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101.
Adriana Gioda Olga L. Mayol-Bracero Gabriel J. Reyes-Rodriguez Gilmarie Santos-Figueroa Jeffrey L. Collett Jr. 《Journal of Atmospheric Chemistry》2008,61(2):85-99
Chemical characterization was performed on cloud and rainwater samples collected as part of the Rain In Cumulus over the Ocean Experiment (RICO). This experiment took place at a mountaintop site (East Peak) in Puerto Rico from December 2004 to March 2007 in order
to determine water-soluble organic and nitrogen fractions in a marine background environment. For cloud water, similar average
concentrations of 1.0 (±0.3) mg/L were found for total organic carbon (TOC) and total nitrogen (TN) and an average concentration
of 0.8 (±0.2) mg/L was found for dissolved organic carbon (DOC). In rainwater, these concentrations were lower, ranging from
0.3 to 0.5 (±0.1) mg/L. Changes in the concentrations of these species were observed in periods under the influence of anthropogenic,
African dust, and volcanic ash air masses. In these periods the concentrations of TOC, DOC, and TN were 2 to 4 times higher
than in periods under the influence of trade winds. The insoluble organic material arriving during African dust events showed
total carbon (TC) concentrations on averaging 1.5 mg/L for cloud water. The TC was composed mainly of organic carbon with
polar compounds from low to high molecular weight (MW). The polar compounds with high MW were probably associated with pollution
(e.g., fossil fuel combustion) from other regions. Crustal species (Al and Fe) dominated particles associated with dust episodes,
confirming the soil origin. Our results suggested that a fraction (40–80%) of TOC and (<100%) of TN in Puerto Rican cloud/rainwater
could be originated from long-range transport of dust, ash and/or pollution. 相似文献
102.
Marcelo C. L. Cohen Paloma Maria Pinto Camargo Luiz C. R. Pessenda Flávio Lima Lorente Adriana V. De Souza José Augusto Martins Corrêa José Bendassolli Marianne Dietz 《第四纪科学杂志》2021,36(6):1013-1027
The high sea-level stand during the mid-Holocene is a benchmark in mangrove dynamics along the north-east/south-east coast of Brazil and provides a reference point for landward and seaward mangrove migrations corresponding to changes in relative sea level (RSL). However, evidence of the impacts associated with RSL fall on the northern Brazilian coast is scarce. Multi-proxy data from the highest tidal flats of the Bragança Peninsula in northern Brazil revealed modern herbaceous areas were occupied by mangroves Rhizophora and Avicennia from ~6250 to ~5850 cal a bp , and only Avicennia between ~5850 and ~5000 cal a bp . The same tidal flats were vegetation-free between ~5000 and ~4300 cal a bp . A combination of a high sea-level stand (0.6 ± 0.1 m) at ~5000 cal a bp and a dry early–middle Holocene in the Amazon probably caused an increase in porewater salinity of tidal flats, which resulted in a mangrove succession from Rhizophora to Avicennia dominance. RSL fall accentuated this process, contributing to mangrove degradation between ~5000 and ~4300 cal a bp . RSL fall, and a wetter period over the past ~4300 cal a bp caused a mangrove migration from highest to lowest flats, followed by expansion of herbaceous vegetation on the highest flats. 相似文献
103.
Ofelia Tófalo María Julia Orgeira Rosa Compagnucci María Susana Alonso Adriana Ramos 《Journal of South American Earth Sciences》2011,31(1):81-92
A new record of the Marine Isotopic Stage 5, the last Interglacial Stage before present is presented in this paper. Sedimentological, micromorphological, trace elements analyses (Rb–Sr) and magnetic polarity determination were performed on Buenos Aires and Ensenada Formation (Late Cenozoic) deposits in the southern Chaco-Pampean Basin (Argentina). This work aims to unravel paleoclimatic and paleoenvironmental information from the analyzed data.The studied deposits encompass a complex and cyclic 8 m-thick sedimentary-pedogenetic sequence formed by loessic sediments and paleosols with volcano-pyroclastic provenance.Four tabular units, with net base and top, were defined from erosion surfaces.An OSL age >126 kyr was obtained from the upper middle part of unit B, which suggests that this unit as well as unit C, could have developed during the latest interglacial stage, equivalent to MIS 5.The occurrence of calcretes indicates periods of little clastic supply and seasonal arid or semiarid climate while iron oxides, smectites and illite-bearing pedogenetic calcretes point to annual rain rates between 100 and 500 mm. No calcretes of any origin occur in present soils of the same zone. According to our proposed interpretation of the available data, climate during MIS 5 was drier than today. The drier conditions may have been related to lower temperatures during summer. 相似文献
104.
Azevedo JS Braga ES Favaro DT Perretti AR Rezende CE Souza CM 《Marine pollution bulletin》2011,62(12):2724-2731
Santos-São Vicente estuary, located in São Paulo State, Brazil, has a history of contamination by inorganic chemicals such as mercury (Hg). In the 1980s the Cubatão was considered one of the most polluted sites in the world as a consequence of the intense industrial activities located in the city close to the estuary. To provide data and evaluate the local biota, total mercury (THg) contents were determined in sediments and in fish, Cathorops spixii, from different areas of the Santos-São Vicente estuary. For comparison, samples were also collected in a non-polluted system with similar hydrochemistry characteristics, the Cananeia estuary. The water characteristics and THg levels in sediment and fish samples confirmed a high human influence in the Santos-São Vicente estuary. The lowest THg values, observed in Cananeia, were evidence of low anthropogenic influence. High values observed in Santos-São Vicente show the necessity for a monitoring program. 相似文献
105.
Adriana Dueñas-Bohórquez Régine Elisabeth da Rocha Jelle Bijma 《Geochimica et cosmochimica acta》2011,75(2):520-532
In order to investigate the interindividual and ontogenetic effects on Mg and Sr incorporation, magnesium/calcium (Mg/Ca) and strontium/calcium (Sr/Ca) ratios of cultured planktonic foraminifera have been determined. Specimens of Globigerinoides sacculifer were grown under controlled physical and chemical seawater conditions in the laboratory. By using this approach, we minimised the effect of potential environmental variability on Mg/Ca and Sr/Ca ratios. Whereas temperature is the overriding control of Mg/Ca ratios, the interindividual variability observed in the Mg/Ca values contributes 2-3 °C to the apparent temperature variance. Interindividual variability in Sr/Ca ratios is much smaller than that observed in Mg/Ca values. The variability due to ontogeny corresponds to −0.43 mmol/mol of Mg/Ca ratio per chamber added. This translates into an apparent decrease of ∼1 °C in Mg/Ca-based temperature per ontogenetic (chamber) stage. No significant ontogenetic effect is observed on Sr incorporation. We conclude that the presence of a significant ontogenetic effect on Mg incorporation can potentially offset Mg/Ca-based temperature reconstructions. We propose two new empirical Mg/Ca-temperature equation based on Mg/Ca measurements of the last four ontogenetic (chamber) stages and whole foraminiferal test: Mg/Ca = (0.55(±0.03) − 0.0002(±4 × 10−5) MSD) e0.089T and, Mg/Ca = (0.55(±0.03) − 0.0001(±2 × 10−5) MSD) e0.089T, respectively, where MSD corresponds to the maximum shell diameter of the individual. 相似文献
106.
Olivia Salmerón-García Jorge Zavala-Hidalgo Adriana Mateos-Jasso Rosario Romero-Centeno 《Ocean Dynamics》2011,61(4):439-448
Regions in the Gulf of Mexico are determined based on the statistical behavior of the long-term monthly means of chlorophyll-a concentration from SeaWiFS satellite estimations. An analysis based on the four largest modes of an empirical orthogonal
decomposition, which account for 84.9% of the variance, results in nine spatial patterns with different statistical behavior
representing 14 connected regions. The time evolution (or principal component) of the first two modes resemble the annual
cycle, but each one with a different phase; the third mode represents a semiannual period and the fourth mode shows three
maxima and minima. A map of the resulting regions is obtained and the oceanographic processes taking place in each region
are discussed. The largest region covers most of the deep Gulf and the continental slope. Other regions in the deep Gulf are
located southeast of the Mississippi River mouth and off-shelf of southern Texas and Tabasco, all associated with seasonal
offshore cross-shelf transports. The shelves are associated with specific regions, but in wide shelves the inner and outer
continental platforms are separated. Among the causes that determine different regions are topographic characteristics and
the seasonal variability of physical processes, mainly entrainment caused by heat and momentum fluxes, upwelling, river plumes,
and cross-shelf transports associated with the convergence of the along-coast currents. 相似文献
107.
Mahnoosh Biglari Claudio Mancuso Anna d’Onofrio Mohammad Kazem Jafari Ali Shafiee 《Computers and Geotechnics》2011
Existing models for predicting the small strain behaviour of unsaturated soil are not capable of predicting the initial shear stiffness during suction reduction under normally consolidated conditions. This problem has been addressed in the present study by combining an existing elastoplastic model and recent experimental data to provide a new model for the initial shear stiffness. The model, which is similar to that typically adopted for saturated soils, uses the average skeleton stress and an additional function of the degree of saturation. This new model not only captures the behaviour of the new experimental results, but it also describes a unique relationship between saturated and unsaturated soils. 相似文献
108.
This study demonstrates that only a combination of a chromous chloride reduction with dual sequential extraction schemes can clearly separate the proportions of Se present in the sulphide versus the organic pools in shales. The data reveals that even small amounts of pyrite outcompete the organic matter for the available Se and pyrite oxidation will control the release of selenium during shale weathering. 相似文献
109.
Adriana Leonhardt Maria Luisa Lorscheitter 《Journal of South American Earth Sciences》2010,29(2):454-463
The palaeoenvironmental history has been studied based on palynology of a sedimentary profile from the Alpes de São Francisco bog (29°29′35′′S, 50°37′18′′W), São Francisco de Paula municipality, Rio Grande do Sul eastern Plateau, extreme Southern Brazil. The results indicate a regional cold and dry climate between 25,000 and 12,500 yr BP, interpreted from the grassland vegetation, forest taxa were present in refuges and the shallow local lake began to fill in. Climatic conditions became more aride after 16,000 yr BP, when grassland became rare. From 12,500 yr BP onwards, the climate began to change and at 11,000–9700 yr BP a warm and moist climate permitted the slight migration of pioneer arboreal taxa from refuges and locally a marsh formation. Between 9700 and 6500 yr BP a warm and dry climate resulted in reduction of grassland, confined the forest in refuges, dried out the marsh. The gradual increase of humidity between 6500 and 4000 yr BP allowed migration of forests from refuges and a bog developed. Between 4000 and 2000 yr BP Araucaria forest spread, indicating moister climate. The local bog expanded. From 2000 yr BP onwards, humid but warmer climate seems to result in a lower reproductive capacity of Araucaria forest taxa limiting its expansion. The bog reached the present-day in a decline condition. The results are compared to previous records from Southern Brazil highlands and some places from Argentina in order to better elucidate the climatic and vegetational history of these important South America areas during the late Quaternary. 相似文献
110.