1,721,038 research outputs found
Significance of replicates: Environmental and paleoenvironmental studies on benthic foraminifera and testate amoebae
No full textForaminifera (Rhizaria) and testate amoebae (Rhizaria and Amoebozoa) are single-celled organisms with marine and continental affinities. They are regarded as valuable bioindicators in transitional areas such as tidal and salt marshes and have been widely used for (paleo)-environmental characterization. Along-lasting debate regularly occurs on the use of living vs. dead fauna to accurately represent modern environments. Moreover, environmentally based benthic foraminiferal and testate amoebaean studies need a reliable sampling strategy to capture the spatial variability, particularly in transitional environments where patchiness complicates the data interpretations. The objective of the present study is therefore to define the minimum required number of replicates for capturing the variability of either living (environment) or dead (paleoenvironment) benthic foraminifera and testate amoebae. To address this question, 49 samples (i.e., replicates) were selected from a square meter zone in the tidal flat-salt marsh transitional zone along the Canche Estuary (Northern France). The range of faunal spatial variability was measured using geostatistical tools. The minimal number of samples for capturing the patchiness was determined using bootstrap resampling procedure. We provide evidence that for both living and dead fauna more than 26 samples (and even higher for some species) are needed to correctly evaluate the patchiness. Indeed, the living and dead fauna do not follow spatial homogenous trends, and this might bias paleoenvironmental interpretations. The commonly-suggested number of three replicates might not be enough to characterize the fauna in such heterogeneous environments
Methods relieving comparison of living and death assemblages
No full textLiving (LAs) and death assemblages (DAs) from the same samples (sites) can be compared based on total densities, species densities, species richness and heterogeneity (evenness). Preferably densities (standing crop), obtained by normalization of absolute frequencies to unit sample size, should be used to compare samples, especially for LAs. Combinations of the above four characteristics enable a better insight into the relations between LAs and DAs. The 'Incorporation Value' weighs the proportions of living individuals on total individual numbers with similarities in species composition between both assemblages, yielding the instantaneous integration grade of living individuals into the death assemblage. Diversity diagrams based on species richness (abscissa) and heterogeneities (ordinate), standardized over all investigated samples, simultaneously characterize differences in diversities. The standardized vector between LA and DA in the above-mentioned coordinate system characterizes differences in species richness and heterogeneity in a combined manner, where all coefficients of species richness and heterogeneities can be used
Thirty new records of marine benthic Foraminifera from Korean waters
No full textAs a part of a survey of indigenous biological resources of Korea, 30 marine benthic foraminiferal species
belonging to 24 genera and seven orders (Astrorhizida, Lagenida, Lituolida, Miliolida, Robertinida,
Rotaliida and Textulariida) were identified. Bottom sediment samples were collected from eight stations
on the west and east coast of South Korea, in April 2015 and May 2016, respectively. Ten species
belonging to nine genera and five orders (Lagenida, Lituolida, Robertinida, Rotaliida, Textulariida) were
identified in the Yellow Sea. Among these taxa, Rotaliida was the dominant order, represented by four
species: Evolvocassidulina tenuis (Phleger & Parker, 1951), Cibicides mabahethi Said, 1949, Cibicides
pseudolabatulus Perelis & Reiss, 1975 and Cibicidoides barnetti Bermudez, 1949. Twenty species
belonging to 15 genera and five orders (Astrorhizida, Lagenida, Lituolida, Miliolida, and Rotaliida) were
identified from the East Sea and the Lagenida was the dominant order, represented by 11 species: Lagena
strumosa Reuss, 1858, Lagena nebulosa (Cushman, 1923), Lagena striata var. semiornata Reuss, 1863,
Procerolagena cylindrocostata Albani & Yassini, 1989, Fissurina bispinata Ujiié, 1963, Oolina laevigata
d’Orbigny, 1839, Polymorphina amplissima McCulloch, 1977, Polymorphina subelliptica McCulloch,
1977, Guttulina succincta McCulloch, 1977, Guttulina neoproblema McCulloch, 1977 and Lagenosolenia
obtecta McCulloch, 1977. The findings described here increased the number of foraminiferal species
in Korea to approximately 1060, and contribute to our understanding of the diversity of foraminifera in
Korean waters
High-Resolution Biostratigraphic Analysis of the Cretaceous/Paleogene Boundary in the Kurdistan Region (NW Iraq)
No full text
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
Osmium Isotopic Evidence for Eccentricity‐Paced Increases in Continental Weathering During the Latest Hauterivian, Early Cretaceous
No full textAbstract The 405‐kyr eccentricity cycle is a consistent orbital parameter throughout the Phanerozoic that is associated with long‐term variations in global continental weathering. However, a lack of reliable geological evidence has hampered the understanding of the relation between the 405‐kyr eccentricity cycle and continental weathering during the Cretaceous. Os isotopic ratios (187Os/188Os) of the sedimentary record reflect the balance between radiogenic Os derived from continental weathering and Os derived from unradiogenic sources (e.g., hydrothermal activity, weathering of mafic rocks, and extraterrestrial sources). This ratio is therefore considered as a good proxy for the evaluation of short‐term changes in continental weathering patterns. To trace orbital‐paced continental weathering, this study reconstructs the marine Os isotopic records in upper Hauterivian to lower Barremian (Lower Cretaceous) carbonate rocks in central Italy, where previous studies have reported that variations in clay mineral composition are paced by the 405‐kyr cycle. Our new Os isotopic record documents periodic oscillations of 187Os/188Os between 0.7 and 0.9 that correspond to the 405‐kyr Earth's eccentricity cycle. Because the sedimentary interval with radiogenic 187Os/188Os values (∼0.9) corresponds to a time interval characterized by a humid climate in areas surrounding the Tethys, variations in the 187Os/188O values likely reflect cyclic changes in continental weathering caused by eccentricity‐paced intensification of monsoonal activity at low latitudes. This variation could have been further amplified by increased input of radiogenic Os from Paleozoic shale and Precambrian crust at higher latitudes that resulted from a latitudinal shift of the intertropical convergence zone
Assessing the potential of nematode metabarcoding for benthic monitoring of offshore oil platforms
No full text: Environmental DNA metabarcoding is gaining momentum as a time and cost-effective tool for biomonitoring and environmental impact assessment. Yet, its use as a replacement for the conventional marine benthic monitoring based on morphological analysis of macrofauna is still challenging. Here we propose to study the meiofauna, which is much better represented in sediment DNA samples. We focus on nematodes, which are the most numerous and diverse group of meiofauna. Our aim is to assess the potential of nematode metabarcoding to monitor impacts associated with offshore oil platform activities. To achieve this goal, we used nematode-optimized marker (18S V1V2-Nema) and universal eukaryotic marker (18S V9) region to analyse 252 sediment DNA samples collected near three offshore oil platforms in the North Sea. For both markers, we analysed changes in alpha and beta diversity in relation to distance from the platforms and environmental variables. We also defined three impact classes based on selected environmental variables that are associated with oil extraction activities and used random forest classifiers to compare the predictive performance of both datasets. Our results show that alpha- and beta-diversity of nematodes varies with the increasing distance from the platforms. The variables directly related to platform activity, such as Ba and THC, strongly influence the nematode community. The nematode metabarcoding data provide more robust predictive models than eukaryotic data. Furthermore, the nematode community appears more stable in time and space, as illustrated by the overlap of nematode datasets obtained from the same platform three years apart. A significative negative correlation between distance and Shannon diversity also advocates for higher performance of the V1V2-Nema over the V9. Overall, these results suggest that the sensitivity of nematodes is higher compared to the eukaryotic community. Hence, nematode metabarcoding has the potential to become an effective tool for benthic monitoring in marine environment
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