1,721,201 research outputs found
Glacial and interglacial changes in southwest Pacific water mass ventilation and circulation.
Full text linkReconstructions on Antarctic ice cores revealed pronounced, millennial-scale variabilities in atmospheric CO2 over the past 800,000 years (e.g. Lüthi et al., 2008; Monnin et al., 2001; Petit et al., 1999; Raynaud et al., 2005; Siegenthaler et al., 2005). Despite these variabilities are known for several decades, the mechanisms, driving these patterns are still not fully resolved. As the ocean contains up to 60 times more carbon than the entire atmosphere, it is considered to be a major driver of the atmospheric CO2 levels (Broecker, 1982): Storing CO2
during glacials, releasing it during deglaciations. Because changes in the global thermohaline circulation are thought to operate on glacial/interglacial timescales, it has been suggested that during glacials, the deep ocean was separated from surface-waters and therefore from the atmosphere by enhanced stratification, resulting in the pronounced accumulation of CO2 and nutrients in the lower levels of the water column. These waters, isolated for millennia, then surfaced during interglacial periods and released their load of ancient CO2. This hypothesis is strongly supported by the record of atmospheric radiocarbon activities (Δ14C; Reimer et al., 2013) in which a telltale drop in Δ14C is shown during the interval of enhanced increase in atmospheric CO2. This drop cannot be explained by the atmospheric formation of 14C and is therefore indicative for the release of an old and hence 14C-depleted and CO2-enriched reservoir (e.g. the deep ocean) to the atmosphere. This release can therefore explain both records (atmospheric CO2 and Δ14C). Indeed, several records from the Atlantic and Pacific
Oceans point to the existence of this carbon pool in glacial deep-waters below 2000 m. However, the spatial extent (vertical and lateral) and particularly the pathways of upwelled waters during the interglacial remain elusive and even contradictory. The aim of this thesis is to improve the knowledge of changes in South Pacific circulation and ventilation over different glacial to interglacial time-scales. The three manuscripts that form the backbone of this thesis are used to: 1) constrain the spatial extent and upwelling pathways of the glacial carbon pool in the South Pacific (0 – 30,000 years); 2) reconstruct boundary shifts between intermediate-waters and the underlying carbon pool in Circumpolar Deep
Water over the last 350,000 years; 3) analyze changes in the South Pacific Gyre’s thermocline during the past 200,000 years. The focus of the first manuscript (Chapter 3) lies on the transition from the last glacial to the current interglacial. The Δ14C-reconstructions on a water mass transect of seven sediment cores from the New Zealand Margin and the East Pacific Rise identify a pool of radiocarbon depleted waters between ~2000 and ~4500 m in the glacial counterpart of Pacific Deep Water. The 14C-depletion of this body of water is up to five times higher than in the modern South Pacific and reaches extreme apparent ventilation ages of ~8000 years. Despite the first deep water rejuvenation begins as early as ~21,000 years B.P., the main signal of rejuvenation and outgassing parallels the rise in atmospheric CO2. The vertical extent of southwest Pacific Antarctic Intermediate Water (AAIW) over the last four glacial/interglacial cycles is analyzed in the second manuscript (Chapter 4). Stable isotope records (δ13C and δ18O) from epibenthic foraminifera of sediment cores bathed in AAIW and Upper Circumpolar Deep Water (UCDW) indicate a shoaling of AAIW during glacial periods. Further support for these findings arises from model reconstructions using the CCSM3-climate model. Throughout glacial maxima, pronounced input of freshwater by melting sea ice into the AAIW significantly increased its buoyancy and hampered its downward expansion. Hence, the upward displacement of the AAIW-UCDW boundary led to an expansion of the glacial carbon pool identified in Chapter 3. In the third manuscript (Chapter 5) the evolution of Southern Ocean Intermediate Waters (SOIWs) is analyzed, using the Mg/Ca paleothermometry on surface- and deep-dwelling species of planktic (Emiliani, 1991) foraminifera. The results suggest opposing glacial subsurface conditions during the LGM and MIS 6 with colder-than-Holocene conditions during the former and warmer-than-LGM conditions during the latter interval. Because of the importance of SOIWs for the ventilation of the South Pacific Gyre (SPG), the results of Chapter 5 reveal the relevance of Southern Ocean subsurface processes on the transfer of
climatic signals from higher to lower latitudes via the SPG. Ultimately, this thesis contributes to the broader understanding of ventilation and circulation changes in the Pacific Sector of the Southern Ocean. The combination of various proxies reveals the highly dynamic processes that affect the Southern Ocean on glacial/interglacial timescales. The results do not only constrain the vertical extent of the glacial carbon pool for
the first time, but they also facilitate its integration in the global context of glacial circulation. Furthermore, the reconstructions shown in this study might help to improve model simulations that are used to both, reconstruct and predict changes in the global climate
Stable isotope record of Cibicidoides wuellerstorfi and Uvigerina perigrina of sediment core SO213/2_82-1
No full textThe dataset show stable isotope data of d13C and d18O measured on benthic foraminifers, C. wuellerstorfi and U. perigrina. The samples were collected in the Bounty Trough off New Zealand during Expedition SO213/2 in 2011. The aim of this study was to reconstruct the dynamics of Southern Ocean water masses on glacial-interglacial timescales
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
Stable and radiogenic isotope record for sediments cores from the Southern Indian Ocean
No full textHere we present reconstructions of water residence times (depicted as ΔΔ14C and δ13C) for the last 32,000 years on sediment records from the Kerguelen Plateau and the Conrad Rise (~570-2500 m water depth), along with simulated changes in ocean stratification from a transient climate model experiment. Our data indicate that Circumpolar Deep Waters in the Indian Ocean were part of the glacial carbon pool
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
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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