1,720,985 research outputs found
Increased erosion of high-elevation land during late Cenozoic: evidence from detrital thermochronology off-shore Greenland
Full text linkMountain regions at high altitudes show deeply incised glacial valleys that coexist with a high-standing low-relief landscape, whose origin is largely debated. Whether the plateaus contributed to sediment production during the late Cenozoic is a currently debated issue in glacial geomorphology and paleoclimatology. In this study, we used detrital apatite fission-track dating of marine sediments to trace provenance and spatial variation in focused erosion over the last 7 million years. The decomposition of age distributions into populations reveals that, moving upwards through the sections, two young populations get younger, while two older populations get progressively older. We interpreted these trends as the effect of glacial erosion on the valley floors and an increased sediment contribution from the high elevations. To test this hypothesis, we compared the measured ages with synthetic age distributions, which represented a change in the elevation of focused erosion. We conclude that the central-eastern Greenland region is the main source of sediments, and in addition to enhanced valley incision, sediments have also been sourced from progressively higher elevations since 7 Ma. The ageing trend provides an unusual case in detrital thermochronology and a strong evidence that intensified Quaternary glaciations amplify the erosional process both in valley bottoms and at high elevations
A detrital apatite fission‐track study of the CIROS‐2 sedimentary record: Tracing ice pathways in the Ross Sea area over the last 5 Ma
No full textMiocene climate cooling and aridification of Antarctica may have enhanced syn-extensional magmatism in the western Ross Sea
Full text linkContinental rift systems are commonly characterized by volcanism with parental basaltic magmas sourced from
the mantle. Erosion of the rift shoulders and sedimentation in the adjacent basins can affect the stress and
thermal fields at depth, thereby affecting partial mantle melting. However, the sensitivity of magmatic activity to
such surface forcing is elusive. Geological observations from the western Ross Sea, Antarctica, suggest rift onset
in the Cretaceous with a transition from wide-rifting to narrow-rifting at the boundary between the Antarctic
craton and the Transantarctic Mountains. Miocene climate cooling during rifting in the western Ross Sea, in
addition, leads to an abrupt decrease in sedimentation rate, synchronous to the emplacement of the McMurdo
Volcanic Group. This represents the largest alkali province worldwide, extending both inland and offshore of
Transantarctic Mountains and western Ross Sea, respectively. Here, we use coupled thermo-mechanical and
landscape evolution numerical modeling to quantify melt production in slowly stretching rift basins due to
changes in erosion/deposition rates. The model combines visco-elasto-plastic deformation of the lithosphere and
underlying mantle during extension, partial rock melting, and linear hillslope diffusion of the surface topography.
The parametric study covers a range of slow extension rates, crustal thicknesses, mantle potential temperatures
and diffusion coefficients. Numerical simulations successfully reproduce the ~150–200-km-wide
extension of western Ross Sea and Miocene-to-present asthenospheric melt production (McMurdo Volcanic
Group). Results further show that slow rifts magmatism is highly sensitive to sediment deposition within the
basin, which inhibits mantle decompression melting and delays the crustal breakup. Regional climate-driven
sedimentation rate changes are thus likely to have affected the syn-rift magmatic history of the western Ross
Sea, Antarctica, supporting the relevance of interactions between surface and deep-seated processes across
extensional settings
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
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
Recurrent E - W oscillations of the ice flow confluence of the East and West Antarctic ice sheets in the central Ross Sea, Antarctica, from the Middle Miocene to the present day
No full textWe present a multidisciplinary provenance study on legacy cores drilled in the 1970s during DSDP Leg 28 at sites
271 and 272, in the central Ross Sea, Antarctica. The two sites combined provide a discontinuous glaciomarine
sedimentary record covering 18 myr, from the Middle Miocene to the present day.
The two boreholes are located on the continental shelf and near the edge of the Ross Ice Shelf, in the middle of
the Ross Sea, at a key site close at 180° longitude that is considered to represent the present confluence between
ice flows fed by West Antarctica and East Antarctica. The study employs U Pb dating of detrital zircons and apatites,
coupled with apatite fission-track dating and trace element and REE compositions. Based on the sedimentary
provenance, our data show a recurrent E-W oscillation of the confluence of the West Antarctica and East
Antarctica ice flows, allowing phases of advance and retreat of the West Antarctic Ice Sheet to be inferr
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