Climatic forcing on hydrography of a Mediterranean bay (Alfacs Bay)     

Jordi Sol  Antonio Turiel  Marta Estrada  Clara Llebot  Dolors Blasco  Jordi Camp  Maximino Delgado  Margarita Fernndez-Tejedor  Jorge Diogne 《Continental Shelf Research》2009,29(15):1786-1800

Time series of meteorological and hydrographic variables were analyzed using Huang's Empirical Mode Decomposition (EMD) to ascertain the relationships among climatic forcings and the hydrographic behavior in an estuarine bay. The EMD method allowed us to separate the different characteristic oscillation patterns (or modes) of a 14 year-long time series of weekly hydrographic (water temperature and salinity) and meteorological (air temperature, pressure, wind and precipitation) data from Alfacs Bay (Ebre delta, NW Mediterranean). In order to explore the relations between couples of oscillation modes from different series, we developed a correlation index based on the phase differences between these modes. Common characteristic modes in the studied series are a seasonal pattern and an inter-annual oscillation. The comparison between series of meteorological and hydrographic variables shows significant correlations of two modes (of 1 year and 2–3 year periods, respectively) of water temperature with the corresponding two modes of air temperature and air pressure. There were also significant positive correlations between wind speed and water temperature. The use of EMD allowed to discover a strong connection between stratification and the use of irrigation channels in the bay; in addition, with the help of this method we can propose a common meteorological forcing mechanism for the observed patterns of variability. Those findings would have been impossible to guess by use of classical Fourier methods, and gives a demonstration of the power of EMD in climatic series analysis.  相似文献   

Comparison of several high-order advection schemes for vertex-based triangular discretization     

Smolentseva  Margarita  Danilov  Sergey 《Ocean Dynamics》2020,70(4):463-479

Ocean Dynamics - Possible extensions of the standard 3rd (upwind) and 4th (centered) order vertex-centered finite-volume advection schemes on unstructured triangular meshes are explored. A...  相似文献   

Benchmarking of two three-dimensional numerical models in time/space domain to predict railway-induced ground vibrations     

Jesus Fernandez-Ruiz  Luis E.Medina Rodriguez  Pedro Alves Costa  Margarita Martinez-Diaz 《地震工程与工程振动(英文版)》2021,20(1):245-256

In the last 30 years,the scientific community has developed and proposed different models and numerical approaches for the study of vibrations induced by railway traffic.Most of them are formulated in the frequency/wave number domain and with a 2.5D approach.Three-dimensional numerical models formulated in the time/space domain are less frequently used,mainly due to their high computational cost.Notwithstanding,these models present very attractive characteristics,such as the possibility of considering nonlinear behaviors or the modelling of excess pore pressure and non-homogeneous and non-periodic geometries in the longitudinal direction of the track.In this study,two 3D numerical approaches formulated in the time/space domain are compared and experimentally validated.The first one consists of a finite element approach and the second one of a finite difference approach.The experimental validation in an actual case situated in Carregado(Portugal)shows an acceptable fitting between the numerical results and the actual measurements for both models.However,there are some differences among them.This study therefore includes some recommendations for their use in practical soil dynamics and geotechnical engineering.  相似文献   

Pseudo-nitzschia spp. (Bacillariophyceae) and dissolved organic matter (DOM) dynamics in the Ebro Delta (Alfacs Bay, NW Mediterranean Sea)     

Sofia Loureiro  Esther Garcs  Margarita Fernndez-Tejedor  Dolors Vaqu  Jordi Camp 《Estuarine, Coastal and Shelf Science》2009,83(4):539-549

Samples were collected during one annual cycle (April 2007–March 2008) at Alfacs Bay (NW Mediterranean Sea) central station in order to assess the influence of organic nutrients in the growth of the microalgae assemblage, with special reference to Pseudo-nitzschia spp. This potentially toxic diatom forms natural and recurrent blooms in the study area. To assess further the relationship between Pseudo-nitzschia spp. and nutrients an enrichment experiment with high molecular weight dissolved organic matter (HMWDOM) was performed with field samples obtained during a Pseudo-nitzschia spp. bloom. HMWDOM was extracted from water collected at Alfacs Bay. Five bioassays were prepared: N + P (seawater with addition of nitrate and phosphate), DOM (addition of HMWDOM), (−N + P) + DOM (nitrogen deficient, with addition of phosphate and HMWDOM), (N + P) + DOM (addition of nitrate, phosphate and HMWDOM), seawater control (without added nutrients), and B + DOM (control of bacteria, without microalgae). The experiment was run in batch mode over 4 days. Results from the field study revealed that the concentrations of organic nutrients mostly surpassed the inorganic pool. Pseudo-nitzschia spp. was the most frequent and abundant taxa of the microalgae community. The micro-planktonic assemblage was arranged according to a seasonal factor (ANOSIM and cluster analysis). DON, nitrate and silicate were the most important abiotic parameters contributing to the dissimilarities between seasons (SIMPER analysis) and thereby potentially influencing the seasonal distribution of microalgae in the representative station. In the experimental investigation, Pseudo-nitzschia cells increased by the end of the experiment in the DOM bioassay but no respective increase was observed for chlorophyll a. This could point to an acquisition of nutrients through the DOM fraction that would conjointly reduce the need of chlorophyll a. The data obtained suggest that organic nutrients may exert an important role in the development of microalgae, including Pseudo-nitzschia spp., in the selected location.  相似文献   

Calcareous nannofossil and planktonic foraminiferal distributional patterns during deposition of sapropels S6, S5 and S1 in the Libyan Sea (Eastern Mediterranean)   总被引：1，自引：1，他引：0  

Maria V. Triantaphyllou  Assimina Antonarakou  Margarita Dimiza  Christos Anagnostou 《Geo-Marine Letters》2010,30(1):1-13

In core ADE3-23 collected in the Libyan Sea, the nannofossil species Coccolithus pelagicus, Coronosphaera spp., Helicosphaera spp., Syracosphaera spp., Calcidiscus spp., small Gephyrocapsa spp., and the planktonic foraminifers Globigerina bulloides, Neogloboquadrina pachyderma, Globorotalia scitula, Turborotalita quinqueloba and Neogloboquadrina dutertrei prevail in sapropel S6 (midpoint at 172 ka b.p.), indicative of cold and highly productive surface conditions. Warm and highly stratified water-column conditions are recorded by the characteristic assemblage of Globigerinoides ruber, Globoturborotalita rubescens, Florisphaera profunda, Rhabdosphaera spp. during the sapropel S5 depositional interval (midpoint at 124 ka b.p.). Compared with S5, Globigerinita glutinata, Globorotalia inflata, Globigerinella siphonifera, Globorotalia truncatulinoides and the calcareous nannofossil Emiliania huxleyi characterise less stratified conditions within sapropel S1 (midpoint at 8.5 ka b.p.). Multivariate statistical analyses of calcareous nannofossil and planktonic foraminifers in core ADE3-23 identify planktonic assemblages which typify sapropels S6, S5 and S1 in the Libyan Sea. A warmer interval is recognised in the middle part of the cold S6, and can be associated with an influx of less saline waters and the occurrence of a faint, temporary deep chlorophyll maximum. Evidence for enhanced surface productivity and breakdown of stratification is observed in the middle–upper part of the warm S5, associated with climatic deterioration. Moreover, an increase in surface productivity in the upper S1 implies weak stratification. Our combined calcareous nannofossil and planktonic foraminiferal data add to the evidence that climate variability was more pronounced than commonly considered to date for all the three studied Eastern Mediterranean sapropel depositional intervals.  相似文献   

Ar-Ar Geochronology in a gneiss dome within the Zagros Orogénic Belt     

Akram Alizadeh  Margarita López Martínez  Khalil Sarkarinejad 《Comptes Rendus Geoscience》2010,342(11):837-846

Exhumation of the Tutak mantled gneiss dome without significant cooling has taken place in a doubly plunging anticline within the Sanandaj-Sirjan HP-LT metamorphic belt in the Zagros Thrust System of Iran. Reconstruction of structural evolution of the Tutak gneiss dome at the contact between Arabian and Iranian plates by ⁴⁰Ar/³⁹Ar geochronology exhibits history of the closure of Neo-Tethyan Ocean. There are two granites of different ages in the core of dome; the oldest corresponds to the central Iranian continental crust and was deformed at about 180 Ma. The younger granite was emplaced in the NE–SW transpression system. The timing of strain-related fabrics and exhumation history of the region illustrates the closure of Neo-Tethys and beginning of continent-continent collision at about 77 Ma, as constrained by a well defined plateau ⁴⁰Ar/³⁹Ar age obtained on biotite. Then, the biotite age corresponds to the second stage of emplacement of the Bendenow granite-gneiss which illustrating repeated orogenic events. Continuing deformation without interruption that by now has been created at about 77 Ma, was largely restricted to the transpression and high proportion of simple shear components relative to the pure shear components along the NE–SW.  相似文献   

The Stellar Imager (SI) project: a deep space UV/Optical Interferometer (UVOI) to observe the Universe at 0.1 milli-arcsec angular resolution     

Kenneth G. Carpenter  Carolus J. Schrijver  Margarita Karovska 《Astrophysics and Space Science》2009,320(1-3):217-223

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI’s science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a “Flagship and Landmark Discovery Mission” in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA’s Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.  相似文献   

The Holocene record of Alberca de Tacámbaro,a tropical lake in western Mexico: evidence of orbital and millennial-scale climatic variability     

Beatriz Ortega-Guerrero  Margarita Caballero  Isabel Israde-AlcáNtara 《第四纪科学杂志》2021,36(4):649-663

Laminated sediments in a core from Alberca de Tacámbaro, western central Mexico, provide a high-resolution record of palaeoclimatic variability for most of the Holocene. Using compositional and textural characteristics we identified 14 facies classified in biogenic, clastic and volcaniclastic groups, in which diatoms and other algal remains are the most common components. In addition to facies analysis, high-resolution geochemical data from continuous core scanning XRF and the analysis of discrete samples for organic and inorganic carbon content, provide the basis for palaeoclimatic reconstruction. The age model indicates that the record spans from 9.4 cal ka bp toad 1760. Three main phases in the sequence are identified, controlled by millennial-scale variability. During the period between 9.4 and 5.7 cal kabp , the lake is dominated by siliceous organisms. Drier conditions between 8.2 and 6.3 cal kabp are linked to decreases in summer insolation and solar irradiance. By 5.7 cal kabp , the change in sedimentation is related to the increase in El Niño Southern Oscillation frequency. Evidence of the occurrence of dry conditions during the archaeological Late Classic period (ad 600–900) and historical droughts are also documented in the Alberca de Tacámbaro record. Unprecedented changes in the landscape are recorded afterad 1520.  相似文献   

High-temperature order–disorder phase transition in nacaphite,Na2CaPO4F     

Margarita S. Avdontceva  Maria G. Krzhizhanovskaya  Sergey V. Krivovichev  Viktor N. Yakovenchuk 《Physics and Chemistry of Minerals》2015,42(8):671-676

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The MIKHNEVO small aperture array enhances the resolution property of seismological observations on the East European Platform     

Irina Alfatovna Sanina  Irina P. Gabsatarova  Oleg A. Chernykh  Oxana Y. Riznichenko  Sergey G. Volosov  Margarita A. Nesterkina  Natalya L. Konstantinovskaya 《Journal of Seismology》2011,15(3):545-556

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