Rock magnetic and geochemical proxies for iron mineral diagenesis in a tropical lake: Lago Verde, Los Tuxtlas, East–Central Mexico     

Beatriz Ortega  Margarita Caballero  Socorro Lozano  Gloria Vilaclara  Alejandro Rodríguez 《Earth and Planetary Science Letters》2006,250(3-4):444-458

Magnetic and non-magnetic mineral analyses were conducted on a lacustrine sequence from Lago Verde in the tropical coast along the Gulf of Mexico that covers the last 2000 years. The site witnessed the transformation of the environment since the early Olmec societies until forest clearance in the last century. Through these analyses we investigated the processes that affected the magnetic mineralogy in order to construct a model of past environmental changes, and compare this model with the archeological record and inferred climatic changes in the northern hemisphere of tropical America. Volcanic activity has played a major influence on sediment magnetic properties, as a purveyor of Ti-magnetites/Ti-maghemites, and as a factor of instability in the environment. Anoxic reductive conditions are evident in most of Lago Verde's sedimentary record.

Direct observations of magnetic minerals and ratios of geochemical (Fe, Ti), and ferrimagnetic (χf) and paramagnetic (χp) susceptibility (χ) data, are used as parameters for magnetite dissolution (χp/χ, Fe/χf), and precipitation (χf/Ti) of magnetic minerals. Intense volcanic activity and anoxia are recorded before A.D. 20, leading to the formation of framboidal pyrite. Increased erosion, higher evaporation rates, lower lake levels, anoxia and reductive diagenesis in non-sulphidic conditions are inferred for laminated sediments between A.D. 20–850. This deposit matches the period of historical crisis and multiyear droughts that contributed to the collapse of the Maya civilization. Dissolution of magnetite, a high organic content and framboidal pyrite point to anoxic, sulphidic conditions and higher lake levels after A.D. 850. Higher lake levels in Lago Verde broadly coincide with the increased precipitation documented during the Medieval Warm Period (A.D. 950–1350) in the northern tropical and subtropical regions of the American continent. For the Little Ice Age (A.D. 1400–1800), the relatively moist conditions inferred are in concordance with the glacial advances recorded in central Mexico. Higher erosion rates reflect destruction of the rainforest over the last 40 years.  相似文献   

Thirty Years of Research on Spatial Data Quality: Achievements,Failures, and Opportunities     

Rodolphe Devillers  Alfred Stein  Yvan Bédard  Nicholas Chrisman  Peter Fisher  Wenzhong Shi 《Transactions in GIS》2010,14(4):387-400

This article reflects on the past 30 years of academic research in the field of spatial data quality and tries to identify the main achievements, failures, and opportunities for future research. Most of this reflection results from a panel discussion that took place during the Sixth International Symposium on Spatial Data Quality (ISSDQ) in July 2009.  相似文献   

Study of the magnetic turbulence in a corotating interaction region in the interplanetary medium     

J. F. Valdés-Galicia  R. A. Caballero 《Annales Geophysicae》1999,17(11):1361-1368

We study the geometry of magnetic fluctuations in a CIR observed by Pioneer 10 at 5 AU between days 292 and 295 in 1973. We apply the methodology proposed by Bieber et al. to make a comparison of the relative importance of two geometric arrays of vector propagation of the magnetic field fluctuations: slab and two-dimensional (2D). We found that inside the studied CIR this model is not applicable due to the restrictions imposed on it. Our results are consistent with Alfvenic fluctuations propagating close to the radial direction, confirming Mavromichalaki et al.’s findings. A mixture of isotropic and magnetoacoustic waves in the region before the front shock would be consistent with our results, and a mixture of slab/2D and magnetoacoustic waves in a region after the reverse shock. We base the latter conclusions on the theoretical analysis made by Kunstmann. We discuss the reasons why the composite model can not be applied in the CIR studied although the fluctuations inside it are two dimensional.  相似文献   

Proper motion Pleiades candidate L‐type brown dwarfs     

G. Bihain  R. Rebolo  V. J. S. Bjar  J. A. Caballero  C. A. L. Bailer‐Jones  R. Mundt 《Astronomische Nachrichten》2005,326(10):1057-1058

We present results of an optical and near‐infrared (IR) 1.8 deg² survey in the Pleiades open cluster to search for substellar objects. From optical I ‐band images from the CFHT and J ‐band images from the 3.5m CAHA Telescope, we identify 18 faint and very red L brown dwarf candidates, with I > 20.9 and I – J > 3.2. The follow‐up observations of nine objects in the H ‐ and K _s‐bands confirm that eight belong to the IR sequence of the cluster and the proper motion measurements of seven candidates confirm that they are Pleiades members. A preliminary estimation of the substellar mass spectrum dN/ dM in the form of a power law M c^–α provides α = +0.57 ± 0.14. We extrapolate this function to estimate the number of planetary mass objects that could be present in the cluster down to 1 M_Jup. Sensitive searches combining far red and near‐IR observations may unveal these objects in a near future. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The 2005 eruption of Ilamatepec (Santa Ana) volcano,El Salvador     

Teresa Scolamacchia  Carlos Pullinger  Lizeth Caballero  Francisco Montalvo  Laura E. Beramendi Orosco  Galia Gonzalez Hernández 《Journal of Volcanology and Geothermal Research》2010,189(3-4):291-318

We report the stratigraphic sequence of the 2005 eruption of Ilamatepec volcano together with sedimentological and chemical analyses of its products.Structural and textural characteristics of the deposits indicate that the eruption was driven by a small-volume rhyolitic intrusion at shallow levels, which resulted first in the collapse of the existing hydrothermally altered fan of previous deposits inside the crater lake, driving phreatic explosions with launching of blocks on ballistic trajectories; later the magma interacted with lake waters producing several hydromagmatic pyroclastic density currents (PDCs). These flows were energetic enough to knock down pine trees up to distances of 1.8 km from the crater in the E-NE sector of the volcano. Finally, ejection of ballistic blocks that landed on previously emplaced, wet pyroclastic density current deposits, caused the generation of a lahar that flowed down the steep eastern flank toward the El Jabillal gully. Subsequent lahars occurred as a result of intense rain caused by hurricane Stan.Radiocarbon ages on paleosols and charcoal fragments, separating previous volcanogenic sequences, indicate that similar eruptions have occurred more frequently in the past centuries, than previously thought.The new data confirms that Ilamatepec volcano is one of the most active volcanoes in El Salvador. Nevertheless, more detailed studies of the eruptive sequence of Ilamatepec volcano are mandatory to establish future eruptive patterns.  相似文献   

Environmental impacts of Little Ice Age cooling in central Mexico recorded in the sediments of a tropical alpine lake     

E. Cuna  E. Zawisza  M. Caballero  A. C. Ruiz-Fernández  S. Lozano-García  J. Alcocer 《Journal of Paleolimnology》2014,51(1):1-14

The Little Ice Age (LIA), AD 1350–1850, represents one of the most recent, persistent global climate oscillations. In Mexico, it has been associated with temperature decreases of 1.5–2 °C and mountain glacier advances, which are not accurately dated. We present new information about the nature of the LIA in central Mexico based on a decadal-resolution sediment sequence from high-altitude, tropical Lake La Luna, in the Nevado de Toluca volcano. We inferred past climatic and environmental changes using magnetic susceptibility, charcoal particles, palynomorphs, diatoms, cladoceran remains and multivariate statistics. The onset of the LIA corresponds with the beginning of a long-term trend to colder and drier climate ca. AD 1360–1910. The coolest and driest episode, ~AD 1660–1760, which corresponds with the Maunder Minimum in solar activity, was characterized by a cladoceran assemblage that showed the greatest dissimilarity to the modern one (no modern analogue), with the presence of cold-water species and Daphnia ephippia. The beginning of a warming trend ca. AD 1760, was identified by a diatom assemblage dominated by species with affinities for higher pH values (>6) and the greatest dissimilarity to the modern assemblage. This less cold, but still dry period, corresponds with historical reports of cattle and crop losses that predated the Mexican wars of Independence (AD 1810–1821) and Revolution (1910–1924). Modern conditions, established around AD 1910, resemble those during the Medieval Climate Anomaly (ca. AD 1200). No clear evidence of modern, human-induced environmental change was recorded, indicating that Lake La Luna is an ideal site in Mexico to monitor future impacts of global change.  相似文献   

On the potential impact of the stratosphere upon seasonal dynamical hindcasts of the North Atlantic Oscillation: a pilot study     

Yvan Joseph Orsolini  I. T. Kindem  N. G. Kvamst? 《Climate Dynamics》2011,36(3-4):579-588

We have investigated the importance of the stratosphere?Ctroposphere linkage on the seasonal predictability of the North Atlantic Oscillation in a pilot study using a high horizontal resolution atmospheric general circulation model, and covering the 14 winters from 1979/1980 to 1992/1993. We made an ensemble of simulations with the Meteo-France ??Arpege Climat?? model (V3.0) with a well-resolved stratosphere, and a broad comparison is drawn with hindcasts from previously published experiments using low-top and lower horizontal resolution models, but covering the same winters with the same ensemble size and verification method. For the January?CFebruary?CMarch North Atlantic Oscillation index, the deterministic hindcast skill score is 0.59, using re-analyses as verification. It is comparable to the reported multi-model skill score (0.57). The largest improvement originates from the winter 1986/1987 characterised by a major stratospheric sudden warming. We demonstrate that there is then a high-latitude zonal-mean zonal wind decrease in the stratosphere?Ctroposphere hindcasts over a broad pressure range. This is consistent with a composite analysis showing that model anomalous vortex events, either weak or strong, lead to a North Atlantic Oscillation index anomaly in the troposphere, which persists, on average, for 1?month after the anomaly peaked in the stratosphere.  相似文献   

Solar modulation of galactic cosmic-ray intensity as seen by neutron monitors during 1990–1999 – I. Rigidity Dependence and Correlations with Solar Activity Parameters     

Caballero  R.  Valdés-Galicia  J.F. 《Solar physics》2003,212(1):209-223

We analyze the evolution of cosmic ray intensity detected by six neutron monitors located at high altitude from 1990 to 1999, that includes most of solar cycle 22 and the start of cycle 23. This set of neutron monitors covers a wide range of geomagnetic cutoff rigidities. We discuss the most significant characteristics of the cosmic ray modulation during the period as: the extraordinary decreases produced by the events of the first half of 1991, the significant two step evolution of the recovery phase of solar cycle 22 and the start of cycle 23. We also determine the rigidity dependence of the different phases of the modulation cycle. Cosmic ray intensity correlations with several solar activity parameters as sunspots, microwave flux at 10.7 cm and solar flares and with the intensity of the interplanetary magnetic field are studied.  相似文献   

A universal kriging approach for spatial functional data     

William Caballero  Ramón Giraldo  Jorge Mateu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(7):1553-1563

In a wide range of scientific fields the outputs coming from certain measurements often come in form of curves. In this paper we give a solution to the problem of spatial prediction of non-stationary functional data. We propose a new predictor by extending the classical universal kriging predictor for univariate data to the context of functional data. Using an approach similar to that used in univariate geostatistics we obtain a matrix system for estimating the weights of each functional variable on the prediction. The proposed methodology is validated by analyzing a real dataset corresponding to temperature curves obtained in several weather stations of Canada.  相似文献   

ESPERE—A Multiple‐Method Microsoft Excel Application for Estimating Aquifer Recharge          下载免费PDF全文

Sandra Lanini  Yvan Caballero  Jean‐Jacques Seguin  Jean‐Christophe Maréchal 《Ground water》2016,54(2):155-156

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