Elemental composition of sediment cores from a mangrove environment using neutron activation analysis     

Julio Cesar Wasserman  Ana Maria G Figueiredo  Fabio Pellegatti  Emmanoel V Silva-Filho 《Journal of Geochemical Exploration》2001,72(2):1013

The geochemistry of Sepetiba Bay was studied in four sediment cores using a multi-element approach. Two cores were sampled in the more contaminated eastern part of the bay and two cores were sampled in the western region. The aim was to determine whether less common elements like the rare earths or the actinides are associated with contaminant metals like zinc in the Bay. Samples were analysed by instrumental neutron activation analysis that permits the quantification of total concentrations of metals (Ba, Co, Cr, Cs, Fe, Hf, Rb, Sc, Zn), rare earth elements (Ce, Eu, La, Lu, Sm and Yb), actinides (Th, U), non-metals and semi-metals (As, Br). Organic carbon and total sulphur were also analysed. The results show very strong zinc contamination in the top layers (more than 1000 μg g⁻¹) and background concentrations in the bottom (15 μg g⁻¹). Elements like chromium which would be expected to be released by the heavy industries of Sepetiba Bay, did not show a contamination profile, and concentrations remained close to those of natural environments. No evidence of any association between the zinc and other potential contaminant elements could be identified in this work.  相似文献   

New Constraints on Ages of Glasses Proposed as Reference Materials for Fission-Track Dating     

Marinella A. Laurenzi  Maria Laura Balestrieri  Giulio Bigazzi  Julio C. Hadler Neto  Pedro J. Iunes  Pio Norelli  Massimo Oddone  Ana Maria Osorio Araya  José G. Viramonte 《Geostandards and Geoanalytical Research》2007,31(2):105-124

New analyses have been performed in order to enhance the data-set on the independent ages of four glasses that have been proposed as reference materials for fission-track dating. The results are as follows. Moldavite - repeated ⁴⁰Ar/³⁹Ar age determinations on samples from deposits from Bohemia and Moravia yielded an average of 14.34 ± 0.08 Ma. This datum agrees with other recent determinations and is significantly younger than the ⁴⁰Ar/³⁹Ar age of 15.21 ± 0.15 Ma determined in the early 1980s. Macusanite (Peru) -four K-Ar ages ranging from 5.44 ± 0.06 to 5.72 ± 0.12 Ma have been published previously. New ⁴⁰Ar/³⁹Ar ages gave an average of 5.12 ± 0.04 Ma. Plateau fission-track ages determined using the IRMM-540 certified glass and U and Th thin films for neutron fluence measurements agree better with these new ⁴⁰Ar/³⁹Ar ages than the previously published ages. Roccastrada glass (Italy) - a new ⁴⁰Ar/³⁹Ar age, 2.45 ± 0.04 Ma, is consistent with previous determinations. The Quiron obsidian (Argentina) is a recently discovered glass that has been proposed as an additional reference material for its high spontaneous track density (around 100 000 cm^-2). Defects that might produce "spurious" tracks are virtually absent. An independent ⁴⁰Ar/³⁹Ar age of 8.77 ± 0.09 Ma was determined and is recommended for this glass. We believe that these materials, which will be distributed upon request to fission-track groups, will be very useful for testing system calibrations and experimental procedures.  相似文献   

A comparison of low-latitude cloud properties and their response to climate change in three AGCMs sorted into regimes using mid-tropospheric vertical velocity     

Matthew C. Wyant  Christopher S. Bretherton  Julio T. Bacmeister  Jeffrey T. Kiehl  Isaac M. Held  Ming Zhao  Stephen A. Klein  Brian J. Soden 《Climate Dynamics》2006,27(2-3):261-279

Low-latitude cloud distributions and cloud responses to climate perturbations are compared in near-current versions of three leading U.S. AGCMs, the NCAR CAM 3.0, the GFDL AM2.12b, and the NASA GMAO NSIPP-2 model. The analysis technique of Bony et al. (Clim Dyn 22:71–86, 2004) is used to sort cloud variables by dynamical regime using the monthly mean pressure velocity ω at 500 hPa from 30S to 30N. All models simulate the climatological monthly mean top-of-atmosphere longwave and shortwave cloud radiative forcing (CRF) adequately in all ω-regimes. However, they disagree with each other and with ISCCP satellite observations in regime-sorted cloud fraction, condensate amount, and cloud-top height. All models have too little cloud with tops in the middle troposphere and too much thin cirrus in ascent regimes. In subsidence regimes one model simulates cloud condensate to be too near the surface, while another generates condensate over an excessively deep layer of the lower troposphere. Standardized climate perturbation experiments of the three models are also compared, including uniform SST increase, patterned SST increase, and doubled CO₂ over a mixed layer ocean. The regime-sorted cloud and CRF perturbations are very different between models, and show lesser, but still significant, differences between the same model simulating different types of imposed climate perturbation. There is a negative correlation across all general circulation models (GCMs) and climate perturbations between changes in tropical low cloud cover and changes in net CRF, suggesting a dominant role for boundary layer cloud in these changes. For some of the cases presented, upper-level clouds in deep convection regimes are also important, and changes in such regimes can either reinforce or partially cancel the net CRF response from the boundary layer cloud in subsidence regimes. This study highlights the continuing uncertainty in both low and high cloud feedbacks simulated by GCMs.  相似文献   

Increasing Aridity is Enhancing Silver Fir Abies Alba Mill.) Water Stress in its South-Western Distribution Limit     

Marc Macias  Laia Andreu  Oriol Bosch  J. Julio Camarero  Emilia Gutiérrez 《Climatic change》2006,79(3-4):289-313

Tree populations located at the geographical distribution limit of the species may provide valuable information about the response of tree growth to climate warming across climatic gradients. Dendroclimatic information was extracted from a network of 10 silver-fir (Abies alba) populations in the south-western distribution limit of the species (Pyrenees, NE Iberian Peninsula). Ring-width chronologies were built for five stands sampled in mesic sites from the Main Range in the Pyrenees, and for five forests located in the southern Peripheral Ranges where summer drought is more pronounced. The radial growth of silver-fir in this region is constrained by water stress during the summer previous to growth, as suggested by the negative relationship with previous September temperature and, to a lesser degree, by a positive relationship with previous end of summer precipitation. Climatic data showed a warming trend since the 1970s across the Pyrenees, with more severe summer droughts. The recent warming changed the climate-growth relationships, causing higher growth synchrony among sites, and a higher year-to-year growth variation, especially in the southernmost forests. Moving-interval response functions suggested an increasing water-stress effect on radial growth during the last half of the 20th century. The growth period under water stress has extended from summer up to early autumn. Forests located in the southern Peripheral Ranges experienced a more intense water stress, as seen in a shift of their response to precipitation and temperature. The Main-Range sites mainly showed a response to warming. The intensification of water-stress during the late 20th century might affect the future growth performance of the highly-fragmented A. alba populations in the southwestern distribution limit of the species.  相似文献   

Phylogeny, diet, and habitat of an extinct ground sloth from Cuchillo Curá, Neuquén Province, southwest Argentina     

Michael Hofreiter  Julio L. Betancourt  Alicia Pelliza Sbriller  Vera Markgraf  H. Gregory McDonald 《Quaternary Research》2003,59(3):364-378

Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.  相似文献   

Cu and Fe associated with humic acids in sediments of a tropical coastal lagoon   总被引：1，自引：0，他引：1  

Julio Cesar Wasserman  Fernanda B. L. Oliveira  Mnica Bidarra 《Organic Geochemistry》1998,28(12):813-822

The amount of Cu and Fe associated with humic acids was estimated in five sediment cores from a tropical coastal lagoon (Piratininga Lagoon, Rio de Janeiro, Brazil). Core samples were analysed for humic acid contents, total Fe and Cu content. Fe and Cu associated with humic acids were also measured. Results show amounts of humic acids ranging from 0.7 to 21.7% of the dry weight of sediment (average 4.6%, standard deviation 4.4%). Concentrations of Fe and Cu ranged from 0.3 to 6.0% (average 2.2%, S.D. 1.2%) and from <1.0 to 65.0 μg g⁻¹ (average 28.6 μg g⁻¹, S.D. 16.4 μg g⁻¹), respectively. The results of strongly bound metals show that while humic acids are the main carrier for Cu, Fe does not seems to be significantly associated with this organic matter.  相似文献   

Response to three‐component seismic motion of arbitrary direction     

Julio J. Hernndez  Oscar A. Lpez 《地震工程与结构动力学》2002,31(1):55-77

This paper presents a response spectrum analysis procedure for the calculation of the maximum structural response to three translational seismic components that may act at any inclination relative to the reference axes of the structure. The formula GCQC3, a generalization of the known CQC3‐rule, incorporates the correlation between the seismic components along the axes of the structure and the intensity disparities between them. Contrary to the CQC3‐rule where a principal seismic component must be vertical, in the GCQC3‐rule all components can have any direction. Besides, the GCQC3‐rule is applicable if we impose restrictions to the maximum inclination and/or intensity of a principal seismic component; in this case two components may be quasi‐horizontal and the third may be quasi‐vertical. This paper demonstrates that the critical responses of the structure, defined as the maximum and minimum responses considering all possible directions of incidence of one seismic component, are given by the square root of the maximum and minimum eigenvalues of the response matrix R , of order 3×3, defined in this paper; the elements of R are established on the basis of the modal responses used in the well‐known CQC‐rule. The critical responses to the three principal seismic components with arbitrary directions in space are easily calculated by combining the eigenvalues of R and the intensities of those components. The ratio r_max/r_SRSS between the maximum response and the SRSS response, the latter being the most unfavourable response to the principal seismic components acting along the axes of the structure, is bounded between 1 and √(3γ_a²/(γ_a² + γ_b² + γ_c²)), where γ_a?γ_b?γ_c are the relative intensities of the three seismic components with identical spectral shape. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Relatively short-term correlation among deformation,degassing, and seismicity: a case study from Concepción volcano,Nicaragua   总被引：1，自引：0，他引：1  

José Armando Saballos  Vladimir Conde  Rocco Malservisi  Charles B. Connor  Julio Álvarez  Angélica Muñoz 《Bulletin of Volcanology》2014,76(8):1-11

Concepción is a frequently active composite volcano in Nicaragua, and is located on Ometepe Island, within Lake Nicaragua. Significant eruptive activity took place at this volcano between March and May 2010, consisting of ash and gas explosions (VEI 1–2). We compare geodetic baseline changes observed with global positioning system (GPS), sulfur dioxide flux (SO₂), and seismic amplitude (SAM) data collected at Concepción during April – June, 2010, and February – April, 2011. Time series analysis reveals a remarkable correlation among the data sets during 2010, when the volcano was erupting. In contrast, the volcano was at its background level of activity in 2011 and the statistical correlation among the time series is not significant for this period. We explain the emergence of correlation among the time series during eruptive activity through modeling of the GPS data with emplacement of a magma column in an open conduit. In the model, magma rose in the conduit, between May 5 and 14, 2010, from a shallow reservoir located at ～ 1.8 km depth. Later, between May 24 and 31, 2010, the top of the magma column descended to almost 600 m depth, corresponding to the cessation of eruptive activity. Thus, cross-correlation and an integrated analysis of these geophysical time series on a timescale of days helps to reveal the dynamics of the magma plumbing system operating below Concepción volcano.  相似文献   

Metal concentrations, fluxes, inventories and chronologies in sediments from Sepetiba and Ribeira Bays: A comparative study     

Franciane de Carvalho Gomes  Jos Marcus Godoy  Maria Luiza D.P. Godoy  Zenildo Lara de Carvalho  Ricardo Tadeu Lopes  Joan Albert Sanchez-Cabeza  Luiz Drude de Lacerda  Julio Cesar Wasserman 《Marine pollution bulletin》2009,59(4-7):123

Three sediment cores were sampled at Sepetiba Bay and four cores at Ribeira Bay, Rio de Janeiro State, Brazil. Sediment accumulation rates and chronologies were obtained from ²¹⁰Pb activity-depth profiles. Sediment accumulation rates in Ribera Bay ranged from 1.2 mm y⁻¹ in the inner bay to 2.6 mm y⁻¹ close to its entrance. In Sepetiba Bay two sediment accumulation rates were observed: a lower rate of 0.35 cm y⁻¹ before the 1960s and 0.76 cm y⁻¹ since then. The cause of this change is due to the construction of the Santa Cecília impoundment (1955) that brings water from the Paraíba do Sul Basin into the Guandu River, which increased its flow from the original 20 m³ s⁻¹ to 160 m³ s⁻¹. Concentration of 44 elements was obtained by ICP-MS after total dissolution of samples from two selected cores. The relative differences between the concentrations of crustal elements, such as Al, Fe and Ti are only about 20% (p < 0.05). Cd and Zn are 15 and four times larger in Sepetiba Bay than in Ribeira Bay, respectively. Other major and minor elements show lower statistically significant differences. The enrichment factors and metal inventories show that Sepetiba Bay can be considered polluted with Bi, Cd, Cr, Cu, Sb and Zn. Particularly, Cd and Zn present concentrations three and four times higher than the Brazilian existing limits.  相似文献   

Increase of nitrous oxide flux to the atmosphere upon nitrogen addition to red mangroves sediments   总被引：6，自引：0，他引：6  

Muñoz-Hincapié M  Morell JM  Corredor JE 《Marine pollution bulletin》2002,44(10):992-996

Response of nitrous oxide N20 sediment/air flux to nitrogen addition was assessed in mangrove (Rhizophora mangle) sediments. Fluxes were enhanced with both ammonium and nitrate loading. Greatest fluxes (52 micromol m(-2) h(-1)) were obtained with ammonium addition and saturation was achieved with additions of 0.9 mol m(-2). Maximum flux following ammonium addition was 2785 times greater than control plots and 4.5 times greater during low tide than with equivalent ammonium addition at high tide. Nitrate enrichment resulted in exponential growth, with maximal mean flux of 36.7 micromolm(-2) h(-1) at 1.9 molm(-2); saturation was not achieved. Differential response to ammonium and nitrate, and to tide and elevation, indicate that microbial nitrification is responsible for most of the observed gas flux. Mangrove sediments constitute an important source of global atmospheric N20 and increases in nitrogen loading will lead to significant increases in the flux of this atmospherically active gas.  相似文献