1,721,035 research outputs found
Discriminating fluid sources in Miocene cold seep systems using REEs in authigenic carbonates
No full textAuthigenic carbonates are a common feature in cold seep environments, where fluids enriched in methane and other hydrocarbon gases escape from the seafloor. Seep-carbonates have been reported worlwide both in modern and ancient sedimentary deposits. In the Northern Apennines (Italy), numerous outcrops of seep-carbonates are particularly well-preserved. Evidences from paleoecological, sedimentological, geochemical and isotopic (O and C stable isotopes) analyses cleary show that they were derived from the microbial oxidation of methane-rich fluids. REE patterns and abundances in fossil seep-carbonates may provide additional informations for better constraining the origin and the composition of the fluids from which they have precipitated.Here, we report REE data for a series of Miocene carbonate samples recovered from various geological settings in the Northern Apennines. Samples were leached with 5% HNO3, prior to analysis by SF-ICPMS using the Tm addition method [1]. Total REE concentrations (ΣREEN) in our studied carbonates are very similar to those reported for modern authigenic carbonates, suggesting negligible post-depositional diagenetic alteration. The shale-normalized REE patterns vary significantly amongst the different authigenic carbonate samples analysed in this study. These data indicate that they were formed from fluids having distinct REE signatures. These results, coupled with other geochemical, petrographic and mineralogical data, allow us to reconstruct the variation of fluid seepage activity in the Northern Appenines during the Miocene
Increased circumpolar deep water flow in the glacial South Atlantic: the cause of apparent North Atlantic deep water weakening
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Sedimentary Fe-Mn oxyhydroxides as paleoceanographic archives and the role of aeolian flux in regulating oceanic dissolved REE
No full textIn the marine environment, authigenic ferromanganese (Fe–Mn) oxides precipitate from seawater, incorporating many dissolved trace elements (such as Nd, Pb) whose isotopic composition is a direct proxy for ambient seawater. Thus, isotopic studies of the Fe–Mn oxyhydroxide component leached from sedimentary records can provide information on changes in erosional input or ocean circulation changes. Such studies may be complicated, however, by the presence of detrital material containing a Fe–Mn oxide component, which may mask the true ‘seawater’ signal. In addition, the formation of Fe–Mn oxyhydroxides in the marine environment remains poorly understood. In particular, the phase (carbonates, detrital particles) that controls the delivery of authigenic Fe–Mn oxides to the sediments has not yet been determined. In this study, we have analysed the REE and Nd isotopic compositions of Fe–Mn oxyhydroxide fractions dispersed in marine sediment cores from the Cape and Angola basins, in the SE Atlantic (cruise IMAGES II). For the Angola Basin deep-sea core, located at ~1000 km south of the Congo River mouth, both the REE and Nd isotopic compositions (Nd) measured in recent Fe–Mn oxyhydroxide fractions are typical of Congo River-borne Fe–Mn oxides. This shows that ‘preformed’ Fe–Mn oxides associated with detrital fractions can locally contaminate the ‘seawater’ signal recorded by ‘authigenic’ oxyhydroxides. By contrast, examination of REE distributions, Nd isotope data and mass accumulation rates in Cape Basin sediments shows paradoxically that the flux of Fe–Mn oxides to sediments is controlled by aeolian particles from the nearby Namib Desert, even though their REE and Nd compositions point clearly to an ‘authigenic’ origin. It is proposed that partial dissolution of aeolian dust occurs in the water column, releasing into solution its easily leachable Fe–Mn component. The dissolved Fe2+ and Mn2+ would then fuel the reprecipitation of authigenic Fe–Mn oxyhydroxides, scavenging additional dissolved trace elements from the ocean, most probably from deep water masses. In this case, calculations suggest that aeolian deposition acts as a net sink for dissolved Nd in the Cape Basin, rather than a source, and allows us to estimate the rate of removal of dissolved Nd associated with atmospheric deposition, yielding a global oceanic residence time for Nd (Nd) of between 500 and 1400 years
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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