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Wignall, P. B.— The worst of times. How life on Earth survived eighty million years of extinction. Princeton University Press, Princeton & Oxford. 2017
No full textÉrard Chr. Wignall, P. B.— The worst of times. How life on Earth survived eighty million years of extinction. Princeton University Press, Princeton & Oxford. 2017. In: Revue d'Écologie (La Terre et La Vie), tome 73, n°3, 2018. pp. 399-400
The carbon isotopic composition of CAMP basalts
No full textIn the geologic record evidence for short-lived and thus devastating perturbations of the global
C-cycle are provided by sudden negative carbon-isotope excursions (CIE’s) in the ocean-atmosphere
system. A well known example is the so-called initial CIE which occurs worldwide shortly before the
Triassic-Jurassic boundary. According to most researchers, the marked size of this shift (up to -8‰)
suggests that, besides volcanogenic CO2 emissions from Central Atlantic magmatic province (CAMP)
basalts, methane from destabilization of ocean floor clathrates (δ13C -60‰) or from contact
metamorphism of organic-rich sediments (δ13C -35‰ to -50‰) may have had a dominant role. This
interpretation is based upon the assumption that basaltic CO2 has a δ13C of approximately -5‰,
comparable to that measured on present-day basaltic volcanoes. In order to test this latter hypothesis,
we measured the bulk carbon isotopic composition of CAMP basalts and gabbros using sealed tube
combustion. The preliminary bulk δ13C of five CAMP basalts are in the range -26‰ to -29‰ while
one basalt yields δ13C of -14‰. However, this latter basaltic lava also has a high C content (1285
ppm), unlike the other basaltic lavas (C = 73-251 ppm) and intrusives (365-596 ppm). The anomalous
basalt sample is quite altered suggesting that its more positive carbon-isotopic composition (-14‰)
may be attributed to the presence of secondary calcite. The strongly negative composition of the other
basalts and gabbros is more puzzling and may indicate contribution from soil-derived organic matter
carbon (δ13C = -22 to -25; Ekart et al., 1999), although it seems surprising that such a process would
result in similar carbon isotopic compositions for apparently unaltered basic rocks coming from
different geographic regions (e.g., central Brazil, Sierra Leone, Morocco, Portugal) and crustal depths.
Whilst we presently can’t constrain where the C is residing in the basalts, we note that the strongly
negative δ13C of CAMP basalts are consistent with some previously published δ13C values for other
LIP basalts (Hansen, 2007) and for mantle rocks (Deines, 2002) indicating that a primary origin of the
low δ13C signature can’t be excluded
Anthropogenic-scale CO2 degassing from the Central Atlantic Magmatic Province as a driver of the end-Triassic mass extinction
Full text linkThe climatic and environmental impact of exclusively volcanic CO2 emissions is assessed during the main effusive phase of the Central Atlantic Magmatic Province (CAMP), which is synchronous with the end-Triassic mass extinction. CAMP volcanism occurred in brief and intense eruptive pulses each producing extensive basaltic lava flows. Here, CAMP volcanic CO2 injections into the surface system are modelled using a biogeochemical box model for the carbon cycle. Our modelling shows that, even if positive feedback phenomena may be invoked to explain the carbon isotope excursions preserved in end-Triassic sedimentary records, intense and pulsed volcanic activity alone may have caused repeated temperature increases and pH drops, up to 5 °C and about 0.2 log units respectively. Hence, rapid and massive volcanic CO2 emissions from CAMP, on a similar scale to current anthropogenic emissions, severely impacted on climate and environment at a global scale, leading to catastrophic biotic consequences
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
A new macrofaunal limit in the deep biosphere revealed by extreme burrow depths in ancient sediments
Full text linkMacrofauna is known to inhabit the top few 10s cm of marine sediments, with rare burrows up to two metres below the seabed. Here, we provide evidence from deep-water Permian strata for a previously unrecognised habitat up to at least 8 metres below the sediment-water interface. Infaunal organisms exploited networks of forcibly injected sand below the seabed, forming living traces and reworking sediment. This is the first record that shows sediment injections are responsible for hosting macrofaunal life metres below the contemporaneous seabed. In addition, given the widespread occurrence of thick sandy successions that accumulate in deep-water settings, macrofauna living in the deep biosphere are likely much more prevalent than considered previously. These findings should influence future sampling strategies to better constrain the depth range of infaunal animals living in modern deep-sea sands. One Sentence Summary: The living depth of infaunal macrofauna is shown to reach at least 8 metres in new habitats associated with sand injections
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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