degraded cave entrance environment. The base of TD10‐1 represents a moist, semi‐sheltered environment associated with anthropogenic input and low sedimentary rates, while the rest of the deposit represents a non‐anthropogenic, more open environment with higher rates of sedimentation. The TD10‐1 archaeological assemblages have not undergone long transport or strong postdepositional disturbance. Further interdisciplinary analyses are needed to characterize the types and intensity of the hominin activities recorded in TD10‐1. © 2008 Wiley Periodicals, Inc.  相似文献   

Erratum     

Carolina Mallol  Eudald Carbonell I Roura 《Geoarchaeology》2008,23(2):321-321

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A high-resolution 43-year atmospheric hindcast for South America generated with the MPI regional model   总被引：1，自引：1，他引：0  

Gabriel Silvestri  Carolina Vera  Daniela Jacob  Susanne Pfeifer  Claas Teichmann 《Climate Dynamics》2009,32(5):693-709

An evaluation of the present-day climate in South America simulated by the MPI atmospheric limited area model, REMO, is made. The model dataset was generated by dynamical downscaling from the ECMWF-ERA40 reanalysis and compared to in-situ observations. The model is able to reproduce the low-level summer monsoon circulation but it has some deficiencies in representing the South American Low-Level Jet structure. At upper levels, summer circulation features like the Bolivian High and the associated subtropical jet are well simulated by the model. Sea-level pressure fields are in general well represented by REMO. The model exhibits reasonable skill in representing the general features of the mean seasonal cycle of precipitation. Nevertheless, there is a systematic overestimation of precipitation in both tropical and subtropical regions. Differences between observed and modeled temperature are smaller than 1.5°C over most of the continent, excepting during spring when those differences are quite large. Results also show that the dynamical downscaling performed using REMO introduces some enhancement of the global reanalysis especially in temperature at the tropical regions during the warm season and in precipitation in both the subtropics and extratropics. It is then concluded that REMO can be a useful tool for regional downscaling of global simulations of present and future climates.  相似文献   

Present Limnological Conditions and Recent (ca. 340 yr) Palaeolimnology of a Tropical Lake in the Sierra de Los Tuxtlas, Eastern Mexico     

Margarita Caballero  Gabriela Vázquez  Socorro Lozano-García  Alejandro Rodríguez  Susana Sosa-Nájera  Ana Carolina Ruiz-Fernández  Beatriz Ortega 《Journal of Paleolimnology》2006,35(1):83-97

The Sierra de Los Tuxtlas is a recently active volcanic field, with eruptions in 1664 and 1792. It holds one of the reserves of tropical evergreen forest in Mexico, as well as several maar lakes. One of them, Lago Verde, was chosen for a three-fold study (1) on its present limnological conditions, (2) on the algal community living in the water column and preserved in the surface sediments; and (3) on its recent history (ca. 340 yr). The palaeolimnological study was based on multiproxy analyses on core material dated by ²¹⁰Pb, ¹³⁷Cs and ¹⁴C. Lago Verde is a small, shallow lake with dilute, slightly alkaline water (CO₃²⁻ + HCO₃⁻ > Cl⁻ > SO₄²⁻, Na⁺ + K⁺ > Ca²⁺ > Mg²⁺). It is turbid, eutrophic, with high phosphorus levels. It is a warm polymictic lake, with thermal and oxygen stratification establishing by midday during the warm months. The lake does not stratify in winter. Diatoms dominate the phytoplankton community in the cold ‘nortes’ season, Cyanobacteria in summer, and Chlorophyta in autumn. Cyanobacteria (Chroococcales) are not well preserved in the surface sediments while Chlorophyta are better preserved. Sedimentary diatoms are well preserved, dominated by the three most abundant species in the water column: Achnanthidium minutissimum, Fragilaria capucina and Aulacoseira granulata. The base of the studied sequences is constrained by the historic eruption of 1664. The period from 1664 to 1963 is characterised by a meso-eutrophic lake. Tropical Forest vegetation reaches maximum values between ca. 1800 and 1963. Between ca. 1785 and 1885 the lake was slightly shallower than in the rest of the 1664–1963 period, probably recording climatic variability. An early pulse of anthropogenic disturbance was recorded by ca. 1921 and after ca. 1963 intense forest clearance and high erosion rates led to a more turbid, more productive, nutrient-rich lake. The highest anthropogenic impact was reached by ca. 1988; afterwards the lake and its basin reached a new balance, with the establishment of the present modern conditions.  相似文献   

Pb chronology and trace metal geochemistry at Los Tuxtlas, Mexico, as evidenced by a sedimentary record from the Lago Verde crater lake     

Ana Carolina Ruiz-Fernández  Claude Hillaire-Marcel  Federico Páez-Osuna  Bassam Ghaleb  Margarita Caballero 《Quaternary Research》2007,67(2):181-192

Lago Verde is a fresh-water maar found on the lower slopes of San Martin volcano, at the Sierra de Los Tuxtlas, Mexico, currently the northernmost remnant of the tropical rain forest in America. ²¹⁰Pb and ¹³⁷Cs analyzed in a sediment core were used to reconstruct the historical fluxes of Ag, Cd, Cu, Pb, Hg and Zn to the site during the last ∼ 150 yr. The ²¹⁰Pb_xs-derived sediment accumulation rates, the magnetic susceptibility, C/N ratios and δ¹³C data evidenced background conditions at the lake until 1960s, when enhanced erosion related to the clearing of large forested areas at Los Tuxtlas promoted higher accumulation rates of a heavier and more magnetic sedimentary material. Recent sediments from Lago Verde were found enriched by Pb (26-fold natural concentration level [NCLs]) and moderately enriched by Cd > Cu > Zn and Hg (6-, 5-, 4- and 4-fold corresponding NCLs, respectively). The fluxes of Cu, Hg, Pb and Zn have significantly increased since 1940s, with peak ratios of total modern to pre-industrial fluxes of 11, 11, 19 and 49, respectively. The lake occupies a relatively pristine, non-industrialized basin, and therefore the increased metal fluxes might be related to long-distance aeolian transport of trace metals.  相似文献   

Crustal seismicity in central Chile     

S. Barrientos  E. Vera  P. Alvarado  T. Monfret 《Journal of South American Earth Sciences》2004,16(8):455

Both the genesis and rates of activity of shallow intraplate seismic activity in central Chile are poorly understood, mainly because of the lack of association of seismicity with recognizable fault features at the surface and a poor record of seismic activity. The goal of this work is to detail the characteristics of seismicity that takes place in the western flank of the Andes in central Chile. This region, located less than 100 km from Santiago, has been the site of earthquakes with magnitudes up to 6.9, including several 5+ magnitude shocks in recent years. Because most of the events lie outside the Central Chile Seismic Network, at distances up to 60 km to the east, it is essential to have adequate knowledge of the velocity structure in the Andean region to produce the highest possible quality of epicentral locations. For this, a N–S refraction line, using mining blasts of the Disputada de Las Condes open pit mine, has been acquired. These blasts were detected and recorded as far as 180 km south of the mine. Interpretation of the travel times indicates an upper crustal model consisting of three layers: 2.2-, 6.7-, and 6.1-km thick, overlying a half space; their associated P wave velocities are 4.75–5.0 (gradient), 5.8–6.0 (gradient), 6.2, and 6.6 km/s, respectively.Hypocentral relocation of earthquakes in 1986–2001, using the newly developed velocity model, reveals several regions of concentrated seismicity. One clearly delineates the fault zone and extensions of the strike-slip earthquake that took place in September 1987 at the source of the Cachapoal River. Other regions of activity are near the San José volcano, the source of the Maipo River, and two previously recognized lineaments that correspond to the southern extension of the Pocuro fault and Olivares River. A temporary array of seismographs, installed in the high Maipo River (1996) and San José volcano (1997) regions, established the hypocentral location of events with errors of less than 1 km. These events are clustered along no particular lineament approximately 25 km away from the San José and Maipo volcanoes. Recurrence intervals, based on a frequency magnitude relationship for lower magnitude events, indicate that earthquakes with magnitudes of 4.7 and 7 have a repeat time of 1 and 1200 years, respectively. Focal mechanisms of the two largest events indicate horizontal maximum and minimum compressive stresses with σ₁ varying from a NW–SE orientation in the north to E–W at the southern extreme.  相似文献   

A teleseismic shear-wave splitting study to investigate mantle flow around South America and implications for plate-driving forces   总被引：2，自引：0，他引：2  

George Helffrich  Douglas A. Wiens  Emilio Vera  Sergio Barrientos  Patrick Shore  Stacey Robertson  Rodrigo Adaros 《Geophysical Journal International》2002,149(1):F1-F7

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