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31.
Yves Lagabrielle Manuel Surez Jacques Malavieille Diego Morata Felipe Espinoza Ren C. Maury Bruno Scalabrino Luis Barbero Rita de la Cruz Eduardo Rossello Herv Bellon 《地学学报》2007,19(6):413-424
Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction. 相似文献
32.
Ana C. F. Silva Vanessa Mendonça Rita Paquete Nuno Barreiras Catarina Vinagre 《Marine Ecology》2015,36(3):530-540
In habitats where competition for space is a shaping force of animal distribution such as in the intertidal rocky ecosystem, new habitats are readily taken by colonising species. We examined the importance of empty Chthamalus spp. tests as a habitat for the intertidal common periwinkle Melaraphe neritoides on Portuguese rocky shores. The role played by the space between neighbouring barnacles as a habitat for other species has been largely studied with regard to how an ecosystem functions, whereas the equivalent role of empty barnacle tests remains largely unknown. The small periwinkle is one of the most abundant snails in European rocky shores and is an important prey for key mobile predators. Biological facilitation is common in the rocky intertidal zone, where biological structures often potentiate the abundance of other species. The role played by barnacles as biological facilitators through habitat provision is not fully understood. In this study, the abundance and morphometric features of empty barnacle tests and their occupants were examined across shore levels and shores with differing exposures, as these are important gradients explaining barnacle distribution. The availability of empty barnacle tests was also experimentally manipulated to examine the percentage, time and length of occupation. Empty barnacles were more abundant on the midshore of sheltered shores and barnacle tests were wider on the upper shore but taller on the midshore. The minimum barnacle test occupation rate by the periwinkle was 70%. Barnacle shell height was an important factor determining snail occupation, where taller barnacles harboured significantly more, but not necessarily larger, snails. Snails outside the barnacle tests were significantly larger than those found within, suggesting that this crustacean group has an increased importance as a habitat for juvenile snails, thus potentially influencing the population dynamics of M. neritoides. We found that occupation of experimentally created empty barnacles was extremely high (70%) on the day after, and remained at 100% after 3 months of monitoring. Our study is the first of its kind to focus on the features of barnacle tests that snails occupy and their occupying snail traits. According to our results, it is clear that barnacles have an important role in providing additional habitat for young gastropods. The small periwinkle is an important grazer and prey for intertidal and subtidal foraging predators; hence, the potential refuge role of barnacle tests for juvenile M. neritoides may be important in the dynamics of intertidal communities. 相似文献
33.
High connectivity and directional gene flow in European Atlantic and Mediterranean populations of Ciona intestinalis sp. A
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Ornella Affinito Nikos Andreakis Luigi Caputi Rita Marino Raimondo Pannone Paolo Sordino Gabriele Procaccini 《Marine Ecology》2015,36(4):1230-1243
Understanding the factors that cause population divergence has long been of interest to marine biologists in their attempts to interpret the effect of human‐mediated vectors. Broadcast‐spawning species with limited dispersal capability are excellent candidates to measure the present‐day patterns of genetic diversity. The tunicate Ciona intestinalis (Ascidiacea) is comprised of a complex of morphologically cryptic species that form vigorous aggregates in eutrophic habitats (harbors, gulfs and lagoons) where they can compete with the epibenthic community and cause biofouling problems. This study investigated biogeographic variability and migration patterns of C. intestinalis sp. A along Northeast Atlantic and Mediterranean coasts using microsatellite markers. Data presented here on 371 specimens collected from 17 populations reveal high genetic polymorphism, but with a deficit of heterozygote deficiency. Absence of evidence for isolation by distance suggests that the genetic patterns do not reflect the geographic distribution of sampled populations. Substantial gene flow and artificial potential for dispersal boost high levels of within‐population genetic variability and prevent genetic differentiation within and between seas. A predominant eastward migration pattern was revealed by the data set, with very limited opportunity for C. intestinalis sp. A to travel westward. This directional movement indicates that other properties (e.g. habitat quality, genetic traits, mating system, life cycle) may cause adaptive divergence at a large biogeographic scale. 相似文献
34.
Geotechnical Characterization by In situ and Lab Tests to the Back-Analysis of a Supported Excavation in Metro do Porto 总被引:1,自引:1,他引:0
António Viana da Fonseca Sara Rios Silva Nuno Cruz 《Geotechnical and Geological Engineering》2010,28(3):251-264
This paper summarizes the geotechnical characterization conducted for the design and subsequent analysis of a strutted excavation in “Metro do Porto”. This region is geologically dominated by heterogeneous weathered granite masses with deep residual soil profiles. Local saprolitic soils exhibit, by their nature, a particular behavior characterized by very sensitive and weak relic micro-structures, due to their specific genesis. This study has included the interpretation of a significant volume of in situ test results, triaxial tests over undisturbed samples and monitoring data, giving rise to specific correlations between testing and design parameters. Real time monitoring enabled a back-analysis by FEM of a well instrumented section of the strutted excavation, which was calibrated taking into account the derived correlations and the deformability behavior of this specific geotechnical ambient. This geomaterial, although revealing very high initial stiffness values (for very small strain ranges) has shown low stiffness values for “medium to high” strain levels, reflecting a singular strong non-linearity in the stress-strain behavior. 相似文献
35.
Rita Loidl Josef Hron Susanne Höfner Uffe G. ørgensen Bernhard Aringer Franz Kerschbaum 《Astrophysics and Space Science》1997,251(1-2):243-246
Exploratory synthetic spectra were computed for carbon-rich long-period variables. We used dynamic model atmospheres of Höfner &; Dorfi (1997) and calculated partial pressures, absorption- and scattering coefficients as input for the spectral synthesis code of Jørgensen et al. (1992). First ISO SWS-observations of the carbon-Mira T Dra are compared with our synthetic spectra. 相似文献
36.
Mark S. Fonseca Joseph C. Zieman Gordon W. Thayer John S. Fisher 《Estuarine, Coastal and Shelf Science》1983,17(4):367-380
Measurements of velocity profiles, bathymetry, and surface sediment characteristics across eelgrass (Zostera marina L.) meadows yielded information on community development processes and functional attributes of this ecosystem. Height/length ratios of the meadows were positively correlated with tidal current velocity. Low, medium, and high current regimes were separated by surface current velocities of approximately 50 and 90 cm s?1. Z. marina can tolerate approximately 120–150 cm/sec current velocities in the areas studied. Per cent silt-clay and organic matter content of the surface sediments are negatively associated with shear velocity, suggesting that meadows in high current areas are sources while meadows in low current areas are sinks of autochthonous detritus. Current velocity maintains seagrass meadows at different equilibrium levels (relative climaxes). We theorize these different equilibrium levels provide unequal habitat utilization potentials for the associated faunal community. 相似文献
37.
The atmospheres and circumstellar envelopes of AGB stars are characterized by complex physical phenomena like shock waves
caused by stellar pulsation or formation of molecules and dust which often lead to a heavy mass loss and have a strong influence
on IR properties as observed by ISO. To allow a physical interpretation of various observations we have constructed improved
dynamical model atmospheres of long-period variables. In this contribution we mainly investigate the dependence of the atmospheric
structure and its variability on stellar pulsation, molecular opacities and time-dependent dust formation. IR spectra resulting
from our models are discussed in detail by Loidl et al. (1997b) and compared to ISO-SWS spectra obtained by Hron et al. (1997).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
Carvalho S Gaspar MB Moura A Vale C Antunes P Gil O da Fonseca LC Falcão M 《Marine pollution bulletin》2006,52(11):1414-1424
This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system. 相似文献
39.
40.
Giovana M. de Espindola Ana Paula D. de AguiarEdzer Pebesma Gilberto CâmaraLeila Fonseca 《Applied geography (Sevenoaks, England)》2012,32(2):240-252
The potential impact of deforestation in the Brazilian Amazon on greenhouse gas emissions to the atmosphere calls for policies that take account of changes in forest cover. Although much research has focused on the location and effects of deforestation, little is known about the distribution and reasons for the agricultural uses that replace forest cover. We used Landsat TM-based deforestation and agricultural census data to generate maps of the distribution and proportion of four major agricultural land uses throughout the Brazilian Amazon in 1997 and 2007. We built linear and spatial regression models to assess the determinant factors of deforestation and those major agricultural land uses - pasture, temporary agriculture and permanent agriculture - for the states of Pará, Rondônia, and Mato Grosso. The data include 30 determinant factors that were grouped into two years (1996 and 2006) and in four categories: accessibility to markets, public policies, agrarian structure, and environment. We found an overall expansion of the total agricultural area between 1997 and 2007, and notable differences between the states of Pará, Rondônia, and Mato Grosso in land use changes during this period. Regression models for deforestation and pasture indicated that determinant factors such as distance to roads were more influential in 1997 than in 2007. The number of settled families played an important role in the deforestation and pasture, the effect was stronger in 2007 than 1997. Indigenous lands were significant in preventing deforestation in high-pressure areas in 2007. For temporary and permanent agricultures, our results show that in 1997 the effect of small farms was stronger than in 2007. The mapped land use time series and the models explain empirically the effects of land use changes across the region over one decade. 相似文献