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   

Estimation of pore‐pressure change in a compacting reservoir from time‐lapse seismic data     

Margarita Corzo  Colin MacBeth  Olav Barkved 《Geophysical Prospecting》2013,61(5):1022-1034

An approach is developed to estimate pore‐pressure changes in a compacting chalk reservoir directly from time‐lapse seismic attributes. It is applied to data from the south‐east flank of the Valhall field. The time‐lapse seismic signal of the reservoir in this area is complex, despite the fact that saturation changes do not have an influence. This complexity reflects a combination of pressure depletion, compaction and stress re‐distribution throughout the reservoir and into the surrounding rocks. A simple relation is found to link the time‐lapse amplitude and time‐shift attributes to variations in the key controlling parameter of initial porosity. This relation is sufficient for an accurate estimation of pore‐pressure change in the inter‐well space. Although the time‐lapse seismic estimates mostly agree with reservoir simulation, unexplained mismatches are apparent at a small number of locations with lower porosities (less than 38%). The areas of difference between the observations and predictions suggest possibilities for simulation model updating or a better understanding of the physics of the reservoir.  相似文献   

Improved expressions for the ellipsoidal harmonic series representing the Earth gravitational potential and its first and second derivatives on and outside the reference ellipsoid of revolution     

Margarita S. Petrovskaya  Andrey N. Vershkov 《Studia Geophysica et Geodaetica》2013,57(3):353-368

The Legendre functions of the second kind, renormalized by Jekeli, are considered in the external space on a set of ellipsoids of revolution which are confocal with respect to the normal ellipsoid. Among these ellipsoids a reference one is chosen which bounds the Earth. New expressions for the first and second order derivatives of the Legendre functions are derived. They depend on two very quickly convergent Gauss hypergeometric series which are obtained by transforming the slowly convergent initial hypergeometric series. The derived expressions are applied for constructing the ellipsoidal harmonic series for the Earth disturbing gravitational potential and its derivatives of the first and second orders. Since outside the chosen reference ellipsoid there are no Earth masses (as compared to the normal ellipsoid) then it is more appropriate for constructing the boundary-value equation and solving it on the basis of surface gravity data reduced to this ellipsoid.  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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