1,721,339 research outputs found
100km-scale isotopic (d18O, dD) variability of the top-meter between B31 and Kohnen, Dronning Maud Land (M samples)
No full textIsotopic composition of the top-meter of the snowpack along a 115km traverse between B31 and D50, near Kohnen station, Dronning-Maud Land, East-Antarctica. Site D2 refers to the firn core drilling site B31. At each sampling site, profiles were sampled at 10 m distance in 90 m long trenches:
_R samples using the dual-tube sampling technique (Dallmayr et al., 2020), 3 subsections of the top-1m were sampled and at sites C4, C5, D2, D7, D24, D38, the top-1m of the trenches were sampled with the dual-tube and 5 single liners were taken and subsampled to 1 - 3 cm resolution (Hirsch, Nora; Hörhold, Maria; Dallmayr, Remi; Laepple, Thomas; Freitag, Johannes; Meyer, Hanno; Weiner, Mikaela (2023): Stable water isotopologues of arrays of high resolution 1 m snow cores from across Dronning Maud Land, East Antarctic Plateau [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.956273)
_M samples: Mixed 4 subsections of the top-1.2m of the 90m long trenches excavated by Pistenbully.
All isotopic analysis were realized by CRDS (Cavity-Ring-Down Spectroscopy) measurements at the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar-und Meeresforschung in Bremerhaven (instrument models L-2120-i, L-2140-i, Picarro Inc.). The samples were shipped frozen to the Alfred-Wegener-Institut and stored at -25°C. Prior to measurements the samples were melted in the sample bags at room temperature. The measurement set-up followed the Van-Geldern Protocol. Each sample was injected four times and the standard deviation is computed
100km-scale isotopic (d18O, dD) variability of the top-meter between B31 and Kohnen, Dronning Maud Land (R samples)
No full textIsotopic composition of the top-meter of the snowpack along a 115km traverse between B31 and D50, near Kohnen station, Dronning-Maud Land, East-Antarctica. Site D2 refers to the firn core drilling site B31. At each sampling site, profiles were sampled at 10 m distance in 90 m long trenches:
_R samples using the dual-tube sampling technique (Dallmayr et al., 2020), 3 subsections of the top-1m were sampled and at sites C4, C5, D2, D7, D24, D38, the top-1m of the trenches were sampled with the dual-tube and 5 single liners were taken and subsampled to 1 - 3 cm resolution (Hirsch, Nora; Hörhold, Maria; Dallmayr, Remi; Laepple, Thomas; Freitag, Johannes; Meyer, Hanno; Weiner, Mikaela (2023): Stable water isotopologues of arrays of high resolution 1 m snow cores from across Dronning Maud Land, East Antarctic Plateau [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.956273)
_M samples: Mixed 4 subsections of the top-1.2m of the 90m long trenches excavated by Pistenbully.
All isotopic analysis were realized by CRDS (Cavity-Ring-Down Spectroscopy) measurements at the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar-und Meeresforschung in Bremerhaven (instrument models L-2120-i, L-2140-i, Picarro Inc.). The samples were shipped frozen to the Alfred-Wegener-Institut and stored at -25°C. Prior to measurements the samples were melted in the sample bags at room temperature. The measurement set-up followed the Van-Geldern Protocol. Each sample was injected four times and the standard deviation is computed
Topographic Effect Creates Non‐climatic Variations in Ice‐Core Based Temperature Records of the Last Millennium in Dronning Maud Land, Antarctica
No full textPast temperature reconstructions from polar ice sheets are commonly based on stable water isotope records in ice-cores. However, despite major efforts in the understanding of the ice-core signal formation, the temperature reconstructions of the last millennium in Antarctica remain uncertain. Here, using a 100 km scale representative surface water isotope dataset, we show that the spatial variability of local surface topography and accumulation rate anomalies influences the isotopic composition of the upper-meter snowpack. The magnitude of this non-temperature effect on water isotopes is comparable to the changes observed over the last millennium. We demonstrate that these spatial anomalies are advected into the deeper firn and ice column, and can explain the diverging millennial water isotope trends observed in two ice-cores near the EPICA Dronning Maud Land drilling site. Furthermore, we provide an estimation of areas where this topographic effect could impact temperature reconstructions over the last millenia
Assessment of continuous flow analysis (CFA) for high-precision profiles of water isotopes in snow cores
Get PDFAbstract. In order to derive climatic information from stable water isotopes of the very recent past, the signal-to-noise ratio in climate reconstructions from ice cores has to be improved. To this end, understanding of the formation and preservation of the climate signal in stable water isotopes at the surface is required, which in turn requires a substantial number of snow surface profiles. However, due to its high porosity and poor stability surface, snow has been rarely measured; i.e., climate records from firn and ice cores often start at several meter depths, and the few discrete samplings of surface snow required large effort. Here we present a new setup to efficiently measure stable water isotopes in snow profiles utilizing a continuous flow analysis (CFA) system enabling measuring multiple snow cores in a reasonable time and with high quality. The CFA setup is described, and a systematic assessment of the mixing of the isotope signal due to the setup is conducted. We systematically determine the mixing length at different parts of the system. We measure and analyze six snow cores from Kohnen station, Antarctica, and find the largest contribution to mixing to originate in the percolation of meltwater on top of the melt head. In comparison to discrete measurements, we show that our CFA system is able to reasonably analyze highly porous snow cores for stable water isotopes. Still, for future developments we recommend improving the melt head with respect to the strong percolation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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