Temperature and distribution of radioactive matter in the upper mantle     

F. Machado 《Bulletin of Volcanology》1968,32(2):403-413

Temperatures of the Earth’s upper mantle, derived from Gutenberg’s seismic velocities, have been revised, using some recent determinations of the clastic constants of dunites. For depths greater than about 50 km the temperature obtained is sufficient to melt the basaltic fraction of a periodotitic mantle (if this low-melting fraction still exists at those depths). The distribution of the radioactive heat sources appears to be fairly uniform down to about 110 km; below this level the radioactive matter is probably absent. This is what would be expected for the upper mantle below the oceans; therefore, Gutenberg’s velocities seem to correspond to oceanic areas, rather than to the mantle below a continental shield.  相似文献   

Pelagic processes and vertical flux of particles: an overview of a long-term comparative study in the Norwegian Sea and Greenland Sea     

B. von Bodungen  A. Antia  E. Bauerfeind  O. Haupt  W. Koeve  E. Machado  I. Peeken  R. Peinert  S. Reitmeier  C. Thomsen  M. Voss  M. Wunsch  U. Zeller  B. Zeitzschel 《International Journal of Earth Sciences》1995,84(1):11-27

Pelagic processes and their relation to vertical flux have been studied in the Norwegian and Greenland Seas since 1986. Results of long-term sediment trap deployments and adjoining process studies are presented, and the underlying methodological and conceptional background is discussed. Recent extension of these investigations at the Barents Sea continental slope are also presented. With similar conditions of input irradiation and nutrient conditions, the Norwegian and Greenland Seas exhibit comparable mean annual rates of new and total production. Major differences can be found between these regions, however, in the hydrographic conditions constraining primary production and in the composition and seasonal development of the plankton. This is reflected in differences in the temporal patterns of vertical particle flux in relation to new production in the euphotic zone, the composition of particles exported and in different processes leading to their modification in the mid-water layers.In the Norwegian Sea heavy grazing pressure during early spring retards the accumulation of phytoplankton stocks and thus a mass sedimentation of diatoms that is often associated with spring blooms. This, in conjunction with the further seasonal development of zooplankton populations, serves to delay the annual peak in sedimentation to summer or autumn. Carbonate sedimentation in the Norwegian Sea, however, is significantly higher than in the Greenland Sea, where physical factors exert a greater control on phytoplankton development and the sedimentation of opal is of greater importance. In addition to these comparative long-term studies a case study has been carried out at the continental slope of the Barents Sea, where an emphasis was laid on the influence of resuspension and across-slope lateral transport with an analysis of suspended and sedimented material.  相似文献   

Perceptions of climate and ocean change impacting the resources and livelihood of small-scale fishers in the South Brazil Bight     

Ivan Machado Martins  Maria A. Gasalla 《Climatic change》2018,147(3-4):441-456

Coastal fishing communities are closely linked to the biological and ecological characteristics of exploited resources and the physical conditions associated with climate and ocean dynamics. Thus, the human populations that depend on fisheries are inherently exposed to climate variability and uncertainty. This study applied an ethno-oceanographic framework to investigate the perceptions of fishers on climate and ocean change to better understand the impacts of climate change on the coastal fishing communities of the South Brazil Bight. Seven coastal fishing communities that cover the regional diversity of the area were selected. Fishers were interviewed using a semi-structured questionnaire. The results suggest that fishers have detected climate-related changes in their environment such as reduced rainfall, increased drought events, calmer sea conditions, increases in air and ocean temperatures, changes in wind patterns and shoreline erosion. The perceptions of the fishers were compared to the available scientific data, and correlations were found with rainfall, wind speed and air and ocean temperatures. New hypotheses were raised based on the perceptions of fishers about sea level, coastal currents and sea conditions such as the hypothesis that the sea has become calmer. These perceived changes have positive and negative effects on the yields and livelihoods of fishers. The present work is the first evaluation of the perceptions of fishers on climate and ocean change and brings new understandings of climate-fishery-human interactions as well as provides inputs for future adaptation plans.  相似文献   

Hard X-ray imaging evidence of nonthermal and thermal burst components     

Marcos E. Machado  Marta G. Rovira  Cora V. Sneibrun 《Solar physics》1985,99(1-2):189-217

We analyze hard X-ray imaging observations of three flares, showing widely different characteristics, in order to try and discriminate the relative efficiency of heating and acceleration in the primary energy release. Using a simplified approach, we compute the hard X-ray distribution and energy deposition due to accelerated electrons, with beam and ambient plasma parameters appropriate for each of the observed events. The results are convolved with the Hard X-Ray Imaging Spectrometer (HXIS) instrumental response and compared with observations. We find that: (a) Many observations are compatible with thick target processes, and with the possibility that flares may have high (>20%) acceleration efficiency. (b) Single hard X-ray sources should be very common in the data available at present (HXIS and HINOTORI), as it is the case, as well as a transition from chromospheric footpoints to single source structures. The latter cannot then be directly interpreted as thermal sources. (c) In the particular case of a limb flare, associated with a rather weak high energy burst, we show that the spatial and spectral behavior of the hard X-ray emission is incompatible with pure nonthermal processes. We thus propose that the observed emission was principally due to the strong heating intrinsic to a reconnection process within the region of interaction between two magnetic structures which are seen in the soft X-ray data. (d) We also study the heating effect of a beam, due to Coulomb losses, during its passage through the flare loops. In some cases, rather large and localized temperature increases can be expected to appear within short timescales ( 1 s), leading to a combination of nonthermal plus thermal output in the hard X-ray spectrum, which renders virtually impossible the determination of the underlying beam parameters. We finally discuss the extent to which our conclusions are valid, considering the instrumental limitations as well as the simple physical treatment that we apply.  相似文献   

Predictive Mapping of Prospectivity in the Gurupi Orogenic Gold Belt,North–Northeast Brazil: An Example of District-Scale Mineral System Approach to Exploration Targeting     

Leandro Duarte Campos  Sulsiene Machado de  Souza  Diogo Alves de  Sordi  Felipe Mattos Tavares  Evandro Luiz Klein  Elem Cristina dos Santos Lopes 《Natural Resources Research》2017,26(4):509-534

The Gurupi Belt hosts a Paleoproterozoic gold province located in north–northeastern Brazil, at the borders of Pará and Maranhão states. It is considered to be an extension of the prolific West African Craton’s Birimian gold province into South America. Additionally, the belt has been the object of recent mineral exploration programs with significant resource discoveries. This study presents the results of predictive mapping using up-to-date mineral system concepts and recently finished regional-scale geological mapping, stream sediment and airborne geophysical surveys conducted by the Geological Survey of Brazil. We relate gold mineralization to an initially enriched crust, metamorphism, deep fluid pathways, structurally controlled damage zones and hydrothermal alteration. Prospective targets were generated using only regional public datasets and knowledge-driven targeting technique. This work did not incorporate any known gold deposits, yet it predicted the largest known deposits and their satellite targets. Besides, high prospective targets mapped almost 40% of known primary gold occurrences within 7% of the project area. This work allowed considerable search area reduction and identification of new target areas, thus collaborating on reducing costs, time and risk of mineral exploration. Results indicate that we achieved an efficient understanding of the geological processes related to the Gurupi Belt mineral system.  相似文献   

Hydrological systems from the Antarctic Peninsula under climate change: James Ross archipelago as study case     

Karina L. Lecomte  Paula A. Vignoni  Francisco E. Córdoba  Marcos A. E. Chaparro  Mauro A. E. Chaparro  Kateřina Kopalová  José D. Gargiulo  Juan M. Lirio  María A. Irurzun  Harald N. Böhnel 《Environmental Earth Sciences》2016,75(7):623

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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   

The Signatures of Structured Winds in T Tauri Stars     

Maria Teresa V.T. Lago  Jorge F. Gameiro  Vitor M. Costa  Leandro Machado  António Pedrosa 《Astrophysics and Space Science》1998,261(1-4):107-116

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SERMIN1 and VIDAC18: Two Proposed Reference Materials for Rare Earth Element Determination in Groundwater     

Rui Santos  M.J. Canto Machado  Leopoldo Cortez 《Geostandards and Geoanalytical Research》2008,32(2):181-191

In this work, homogeneous samples of two Portuguese mineral waters, SERMIN1 and VIDAC18, have been analysed for their REE contents. The participation of twenty international laboratories made it possible to evaluate the data by robust statistical procedures. Eighty-one percent of the participants used ICP-QMS for REE determination in these two candidate reference materials. Assigned values are reported for SERMIN1, covering the fourteen naturally occurring lanthanides (La-Lu). For VIDAC18, assigned values are presented only for ten REE, since accurate assigned values for La, Ce, Tb and Eu need further analytical work to improve data quality.  相似文献   

Amazonian climate: results and future research   总被引：1，自引：0，他引：1  

J. H. C. Gash  C. Huntingford  J. A. Marengo  R. A. Betts  P. M. Cox  G. Fisch  R. Fu  A. W. Gandu  P. P. Harris  L. A. T. Machado  C. von Randow  M. A. Silva Dias 《Theoretical and Applied Climatology》2004,78(1-3):187-193

Summary Some of the results from the climate component of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), which are presented in this Special Issue are summarised. Recent advances in Amazonian climate modelling are also discussed. There is a range of papers which fall into three groups: surface fluxes and boundary layer growth; convection, clouds and rainfall; and climate modelling. The new insight given by this work is discussed and an argument is made for future research to employ a wider approach to Amazonian climate modelling.  相似文献