1,720,988 research outputs found
Vegetation and climate reconstruction during the Last Interglacial Complex: the pollen record of Lake Ohrid (Albania/Fyrom), the oldest European lake
Full text linkThis thesis is focussed on the palaeonvironmental and climatic changes occurred during the period between 130 and 70 ka (including the whole Last Interglacial Complex), with the aims to investigate the long-term climate variability on environment, on the basis of high resolution pollen data from Lake Ohrid sediments (Albania/F.Y.R.O.M. border), the oldest lake in Europe and one of most ancient in the world. The climate reconstruction obtained from pollen data is based on a wider interval, 160-70 ka.
Lake Ohrid is located in a key region at the confluence of central European and Mediterranean climate influences and as already demonstrated by previous studies, has an important role for the study of the climatic and environmental changes occurred during the millennia in the Balkan and European areas.
The investigated pollen material comes from the sediments retrieved in spring 2013 in the frame of the project SCOPSCO (Scientific Collaboration on Past Speciation Conditions in Lake Ohrid) whose drilling was financed by the ICDP (International Continental Scientific Drilling Program). During the drilling campaign 6 parallel cores have been collected from the depocenter of Lake Ohrid obtaining an extraordinary composite sequence 569 m long (DEEP).
The upper 247.8 m of DEEP core have been dated using tephrostratigraphic information and tuning of biogeochemical proxy data to orbital parameters and covers the last 637 ka. In the framework of this careful temporal establishment, an even more precise chronology for the Last Interglacial Complex, and in particular for the transition between MIS6 and 5, was obtained by comparing pollen data from the same period with other DEEP and Mediterranean proxies. This make Lake Ohrid extremely important because for the other records from Mediterranean and European area such chronological constrains are not available and so the chronologies are less precise.
The pollen analysis results come from the uppermost 200 m of the DEEP core (covering the last 500 ka) and revealed a succession of non-forested and forested periods clearly connected with glacial–interglacial cycles of the marine isotope stratigraphy.
Among the different glacial-interglacial cycle, the new high-resolution pollen stratigraphy of the Last Interglacial Complex shows the classical alternation of periods characterized by forest (interstadials, warm and wet periods) and open vegetation (stadials, cold and dry periods), clearly resembling the well-known vegetational and climate succession of other European records.
Concerning the Last Interglacial (or Eemian, 128-112 ka, roughly equivalent to MIS5e), pollen analysis and climate quantitative reconstructions identify three key phases with a slight different timing, with an initial phase characterized by a sudden warming (propagation of mesophilous forests), then a decrease of temperatures associated with wet conditions (expansion of Carpinus betulus) and at the end a progressive establishment towards cold and dry conditions until the termination of Eemian at 112 ka, confirming what other previous studies on European records said, namely Eemian was not a stable period.
Several abrupt events are in also identified, during the successive stadials and interstadials (Early Last Glacial), probably correlated to the succession of cold events recorded in the Greenland ice core records, associated to a weakening of the North Atlantic Meridional Overturning Circulation.
This work provides a new pollen reference sequence for the Last Interglacial Complex in Europe and concerning climate reconstruction provides new information for a period (160-70 ka, from the last part of Riss Glaciation to the beginning of Würm Glaciation) still poorly investigated in Europe, mostly in the south (< 45° lat. N), where only one record has been studied for the whole interval, with high resolution time.
According to my results, Lake Ohrid can be considered a key role site for the investigation of the climatic changes occurred in centennial and millennial scale in a region of mid-altitude between European and Mediterranean areas, providing furthermore new evidence for the connection between the Europe and Northern Hemisphere climate oscillations
Late Holocene lacustrine records of environmental and human history in central Mediterranean
No full textLake Butrint, Albania: paleoenvironmental reconstruction of the past four millennia through pollen analysis.
No full textNew palynological data for the period between 190 ka and 110 ka from the oldest European lake.
No full textHuman–climate interactions in the central Mediterranean region during the last millennia: The laminated record of Lake Butrint (Albania)
No full textLake Butrint (39°47 N, 20°1 E) is a ca. 21 m deep, coastal lagoon located in SW Albania where finely-laminated sediments have been continuously deposited during the last millennia. The multi-proxy analysis (sedimentology, high-resolution elemental geochemistry and pollen) of a 12 m long sediment core, supported by seven AMS radiocarbon dates and 137Cs dating, enable a precise reconstruction of the environmental change that occurred in the central Mediterranean region during the last ∼4.5 cal kyrs BP. Sediments consist of triplets of authigenic carbonates, organic matter and clayey laminae. Fluctuations in the thickness and/or presence of these different types of seasonal laminae indicate variations in water salinity, organic productivity and runoff in the lake's catchment, as a result of the complex interplay of tectonics, anthropogenic forcing and climate variability. The progradation of the Pavllo river delta, favoured by variable human activity from the nearby ancient city of Butrint, led to the progressive isolation of this hydrological system from the Ionian Sea. The system evolved from an open bay to a restricted lagoon, which is consistent with archaeological data. An abrupt increase in mass-wasting activity between 1515 and 1450 BC, likely caused by nearby seismic activity, led to the accumulation of 24 homogenites, up to 17 cm thick. They have been deposited during the onset of finely laminated sedimentation, which indicates restricted, anoxic bottom water conditions and higher salinity. Periods of maximum water salinity, biological productivity, and carbonate precipitation coincide with warmer intervals, such as the early Roman Warm Period (RWP) (500 BC–0 AD), the Medieval Climate Anomaly (MCA) (800–1400 AD) and recent times (after 1800 AD). Conversely, lower salinity and more oxic conditions, with higher clastic input were recorded during 1400–500 BC, the Late Roman and the Early Medieval periods (0–800 AD) and during the Little Ice Age (1400–1800 AD). Hydrological fluctuations recorded in Butrint are in phase with most central and western Mediterranean records and correlate with NAO variability. In contrast, opposite hydrological patterns have been recorded in the Eastern Balkans and the Levant during the last millennium, emphasizing a complex spatial variability in the region. Phases of maximum settlement intensity in Butrint (Roman-Late Antique) coincide with warmer and/or stable climate periods (0–800 AD and MCA, respectively), indicating a long-term influence of climatic conditions on human activities. The Late Holocene sedimentary record of Lake Butrint demonstrates the complex interplay of climate variability, tectonics and human impact in the recent evolution of coastal Mediterranean regions
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
Vegetation and climate reconstruction during the last interglacial : the pollen record of Lake Ohrid (Republic of Macedonia) the oldest European lake
No full textCette thèse est centrée sur les changements paléoenvironnementaux et climatiques survenus dans le période entre 130 et 70 ka (Dernier Complexe Interglaciaire), pour étudier la variabilité du climat à long terme sur l'environnement, sur la base des données de pollen à haute résolution provenant des sédiments du lac Ohrid (Albanie / F.Y.R.O.M), le plus ancien lac d'Europe. La reconstruction du climat obtenue à partir des données polliniques est basée sur un intervalle plus large, 160-70 ka.Le matériel pollinique provient des sédiments prélevés en 2013, dans le cadre du projet SCOPSCO (Scientific Collaboration On Past Speciation Conditions in Lake Ohrid) dont le carottage a été financé par l'ICDP (International Continental Scientific Drilling Program). Pendant la campagne de carottage, 6 carottes parallèles ont été prélevées à partir de l’épicentre du lac, obtenant une séquence composite extraordinaire de 569 m (DEEP).Les 247.8 m supérieurs de la carotte DEEP ont été datés et ils couvrent les derniers 637 ka. Nous avons amélioré le modèle d’âge pour le Dernier Complexe Interglaciaire et en particulier pour la transition entre MIS6 et 5, en comparant les données polliniques avec d'autres proxies de la carotte DEEP et de la Méditerranée. Cela rend le lac Ohrid extrêmement important car pour les autres enregistrements de la région Européenne, de telles contraintes chronologiques ne sont pas disponibles.L'analyse des premiers 200 m de la carotte DEEP, couvrant les derniers 500 ka, a été étudiée avec une résolution de 1,6 ka. La séquence a révélé une alternance entre des ouvertures forestières et périodes boisées reflétant une cyclicité glaciaires-interglaciaires comparable à celle de la stratigraphie des isotopes marins. Parmi les différents cycles glaciaires-interglaciaires, l’analyse pollinique à haute résolution du Dernier Complexe Interglaciaire montre l'alternance classique de périodes caractérisées par la forêt (interstades, périodes chaudes et humides) et la végétation ouverte (stades, et périodes sèches), ressemblant clairement à la succession végétale et climatique bien connue des autres séquences européennes.Concernant le Dernier Interglaciaire (ou Eémien, 128-112 ka), l'analyse pollinique et les reconstructions quantitatives climatiques basées sur ces dernières identifient trois phases clés : une phase initiale caractérisée par un réchauffement soudain (propagation des forêts mésophiles), puis une diminution des températures associées à des conditions humides (expansion de Carpinus betulus) et à la fin un établissement progressif vers des conditions froides et sèches jusqu'à la fin de Eemian à 112 ka, confirmant l’hypothèse déjà avancée par plusieurs études antérieures basées sur des séquences polliniques européennes , à savoir que l’Eemien n'était pas une période climatiquement stable.D’autres changements climatiques sont également visibles dans la région du lac Ohrid entre 112-70 ka et probablement liés à la succession d'événements froids enregistrés dans les carottes de glace du Groenland, associé à un affaiblissement de l’AMOC (Atlantic Meridional Overturning Circulation).Ce travail a permis de fournir une nouvelle séquence de référence pollinique pour le Dernier Complexe Interglaciaire en Europe. Ce travail a également permis de quantifier les paléoclimats pour la période 160-70 ka, encore peu étudiée en Europe, principalement dans le sud (<45 ° lat. N), où un seul enregistrement a été étudié pour toute la période, avec une résolution temporelle élevée.Sur la base de ces résultats, le lac Ohrid apparait comme un site clé pour l'étude des changements climatiques survenus à une échelle centenaire et millénaire dans une région de moyenne altitude entre les régions européennes et méditerranéennes, fournissant en outre des nouvelles informations sur la connexion entre les oscillations climatiques de la région méditerranéenne et de l'Hémisphère du Nord.This thesis is focussed on the palaeonvironmental and climatic changes occurred during the period between 130 and 70 ka (Last Interglacial Complex), with the aims to investigate the long-term climate variability on environment, on the basis of high resolution pollen data from Lake Ohrid sediments (Albania/F.Y.R.O.M. border), the oldest lake in Europe. The climate reconstruction obtained from pollen data is based on a wider interval, 160-70 ka.The investigated pollen material comes from the sediments retrieved in spring 2013 in the frame of the project SCOPSCO (Scientific Collaboration On Past Speciation Conditions in Lake Ohrid) whose drilling was financed by the ICDP (International Continental Scientific Drilling Program). During the drilling campaign 6 parallel cores have been collected from the depocenter of Lake Ohrid obtaining an extraordinary composite sequence 569 m long (DEEP).The upper 247.8 m of DEEP core have been dated using tephrostratigraphic information and tuning of biogeochemical proxy data to orbital parameters and covers the last 637 ka. In the framework of this careful temporal establishment, an even more precise chronology for the Last Interglacial Complex, and in particular for the transition between MIS6 and 5, was obtained by comparing pollen data from the same period with other DEEP and Mediterranean proxies. This make Lake Ohrid extremely important because for the other records from Mediterranean and European area such chronological constrains are not available and so the chronologies are less precise.The pollen analysis results come from the uppermost 200 m of the DEEP core (covering the last 500 ka) and revealed a succession of non-forested and forested periods clearly connected with glacial–interglacial cycles of the marine isotope stratigraphy.Among the different glacial-interglacial cycle, the new high-resolution pollen stratigraphy of the Last Interglacial Complex shows the classical alternation of periods characterized by forest (interstadials, warm and wet periods) and open vegetation (stadials, cold and dry periods), clearly resembling the well-known vegetational and climate succession of other European records.Concerning the Last Interglacial (or Eemian, 128-112 ka, roughly equivalent to MIS5e), pollen analysis and climate quantitative reconstructions identify three key phases with a slight different timing, with an initial phase characterized by a sudden warming (propagation of mesophilous forests), then a decrease of temperatures associated with wet conditions (expansion of Carpinus betulus) and at the end a progressive establishment towards cold and dry conditions until the termination of Eemian at 112 ka, confirming what other previous studies on European records said, namely Eemian was not a stable period.Several abrupt events are in also identified, during the successive stadials and interstadials (Early Last Glacial), probably correlated to the succession of cold events recorded in the Greenland ice core records, associated to a weakening of the North Atlantic Meridional Overturning Circulation.This work provides a new pollen reference sequence for the Last Interglacial Complex in Europe and concerning climate reconstruction provides new information for a period (160-70 ka, from the last part of Riss Glaciation to the beginning of Würm Glaciation) still poorly investigated in Europe, mostly in the south (< 45° lat. N), where only one record has been studied for the whole interval, with high resolution time.According to my results, Lake Ohrid can be considered a key role site for the investigation of the climatic changes occurred in centennial and millennial scale in a region of mid-altitude between European and Mediterranean areas, providing furthermore new evidence for the connection between the Europe and Northern Hemisphere climate oscillations
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