1,721,072 research outputs found
Boron based insights into Plio-Pleistocene carbon cycle changes and global climate evolution
No full textFrom the Pliocene to the modern, the Earth’s climate has undergone a vast and significant change from a world dominated by continental ice restricted only to Antarctica with a rhythmic 41 kyr beat, through a period of declining atmospheric CO2 and cooling culminating with the bihemispheric glaciation known today, dominated by 100 kyr cyclicity. Ocean circulation is often given a central role in the dynamics of the late Neogene although many questions, such as the role of the North Atlantic in glacial-interglacial CO2 change remain. It is a well-studied region however and as such provides an ideal location for further study with novel proxies that may potentially provide new insights. Similarly, atmospheric CO2 is often thought to be the most crucial single variable driving Plio-Pleistocene climate change. Atmospheric CO2 reconstructions so far published beyond the end of the 800 ka Dome C ice core record are however few and of relatively low resolution and/or precision. This is at present hampering our understanding of CO2-climate interaction for climates warmer than the present and must be addressed as a priority given humanity’s ever-increasing CO2 emissions and anthropogenic global warming. This thesis aims to address these issues using boron-based proxies in foraminiferal carbonate. The potential power of these boron based proxies to directly quantify the marine carbonate system in the past has an enormous draw, both as a pH-CO2 proxy, but also for identifying the role of the deep ocean circulation changes in ocean carbon storage and release on orbital timescales. The first half of this thesis aims to better address the role of ocean circulation in rapid climate change and carbon storage over glacial-interglacial cycles. ?11B and B/Ca records from benthic foraminifera (Cibicidoides wuellerstorfi) from three cores in the North Atlantic spanning the last full glacial cycle and making up a depth, latitude and longitude transect are presented. These show that over this period, North Atlantic circulation is both dynamic and complex, presenting new and demonstrable links between climate change and the deep ocean carbonate system. Within this record a high-resolution section was taken focusing on the last 40 thousand years to search for any rapid changes in circulation associated with Heinrich events. It is demonstrated here that the boron based proxies can remove ambiguity from the existing records of deep ocean circulation change and challenge the established theory of deep water formation (DWF) shutdown in the Northern hemisphere during H-events.In the second half of this thesis atmospheric CO2 records, beyond the reach of the ice cores, derived from the ?11B of planktonic foraminifera (Globigerinoides ruber) from the tropical Atlantic basin and Caribbean Sea are presented. Here the relationship between the climate system (both in terms of ice-volume/sea level and temperature) is examined in climate states warmer than today. These include a suborbitally resolved record from 1.0-1.2 Ma to observe the nature of CO2 cycles before the ‘over thickening’ of the Laurentide ice sheet and the associated switch from 41 kyr to 100 kyr climate cycles at the Mid Pleistocene Transition (MPT). This study reveals the existence, around 1 million years ago, of high amplitude CO2 cycles with a 41 kyr cyclicity, and a mean CO2 level around 25 ppm above the Late Pleistocene. The relationship between CO2 and ice volume/SL prior to the MPT is significantly different to that post MPT, implying that CO2 decline and some other boundary condition change, probably related to the sub-glacial regolith, were both responsible for this most recent major climatic transition. Also reconstructed is a multisite reconstruction of atmospheric CO2, extending through the last 3.5 million years, including the onset of Northern Hemisphere Glaciation (iNHG). In order to gain a quantitative understanding of the role of CO2 decline in Plio-Pleistocene cooling a comprehensive compilation of sea surface temperature data is also presented. A combination of this record of “global” sea surface temperature data with the longterm CO2 data confirms that Plio-Pleistocene cooling was driven by CO2 decline amplified by the ice-sheet albedo feedback
Dataset 'Late Pleistocene d11B based carbon dioxide levels from ODP Site 154-926'
No full textThis dataset supports the article 'Late Miocene cooling coupled to carbon dioxide with Pleistocene-like climate sensitivity' In Nature Geoscience
This dataset contains data which are used for generating Fig.1 - Fig.3.
Supplementary Table 1: Reports information relevant to site location, sampling resolution and references to sources of original temperature measurements for Late Miocene SST stack.
Supplementary Table 2: Data for stable isotopes (δ11B, δ13C and δ18O), elemental ratios (Al/Ca, Mg/Ca and B/Ca), and pH and CO2 estimates based on δ11B.
Supplementary Table 3: Compilation of key Equilibrium Climate Sensitivity studies.
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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
Mapping coral calcification strategies from in situ boron isotope and trace element measurements of the tropical coral Siderastrea siderea
No full textBoron isotopic and elemental analysis of coral aragonite can give important insights into the calcification strategies employed in coral skeletal construction. Traditional methods of analysis have limited spatial (and thus temporal) resolution, hindering attempts to unravel skeletal heterogeneity. Laser ablation mass spectrometry allows a much more refined view, and here we employ these techniques to explore boron isotope and co-varying elemental ratios in the tropical coral Siderastrea siderea. We generate two-dimensional maps of the carbonate parameters within the calcification medium that deposited the skeleton, which reveal large heterogeneities in carbonate chemistry across the macro-structure of a coral polyp. These differences have the potential to bias proxy interpretations, and indicate that different processes facilitated precipitation of different parts of the coral skeleton: the low-density columella being precipitated from a fluid with a carbonate composition closer to seawater, compared to the high-density inter-polyp walls where aragonite saturation was ~5 times that of external seawater. Therefore, the skeleton does not precipitate from a spatially homogeneous fluid and its different parts may thus have varying sensitivity to environmental stress. This offers new insights into the mechanisms behind the response of the S. siderea skeletal phenotype to ocean acidification
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
Estimates of Northern Component Water based on benthic foraminifera d13C measurement of IODP Site 306-U1313
No full textIn supplement to: Lang, DC et al. (2016): Incursions of southern-sourced water into the deep North Atlantic during late Pliocene glacial intensification. Nature Geoscience, 9(5), 375-379</span
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
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