1,721,076 research outputs found
Seismic stratigraphy of the north-westernmost area of the Malta Plateau (Sicily Channel): The Middle Pleistocene-Holocene sedimentation in a tidally influenced shelf
No full textIn this study we present the results of a seismic-stratigraphic analysis of sub-bottom profiles in the north-westernmost area of the Malta Plateau in order to define the depositional mechanisms for the upper Quaternary sequences. During this interval the morphology of the Malta Plateau was characterized by a ramp and bathymetries not exceeding 200 m. Two major unconformities, related to MIS 6 and MIS 2 (the latter corresponding to the Last Glacial Maximum, LGM), characterize the upper Quaternary sequences. The geometries of the recognized seismic units indicate as depositional mechanisms were controlled by subsidence and sea-level fluctuations. In detail, deposits related to the last glacial event were recognized through their seismic pattern and have been interpreted as formed by the interaction between tide and wave dynamics. Contrary to the northern Sicilian continental margin, in the Malta Plateau ramp no LGM-related lowstand prograding wedge was recognized due to the absence of an effective shelf edge. It is considered as a consequence of the morphology and the dominant deposition processes in the Malta Plateau. Afterwards the ramp morphology allowed a rapid drowning of the Malta Plateau instead with the formation and preservation of transgressive deposits revealed as bedforms. The highstand deposits appear as prograding bodies and have been classified as infralittoral prograding wedge
Gathering different marine geology data (seismics, acoustics, sedimentological) to investigate active fluid seepage (AFS) in the southern region of the central Mediterranean Sea
Full text linkActive Fluid Seepage (AFS) at the seafloor is a global phenomenon associated with seafloor morphologies in different geodynamic contexts. Advances geophysical techniques have allowed geoscientists to characterise pockmarks, mounds and flares associated with AFS. We present a range of marine geological data acquired in the central Mediterranean Sea (northern Sicily continental margin, northwestern Sicily Channel and offshore the Maltese Islands), which allow us to identify AFSs. The AFSs are spatially distributed as clusters, aligned or isolated at different depths, ranging from few decametres offshore the Maltese Islands, up to 400 m offshore north Sicily and in the northwestern Sicily channel. Mounds have heights ranging from 2 to 15 m and form hummocky surfaces. Pockmarks with sub-circular planform shapes and U/V-shaped cross-sections are found in sizes ranging from 5 to 530 m. Gas flares occur on both the continental shelf and upper slope
Evidence of active fluid seepage (AFS) in the southern region of the central Mediterranean Sea
No full textActive fluid seepage (AFS) at the seafloor is a global phenomenon associated with seafloor morphologies in different geodynamic contexts. Advanced geophysical techniques have allowed geoscientists to characterise pockmarks, mounds and flares associated with AFS. We present a range of new marine geological data acquired in the southern region of the central Mediterranean Sea (northern Sicily continental margin, northwestern Sicily Channel and offshore of the Maltese Islands), which allow us to identify AFSs. AFSs are spatially distributed as clusters, aligned or isolated at different depths, ranging from few decametres offshore of the Maltese Islands; up to 400 m offshore of northern Sicily and in the northwestern Sicily Channel. Mounds have heights ranging from 2 to 15 m and form hummocky surfaces. Seafloor samples were collected at the top of the mounds and were analysed using a SEM with an EDX. Geochemical features reveal that seafloor samples are slightly enriched in O, S and Ba and seem to indicate the existence of an external source of fluids and the occurrence of sediment-fluids interaction processes. Pockmarks with sub-circular planform shapes and U/V-shaped cross-sections are found in sizes ranging from 5 to 530 m. Gas flares occur on both the continental shelf as well as the upper slope
Depositional mechanism of the upper Pliocene-Pleistocene shelf-slope system of the western Malta Plateau (Sicily Channel)
No full textA high resolution seismic stratigraphic study of the western edge of the Malta Plateau (central Mediterranean Sea) was conducted to reconstruct the depositional mechanisms of the shelf-slope system since the end of the Messinian salinity crisis (MSC; 5.3 Ma). The accurate interpretation of a large grid of variable-resolution seismic reflection profiles (multichannel and Sub Bottom) allows us to identify and map a Plio-Quaternary sedimentary sequence overlying the Messinian evaporites. The stratal pattern of this sequence is the result of a clinoform prograding system that constitutes the internal structure of a sedimentary shelf developed in a ramp about 2° slope with bathymetries that do not exceed 200 m. This type of shelf is a physiographic feature where the shelf edge separates littoral from bathyal realms, differing from the definition of continental shelf that implies the presence of a continent-ocean margin. The evolution of the western edge of Malta Plateau differs from adjacent sectors. Unlike to the nearby Gela Basin, where the Plio-Quaternary sedimentary sequences were affected by the thrusting of the Sicilian-Maghrebian chain until Middle Pleistocene, in the Malta Plateau the post-Messinian sedimentation was mainly controlled by subsidence and sea level fluctuations. In particular, the Malta Plateau represents a back bulge depozone where moderate fluvial sediment supply together with continuous subsidence favoured the progradation of the upper Pliocene-Pleistocene shelf-slope system at bathymetries not exceeding 200 m
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
Stochastic models for phytoplankton dynamics in Mediterranean Sea
Full text linkIn this paper, we review some results obtained from three one-dimensional stochastic models, which were used to analyze picophytoplankton dynamics in two sites of the Mediterranean Sea. Firstly, we present a stochastic advection–reaction–diffusion model to describe the vertical spatial distribution of picoeukaryotes in a site of the Sicily Channel. The second model, which is an extended version of the first one, is used to obtain the vertical stationary profiles of two groups of picophytoplankton, i.e. Pelagophytes and Prochlorococcus, in the same marine site as in the previous case. Here, we include intraspecific competition of picophytoplanktonic groups for limiting factors, i.e. light intensity and nutrient concentration. Finally, we analyze the spatio-temporal behaviour of five picophytoplankton populations in a site of the Tyrrhenian Sea by using a reaction–diffusion–taxis model. The study is performed, taking into account the seasonal changes of environmental variables, obtained starting from experimental findings. The multiplicative noise source, present in all three models, mimics the random fluctuations of temperature and velocity field. The vertical profiles of chlorophyll concentration obtained from the stochastic models show a good agreement with experimental data sampled in the two marine sites considered. The results could be useful to devise a new class of models based on a stochastic approach and able to predict future changes in biomass primary production
Female reproductive cycle and batch fecundity in the central-southern Adriatic population of Engraulis encrasicolus (Osteichthyes: Engraulidae).
No full textThe European anchovy, Engraulis encrasicolus, is a multiple-spawning small pelagic fish with a comparatively long reproductive season. From April to October 2009, ovary samples were collected from individuals of the southwestern Adriatic Sea in order to examine ovarian histological changes and assess batch fecundity monthly variations throughout the whole reproductive season. To assess monthly variations of the relative batch fecundity, the correlation between batch fecundity (F) - i.e. the number of oocytes released at each spawning act - and ovary-free body mass (W*) was tested by four regression models; the power equation () was found to be the most suitable to describe correlations. The reproductive season of the anchovy of the central-southern Adriatic population lasts from May to September; in this period, all the oocyte development stages were observed, including hydrated oocytes and postovulatory follicles. In April, most fish had only unyolked oocytes; in October, an extensive atresia of yolked follicles was observed. The slope of all the on monthly regressions did not differ significantly from 1, which shows that relative batch fecundity is constant all over the anchovy size range, throughout the spawning season. In the central-southern Adriatic anchovy population, batch fecundity increased from May to July and then gradually decreased until September. Differences in batch fecundity of the anchovy from different areas of the eastern Atlantic and Mediterranean could possibly be due to both environmental parameters and genetic differences among the different populations
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