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Paleoenvironmental and paleoclimatic variations during the Holocene at Rio Grande do Norte inferred from studies about sediment geochemistry of lakes and caves
No full textA porção norte da região Nordeste do Brasil é uma das áreas mais interessantes para estudo dos mecanismos e processos relacionados à variação de pluviosidade dos trópicos, pois a maior parte da precipitação anual está associada à migração meridional da Zona de Convergência Intertropical do Atlântico (ZCIT). O clima no Nordeste sofreu alterações durante o Holoceno, no entanto, as interpretações paleoclimáticas são ainda muito controversas devido a pequena quantidade de estudos. De forma a contribuir para a discussão sobre mudanças paleoclimáticas e paleoambientais do Nordeste brasileiro, este estudo realizou análises geoquímicas, micropaleontológicas, biogeoquímica e de isótopos de deuterium e carbono em sedimentos lacustres e guano, e análises de isótopos de oxigênio e carbono em espeleotemas do Holoceno Médio e Tardio. Os estudos da Lagoa do Boqueirão sugeriram que sua formação ocorreu devido a dinâmica fluvio-eólica, que resultou em barramentos dos canais fluviais durante o período úmido do Holoceno. A transição entre o sistema fluvial e lacustre, que marca o barramento, foi definido em torno de 4.500 anos BP pela substituição de espículas de esponjas, tipicamente fluviais, pelas diatomáceas lacustres, predominantemente Mastogloia smithii var. lacustres. Foi demonstrado que a formação e as flutuações da profundidade da Lagoa do Boqueirão não estavam associadas a precipitação regional. As variações paleoclimáticas da Lagoa do Boqueirão e da Caverna do Trapiá puderam ser acessadas através dos dados de \'delta\'D em ácidos n-alcanóicos de 28 carbonos, produzidos por vegetação terrestre e macrófitas aquáticas, e dados de \'\'delta\'POT.18\'O dos espeleotemas. Valores mais positivos (negativos) desses isótopos indicaram que durante o MCA (LIA) a região apresentava condições de seca (umidade), devido ao posicionamento mais ao Norte (Sul) da ZCIT, que migrou em direção ao Hemisfério mais aquecido de acordo com a correlação observada com a Oscilação Multidecadal do Atlântico (OMA). A porção norte do NEB apresentou paleoclima diferente em relação ao da porção sul do NEB durante o LIA, que estava seco devido ao deslocamento da Zona de Convergência do Atlântico Sul (ZCAS) mais para sul, assim como a ZCIT, que não afetou a porção sul do NEB. Mudanças paleoambientais foram também definidas com base na idade de sequências sedimentares clásticas datadas por LOI e pelos depósitos de guano em condutos de cavernas em Felipe Guerra-RN. A deposição de sedimentos terrígenos na caverna Urubu entre 7 to 4 ky B.P. cave foi cronologicamente associada a clima mais úmido, o que é apoiado pelo baixos valores de \'\'delta\' POT.18\'O values de espeleotemas. Esse período também foi marcado pelo aumento da contribuição de de carbono orgânico do solo como indicado por valores mais baixos de \'\'delta\'POT.13\'C dos mesmos espeleotemas. Uma transição abrupta para clima mais seco pode está associada ao final da sedimentação clástica na caverna por volta de 4.2 ky devido a interrupção do fluxo do rio subterrâneo e completa erosão do solo ao redor da caverna. A erosão do solo é ressaltada por altos valores de \'\'delta\'POT.13\'C dos espeleotemas próximos aos da rocha encaixante (~0 %0). Estes resultados demonstraram uma relação entre preenchimento sedimentar da caverna Urubu com a formação e erosão de solo na sua volta. Esse aumento de aridez, particularmente nos últimos três mil anos na região, foi também importante para preservação de depósitos de guano sobre os sedimentos clásticos, visto que esse material é bastante solúvel. As idades das camadas de guano foram utilizadas para definir períodos de alta ocupação das cavernas por morcegos entre 1730 and 677 cal. anos A.P. e 200 cal anos A.P. até o recente. Durante o evento MCA houve redução na acumulação de guano que levou a um hiato deposicional por conta que o clima seco desfavoreceu a sobrevivência dos morcegos na região. A acumulação de guano voltou a ocorrer a 200 anos atrás, provavelmente porque a população de morcegos foi reestabelecida, devido a clima mais úmido.The northern sector of Nordeste of Brazil (NEB) is one of the most interesting regions to study mechanisms and processes related to fluctuations tropical rainfall, as the majority of annual precipitation is associated to the meridional migration of Intertropical Convergence Zone (ITCZ). Climate in NEB changed during the Holocene, although paleoclimatic interpretations are still controversial due to small number of studies. This study contribute to the discussion about paleoclimatic and paleoenvironmental changes of NEB by using geochemistry, micropaleontological, biogeochemistry and deuterium and carbon isotope analyses in lacustrine sediments and bat guano, and also speleothem isotope records from middle to late Holocene. Studies from Boqueirão Lake suggested that its formation occurred due to the fluvio-eolian dynamic, which resulted in blockage of fluvial channels during the holocenic humid period. Transition between fluvial and lacustrine system recorded the barrage formation and was defined around 4,500 years BP and suggested by the substitution of fluvial sponge spicules to lacustrine diatoms, mainly Mastogloia smithii var. lacustres, preserved in sediments. These data demonstrated that depth fluctuations of Boqueirão Lake were not associated to local precipitation accumulation. Paleoclimatic changes were reconstructed from Boqueirão Lake and Trapiá Cave based on \'delta\'D of n-alkanoic acids of 28 carbons, which are produced by terrestrial vegetation and macrophytes, and from \'\'delta\'POT.18\'O of speleothems. More positive (negative) isotope ratios indicate persistent dry (wet) climatic conditions during the MCA (LIA) there, due to a north (south) displacement of ITCZ. This climate system migrated toward the warmest ocean according to the correlation with Atlantic Multidecal Oscillation (AMO). The northern portion of the NEB (nNEB) presented different paleoclimate conditions when compared to the southern NEB portion (sNEB) during the LIA. LIA in sNEB was dry due to the displacement of the South Atlantic Convergence Zone (SACZ) to a southernmost position. Paleoenvironmental changes were attested by determining the age of clastic sequences filling cave conduits dated by OSL method and also by radiocarbon in bat guano. The deposition of terrigenous sediments in Urubu cave from 7 to 4 ky B.P. cave was chronologically associated with more humid climate indicated by low \'\'delta\'POT.8\'O values in speleothems. In addition, this period was marked by increased contribution of organic carbon from soil indicated by negative values of \'\'delta\'POT.13\'C of the same speleothems. An abrupt transition to dry climate was indicated by the end of clastic sedimentation at about 4.2 ky because interruption of underground river flow and complete erosion of soil surrounding the cave as indicated by abrupt enrichment of \'\'delta\'POT.13\'C values of speleothems, reaching values similar to the carbonate bedrock (~0 %o). These data demonstrated the relationship between the sedimentary filling of the Urubu Cave and the formation and soil erosion in the region. These predominant dry conditions during last three millenniums in the region were also important for preservation ofbat Guano deposits above terrigenous sediments. The chronological data of guano was also used to indicate two periods of high accumulation associated with intense occupation of caves by bat colonies between 1,730 and 677 years cal BP and 200 cal years BP until recently. During the MCA occurred a reduction in guano accumulation until a complete hiatus, because dry conditions did not favor bats survival. Guano deposit accumulated again only 200 years ago, when the population of bats restored with stabilization of relatively humid conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fossils in quaternary micrites of Bodoquena Range, Bonito-MS and their application in paleoenvironmental studies
No full textO município de Bonito e arredores em Mato Grosso do Sul apresentam atrações turísticas relacionadas a diversos tipos de depósitos carbonáticos quaternários, que formam cachoeiras, barragens naturais e tornam as águas de turbidez quase nula. A área está inserida no Parque Nacional da Serra da Bodoquena e na Reserva da Biosfera do Pantanal (UNESCO). As tufas calcárias são rochas porosas formadas pela precipitação do carbonato de cálcio em água doce e podem conter diversos tipos de fósseis. Apresentam-se sob a forma de cachoeiras, barragens e sedimentos lacustres que formam depósitos micríticos inconsolidados, descritos dentro da Formação Xaraiés. Os micritos são extensos e relativamente espessos em toda a região. Contudo, a maior parte das ocorrências está intemperizada, parcialmente erodida e distribuída em áreas limitadas. O presente estudo foca a caracterização paleontológica, granulométrica e geoquímica (elementos maiores, menores, traços e isótopos de carbono e oxigênio), através de levantamento de detalhe dos micritos da área da Mineração Calcário Xaraés, em Bonito (MS). As amostras foram obtidas por furo de trado, coleta de amostras superficiais e de bloco decimétrico orientado para estudo tafonômico, complementado com investigação de campo e amostragem de algumas áreas na Serra da Bodoquena, Pantanal e Corumbá. Os micritos da Mineração Calcário Xaraés, são depósitos lacustres e podem ser descritos em três eventos: 1: base afossilífera, oncólitos, argilominerais e dados isotópicos marcam um período de maior umidade; 2: ostracodes, algas caráceas e gastrópodes fósseis que colonizaram este estágio e a baixa variação dos dados isotópicos sugerem um período estável; 3: gastrópodes de água doce resistentes a ressecamento colonizaram esta etapa, em associação com os dados isotópicos sugerem processos alternados de evaporação e umidade. O topo da seção estudada é marcada por evaporação total da água do lago, morte em massa do gastrópode Biomphalaria e instalação do gastrópode Idiopyrgus. A ausência de estruturas sedimentares, orientação, seleção e fragmentação dos bioclastos e o empacotamento fraco a disperso e feições de alteração dos bioclastos por tempo de exposição na interface água-sedimento denotam condições estáticas do ambiente durante o processo final de deposição. Estas características também sugerem abastecimento do lago por águas subterrâneas, pois produzem menor taxa de alteração dos bioclastos e manutenção das condições químicas da água, como demonstrado pela homogeneidade dos dados geoquímicos. Outros depósitos estudados de micritos também apresentam resultados semelhantes. Há forte presença de indivíduos do gênero Biomphalaria e da Família Hydrobiidae nos depósitos. Dados de campo mostram os depósitos de tufas calcárias na região com extensão maior que as registradas, ocorrendo principalmente próximos aos leitos dos rios atuais, que os dissolvem nos períodos chuvosos. Os depósitos de tufas calcárias da Serra da Bodoquena, principalmente os micríticos, provavelmente foram formados nos últimos 10.000 anos, indicando período mais quente e seco que o atual. Os últimos 2.700 na região podem ser caracterizados por aumento da umidade, extinção dos depósitos micríticos e instalação dos depósitos de tufas de cachoeira e barragens.Bonito town and surrounding areas in Mato Grosso do Sul state are tourist attractions related with many quaternary carbonate deposits which form waterfalls, dams and render almost zero turbidity waters. That area is part of the National Park of Bodoquena Range and Pantanal Biosphere Reserve (UNESCO). Calcareous tufa are porous rocks formed by calcium carbonate laid down in freshwaters containg a great variety of fossils. They were presented in form of waterfalls, dams and lacustrine sediments, forming unconsolidated micritic deposits, being part of the Xaraés Formation. Micritic deposits are extensive and thick in whole area. Most of the deposits are weathered, partly eroded and distributed in restricted areas. The present study focuses on paleontological, granulometric, and geochemical (major, minor and trace elements, carbon and oxygen isotopes) data. The micritic deposits of Calcário Xaraés Mine in Bonito (MS) are detailed studied. Samples were obtained by auger drilling, also in outcrops area and one orientated centimetric indeformed block for taphomic study. The research was complemented with field study and sampling in the Bodoquena Range, Pantanal and Corumbá. Calcário Xaraés Mine micrites are lacustrine deposits. We described through three events: 1: their base does not contain fossils, but bears oncoids, clayminerals. Isotope data point to a wetter period, 2: ostracods, charophytes and gastropods fossils colonized this episode and homogeneity of isotope data suggest a stable event, 3: freshwater gastropods endured scarce water conditions so colonized the area. The isotope data then was varied suggesting alternated periods of evaporation and humidity. Total water lake evaporation resulted in the mass death of the Biomphalaria gastropod and consequent with diffusion of Idiopyrgus gastropod. Absence of sedimentary structures, bioclastic orientation, selection and fragmentation, weak to dispersal packing bioclast and bioclastic alteration features, are indications of long durantion in the water-sediment interface. These features suggest environmental static conditions during the final deposition. These features also suggest groundwater supplies to the lake, leading to less bioclastic alteration, and maintaing chemical water conditions, such as homogeneity of geochemical data. Other studied micritic deposits show almost the same results. There is strong presence of gastropod Biomphalaria and Hydrobiidae Family on these deposits. Field data show calcareous tufa deposits with an extension larger than the studied area, occurring mainly next to the rivers, which dissolve micritic in the rainy period. Bodoquena Range calcareous tufa deposits, mainly micritic sediments, probably were formed in the last 10.000 years, indicating a hotter and drier period than nowadays. The last 2.700 years in this region can be characterized by humidity increase, micritic deposits extinctions and installation of waterfalls and dams tufa depositions
Tropical South Atlantic influence on Northeastern Brazil precipitation and ITCZ displacement during the past 2300 years
Get PDFRecent paleoclimatic studies suggest that changes in the tropical rainbelt across the Atlantic Ocean
during the past two millennia are linked to a latitudinal shift of the Intertropical Convergence Zone
(ITCZ) driven by the Northern Hemisphere (NH) climate. However, little is known regarding other
potential drivers that can affect tropical Atlantic rainfall, mainly due to the scarcity of adequate
and high-resolution records. In this study, we fill this gap by reconstructing precipitation changes
in Northeastern Brazil during the last 2,300 years from a high-resolution lake record of hydrogen
isotope compositions of plant waxes. We find that regional precipitation along the coastal area of
South America was not solely governed by north-south displacements of the ITCZ due to changes in
NH climate, but also by the contraction and expansion of the tropical rainbelt due to variations in sea
surface temperature and southeast trade winds in the tropical South Atlantic Basin.This work was supported by the Fundação
de Amparo a Pesquisa do Estado de São Paulo (FAPESP), Brazil through NSF Dimensions-Biota FAPESP grant
2013/50297 and PIRE NSF-FAPESP Grants 2017/50085-3 to F.W.C as well as the post-doc fellowship to V.F.N
(2016/15807-5) and the US National Science Foundation NSF grants AGS-1303828 and OISE-1743738 to MV
and 1103403 to R.L.E and H.C. We thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior,
Brazil (CAPES) fellowship to G.U. Grant 99999.012754/2013-07 as well as the post-doc fellowship through the
Postgraduate Program on Geochemistry and Geotectonics, Geoscience Institute of the University of São Paulo
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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