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21.
We have studied the petrologic characteristics of sulfide‐metal lodes, polymineralic Fe‐Ni nodules, and opaque assemblages in the CR2 chondrite Graves Nunataks (GRA) 06100, one of the most altered CR chondrites. Unlike low petrologic type CR chondrites, alteration of metal appears to have played a central role in the formation of secondary minerals in GRA 06100. Differences in the mineralogy and chemical compositions of materials in GRA 06100 suggest that it experienced higher temperatures than other CR2 chondrites. Mineralogic features indicative of high temperature include: (1) exsolution of Ni‐poor and Ni‐rich metal from nebular kamacite; (2) formation of sulfides, oxides, and phosphates; (3) changes in the Co/Ni ratios; and (4) carbidization of Fe‐Ni metal. The conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 °C. Opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides, Fe‐rich carbonates, including endmember ankerite, and the sulfide‐silicate‐phosphate scorzalite. We suggest that these materials formed via impact‐driven metamorphism. Mineralogic features indicative of impact metamorphism include (1) the presence of sulfide‐metal lodes; (2) the abundance of polymineralic opaque assemblages with mosaic‐like textures; and (3) the presence of suessite. Initial shock metamorphism probably resulted in replacement of nebular Fe‐Ni metal in chondrules and in matrix by Ni‐rich, Co‐rich Fe metal, Al‐Ti‐Cr‐rich alloys, and Fe sulfides, while subsequent hydrothermal alteration produced accessory oxides, phosphates, and Fe carbonates. An extensive network of sulfide‐metal veins permitted effective exchange of siderophile elements from pre‐existing metal nodules with adjacent chondrules and matrix, resulting in unusually high Fe contents in these objects. 相似文献
22.
M. J. Matias J. M. Marques P. Figueiredo M. J. Basto M. M. Abreu P. M. Carreira C. Ribeiro A. Flambó J. Feliciano E. M. Vicente 《Environmental Geology》2009,56(6):1227-1235
Santa Margarida Military Camp (S.M.M.C.) is the only one Portuguese military training area, including firing ranges for tactical
military manoeuvres of mechanised divisions. For this reason, various negative effects on the environment were expected due
to the military activities, as the Military Camp’s area is classified as a high vulnerability area to pollution of its multilayer
porous aquifers. The aim of this study was to identify and characterise local/regional geochemical impacts caused by the continuing
military training activities performed at S.M.M.C. in the course of 52 years. An overview of the geochemical research issues
as a basis for risk assessment is presented. A special attention has been put on the quality of local and regional surface
waters, shallow groundwaters and groundwaters. Local soils and sediments as well as fragments of shells and bullets were sampled
and analysed. The results so far obtained, indicated that none pollution effects were a consequence of the military training
activities. Till now, the geochemical signatures such as, high levels of K, Cl and NO3 in waters, detected in particular sites, should be faced as tracers of diffuse pollution ascribed to urban waste disposal
and cattle breading. 相似文献
23.
Paulo C. Abreu Marli Bergesch Luis A. Proen?a Carlos A. E. Garcia Clarisse Odebrecht 《Estuaries and Coasts》2010,33(2):554-569
In the shallow microtidal Patos Lagoon estuary, southern Brazil (32° 07′ S–52° 06′ W), chlorophyll a (Chl a) variability was studied at different time scales during the last 25 years (hourly–daily sampling in 1984/1985; weekly sampling
in 1986 and from 1988 to 1990; monthly sampling from 1993 to 2008). Phytoplankton biomass variation seems to be most influenced
by hydrology, which is primarily driven by meteorological factors like wind, rainfall, and evaporation. However, it was observed
that the hydrological driving forces play different roles at different time scales. For instance, short-term Chl a variability is mainly controlled by winds, while long-term changes are related to the freshwater input by rainfall. Significant
correlation was found between the total amount of rain in the year and the mean annual value of Chl a, though this relationship was linear until 1,500 mm of rain per year. After this threshold, mean annual Chl a values dropped significantly, probably due to a washout of the produced biomass from the estuary. Similarly, low rainfall
levels and drought years lead to small phytoplankton biomass due to scarcity of nutrient, mainly silicate, or a possible inhibitory
effect generated by high ammonium concentration. In this sense, large-scale Chl a variability would be related to the El Ni?o-Southern Oscillation climatic anomaly, which influences the rainfall levels in
Southern Brazil, though sampling periodicity has also great influence on this relationship. No Chl a or nutrient enrichment was observed in the estuarine region along the last years, indicating that this estuary is not subject
to an eutrophication process. In contrast, signals of an ongoing oligotrophication are observed, possibly a remote effect
of the eutrophication in the Northern area of the lagoon where the phytoplankton nutrients uptake may act as a biological
filter mechanism. 相似文献
24.
Mônica Cavalcanti Sá de Abreu Paloma de MattosAntonio Domingos Padula 《Ocean & Coastal Management》2011,54(9):658-667
In Brazil, farm shrimp production has remained constant over the last five years but exports have fallen sharply and almost all production is now consumed domestically. This situation exists despite adequate water resources, available labour and climatic conditions which allow three production cycles per year. This paper is based on an assessment of the shrimp industry at a critical time when exports had reached their maximum level and were about to fall precipitously. It examines the reasons for the shrimp export market failure and discusses sustainability challenges for the future. Data were collected through interviews with hatchery, farm and processing plant managers and other stakeholders in Rio Grande do Norte state, the largest Brazilian farmed shrimp producer. It was found that market failure was the result of inadequate industry planning, inappropriate public policy and a lack of coordinated actions among the various shrimp producers and stakeholders. The research demonstrates that sustainable Brazilian shrimp farming will require technological and management improvements, institutional changes and an appropriate environmental and social framework. 相似文献
25.
Carlos G. Massone Angela de L.R. Wagener Henrique Monteiro de Abreu Álvaro Veiga 《Marine pollution bulletin》2013
The aim of this work was to test the efficiency of statistical methods as compared to the traditional diagnostic ratios to improve hydrocarbon source identification in sediments subjected to multiple inputs. Hydrocarbon determination in Guanabara Bay sediments pointed out high degradation and ubiquitous petrogenic pollution through the presence of high unresolved complex mixture. Polycyclic aromatic hydrocarbon (PAHs) ratios suggested pervasive contamination derived from combustion in all sediments and failed discriminating samples despite the specificity of sources in different sampling sites. Principal component analysis (PCA) effectively distinguished the petrogenic imprint superimposed to the ubiquitous combustion contamination, since this technique reduces the influence of PAHs distribution which is common to all samples. PCA associated to multivariate linear regression (MLR) allowed a quantitative assessment of sources confirming predominance of the pervasive contaminant component superimposed to a generalized petrogenic imprint. The pervasive component derives from combustion contributions as well as from differential PAHs degradation. 相似文献
26.
F. R. Martins S. A. B. Silva E. B. Pereira S. L. Abreu 《Meteorology and Atmospheric Physics》2008,99(3-4):169-180
Summary Cloud cover index (CCI) obtained from satellite images contains information on cloud amount and their optical thickness. It is the chief climate
data for the assessment of solar energy resources in most radiative transfer models, particularly for the model BRASIL-SR
that is currently operational at CPTEC. The wide range of climate environments in Brazil turns CCI determination into a challenging activity and great effort has been directed to develop new methods and procedures to improve
the accuracy of these estimations from satellite images (Martins 2001; Martins et al. 2003a; Ceballos et al. 2004). This work
demonstrates the influence of CCI determination methods on estimates of surface solar irradiances obtained by the model BRASIL-SR comparing deviations among
ground data and model results. Three techniques using visible and/or thermal infrared images of GOES-8 were employed to generate
the CCI for input into the model BRASIL-SR. The ground-truth data was provided by the solar radiation station located at Caicó/PE,
in Brazilian Northeast region, which is part of the UNEP/GEF project SWERA (Solar and Wind Energy Resources Assessment). Results
have shown that the application of the bi-spectral techniques have reduced mean bias error up to 66% and root mean square
error up to 50% when compared to the usual technique for CCI determination based on the straightforward determination of month-by-month extremes for maximum and minimum cloud states.
Correspondence: Fernando R. Martins, Brazilian Institute for Space Research (INPE), P.O. Box 515, S?o José dos Campos, 12245-970
S?o Paulo, Brazil 相似文献
27.
Vincent J. Abreu 《Planetary and Space Science》1985,33(9):1049-1055
The theoretical development of a technique to recover velocities measured with a Fabry-Perot interferometer in the presence of scattered light is presented. Simulations are carried out which show that the inversion is effective in recovering actual velocities, especially in instances when the observed brightness is dominated by scattered light. 相似文献
28.
This paper examines the spatial dynamics of urbanism in Rio de Janeiro during the early nineteenth century. Conventional narratives of modernisation fail to capture the complexities of this moment, between 1808 and 1821, when the city replaced Lisbon as the capital of the Portuguese empire. The position of colony and metropolis were inverted, Portuguese absolutism was bolstered by British liberalism, and a market-economy arose alongside the expansion of slavery. As the newly-created imperial capital, Rio felt the effects of these various transformations: the physical boundaries of the city rapidly expanded, its economy diversified and the cultural life of the city was re-shaped. Our aim in this paper is to understand this particular moment of urban transformation as a product of the intersection of global networks of trade, slavery and industrial capitalism. Rather than depicting the historical geography of the city as a passive space for European conquest and expansion, we consider the extent to which its urban dynamics were shaped by a distinct local geography of globalisation. In particular, we examine the interrelated spatialities that are part and parcel of the modernising process. 相似文献
29.
The present study involved determination of the experimental energy receipt partitioning over the tropical Amazon forest. Diurnal variation of net radiation (Q
*), sensible heat flux (Q
H) and latent heat flux (Q
E) is presented. The daytimeQ
E is in phase withQ
* and it is always an important term in the energy balance. The daily averagedQ
E is 59 to 100% of the dailyQ
* whereasQ
H is 5 to 28% at the Amazon forest site (2° 57 S; 59° 57 W) for the sample periods. The results present evidence thatQ
E over the Amazon forest is greater thanQ
* in the afternoon hours. The role of sensible heat advection in maintaining largeQ
E over the forest surface is discussed. Hourly Bowen ratio () values for two campaigns of the Amazon forest micrometeorological experiment are presented. During daylight hours, the differences in are not significant, and exhibit a systematic pattern. The only time that the variation in Bowen ratio increased significantly was at sunrise and sunset when the thermal structure of the air was changing from a strong inversion to lapse and vice versa. The diurnal values changed from –3.50 to 0.85. The mean hourly calculated from values from 07.00 to 16.00 h, varied from 0.05 to 0.85.Diese Studie beschäftigt sich mit der Aufteilung der empfangenen Energie über dem tropischen Amazonasurwald. Es wird der Tagesgang der Strahlungsbilanz (Q
*), des fühlbaren (Q
H) und des latenten Wärmestromes (Q
E) vorgestellt. Während der Tagesstunden istQ
E in Phase mitQ
* und ist immer ein wichtiger Term der Energiebilanz. Das Tagesmittel vonQ
E beträgt 59 bis 100%,Q
H 5 bis 28% des täglichenQ
* an den Meßtagen bei der Amazonasurwaldstation (2° 57 S; 59° 57 W). Die Ergebnisse legen nahe, daß in den NachmittagsstundenQ
E über dem Amazonasurwald größer ist alsQ
*. Die Rolle der Advektion von fühlbarer Wärme zur Aufrechterhaltung des großenQ
E über der Waldoberfläche wird diskutiert. Für zwei Meßkampagnen wurden die stündlichen Bowenverhältnisse () vorgestellt. Während der Tagesstunden ergaben sich keine signifikanten Änderungen von, während bei Sonnenaufgang und -untergang, wenn der thermische Aufbau der Luft von einer starken Inversion zu neutral und umgekehrt wechselt, die Unterschiede deutlich anstiegen. Die Tageswerte von lagen zwischen –3.50 und 0.85. Die Stundenmittel von 7.00 bis 16.00 Uhr schwankten zwischen 0.05 und 0.85.
With 3 Figures 相似文献
With 3 Figures 相似文献
30.
Ion de Abreu Cunha Aroldo Misi Marly Babinski Sundaram Sankara S. Iyer 《Gondwana Research》2007,11(3):382-395
The Neoproterozoic Vazante Group at the western border of the São Francisco Craton, Brazil, hosts the largest Zn–Pb district in South America. Several authors have classified this mineral district as Mississippi Valley-type (MVT), based on the intimate association with carbonates and the epigenetic character of most ore bodies. In this paper, we present 47 new lead isotope data from four deposits located along the 300 km N–S Vazante–Paracatu–Unai linear trend. Pb isotope ratios indicate sources with relatively high U/Pb and Th/Pb ratios. Considering the 206Pb/204Pb and 208Pb/204Pb ratios as indicative parameters for the source, we suggest an upper crustal source for the metals. The small variation on the Pb isotope ratios compared to those observed in the classical MVT deposits, and other geological, fluid inclusion and sulphur isotopic data indicates a metallogenic event of long duration. It was characterized by focused circulation of hydrothermal fluids carrying metals from the basement rocks and from the sedimentary pile. The data obtained are more compatible with an evolution model similar to that of IRISH-type deposits. The existence of three Pb isotopic populations could be the result of regional differences in composition of the source rocks and in the fluid–rock interaction since the mineralization is a long-term process. 相似文献