1,721,009 research outputs found
A twenty year reversal in water mass trends in the subtropical North Atlantic
No full textTemperature and salinity changes have been compared along three repeat sections at 36°N in the North Atlantic. The principal changes, cooling of the upper waters and warming of the intermediate waters observed between 1959 and 1981, were reversed between 1981 and 2005. The controlling mechanisms for the changes over the two time periods differed through the water column. Neutral density surfaces over the upper 800 m were firstly uplifted and secondly depressed by typically 50 m, which is broadly consistent with the changes in thermocline thickness implied by the temporal changes in Ekman pumping. In contrast, the intermediate waters (800–2500 m) firstly became warmer and saltier and secondly became cooler and fresher. This change in the intermediate waters was controlled by water mass changes along neutral density surfaces suggesting a change in the source waters, principally Labrador Sea Water and Mediterranean Outflow Water
The role of eddies in the isopycnic transfer of nutrients and their impact on biological production
Full text linkEddies provide a systematic, large-scale transfer of tracers and nutrients along isopycnals through a combination of eddy-induced diffusion and advection. The nutrient distribution is controlled by advection, rather than diffusion, when the nutrient lifetime exceeds a timescale given by κ/V2 where κ is the lateral diffusivity and V is the characteristic transport velocity. Idealized, eddy-resolving experiments are conducted using an isopycnic model configured for a zonal channel. Whether the eddies act to enhance or inhibit biological production depends on the location of the nutrient source and the nutrient lifetime. For a subtropical gyre and the Southern Ocean, the eddy-induced diffusion and advection are likely to oppose each other over the euphotic zone but reinforce each other at depth. Over the euphotic zone, the combination of eddy diffusion and Ekman advection of nutrients should dominate the opposing eddy-induced advection. This lateral transfer becomes more important for long-lived nutrients, such as dissolved organic nitrogen, within the euphotic zone
Modelling the effects of chromatic adaptation on phytoplankton community structure in the oligotrophic ocean
No full textWe explored the role of chromatic adaptation in shaping vertical phytoplankton community structures using a trait-based ecosystem model. The model included 1000 ‘phytoplankton types’ and was applied to the oligotrophic South Atlantic Gyre in a 1-dimensional framework, where ‘phytoplankton types’refers to the model phytoplankton that were stochastically assigned unique physiological characteristics. The model incorporates multi-spectral optics and light absorption properties for the different phytoplankton. The model successfully reproduced observed vertical gradients in the nitrate, bulk phytoplankton properties and community structure. Model phytoplankton types with Synechococcus-like spectral light absorption properties were outcompeted at depth, where eukaryote-like spectral properties were advantageous. In contrast, photoinhibition was important for vertical separation of high-light and low-light Prochlorococcus model analogues. In addition, temperature dependence was important for selection of phytoplanktontypes on the temperature gradient. The fittest, or successful, phytoplankton types were characterised by combinations of simultaneously optimal traits that suited them to a particular depth in the water column, reflecting the view that phytoplankton have co-evolved multiple traits that are advantageous in a particular environmental condition or niche
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
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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