1,354,093 research outputs found
Shear enhanced nutrient supply at the Mesoscale
No full textPhytoplankton live almost exclusively in the sunlit waters of the euphotic zone. However, in addition to sunlight, phytoplankton require a regular supply of nutrients to grow. In the open ocean such nutrients are abundant in the dark waters below the euphotic zone. Hence, to a large extent it is the physical mechanisms driving the transfer of nutrient rich water into the euphotic zone which dictate patterns of phytoplankton growth. Using a combination of observation and high resolution computer modelling this thesis investigates whether shear associated with mesoscale features leads to locally enhanced turbulent mixing and a shear-enhanced nutrient supply. Measurements of turbulent diffusivity and nutrient concentrations have been made in a region containing an eddy dipole, a strong mesoscale feature, consisting of a cyclonic eddy and an anti-cyclonically rotating mode-water eddy. The effect of this strong mesoscale feature on vertical turbulent mixing is assessed by investigating whether variations in vertical shear associated with the mesoscale feature enhance the observed vertical turbulent mixing. Using these observations of turbulent diffusivity, augmented by further measurements from two other ocean regions, a new parametrization of shear-enhanced vertical turbulent mixing is developed. The new shear-enhanced mixing parametrization is implemented in a high-resolution computer model of a mode-water eddy. This model is then used to examine the effect of interactions between the eddy and the wind on vertical nutrient fluxes. The shear enhancement to nutrient supply by mesoscale circulation is found to be potentially of much greater significance than has previously been considered. Modelling suggests that when forced by high variability winds mode-water eddies appear to be capable of locally enhancing the vertical turbulent nutrient flux by up to an order of magnitude. The work in this thesis suggests that vertical turbulent flux may well be underestimated as a stimulus to new production
Code and data for the Galapagos macroplastic connectivity analysis
No full textCode and data for 'Detecting most effective cleanup locations using network theory to reduce marine plastic debris: A case study in the Galapagos Marine Reserve' by S.L. Ypma, Q. Bohte, A. Forryan, A.C. Naveira Garabato, A. Donnelly and E. van Sebille. Accepted for publication in the journal 'Ocean Science'
Evaluating the balance between vertical diffusive nitrate supply and nitrogen fixation with reference to nitrate uptake in the eastern subtropical North Atlantic Ocean
No full textThe balance between N2 fixation and diffusive NO3− supply is a key determinant for assessing the importance of both processes for new production in subtropical waters. Here we report observations of integrated N2 fixation rates from the eastern subtropical North Atlantic Ocean with coincident estimates of diffusive NO3− supply. We find the average rate of N2 fixation is equivalent to 62% of the diffusive NO3− supply, though N2 fixation could exceed the diffusive flux at individual stations. Turbulent diffusivity measurements across the nitracline indicate a mean diffusivity of 0.077 cm2 s−1. If approximations for methodological underestimates in the dominant N2 fixation technique are considered, the magnitude of N2 fixation is shown to represent 100% of the NO3− flux on average, and can be almost threefold higher at individual stations. As the study site is characterized by low rates of N2 fixation compared to other sectors of the North Atlantic this confirms N2 fixation as a major source term across the subtropical North Atlantic. The seasonal context of our observations suggests environmental factors underlie the in situ variability in observed N2 fixation rates, and may well explain lower previous assessments of the importance of N2 fixation relative to diffusive NO3− supply in this region. The diffusive NO3− supply provides <20% of measurable NO3− uptake with the remainder supplied via other mechanisms, most notably nitrification. The mean integrated rate of N2 fixation equates to just 8% of the NO3− consumed on a daily basis by the phytoplankton community
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Turbulent mixing in the eddy transport of Western Mediterranean Intermediate Water to the Alboran Sea
No full textWestern Mediterranean Intermediate Water (WIW) is formed in winter in the North-Western Mediterranean. WIW, identifiable as a distinct temperature minimum layer between Atlantic-Mediterranean Interface waters and the denser Levantine Intermediate Water, is carried down the east coast of Spain in anticyclonic mode water eddies, or “weddies” eventually reaching the Alboran sea. A previous detailed analysis of a weddy in the vicinity of the Almeria-Oran front indicated that it could have accounted for 10% of a winter's production of WIW, but this analysis was unable to consider turbulent dissipation. In this study we present microstructure measurements across a similar observation of WIW in the vicinity of the Almeria-Oran front and show that this figure could be conservative by 15–50% due to the turbulent dissipation associated with a weddy
Turbulent nutrient fluxes in the Iceland Basin
No full textAs part of a multidisciplinary cruise to the Iceland Basin in July–August 2007, near to the historical JGOFS Ocean Weather Station India site (?59° N, ?19° W), observations were made of vertical turbulent nutrient fluxes around an eddy dipole, a strong mesoscale feature consisting of a cyclonic eddy and an anti-cyclonically rotating mode-water eddy. Investigation of the spatial distribution of vertical turbulent diffusivity around the dipole shows an almost uniform horizontal distribution despite the strong horizontal gradients in water velocity and density observed. An area mean turbulent diffusivity was calculated as 0.21 (95% confidence interval: 0.17–0.26)×10?4 m2 s?1 at the base of the euphotic zone. The vertical turbulent fluxes of three major macro-nutrients into the euphotic zone were calculated as 0.13 (95% confidence interval 0.08–0.22) mmol m?2 day?1 for nitrate, 0.08 (0.05–0.12) mmol m?2 day?1 for silicate and, 8.6 (13.0–5.2 )×10?3 mmol m?2 day?1 for phosphate. The vertical turbulent flux of dissolved iron (dFe) into the euphotic zone was calculated to be 2.6 (95% confidence interval 1.3–4.3)×10?6 mmol m2 day?1. Turbulent macro-nutrient flux is estimated to contribute up to 14% of the deep winter mixing supply of silicate, nitrate and phosphate in the region. The magnitude of turbulent dFe flux is estimated to be at most 8% of the deep winter mixing supply of dFe. Deep winter mixing is hypothesised to supply an adequate amount of iron to fully utilise the deep winter mixed supply of silicate but not the deep winter mixed supply of nitrate. This suggests that while the iron supply may not limit the magnitude of the spring bloom, iron limitation may be occurring post bloom
Variations on the Author
No full text“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
No full textWe 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
No full textWe 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
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
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