1,720,991 research outputs found
Preliminary paleoecological observations on benthic foraminiferal assemblages from an eastern equatorial Atlantic deep-sea core
No full textQuantitative analyses of benthic foraminiferal assemblages were carried out on the late Pleistocene - Holocene succession of the core S13-33 (PRIMAR project, Leg 13, eastern equatorial Atlantic, Lat.: 0°51'S, Long.: 12°45'W, water depth: 3500 m). The 503 cm thick succession is constituted by a “Globigerina ooze”, which changes in colour at 356 cm from the top from dark grey in the lower part to light grey in the upper part. Planktonic foraminiferal assemblages occurring from the base to the top of the succession correlate with those of the five Ericson & Wollin (1968) climatic zones, going from V zone-upper part (late Pleisto¬cene) to Z zone (Holocene) included. Benthic foraminiferal assemblages are mainly represented from the base to the top by Epistominella exigua, Eponides pusillus and Globocassidulina subglobosa, and subordinately by Cibicidoides wuellerstorfi, Cibicidoides spp., Gyroidina spp., Melonis barleeanum, Oridorsalis umbonatus and Uvigerina auberiana. The predominance of E. exigua, E. pusillus and G. subglobosa, opportunistic species adapted to seasonal pulses of food supply (phytodetritus) in a food-limited environment, indicates that the bottom water masses were characterized by a relatively low organic matter content mainly constituted by phytodetritus, which originates in the euphotic zone and settles rapidly to the seafloor following the spring bloom. The abundance curve of C. wuellerstorfi shows a slightly increasing trend from the base to the top suggesting a correspondent slight intensification of the bottom water circulation. This hypothesis is also supported by the patterns of Cibicidoides spp., oxic species, and of Gyroidina spp. and M. barleeanum, suboxic species. U. auberiana trend suggests a clearly subordinate influence of upwelling on the composition of benthic foraminiferal assemblages with respect to that of spring bloom. The curve of the total number of benthic specimens per gram (BN) shows average values mainly ranging from 371 to 1088, and it is characterized by some significant positive peaks occurring in the lower part of the succession, at about 200 cm and at 59.5 cm. The benthic foraminiferal assemblages trends point out that during the late Pleistocene - Holocene in the investigated area the bottom paleoecological conditions were mostly influenced by the spring bloom and subordinately by upwelling phenomena, and were characterized by a generally low organic matter content mainly constituted by phytodetritus. Moreover the changes observed in the abundance curves of E. exigua, G. subglobosa and U. auberiana and in the BN pattern testify that such conditions slightly differentiate in the dark grey coloured lower part (core bottom to 356 cm), where a relative decrease of phytodetritus and a moderate increase of surface productivity occur, with respect to the light grey coloured middle and upper parts of the succession (356 cm to core top), where the surface productivity is even more subordinated. Nevertheless in this last interval two episodes of relative increase of surface productivity, due to discontinuous intensified upwelling phenomena, may be inferred by two concomitant peaks of U. auberiana and of BN
Paleoecology and paleoceanography of a Langhian succession (Tremiti Islands, southern Adriatic Sea, Italy) based on benthic foraminifera
No full textThe results of a detailed quantitative and statistical analysis on benthic foraminiferal assemblages from the Langhian Cretaccio composite section cropping out at Tremiti Islands (southern Adriatic Sea, eastern Mediterranean Sea) are presented. The distribution patterns of the species allowed us to estimate a paleodepth of about 600 m for the entire composite section. The abundance curve of the oxic species indicates relatively well oxygenated conditions of bottom water masses with a weak but gradual decline which culminates at about 37 - 38 m after the First Occurrence (FO) of Orbulina suturalis. The discontinuous distribution of Cibicidoides wuellerstorfi is suggested to be indicative of alternating episodes of active and relatively sluggish circulation of bottom water masses. Two major changes in the benthic foraminiferal assemblages are recorded along the succession. The first one occurring in correspondence of the lithologic colour change at about 15 m is characterized by the sharp decrease of Bulimina costata, Gyroidina spp., Hanzawaia boueana and Melonis barleanum testifying a decrease in productivity. The second one is more gradual and it is characterized by the regular increase of U. semiornata and U. striatissima from 8 m to 37 - 38 m indicating a gradual change in oxygen content. A third less pronounced change concerns the last meters of the section suggesting an amelioration of the bottom conditions. These changes are interpreted as the first response to paleoceanographic variations related to the closure of the connections between Tethyan and Indo-Pacific water masses. In term of chronology the section is estimated spanning the interval preceding the Paracme End (PE) of Sphenolithus heteromorphus (estimated approximately at 15.65 Ma) and postdating the FO of O. universa (dated at 14.36 Ma)
Lo studio delle associazioni a foraminiferi bentonici per la valutazione dello stato di inquinamento dell’ambiente marino: un esempio dall’Area Marina Protetta di Punta Campanella (Tirreno Meridionale)
No full text
BENTHIC FORAMINIFERA AS INDICATORS OF PALEOECOLOGICAL BOTTOM CONDITIONS IN THE SERRAVALLIAN TREMITI SECTIONS (EASTERN MEDITERRANEAN, ITALY).
Full text linkQuantitative analysis of benthic foraminifera from the Serravallian S. Nicola composite section (Tremiti Islands, Adriatic Sea) and about 37 m thick, pointed out changes of bottom paleoecological conditions in this eastern Mediterranean area during the analyzed time interval. Benthic foraminiferal assemblages are typical of bathyal environment and indicate a constant paleobathymetry of about 1,000 m. Changes in benthic foraminiferal assemblages allowed us to identify five intervals, which were calibrated on the astrochronological scale to reconstruct paleoecological evolution of bottom conditions. In particular starting from the base of the section the following different bottom conditions have been identified: 1) between about 12.62 to about 12.29 Ma high surface productivity, active bottom water circulation and, consequently, moderate bottom food supply; this paleoenvironment slightly changed between about 12.49 and 12.29 Ma, where benthic assemblages testify unstable bottom conditions with periods of active circulation (relative abundance of Cibicidoides wuellerstorfi), alternated with periods of sluggish circulation (peaks of Bulimina subulata group); 2) relatively oxygenated paleoenvironment together with low food supply between about 12.29 - 12.08 Ma; 3) increase of organic matter content (abundance of U. peregrina-pygmaea), due to higher surface productivity and/or greater preservation of organic matter at bottom from 12.08 to 11.81 Ma; 4) relatively oxygenated conditions with low food supply from 11.81 to about 11.45 Ma; 5) similar conditions to those of the basal part (about 12.62 - 12.29 Ma) of the section from about 11.45 to 11.10 Ma, but with an increase of organic matter content. Finally, the comparison between the paleoecological reconstruction of the S. Nicola composite section and Ras il-Pellegrin (Malta) composite section (reported in this volume) in the interval between about 12.6 and 12.2 Ma, pointed out very different extimated paleobatimetries, but similar paleoecological bottom conditions with evidence of relative high productivity
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
Metodologie di prelievo, preparazione di campioni e analisi delle associazioni a foraminiferi nei sedimenti di mare profondo: un esempio dall’Atlantico equatoriale orientale (Carota S13-33)
No full textIn questa nota sono descritte le metodologie di campionatura, di trattamento dei campioni e di analisi delle associazioni a foraminiferi dei sedimenti della carota S13-33 prelevata nell'Oceano Atlantico equatoriale orientale (coor¬dinate geografiche: Lat. 0°51'S, Long. 12°45'W; profondità -3500 m). La zona studiata si colloca su un margine di tipo trasforme, nella regione a sud della zona di frattura "Chain". Essa è interessata dalla Corrente calda Sud-Equatoriale ed è ubicata a Nord della regione caratterizzata dalla Corrente di upwelling del Benguela.Le ricerche micro¬paleontologiche sui sedimenti di questa carota sono inquadrate nell’ambito di un pro¬gramma di geologia marina nella regione atlantica suddetta, coordinato dal prof. B. D'Argenio ed inserito nel progetto multi¬disciplinare "Primar" ("Project Russian Italian Mid-Atlantic Ridge") in collaborazione tra gli Istituti di Geologia Marina del CNR di Bologna e Napoli, l'OGS di Trieste e l'Accademia Russa delle Scienze di Mosca.
Gli studi sulle associazioni a foraminiferi saranno sistematicamente integrati con le analisi degli isotopi stabili dell’ossigeno (*18O) nei gusci di specie selezionate di foraminiferi sia planctonici che bentonici e con la datazione radiometrica di alcuni livelli della carota per perseguire i seguenti obiettivi principali:
•ricostruzione stratigrafica ed evoluzione paleoclimatica durante l’intervallo temporale considerato attraverso lo studio integrato dei dati quantitativi e statistici dei foraminiferi planctonici e dei dati geochimici;
•evoluzione paleoecologica e paleoceanografica durante l’intervallo temporale considerato attraverso lo studio integrato dei dati quantitativi e statistici dei foraminiferi bentonici e planctonici e dei dati geochimici
- …
