1,721,154 research outputs found
Spatially explicit bathymetric reconstruction of the Pertuis Charentais (France) from lead line depth soundings of the late 17th century
No full textSequences of repeated bathymetric surveys through time have been successfully used to document the morphodynamical evolution of coastal environments within historical times. Most chronobathymetric sequences have a restricted temporal coverage, as surveys rarely date back earlier than the 19th century. The aim of this study is to explore the potential of older lead line depth measurements as a reliable source of bathymetric data. A late 17th century marine chart of the Pertuis Charentais (France) was used as a test case. High-resolution scans of the chart sheets were retrieved from a public online digital library. A rare manuscript contemporary to the chart was obtained from the French National Archives, in order to constrain the methodology used to acquire depth measurements. A spatially explicit bathymetry covering 1500 km² was reconstructed from the interpolation of about 4600 georeferenced depth soundings. Vertical error was estimated by assuming the equivalence of depth values between the late 17th century and the recent (1960) bathymetries above subtidal rocks outcropping on the seafloor. Documentary data indicated that the chart author did not acquire depth measurements on purpose but instead collected data taken by local sailors and coasting pilots over an unknown period of time, probably ranging from a few years to a few decades. The large vertical error estimated to ±4.5 m error margin mainly resulted from the lack of tide correction. Bathymetric difference maps could not be computed, but despite these weaknesses, the large-scale sediment infilling of the area and the long-term evolution of an estuarine sandbank could be documented, in agreement with previous works. Beyond its utility for local studies, this article provides insights into the processing of depth measurements acquired long before modern hydrography surveys, and demonstrates that such old marine charts deserve consideration, provided conditions are met for their critical assessment
Sediment budget on an urban embayed beach under different erosion protection structures: La Barceloneta Beach (Catalonia, NW Mediterranean)
No full textTrabajo final presentado por Anaïs Mollier para el Máster en Environmental Sciences impartido por la Université de La Rochelle, realizado bajo la dirección de la Dra. Ruth Durán del Institut de Ciències del Mar (ICM-CSIC) y del Dr. Eric Chaumillon.-- 21 pages, 13 figures, 3 tables, 4 appendices[EN] The city of Barcelona (NW Mediterranean) suffered a significant transformation of the sea front because of the Olympic Games in 1992. La Barceloneta, located between the Barcelona Commercial Harbour and the Olympic Marina, used to be the largest beach of the city. In this beach, several sand nourishments have taken place since 1991, and a detached breakwater and associated tombolo were built in 2006-2007 dividing the beach in two sections. The aim of this study is to quantify and compare the morphological changes of this beach before and after the detached breakwater construction. Using orthophotos, bathymetric and topographic data covering the period 2003-2017, the morphological changes are analysed, including variations in the emerged and submerged beach areas, volume and shoreline displacement. Results reveal an important erosion before the breakwater construction. Interestingly, an intensification of the erosion appears immediately after the construction of the detached breakwater, particularly in the northern part of the beach. The sediment budget was partially balanced with new nourishments that led to a strong accretion of the beach for a short time-scale. These protection measures contribute to reduce beach mobility and losses of sediment of the beach system, but the sediment budget is still negative due to the absence of new natural sedimentary inputs[FR] En Espagne, et plus précisément en Catalogne, la ville de Barcelone (NO Méditerranée) a subi une transformation significative de sa frange côtière notamment dû à une urbanisation accrue de celle-ci, avec l’organisation des Jeux Olympiques de 1992. La Barceloneta, située entre le Port Commercial et la Marina Olympique, est la plage la plus importante de la ville. Elle a subi de nombreux rechargements sédimentaires depuis 1991, enfin entre 2006 et 2007, un brise-lame détaché associé à un tombolo a été érigé divisant ainsi la plage en deux sections. Le but de cette étude est de quantifier mais aussi de voir les changements ainsi que les évolutions morphologiques qui ont pu s’opérer sur cette plage, avant et après la construction du brise-lame. À l’aide d’orthophotos, de données bathymétriques et topographiques, les changements morphologiques ont été analysés incluant les variations de la plage émergée et submergée, les volumes et les déplacements de position du trait de côte, sur une période qui s’étend de 2003 à 2017. Les résultats révèlent qu’une érosion importante existait déjà avant la construction de ce brise-lame. Fait intéressant, qui s’additionne avec une intensification de l’érosion instantanément après la construction du brise-lame détaché, et ce, particulièrement dans la partie nord de la plage. Le budget sédimentaire a été partiellement maintenu en équilibre grâce à de nouveaux rechargements sédimentaires, qui ont permis une forte accrétion de la plage, temporairement. Ces mesures de protection contribuent à réduire la mobilité de la plage et les pertes dues à une interruption du transit sédimentaire. Cependant, le budget de la plage de La Barceloneta reste encore déficitaire en raison de l’absence de nouveaux apports naturelsPeer Reviewe
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
Sedimentary signature of storm induced marine flooding in the back barrier area : the example of the Charente Maritime
No full textCette thèse présente l’étude de la signature sédimentaire des submersions marines de tempête, dans le domaine rétrolittoral. Cette signature peut être extrêmement variable principalement en fonction des paramètres météo-océaniques menant à la submersion, de la morphologie de l’avant-côte et du domaine rétrolittoral et du disponible sédimentaire. Premièrement, l’étude de dépôts de washover mis en place lors de l’hiver 2013-2014, au sud de l’île d’Oléron, particulièrement énergétique en terme de climat de vagues, via une approche couplant processus hydrodynamiques et sédimentologie, a permis (1) de mettre en évidence l’importance des ondes infragravitaires, sur une côte dissipative à caractère macrotidal, dans le déclenchement de l’overwash de la barrière et la mise en place de washovers ; et de (2) proposer un nouveau modèle de faciès des dépôts de washover mis en place par des ondes infragravitaires combinées à la marée haute. Deuxièmement, la caractérisation de la signature sédimentaire des submersions marines en domaine rétrolittoral plus distal a montré que dans le contexte morphologique des marais de Charente-Maritime, les apports extrêmement faibles de sédiments en provenance du domaine continental, entre deux évènements de submersion marine, empêche la distinction des différents niveaux de submersion. Cependant cette étude a permis de valider des proxies tels que la microfaune ou l’isotopie de la matière organique pour l’identification de niveaux de submersion marine, permettant en partie de pallier aux limites inhérentes à l’anomalie granulométrique généralement utilisée. Cette étude a aussi permis la mise en évidence d’une variabilité dans la signature sédimentaire des submersions marines entre deux marais géomorphologiquement contrastés et plus ou moins exposés aux houles en provenance de l’océan.This thesis presents the study of the sedimentary signature of marine submersions triggered by storms, in the back barrier area. This signature can be extremely variable mainly according to the meteo-oceanic parameters leading to the submersion of the back barrier area, the morphology of the nearshore, shore and back barrier area, and sediment availability. Firstly, the study of washover deposits emplaced during the winter of 2013-2014 on the southern end of the Oléron Island, characterized by an exceptional wave climate, via a coupled hydrodynamical and sedimentological approach, allowed us to (1) highlight the importance of infragravity waves, on macrotidal and dissipative coasts, in triggering the overwash and emplace washover deposits ; and (2) to suggest a new facies model of washover deposits emplaced by infragravity waves combined to high tides. Secondly, the characterization of the sedimentary signature of marine submersions in the distal part of the back barrier area showed that in the morphological context of the Charente-Maritime coastal marshes, the extremely limited amounts of sediments in provenance from the continent, between two submersion events, prevent the distinction of the different marine submersion sedimentary layers. Nevertheless, this study allowed validating new proxies as microfauna and organic matter isotopy for the identification of marine submersion sedimentary signature, allowing to work independently of the granulometric anomaly proxy and its known limits. This study also allowed evidencing the variability in the sedimentary signature of marine submersions in geomorphologically contrasted marshes and that this variability was linked to the ocean waves exposure
Sedimentary records of millennial to centennial environmental changes with coastal benthic micro- and macrofauna
No full textDiscriminer l'influence des activités humaines de celle des processus naturels sur les changements environnementaux récents est un enjeu scientifique important. Dans ce but, les mollusques et les foraminifères fossiles des Pertuis Charentais (ouest de la France) ainsi que les sédiments déposés pendant l'Holocène dont ils sont issus ont été étudiés. L'objet d'étude central est un drapage vaseux qui constitue une grande partie du comblement sédimentaire terminal des Pertuis. Les résultats obtenus montrent qu'il est composé de sédiments fins d'origine continentale déposés à partir de 1400 AD. Il est la conséquence d'une augmentation de l'érosion des sols, favorisée par la déforestation entreprise au Moyen-Age. Le taux de sédimentation de cette vase a augmenté brutalement, suite à une période d'augmentation des précipitations hivernales à la fin du Petit Age Glaciaire qui a accéléré l'érosion des sols sur ces territoires fragilisés car déforestés. Le dépôt brutal de sédiments fins dans les Pertuis Charentais a eu peu de répercussions sur les communautés de mollusques benthiques, excepté l'extinction locale du bivalve \textit{Lepton squamosum} de la baie de Marennes-Oléron. En revanche, l'augmentation des apports sédimentaires a été à l'origine d'une succession écologique au sein des communautés de foraminifères (résistance - perturbation - adaptation). Les résultats obtenus démontrent comment des milieux perturbés par les activités humaines deviennent plus sensibles aux changements climatiques. Ils soulignent aussi le potentiel de la paléoécologie dans la compréhension des changements environnementaux récents dans les zones côtières à une échelle millénaire à séculaire.Unraveling the respective influence of human activities and natural processes on recent environmental changes is a critical issue. In this respect, fossil molluscs and foraminifers of the Pertuis Charentais area (western France) as well as the sediments deposited during the Holocene they originate from have been studied. The study is focused on a mud drape that corresponds to the upper, most recent sediment infill of the area. The results show that it is composed of fine grained sediments originating from the adjacent catchments deposited from 1400 AD onwards. This major environmental change was the consequence of an increase in soil erosion promoted by intense deforestation started during the Middle Ages. Mud sedimentation rate increased suddenly in ca. 1760 AD, owing to a short-lived increase of winter rainfall which triggered more intense soil erosion on vulnerable deforested lands. The sharp deposition of fine grained sediments in the Pertuis Charentais has had few consequences on the past benthic mollusc communities, except the local extinction of the bivalve \textit{Lepton squamosum} in the Marennes-Oléron Bay. On the contrary, the increase in mud supply has triggered an ecological succession among benthic foraminifer communities (resistance - disturbance - adaptation). As a whole, the results demonstrate that environments disrupted by human activities become more sensitive to high-frequency climate changes. They also highlight the potential of paleoecology for a better understanding of recent environmental changes occurring within coastal areas at a millennial to centennial scale
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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