1,720,972 research outputs found
Emiliania huxleyi calcite mass variability during periods of atmospheric CO2 rising in the Mediterranean Sea
No full textMediterranean carbonate system dynamics and planktonic biocalcification during the last 19,000 years
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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
Local hydrodynamic in coastal system affects the coccolithophore community at a short spatial scale
No full textCoccolithophores are an ecologically and biogeochemically important group of calcifying marine plankton, contributing globally to both the organic carbon pump and the carbonate counter pump. Understanding their distribution in today's ecosystems is crucial for both paleoenvironmental reconstruction and for predicting their fate under climate change and environmental pollution. Traditionally regarded as open ocean dwellers, more recent studies have highlighted their importance in coastal systems.Here we describe the coccolithophore community in the Catalan Sea (Northwestern Mediterranean), off the Ebro River Delta, based on an oceanographic survey conducted in autumn 2019. We identify three environmentally distinct regimes: mixed (mostly shallow), transition (upper photic layers offshore), and stratified deep waters (below 75 m). Total coccolithophore density is driven by Emiliania huxleyi and peaks in the mixed zone where nutrient concentrations are low, but nitrite concentrations are high. We propose that peak cell densities are partly explained by a switch from nitrate to nitrite usage similar to the behavior of diatoms. Species diversity peaks in deeper offshore waters due to vertical stratification. Helicosphaera carteri and Algirosphaera robusta benefit from E.huxleyi decrease both in coastal and offshore environment
Enhanced E. huxleyi carbonate counterpump as a positive feedback to increase deglacial pCO2sw in the Eastern Equatorial Pacific
No full textThe modern Eastern Equatorial Pacific (EEP) Ocean is a high nutrient low chlorophyll (HNLC) upwelling region and a large oceanic source of carbon to the atmosphere. During the last deglaciation, the EEP played a major role in the outgassing of carbon dioxide into the atmosphere from the upwelling surface water system of CO2-enriched deep-water masses originating from the Southern Ocean. The EEP upwelling system is also fertilizing the surface waters and enhancing the biological pump. Here we present data on the mass and calcification dynamics of the coccolithophore species Emiliania huxleyi spanning the last 30 ky at Site ODP 1238 (1°52.310′S, 82°46.934′W; 2203 m) in the EEP. Our results show an increased coccolith calcification degree during times of high pCO2 and low surface water pH conditions; this unexpected result is tentatively explained as related to changes in homeostasis equilibrium at the site of calcification and between the cell and the seawater environment. We estimated the E. huxleyi particulate inorganic to organic carbon ratio (PIC:POC) in order to detect changes in the carbonate counter-pump to carbon pump activity, which can act as either a positive or negative feedback to atmospheric CO2 modulating air-sea gas exchange. Our study indicates an enhanced coccolithophore biological pump during the last glacial that could have buffered, at least partially, the excess of pCO2atm via absorption into the ocean. Finally, during the last deglaciation, the enhanced carbonate counter pump was a major source of high pCO2sw in the EEP surface ocean
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
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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