1,721,487 research outputs found
Biomarker constraints on Mediterranean climate and ecosystem transitions during the Early-Middle Miocene
No full textCompound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction
No full textA leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date
Alkenone concentration and sea surface temperature in surface sediments
No full textAlkenone concentration and radiocarbon age in 7 gobally-distributed surface sediment samples and their associated grain-size fractions. Total organic carbon (TOC) and fractional abundance of grain-size fractions from bulk sediments (Bulk%) are taken from Ausín et al. (2021). Analytical precision of Uk'37 is 0.003 units. Uk'37-SST propagated error is ±0.51℃. These parameters were measured to explore the influence of alkenone-mineral associations and hydrodynamic mineral sorting processes on alkenone proxy signals. Bulk sediment samples were fractionated into four grain-size fractions (sand (>300-63 µm); coarse silt (63-10 µm); fine silt (10-2 µm); and clay (< 2 µm) prior to lipid extraction and manual column chromatography to obtain a ketone fraction containing the alkenones. The concentration and distribution of C37 alkenones was analyzed using gas chromatography with flame ionization detection (GC-FID) at the Biogeoscience Group Laboratories, ETH Zürich in 2018. The ketone fractions used for determination of alkenone concentration and unsaturation were further purified for compound specific radiocarbon analysis following Ohkouchi et al. (2005). Samples, were measured as CO2 using an Elemental-Analyzer system interface coupled to a gas ion source (GIS)-equipped Minicarbon Dating System (MICADAS) at the Laboratory of Ion Beam Physics, ETH Zürich in 2018. References Ausín, B., Bruni, E., Haghipour, N., Welte, C., Bernasconi, S. M., & Eglinton, T. I. Controls on the abundance, provenance and age of organic carbon buried in continental margin sediments. Earth and Planetary Science Letters, 558, 116759, doi:10.1016/j.epsl.2021.116759, 2021. Ohkouchi, N., Xu, L., Reddy, C. M., Montluon, D., & linton, T. I. Radiocarbon dating of alkenones from marine sediments: I. Isolation Protocol Radiocarbon, 47, 401-412, doi:10.1017/S0033822200035189, 2005
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
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