1,721,044 research outputs found
Quantifying OAE2 marine oxygen levels from coupled Mo and U isotopes: A Tethyan perspective.
Full text linkU and Mo isotopes are promising geochemical proxies for globally averaged ocean redox conditions in deep time. Because the Mo and U isotope compositions of seawater are controlled primarily by variation in ocean redox conditions, coupled Mo and U isotope records can be used to reconstruct variation in the relative sizes of oxic/suboxic, anoxic and euxinic sinks over geological time. The different sensitivities of Mo and U to anoxic and euxinic conditions creates a situation in which joint evaluation of the Mo and U isotope records provide greater constraints on variation in ocean redox conditions than either proxy can in isolation.
Here we report new and published Mo- and U-isotope data from shallow and deep marine black shales spanning the OAE2 along the subtropical Western Tethys. These data are used to infer the evolution of the seawater Mo and U isotope compositions and to investigate changes in marine oxygen levels during this interval. Because the incorporation of Mo and U isotopes into organic rich sediments is influenced by local bottom water redox conditions, we also report Fe speciation data from which oxygen levels in the marine substrate were determined in a sample-bysample basis. Our Fe speciation data suggest expansion of the Oxygen Minimum Zones (OMZs)
into the shallow western Tethys ocean waters; as well as the presence of an oxygenated deep Tethys ocean.
These differences in bottom water redox conditions explain observed heterogeneities on black shale Moisotope
compositions within the Western Tethys. Box modeling of the seawater coupled Mo- and U- isotope system suggest that anoxic and euxinic bottom water redox conditions occupied approximately 40 % and 15 % of the marine substrate respectively. These estimates are in accordance with previous estimates based on U-isotopes. The similar evolution of the seawater Mo, U and C isotope compositions suggest enhanced shallow marine anoxia as an important mechanism controlling the C-cycle during the OAE2.
The observed heterogeneities in ocean bottom water redox conditions may explain the differences on the degree of affection of marine life during the OAE2
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
Marble and stone revetment and pavements: Context and provenance
No full textEarlier excavations and survey at Vagnari furnished hardly any evidence for the use of marble at the site, and so the vicus was considered to be a low status
settlement, with only a few rooms having been elegant enough to decorate them with marble floors or revetment. The fragments recovered were not analysed scientifically to determine the location of the quarries from which the marbles came. Of particular interest, however, were two small fragments of inscriptions on white marble retrieved from the rubble fill dumped in the 4th century AD in the reservoir.
These originally may have been attached, when intact, to votive or funerary monuments, suggesting that the occasional commemorative monument was set up in the vicus and its cemetery, but they have little bearing here on the use of marble for architectural purposes. From 2012, considerably more marble was found that had been used in cladding and pavements, and these fragments were subjected to a geochemical and petrographic analysis
Planktonic foraminifera as proxies of the Holocene climatic variability (Tyrrhenian, Mediterranean Sea)
Full text linkIntroduction. The focus of this study is the paleoclimatic reconstruction of the southern Tyrrhenian
between ~9.2 and 2.9 ka, through the study of planktonic foraminiferal assemblages and stable
isotopes, and comparing data with other coeval intervals. Several authors have studied the climatic
sensitivity of Holocene planktonic foraminifera in different parts of the Mediterranean. Planktonic
foraminifera produce good records of Holocene climatic variability, especially as regards the suborbital
events such as Bond events (Bond et al., 1997) and other cooling/warming oscillations.
Therefore, the obtained eco-biostratigraphy has allowed us to analyze how climatic forcing influenced
sea surface temperature (SST) and water column structure during the Holocene in this sector
of the southern Tyrrhenian Sea.
Methodology. A sedimentary core (196 cm long) was collected in the Gulf of Palermo at the base
of the upper continental slope (990 m bsl) and sub-sampled every 2 cm. Micropaleontological and
geochemical analyses were performed on 98 samples, and three AMS 14C dates were determined.
Micropaleontological analyses consisted of qualitative and quantitative characterization of the
planktonic foraminiferal assemblages, in the size fraction greater than 125 μm. Geochemical analyses
were performed on 8–10 specimens of Globigerina bulloides.
Results. The calibrated AMS 14C ages, together with planktonic foraminiferal fluctuations and G.
bulloides oxygen isotope records, were used to develop an age model of the studied interval. In order
to obtain additional age control points, the studied records were also tuned to the NGRIP δ18O
(GICC05) (Svensson et al., 2008) and GISP2 ice core temperature (Alley, 2000) records.
Twenty species and eco-morphotypes were recognized in the planktonic foraminiferal assemblage
and grouped depending upon their climatic and feeding affinity. The warm-water species, minus
the typical cold-water species, were used to obtain the paleoclimatic curve, whilst the herbivorous/
carnivorous ratio has permitted us to reconstruct the trophism of the southern Tyrrhenian. In
particular, between ~8 and 6.4 ka, an important warming phase was recognized, clearly indicated
by the increase of Globigerinoides gr. ruber and G. gr. quadrilobatus. This interval corresponds to
the deposition of Sapropel S1b-equivalent stage (Sprovieri et al., 2003; Lirer et al., 2013; Siani et
al., 2013), when high SSTs and oligotrophy characterized the entire Mediterranean region, especially
during the summer seasons. Between ~5.9 and 4.2 ka, another warming phase occurred in the
Gulf of Palermo, differing from the previous one due to the enhanced winter mixing of the water
column, testified by the high abundance of deep dweller species, such as Globorotalia truncatulinoides
and Globorotalia inflata left coilings. The last important warming phase corresponds to the
Minoan Warm Period, briefly interrupted by a rapid cooling event (at ~3.5 ka).
Among these warm climatic phases, several rapid cold-cool events were recognized. In particular,
Neogloboquadrina pachyderma and Turborotalita quinqueloba represent the best cold-water indicators,
increasing in abundance during the Bond events (B2, B3, B4, B5, B6) and other rapid cooling
events that characterized the western (M3, M4, M5, M6, M7) (Frigola et al., 2007) and central
Mediterranean (TC2, TC3, TC4) (Cacho et al., 2001) during the 9.2–2.9 ka interval.
Conclusions. Planktonic foraminifera and oxygen isotope variations highlight the climatic oscillations
of the relatively stable Holocene stage. These oscillations are linked to the North Atlantic millennial
scale climatic variability that forced cool/high productivity periods and warm/oligotrophic
conditions. In particular, during the ~8–6.4 (S1b-equivalent), ~5.9–4.2, and ~3.7–3.2 (Minoan
Warm Period) ka intervals, warm surface waters characterized the Gulf of Palermo. On the contrary,
during rapid climatic phases, centered at 9.1, 8.2, 7.2, 6.2–5.9, 5.4, 4.7, 3.9, 3.5, and 3 ka,
cool/high productivity conditions occurred in this sector of the southern Tyrrhenian.
References
Alley, R.B., 2000. The Younger Dryas cold interval as viewed from central Greenland. Quaternary
Science Reviews 19(1–5): 213–226.
Bond G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., de Menocal, P., Priore, P., Cullen, H.,
Hajdas, I. and Bonani, G., 1997. A pervasive millennial-scale cycle in North Atlantic
Holocene and glacial climates. Science 278: 1257–1266.
Cacho, I., Grimalt, J.O., Canals, M., Sbaffi, L., Shackleton, N.J., Schönfeld, J., and Zahn, R., 2001.
Variability of the Western Mediterranean Sea surface temperature during the last 30,000
years and its connection with the northern hemisphere climatic changes. Paleoceanography
16(1): 40–52.
Frigola, J., Moreno, A., Cacho, I., Canals, M., Sierro, F.J., Flores, J.A., Grimalt, J.O., Hodell, D.A.,
and Curtis, J.H., 2007. Holocene climate variability in the western Mediterranean region
from a deepwater sediment record. Paleoceanography 22(2): PA2209.
Lirer, F., Sprovieri, M., Ferraro, L., Vallefuoco, M., Capotondi, L., Cascella, A., Petrosino, P.,
Insinga, D.D., Pelosi, N., Tamburrino, S., and Lubritto, C., 2013. Integrated stratigraphy
for the late Quaternary in the eastern Tyrrhenian Sea. Quaternary International 292, 71–
85.
Siani, G., Magny, M., Paterne, M., Debret, M., and Fontugne, M., 2013. Paleohydrology
reconstruction and Holocene climate variability in the South Adriatic Sea. Climate of the
Past 9: 499–515.
Sprovieri, R., Di Stefano, E., Incarbona, A., and Gargano, M.E., 2003. A high-resolution record of
the last deglaciation in the Sicily Channel based on foraminiferal and calcareous
nannofossil quantitative distribution. Palaeogeography, Palaeoclimatology, Palaeoecology
202(1–2): 119–142.
Svensson, A., Andersen, K.K., Bigler, M., Clausen, H.B., Dahl-Jensen, D., Davies, S.M., Johnsen,
S.J., Muscheler, R., Parrenin, F., Rasmussen, S.O., Röthlisberger, R., Seierstad, I.,
Steffensen, J.P., and Vinther, B.M., 2008.
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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