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181.
182.
Measuring and modeling vertical gradients in suspended sediments in the Solimões/Amazon River
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E. Armijos A. Crave R. Espinoza P. Fraizy A.L.M.R. Dos Santos F. Sampaio E. De Oliveira W. Santini J.M. Martinez P. Autin N. Pantoja M. Oliveira N. Filizola 《水文研究》2017,31(3):654-667
Accurately measuring sediment flux in large rivers remains a challenge due to the spatial and temporal cross‐sectional variability of suspended sediment concentrations in conjunction with sampling procedures that fail to accurately quantify these differences. This study presents a field campaign methodology that can be used to improve the measurement of suspended sediment concentrations in the Amazon River or similarly large rivers. The turbidity signal and Rouse model are together used in this study to define the spatial distribution of suspended sediment concentrations in a river cross‐section, taking into account the different size fractions of the sediment. With this methodology, suspended sediment fluxes corresponding to each sediment class are defined with less uncertainty than with manual samples. This paper presents an application of this methodology during a field campaign at different gauging stations along a 3,000‐km stretch of the Solimões/Amazon River during low water and flood periods. Vertical concentration profiles and Rouse model applications for distinctive sediment sizes are explored to determine concentration gradients throughout a cross‐section of the river. The results show that coupling both turbidity technology and the Rouse model may improve our understanding of the spatial distribution of different sediments fractions sizes in the Solimões/Amazon River. These data are very useful in defining a pertinent monitoring strategy for suspended sediment concentrations in the challenging context of large rivers. 相似文献
183.
Interactions between fresh groundwater and seawater affect significantly the nearshore pore water flow, which in turn influences the fate of nutrients and contaminants in coastal aquifers prior to discharge to the marine environment. Field investigations and numerical simulations were carried out to examine the groundwater dynamics in the intertidal zone of a carbonate sandy aquifer on the tropical island of Rarotonga, Cook Islands. The study site was featured by distinct cross‐shore slope breaks on the beach surface. Measured pore water salinities revealed different distributions under the influences of different beach profiles, inland heads, and tidal oscillations. Fresh groundwater was found to discharge around a beach slope break located in the middle area of the intertidal zone. The results indicate a strong interplay between the slope break beach morphology and tidal force in controlling the nearshore groundwater flow and solute transport. The fresh groundwater discharge location was largely determined by the beach morphology in combination with the tidal force. The nearshore groundwater flow can be very sensitive to beach slope breaks, which induce local circulation and flow instabilities. As slope breaks are a common feature of beaches around the world, these results have important, general implications for future studies of nutrients transport and transformations in nearshore aquifers and associated fluxes via submarine groundwater discharge. 相似文献
184.
Telmo M. Bento dos Santos José M. Munhá Colombo C.G. Tassinari Paulo E. Fonseca 《Journal of South American Earth Sciences》2011,31(2-3):262-278
Elemental and Sr–Nd isotopic data on metatexites, diatexites, orthogneisses and charnockites from the central Ribeira Fold Belt indicate that they are LILE-enriched weakly peraluminous granodiorites. Harker and Th–Hf–La correlation trends suggest that these rocks represent a co-genetic sequence, whereas variations on CaO, MnO, Y and HREE for charnockites can be explained by garnet consumption during granulitic metamorphism.Similar REE patterns and isotopic results of ?Nd565 = ?5.4 to ?7.3 and 87Sr/86Sr565 = 0.706–0.711 for metatexites, diatexites, orthogneisses and charnockites, as well as similar TDM ages between 2.0 and 1.5 Ga are consistent with evolution from a relatively homogeneous and enriched common crustal (metasedimentary) protolith.Results suggest a genetic link between metatexites, diatexites, orthogneisses and charnockites and a two-step process for charnockite development: (a) generation of the hydrated igneous protoliths by anatexis of metasedimentary rocks; (b) continuous high-grade metamorphism that transformed the “S-type granitoids” (leucosomes and diatexites) into orthogneisses and, as metamorphism and dehydration progressed, into charnockites. 相似文献
185.
Luis Ricardo Lage Rodrigues Francisco Javier Doblas-Reyes Caio Augusto dos Santos Coelho 《Climate Dynamics》2014,42(3-4):597-616
Different combination methods based on multiple linear regression are explored to identify the conditions that lead to an improvement of seasonal forecast quality when individual operational dynamical systems and a statistical–empirical system are combined. A calibration of the post-processed output is included. The combination methods have been used to merge the ECMWF System 4, the NCEP CFSv2, the Météo-France System 3, and a simple statistical model based on SST lagged regression. The forecast quality was assessed from a deterministic and probabilistic point of view. SSTs averaged over three different tropical regions have been considered: the Niño3.4, the Subtropical Northern Atlantic and Western Tropical Indian SST indices. The forecast quality of these combinations is compared to the forecast quality of a simple multi-model (SMM) where all single models are equally weighted. The results show a large range of behaviours depending on the start date, target month and the index considered. Outperforming the SMM predictions is a difficult task for linear combination methods with the samples currently available in an operational context. The difficulty in the robust estimation of the weights due to the small samples available is one of the reasons that limit the potential benefit of the combination methods that assign unequal weights. However, these combination methods showed the capability to improve the forecast reliability and accuracy in a large proportion of cases. For example, the Forecast Assimilation method proved to be competitive against the SMM while the other combination methods outperformed the SMM when only a small number of forecast systems have skill. Therefore, the weighting does not outperform the SMM when the SMM is very skilful, but it reduces the risk of low skill situations that are found when several single forecast systems have a low skill. 相似文献
186.
Simona Petrosino Paola Cusano Mario La Rocca Danilo Galluzzo Justo Orozco-Rojas Mauricio Bretón Jesus Ibáñez Edoardo Del Pezzo 《Bulletin of Volcanology》2011,73(7):887-898
This paper presents an analysis of seismicity associated with the volcanic activity of Volcàn de Colima (México) and recorded
in the period November 2005–April 2006 during a field survey by the Istituto Nazionale di Geofisica e Vulcanologia (INGV)–Osservatorio
Vesuviano, the Observatorio Vulcanologico de Colima of Colima University and the Instituto Andaluz de Geofisica, University
of Granada. Three different types of volcanic earthquakes have been identified on the basis of their spectral properties:
Type A (0.3–1 Hz), Type B (1–5 Hz) and Type C (3–4 Hz). Results of polarization analysis applied to Type A events show a predominance
of radial motion, indicating that the wavefield comprises compressional waves (P) and shear waves polarized in the vertical
plane (SV), while the signal always begins with a negative polarity. Type A, B and C earthquakes have been located using both
a flat layered model and a 3D model including topography. Hypocentre distributions indicate that the source of Type A signals
is very shallow and confined to a small volume lying about 1 km below the crater. In contrast, the source of Type B and C
events is significantly deeper, with most hypocentres located in a volume of about 1 km3 centred at 2.5–3 km depth. A cluster analysis based on the cross-correlation among the waveforms of different events recorded
at the same station was applied to Type A earthquakes. Only two clusters, which include only a small percentage of events
were found, indicating that earthquake families were uncommon during the period of our survey. 相似文献
187.
Carmela Freda Mario Gaeta Biagio Giaccio Fabrizio Marra Danilo M. Palladino Piergiorgio Scarlato Gianluca Sottili 《Bulletin of Volcanology》2011,73(3):241-256
Generally, the intensity and magnitude of explosive volcanic activity increase in parallel with SiO2 content. Pyroclastic-flow-forming eruptions in the Colli Albani ultrapotassic volcanic district (Italy) represent the most
striking exception on a global scale, with volumes on the order of tens of cubic kilometres and K-foiditic compositions (SiO2 even <42 wt.%). Here, we reconstruct the pre-eruptive scenario and event dynamics of the ~456 ka Pozzolane Rosse (PR) eruption,
the largest mafic explosive event of the Colli Albani district. In particular, we focus on the driving mechanisms for the
unusually explosive eruption of a low-viscosity, mafic magma. Geologic, petrographic and geochemical data with mass balance
calculations, supported by experimental data for Colli Albani magma compositions, provide evidence for significant ingestion
of carbonate wall rocks by the Pozzolane Rosse K-foiditic magma. Moreover, the scattered occurrence of cored bombs in Pozzolane
Rosse pyroclastic-flow deposits records carbonate entrainment even at the eruptive time scale, as also tested quantitatively
by thermal modelling of magma–carbonate interaction and carbonate assimilation experiments. We suggest that the addition of
free CO2 from decarbonation of country rocks was the major factor controlling magma explosivity. High CO2 activity in the volatile component, coupled with magma depressurisation, produced extensive leucite crystallisation at short
time scales, resulting in a dramatic increase in magma viscosity and volatile pressurisation, which was manifested a change
of eruptive dynamics from early effusion to the Pozzolane Rosse's highly explosive eruption climax. 相似文献
188.
Jaime A. Santos Pedro Chitas Isabel Lopes Carlos Sousa Oliveira Isabel Moitinho de Almeida João Carlos Nunes 《Soil Dynamics and Earthquake Engineering》2011
The Azores archipelago is located at the North America, Eurasia and Africa triple junction and shows seismicity and volcanism typical of an active plate boundary. Terceira Island has been affected by several damaging earthquakes being the 1980 January 1st event (M=7.2) the strongest in Azores during the last century. 相似文献
189.
The inter-annual variability of the sea surface temperature (SST) was analyzed along the western Iberian Peninsula in the region ranging from 9.5 °W to 21.5 °W and from 37.5 °N to 42.5 °N with a spatial resolution of 1°×1° from 1900 to 2008. Both coastal and oceanic SST showed an overall increase with warming and cooling cycles similar to those observed in the North Atlantic region and in previous regional studies. In addition, the evolution of coastal and ocean water has been observed to be different. In general, ocean water is more affected by the different warming–cooling cycles than coastal water. In spite of coast and ocean are highly influenced by global changes affecting the whole North Atlantic region, near shore SST has been observed to be correlated with local wind regime, which is itself a manifestation of the Eastern Atlantic (EA) teleconnection pattern. 相似文献
190.
David Lopes de Castro Nilo Costa Pedrosa Jr.Fernando Acácio Monteiro Santos 《Journal of Applied Geophysics》2011,75(3):431-443
A joint inversion of gravity and geoelectrical data has been performed along a 100 km long profile across the oil-bearing Potiguar rift basin in NE Brazil. The integrated approach is based on the connection between density and resistivity of a sedimentary sequence through the porosity. Seventy-one gravity stations and twenty-nine vertical electrical soundings were carried out across the central part of the Early Cretaceous basin in the Precambrian Borborema Province to apply the proposed joint inversion. Both the physical properties and geometry of the multilayer deep model were well constrained by a wide set of prior information obtained by surface mapping, geophysical logs and seismic sections. The results reveal a rift architecture formed by a 5000 m thick half-graben structure separated by an intervening basement high and an extensive adjacent platform with a sedimentary infill of about 300 m thick. The calculated model shows geometries for the sedimentary density/resistivity interfaces in agreement with the seismostratigraphic sequences revealed by seismic section, representing a substantial improvement in comparison with previously published gravity models. 相似文献