1,721,050 research outputs found
Tertiary geodynamics of Sakhalin (NW Pacific) from anisotropy of magnetic susceptibility fabrics and paleomagnetic data
No full textSakhalin has been affected by several phases of Cretaceous and Tertiary deformation due to the complex interaction of plates in the northwest Pacific region. A detailed understanding of the strain is important because it will provide constraints on plate-scale processes that control the formation and deformation of marginal sedimentary basins. Anisotropy of magnetic susceptibility (AMS) data were obtained from fine-grained mudstones and siltstones from 22 localities in Sakhalin in order to provide information concerning tectonic strain. AMS data reliably record ancient strain tensor orientations before significant deformation of the sediments occurred. Paleomagnetically determined vertical-axis rotations of crustal rocks allow rotation of the fabrics back to their original orientation. Results from southwest Sakhalin indicate a ~N035°E-directed net tectonic transport from the mid-Paleocene to the early Miocene, which is consistent with the present-day relative motion between the Okhotsk Sea and Eurasian plates. Reconstruction of early–late Miocene AMS fabrics in east Sakhalin indicates a tectonic transport direction of ~N040°E. In west Sakhalin, the transport direction appears to have remained relatively consistent from the Oligocene to the late Miocene, but it has a different attitude of ~N080°E. This suggests local deflection of the stress and strain fields, which was probably associated with opening of the northern Tatar Strait. A northward-directed tectonic transport is observed in Miocene sediments in southeast Sakhalin, mid-Eocene sediments in east Sakhalin, and in Late Cretaceous rocks of west and northern Sakhalin, which may be associated with northwestward motion and subduction of the Pacific Plate in the Tertiary period. The boundaries of the separate regions defined by the AMS data are consistent with present-day plate models and, therefore, provide meaningful constraints on the tectonic evolution of Sakhalin
The parameterisation of Mediterranean–Atlantic water exchange in the Hadley Centre model HadCM3, and its effect on modelled North Atlantic climate
Get PDFMultiple palaeo-proxy and modelling studies suggest that Mediterranean Outflow Water (MOW) is an important driver of Atlantic Meridional Overturning Circulation (AMOC), particularly during periods of weak overturning. Here, we employ the HadCM3 ocean–atmosphere General Circulation Model (GCM) to investigate the effect of using different parameterisations of Mediterranean–Atlantic water exchange on global ocean circulation and climate. In HadCM3, simulating flow through the Gibraltar Straits with an ‘open seaway’ rather than a ‘diffusive pipe’ causes a shoaling and strengthening of the MOW plume. This reorganises shallow Atlantic circulation, producing regional surface air temperature anomalies of up to + 11 °C and ?7.5 °C. We conclude that when investigating the influence of MOW on modelled ocean circulation and climate, an accurate parameterisation of Mediterranean–Atlantic exchange is important and should match observed fresh water and salinity flux constraints. This probably cannot be achieved through a simple ‘diffusive pipe’ with depth invariant mixing coefficient
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
Birth, evolution and demise of the Mediterranean Lago-Mare: A biogeochemical perspective on water level and connectivity changes during the final phase of the Messinian Salinity Crisis
Get PDFThe Mediterranean Sea is a large sea almost completely enclosed by Europe, Africa, and SW Asia. Today, the continuous flow of Atlantic seawater through the Strait of Gibraltar balances the net water loss due to the excess of evaporation over input from rain and rivers and keeps the Mediterranean a marine basin with the water level equal to the global ocean level. In the late Miocene, the input of Atlantic seawater was through shallow gateways in southern Spain and northern Morocco. The exhumation of the Betic and Rif Cordilleras and orbitally-controlled regional climate change contributed to the step-by-step close these marine gateways and transformed the Mediterranean into an inhospitable evaporitic sea, starting at 5.96±0.02 Ma. The environmental and hydrological crisis that followed, known as the Messinian Salinity Crisis, peaked at ~5.55 Ma, when a 1.5-2 km-thick salt layer precipitated on the sea floor, and terminated at ~5.332 Ma, when normal marine conditions were re-established, perhaps as a consequence of catastrophic flooding at Gibraltar. The transitional interval from the giant salina to Mediterranean Sea that resembles what we know today is known as the Lago-Mare phase. Gypsum and brackish water biota from the Central Paratethys (approximately coinciding with the present-day Hungary-Slovenia) are both characteristic of Lago-Mare successions. This sedimentary and paleontological evidence suggest that the Mediterranean, during the Lago-Mare phase, experienced a complex history of inter- and extrabasinal connections, base-level fluctuations and extreme environmental and biological changes. This thesis aims to reconstruct the fiercely debated Mediterranean water level changes and identify the hydrological fluxes responsible for these Lago-Mare environmental and biological turnover events. It focuses on key sections exposed on-land and recovered from deep sea cores along an E-W transect across the Mediterranean with a multi-disciplinary approach that integrates biocyclostratigraphic analyses with high-resolution Sr-isotope ratios. The new data show that the Lago-Mare phase was a far more dynamic period of the Mediterranean history than previously thought. Large areas of the Mediterranean were occupied by an anomalohaline water mass predominantly formed by low-salinity waters from the Eastern Paratethys (i.e. the present-day Black-Caspian seas) and from the larger circum-Mediterranean rivers such as the Nile, the Rhône and currently dried North-African rivers. A small and possibly episodic Atlantic flux was a minor contributor. The regular variability of the Mediterranean’s freshwater budget with the astronomic precession combined with fluctuating Atlantic inflow and negligible outflow resulted in a Mediterranean base level that oscillated dramatically, but consistently below eustatic sea level. These precession-paced fluctuations caused the low-salinity Paratethyan biota to colonize the marginal areas of the Mediterranean at times of high base level and central areas during phases of low base level, gypsum to precipitate only in the deeper basins during the regressive phases and silled regions such as the Adriatic and the North Aegean to exist for long as some of the largest endorheic lakes
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
Precessional drivers of late Miocene Mediterranean sedimentary sequences:African summer monsoon and Atlantic winter storm tracks
Get PDFCyclic sedimentary patterns in the marine record of the Mediterranean Sea have been consistently correlated with orbitally-driven shifts in climate. Freshwater input driven by the African summer monsoon is thought to be the main control of such hydrological changes, where the runoff signal is transferred from the Eastern to the Western Mediterranean. The geological record from the Atlantic Margin also contains precession-driven dilution cycles that have been correlated with the sedimentary sequences in the Western and Eastern Mediterranean, despite the lack of a direct connection with the basin. In these regions, Atlantic winter storms have also been invoked to explain the wet phases. In the absence of seasonally-resolved proxy data, climate simulations at high temporal resolution can be used to investigate the drivers of Mediterranean hydrologic changes both on precessional and seasonal timescales. Here, we use the results of ocean-atmosphere vegetation simulations through an entire late Miocene precession cycle. These show that the African summer monsoon drives the hydrologic budget in the Eastern Mediterranean during precession minima, while the Western marginal basins are generally dominated by local net evaporative loss. During precession minima, the Western Mediterranean and the Atlantic Margin are also influenced by enhanced winter precipitation from the Atlantic storm tracks. We can, therefore, identify two different moisture sources affectingthe circum-Mediterranean area, characterized by the same phasing with respect to precession, but with opposite seasonality. This supports the inter-regional correlation of geological sections in these areas, as we show for the Messinian and speculate for other time periods
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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