Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties   总被引：1，自引：0，他引：1  

Elena Piñero  Eulàlia Gràcia  Francisca Martínez-Ruiz  Juan Cruz Larrasoaña  Alexis Vizcaino  Gemma Ercilla 《Geo-Marine Letters》2007,27(2-4):279-288

Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers. The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect to the other samples from the southern Hydrate Ridge.  相似文献   

Contributions of boron isotopes to understanding the hydrogeochemistry of the coastal detritic aquifer of Castellón Plain,Spain   总被引：1，自引：0，他引：1  

Elena Giménez Forcada  Ignacio Morell Evangelista 《Hydrogeology Journal》2008,16(3):547-557

The Castellón Plain alluvial aquifer, Spain, is intensively exploited to meet the demand for agricultural irrigation and industrial water supply. The geochemistry of its groundwater shows complex salinization in the northern and southern parts of the aquifer, with significant pollution from human origin in the central portion. Boron content and B isotope geochemistry are useful for distinguishing between various sources of pollution and their relative importance in different parts of this aquifer. Boron concentrations in the groundwater vary between 0.01 and 0.85 mg/L. In the more saline groundwaters, found at the northern and southern ends of the study area, the presence of B is linked to inputs from seawater and water with a calcium-magnesium sulphate facies, which feed the aquifer and clearly influence the chemistry of its waters. Evidence of B adsorption processes in some samples is shown by the low B/Cl ratios and the high values of δ¹¹B. In the central portion of the aquifer, the high B/Cl ratios and the strongly negative δ¹¹B are related to pollution of human origin.  相似文献   

Exploring seven hundred years of transhumance,climate dynamic,fire and human activity through a historical mountain pass in central Spain     

José Antonio López-Sáez  Francisca Alba-Sánchez  Sandra Robles-López  Sebastián Pérez-Díaz  Daniel Abel-Schaad  Silvia Sabariego-Ruiz  Arthur Glais 《山地科学学报》2016,13(7):1139-1153

A high-altitude peat sequence from the heart of the Spanish Central System (Gredos range) was analysed through a multi-proxy approach to determine the sensitivity of high-mountain habitats to climate, fire and land use changes during the last seven hundred years, providing valuable insight into our understanding of the vegetation history and environmental changes in a mountain pass close to a traditional route of transhumance. The pollen data indicate that the vegetation was dominated by shrublands and grasslands with scattered pines in high-mountain areas, while in the valleys cereals, chestnut and olive trees were cultivated. Strong declines of high-mountain pines percentages are recorded at 1540, 1675, 1765, 1835 and 1925 cal AD, which may be related to increasing grazing activities and/or the occurrence of anthropogenic fires. The practice of mountain summer farming and transhumance deeply changed and redesigned the landscape of the high altitudes in central Spain (Gredos range) since the Middle Ages, although its dynamics was influenced in some way by climate variability of the past seven centuries.  相似文献   

Combining European Earth Observation products with Dynamic Global Vegetation Models for estimating Essential Biodiversity Variables     

Mateus Dantas de Paula  Marta Gómez Giménez  Aidin Niamir  Martin Thurner  Thomas Hickler 《International Journal of Digital Earth》2020,13(2):262-277

ABSTRACT

Global, fast and accessible monitoring of biodiversity is one of the main pillars of the efforts undertaken in order to revert it loss. The Group on Earth Observations Biodiversity Observation Network (GEO-BON) provided an expert-based definition of the biological properties that should be monitored, the Essential Biodiversity Variables (EBVs). Initiatives to provide indicators for EBVs rely on global, freely available remote sensing (RS) products in combination with empirical models and field data, and are invaluable for decision making. In this study, we provide alternatives for the expansion and improvement of the EBV indicators, by suggesting current and future data from the European Space Agencýs COPERNICUS and explore the potential of RS-integrated Dynamic Global Vegetation Models (DGVMs) for the estimation of EBVs. Our review found that mainly due to the inclusion of the Sentinel constellation, Copernicus products have similar or superior potential for EBV indicator estimation in relation to their NASA counterparts. DGVMs simulate the ecosystem level EBVs (ecosystem function and structure), and when integrated with remote sensing data have great potential to not only offer improved estimation of current states but to provide projection of ecosystem impacts. We suggest that focus on producing EBV relevant outputs should be a priority within the research community, to support biodiversity preservation efforts.  相似文献   

Tagging-the-triangle algorithm for partitioning features with inconsistent boundaries     

Sunghwan Cho  M. Xavier Punithan  Jonggun Gim 《International journal of geographical information science》2014,28(12):2533-2550

In spatial data sets, gaps or overlaps among features are frequently found in spatial tessellations due to the non-abutting edges with adjacent features. These non-abutting edges in loose tessellations are also called inconsistent boundaries or slivers; polygons containing at least one inconsistent boundary are called inconsistent polygons or sliver polygons. The existing algorithms to solve topological inconsistencies in sliver polygons suffer from one or more of three major issues, namely determination of tolerances, excessive CPU processing time for large data sets and loss of vertex history. In this article, we introduce a new algorithm that mitigates these three issues. Our algorithm efficiently searches the features with inconsistent polygons in a given spatial data set and logically partitions them among adjacent features. The proposed algorithm employs the constrained Delaunay triangulation technique to generate labelled triangles from which inconsistent polygons with gaps and overlaps are identified using label counts. These inconsistent polygons are then partitioned using the straight skeleton method. Moreover, each of these partitioned gaps or overlaps is distributed among the adjacent features to improve the topological consistency of the spatial data sets. We experimentally verified our algorithm using the real land cadastre data set. The comparison results show that the proposed algorithm is four times faster than the existing algorithm for data sets with 200,000 edges.  相似文献   

Spectral Trends of Solar Bursts at Sub-THz Frequencies     

L. O. T. Fernandes  P. Kaufmann  E. Correia  C. G. Giménez de Castro  A. S. Kudaka  A. Marun  P. Pereyra  J.-P. Raulin  A. B. M. Valio 《Solar physics》2017,292(1):21

Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012?–?2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5?–?40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.  相似文献   

Eclipse monitoring of eccentric binary systems     

Alvaro Giménez 《Experimental Astronomy》1994,5(1-2):91-97

The observation of apsidal motions in eclipsing binaries is a very rewarding area of research which requires only moderate or small telescopes equipped with a photoelectric photometer. Important contributions can be made to the study of stellar internal structure through these observations, as well as the verification of the theory of general relativity using the equations of orbital motion. The main objectives of such an observational effort are described, together with a list of candidate binary systems. An appeal to photometrists with small telescopes around the world is made to observe these eccentric and well-detached eclipsing binaries.  相似文献   

Triggering factors,behavior, and social impact of the January 2021 hail-debris flows at the Central Valley of Chile     

Romero  Jorge E.  Vergara-Pinto  Francisca  Aguilar  Germ&#;n  Garc&#;s  Alex  Montserrat  Santiago 《Landslides》2022,19(4):865-883

Landslides - An extreme precipitation event produced catastrophic debris flows in central Chile during 29–31 January 2021 (austral summer). Our study focuses on the triggering factors and...  相似文献   

Human-induced coastal landslide reactivation. Monitoring by PSInSAR techniques and urban damage survey (SE Spain)   总被引：1，自引：1，他引：0  

Davide Notti  Jorge Pedro Galve  Rosa María Mateos  Oriol Monserrat  Francisco Lamas-Fernández  Francisca Fernández-Chacón  Francisco Javier Roldán-García  José Vicente Pérez-Peña  Michele Crosetto  José Miguel Azañón 《Landslides》2015,12(5):1007-1014

  相似文献   

Joint Measurements of Flare Flux Densities at 210 – 212 GHz by Two Different Radio Telescopes     

J.-P. Raulin  G. Trottet  G. Giménez de Castro  T. Lüthi  P. Kaufmann 《Solar physics》2014,289(4):1227-1237

Multiple-beam observations of solar flares at submillimeter wavelengths need detection with at least four beams to derive the flux density $\mbox{$F$} $ of the emitting source, its size, and centroid position. When this condition is not fulfilled, the assumptions on the location and/or size of the emitting source have to be made in order to compute $\mbox{$F$}$ . Otherwise, only a flux density range $\mbox{$\Delta F$}$ can be estimated. We report on simultaneous flare observations at 212 and 210 GHz obtained by the Solar Submillimeter Telescope (SST) and the Bernese Multibeam Radiometer for Kosma (BEMRAK), respectively, during two solar events on 28 October 2003. For both events, BEMRAK utilized four beam information to calculate the source flux density F ₂₁₀, its size and position. On the other hand, the SST observed the events with only one beam, at low solar elevation angles and during high atmospheric attenuation. Therefore, because of these poor observing conditions at 212 GHz, only a flux density range ΔF ₂₁₂ could be estimated. The results show that ΔF ₂₁₂ is within a factor of 2.5 of the flux density F ₂₁₀. This factor can be significantly reduced (e.g. 1.4 for one of the studied events) by an appropriate choice of the 212 GHz source position using flare observations at other wavelengths. By adopting the position and size of the 210 GHz source measured by BEMRAK, the flux density at 212 GHz, F _212b, is comparable to F ₂₁₀ within the uncertainties, as expected. Therefore our findings indicate that even during poor observing conditions, the SST can provide an acceptable estimate of the flux density at 212 GHz. This is a remarkable fact since the SST and BEMRAK use quite different procedures for calibration and flux density determination. We also show that the necessary assumptions made on the size of the emitting source at 212 GHz in order to estimate its flux density are not critical, and therefore do not affect the conclusions of previous studies at this frequency.  相似文献