Effects of recent climate and environmental changes on the ecology of a boreal forest lake in Manitoba,Canada     

Luszczek  C. E.  Medeiros  A. S.  Wolfe  B. B.  Quinlan  R. 《Journal of Paleolimnology》2021,66(1):15-27

Journal of Paleolimnology - Application of paleoenvironmental approaches provides insight into the magnitude and timing of responses to climate warming in aquatic-ecosystems of northern Canada. We...  相似文献   

Cosmo-SkyMed X-band SAR data for classification of ice-free areas and glacier facies on Potter Peninsula,King George Island Antarctica     

André Medeiros de Andrade  Jorge Arigony-Neto  Ulisses Franz Bremer  Roberto Ferreira Machado Michel  Alice César Fassoni-Andrade  Carlos Ernesto Goncalves Reynaud Schaefer 《国际地球制图》2016,31(7):803-812

The climate change phenomena have been influencing terrestrial and glacial ecosystems around the planet. Maritime Antarctica is especially sensitive to these climate variations and over the last 50 years increasing global air temperatures have caused extensive glacial retreat. The objective of this study is to evaluate the potential use of the SAR technology in monitoring the surface dynamics of the Potter Peninsula, King George Island, maritime Antarctica. An image generated by the SAR satellite COSMO-SkyMed, obtained on 2 February 2011, was used to extract the backscattering values of targets on the surface for further processing and classification, using a supervised statistic classifier of maximum likelihood for the determination of the surface classes. The average backscattering of water bodies presented high similarity, which made its separation unattainable. On the other hand, the surface classes’ bare ice and wet snow over the glacier presented distinct average backscattering values, which allowed an efficient and precise classification using only this parameter. The classification process showed satisfactory results for periglacial environments, presenting high fidelity to the field data.  相似文献   

Minette mafic microgranular enclaves and their relationship to host syenites in systems formed at mantle pressures: major and trace element evidence from the Piquiri Syenite Massif, southernmost Brazil     

L. V. S. Nardi  J. Plá Cid  M. F. Bitencourt 《Mineralogy and Petrology》2007,91(1-2):101-116

Summary Mafic microgranular enclaves in the ultrapotassic Piquiri Syenitic Massif (611 ± 1 Ma) in southern Brazil represent a minette magma mingled with a syenitic one, both produced from similar mantle sources and emplaced in a post-collisional setting of Neoproterozoic age. The minette magma is compositionally close to typical minettes and high-SiO₂ lamproites, with relatively high contents of LREE, Cs and Rb. It is slightly silica-undersaturated, ultrapotassic and metaluminous, with K₂O/Na₂O ratios around 2–3, and about 4–7 wt% K₂O. The Piquiri minettes contain K-clinopyroxene and pyrope, which are interpreted to have crystallized under pressures about 5 GPa. Whole-rock and mineral chemistry indicate that the most suitable source for the minette magma is clinopyroxene-phlogopite-apatite-amphibole-sulphide ± garnet mantle veins, under pressures of about 5 GPa and melting temperatures over 1,000 °C. Fractional melting is admitted in order to explain the extremely high Rb, Cs and LREE contents of the minette melt, and is consistent with its estimated rheological behavior. The syenitic host-rock parental magma was produced from a similar source, probably at lower pressures, and the co-mingling probably occurred still at large depth, under pressures around 3 GPa. Rheological and geochemical considerations support a model based on fractional melting of a veined mantle which had been metasomatized during previous (760–700 Ma) ocean-plate consumption. The subduction-related metasomatism in the source is indicated by low LREE/(Nb or Ta) ratios, high Nb/Ta and U/Th ratios, and low Ti contents. The compositional similarity and close spatial and temporal association of minette and syenitic magmas can be explained by their common source region. Compared to typical lamproitic magmatism, the major difference is that the Piquiri minette magmas are derived from a subduction-modified source.  相似文献   

Shrimp U–Pb zircon dating and palynology of bentonitic layers from the Permian Irati Formation, Paraná Basin, Brazil     

Roberto Ventura Santos  Paulo A. Souza  Carlos Jos Souza de Alvarenga  Elton Luiz Dantas  Marcio Martins Pimentel  Claudinei Gouveia de Oliveira  Laury Medeiros de Araújo 《Gondwana Research》2006,9(4):456-463

This paper presents the first SHRIMP zircon age data from bentonitic ash fall layers intercalated with the Irati sedimentary rocks, as well as palynofossils retrieved from the PETROBRAS-Six mine, Paraná State, southern Brazil. The Permian Irati Formation is one the most important oil source horizons within the Paraná Basin, and consists mainly of siltstones, gray claystones, as well as organic-rich claystones intercalated with limestones. Zircon morphology based on cathodoluminescence images includes two different populations: a dominant population of euhedral, prismatic, elongate to acicular grains which are most likely related to an ash fall volcanism; and a population of rounded to large prismatic grains, that were interpreted as detrital grains. SHRIMP analysis performed on the euhedral and prismatic grains revealed an age of ca. 278.4 ± 2.2 Ma (7 points with 95% confidence) interpreted as the crystallization age of the volcanic eruption. Based on this new dating, the Irati Formation should be placed on the Lower Permian (Cisuralian), Artinskian in age, modifying substantially the traditional ages previously attributed to this unit. The palynofossils from this level include key species of the Lueckisporites virkkiae Zone (such as L. virkkiae, L. densicorpus, L. stenotaeniatus, Weylandites lucifer, Alisporites splendens). Typical species of this zone also occur in African and other South American (Argentina) Permian strata, allowing stratigraphical correlations. The origin of the ash falls is not clearly defined. It may be related either to calc-alkaline arc magmatism associated to the Sanrafaelica Orogeny (275 and 250 Ma) or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern Gondwana at ca. 278 My. The dating of this unit is significative to calibrate biostratigraphic schemes along the Paraná Basin, as well as equivalent zones in Gondwana areas, mainly in its Occidental portion.  相似文献   

FOREWORD     

Josef Horálek  Tomá? Fischer  Alena Bou?ková  Petr Jedli?ka 《Studia Geophysica et Geodaetica》2000,44(2):1-5

Foreword

FOREWORD  相似文献   

Nonpoint pollution load in river catchments with different anthropic impacts: a case study in Southern Brazil     

Marielle Medeiros de Souza  Maria do Carmo Cauduro Gastaldini  Glaucia Ghesti Pivetta 《Environmental Earth Sciences》2017,76(24):833

Diffuse or nonpoint source (NPS) pollution results in different pollutant concentrations, which depend on river catchments, land use and precipitation events and may vary along a single event. This study aimed to assess NPS pollution loads of organic matter, nutrients, bacteria and heavy metals in four river catchments associated with different types of land use in Southern Brazil. Cluster analysis was used to identify similarities between basins and main component analysis (PCA) to identify the main variables that characterize diffuse pollution in each basin. The use and occupation of the soil were determinant in the formation of the clusters. The basins with rural characteristics formed one group, whereas the basin with urban characteristic generated another group. PCA suggests that changes in the water quality of the catchments in this study can be explained by organic pollutants and farming activities. The Rancho do Amaral catchment, with 55.8% of native forest, displayed the lowest NPS pollution load for all tested parameters. The Alto da Colina catchment, with the largest urban area and largest agricultural land use (50%), showed the highest NPS for all variables in the study, even though it has the smallest area. The differences in pollutant loads can be attributed to the intense degradation processes associated with anthropic activities, such as urbanization, agricultural activity and the discharge of effluents, which are different for each catchment.  相似文献   

Biochemical responses in farmed mussel Perna perna transplanted to contaminated sites on Santa Catarina Island, SC, Brazil.   总被引：3，自引：0，他引：3  

A C Bainy  E A Almeida  I C Müller  E C Ventura  I D Medeiros 《Marine environmental research》2000,50(1-5):411-416

The effects of contaminants on the biochemical parameters of the intensively farmed mussel Perna perna, are unknown. The aim of this study was to compare biochemical responses in mussels held in clean and contaminated sites in Santa Catarina Island, Brazil. Mussels were transplanted from a farming area, Ratones Grande Island (RGI), to two contaminated sites, Itacorubi (ITAC) and Hercílio Luz Bridge (HLB). A reference group was kept at RGI. After 150 and 180 days of exposure, the digestive glands of the mussels were analyzed for catalase, glucose 6-phosphate dehydrogenase (G6PDH) and glutathione S-transferase (GST) activities. No changes were observed in the catalase activity, in both periods. Low G6PDH activity was observed in mussels transplanted for 150 days at the ITAC site. Increased GST activity was observed in mussels from ITAC and HLG sites after 180 days. These responses are probably related to the augmented discharges of domestic effluents associated with elevated rainfall index.  相似文献   

Temporal and spatial adjustments of channel migration and planform geometry: responses to ENSO driven climate anomalies on the tropical freely‐meandering Aguapeí River,São Paulo,Brazil          下载免费PDF全文

Tainá Medeiros Suizu  Gerald C. Nanson 《地球表面变化过程与地形》2018,43(8):1636-1647

Two reaches of Aguapeí River, a left‐bank tributary of the Paraná River in western São Paulo state, Brazil, were studied with the objective of assessing the role of bend curvature on channel migration in this wet‐tropical system and examining if land‐use changes or ENSO (El Niño Southern Oscillation) driven climate anomalies over nearly half a century have changed migration behaviour and planform geometry. Meander‐bend migration rates and morphometric parameters including meander‐bend curvature, sinuosity, meander wavelength and channel width, were measured and the frequency of bend cutoffs was analysed in order to determine the rate of change of channel adjustment over a 48 year period to 2010. Results show that maximum average channel migration rates occur in bends with curvatures of about 2–3 r_c/w, similar to other previously studied temperate and subarctic freely meandering rivers although not as pronounced and with a tendency to favour tighter curvature. From 1962 to 2010 the Aguapeí River has undergone a significant reduction in sinuosity, a shift from tightly curving to more open bends, an overall decline in channel migration rates, an associated decrease in the frequency of neck‐cutoffs and an overall increase in channel width. As the majority of the drainage basin (96%) was already deforested in 1962, channel form and process changes were, unlike an interpretation for an adjacent river system, not attributed to altered land‐use but rather to a sharp ENSO‐driven increase in the magnitude of peak flow‐discharges of some 32% since 1972. In summary, this research revealed that recent climate and associated flow regime changes are having a pronounced effect on river channel behaviour in the Aguapeí River investigated here. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

The Role of Solar Wind Structures in the Generation of ULF Waves in the Inner Magnetosphere     

L. R. Alves  V. M. Souza  P. R. Jauer  L. A. da Silva  C. Medeiros  C. R. Braga  M. V. Alves  D. Koga  J. P. Marchezi  R. R. S. de Mendonça  R. S. Dallaqua  M. V. G. Barbosa  M. Rockenbach  A. Dal Lago  O. Mendes  L. E. A. Vieira  M. Banik  D. G. Sibeck  S. G. Kanekal  D. N. Baker  J. R. Wygant  C. A. Kletzing 《Solar physics》2017,292(7):92

The plasma of the solar wind incident upon the Earth’s magnetosphere can produce several types of geoeffective events. Among them, an important phenomenon consists of the interrelation of the magnetospheric–ionospheric current systems and the charged-particle population of the Earth’s Van Allen radiation belts. Ultra-low-frequency (ULF) waves resonantly interacting with such particles have been claimed to play a major role in the energetic particle flux changes, particularly at the outer radiation belt, which is mainly composed of electrons at relativistic energies. In this article, we use global magnetohydrodynamic simulations along with in situ and ground-based observations to evaluate the ability of two different solar wind transient (SWT) events to generate ULF (few to tens of mHz) waves in the equatorial region of the inner magnetosphere. Magnetic field and plasma data from the Advanced Composition Explorer (ACE) satellite were used to characterize these two SWT events as being a sector boundary crossing (SBC) on 24 September 2013, and an interplanetary coronal mass ejection (ICME) in conjunction with a shock on 2 October 2013. Associated with these events, the twin Van Allen Probes measured a depletion of the outer belt relativistic electron flux concurrent with magnetic and electric field power spectra consistent with ULF waves. Two ground-based observatories apart in 90^° longitude also showed evidence of ULF-wave activity for the two SWT events. Magnetohydrodynamic (MHD) simulation results show that the ULF-like oscillations in the modeled electric and magnetic fields observed during both events are a result from the SWT coupling to the magnetosphere. The analysis of the MHD simulation results together with the observations leads to the conclusion that the two SWT structures analyzed in this article can be geoeffective on different levels, with each one leading to distinct ring current intensities, but both SWTs are related to the same disturbance in the outer radiation belt, i.e. a dropout in the relativistic electron fluxes. Therefore, minor disturbances in the solar wind parameters, such as those related to an SBC, may initiate physical processes that are able to be geoeffective for the outer radiation belt.  相似文献   

Evaluation of Soil Re-mineralizer from By-Product of Volcanic Rock Mining: Experimental Proof Using Black Oats and Maize Crops     

Ramos  Claudete Gindri  dos Santos de Medeiros  Diego  Gomez  Leandro  Oliveira  Luis Felipe Silva  Schneider  Ivo André Homrich  Kautzmann  Rubens Muller 《Natural Resources Research》2020,29(3):1583-1600

Natural Resources Research - This study was focused on physical, petrographical, mineralogical, and chemical characterization of a volcanic-rock mining by-product (dacite rock), as well as on...  相似文献