1,721,770 research outputs found
Small scale physical processes and phytoplankton growth in self seas
No full textDetailed physical and biological observations collected in shelf sea regions, dominated by tidal mixing fronts or internal tides, are analysed in terms of the effect of physical forcing on phytoplankton growth. Microstructure measurements are used to quantify differences in vertical mixing and hence nutrient and light supply across regimes. The Fast Repetition Rate Fluorometer (FRRF) is used to obtain high-resolution data on the physiological state of the associated phytoplankton communities, with the aim of testing hypotheses relating growth to changing environmental conditions. Observations were made during three research cruises, RRS Challenger, in the Western English Channel, 1999 and RV Kaharoa, off the North East New Zealand coast, 1998 and 2000. The work represents one of the first attempts to collect and interpret FRRF data in a defined physical context within natural ecosystems.Results from the 1999 cruise indicate that physical forcing in the region of a tidal mixing front has a pronounced influence on the physiology of the associated phytoplankton communities. FRRF based observations were consistent with nutrient limitation towards the stratified side of tidal mixing fronts, while deep vertical mixing caused light limitation within the mixed region. The observed enhancement of chlorophyll in the region of tidal mixing fronts therefore results, at least partly, from in situ growth.Results from the 1998 and 2000 cruises demonstrate that internal tide dissipation can be responsible for high vertical nitrate fluxes and pronounced variations in phytoplankton light climate. Interpretation of physiological data from the 2000 cruise was difficult due to the complexity of the physical processes observed. However, physiological variability due to vertical motions and upwelling in the region is demonstrated.Changes in FRRF derived photophysiology, as described by the photosynthetic efficiency (Fv/Fm) and the functional absorption cross section (σPSH), are shown to be related to photosynthetic parameters measured by 14C derived carbon fixation. In particular a striking inverse correlation between FRRF derived σPSH and 14C P* vs. E derived maximal photosynthetic rates (P*max) was observed. FRRF derived photosynthetic rates are shown to compare favourably with 14C derived rates, given the limitations of both techniques.</p
Dataset of ocean nutrient addition bioassay experiments
No full textDataset of ocean nutrient addition bioassay experiments. Accompanies publication: 'Global analysis of ocean phytoplankton nutrient limitation reveals high prevalence of co-limitation' by Thomas J. Browning and C. Mark Moore.</span
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
Global analysis of ocean phytoplankton nutrient limitation reveals high prevalence of co-limitation
No full textAbstract Nutrient availability limits phytoplankton growth throughout much of the global ocean. Here we synthesize available experimental data to identify three dominant nutrient limitation regimes: nitrogen is limiting in the stratified subtropical gyres and in the summertime Arctic Ocean, iron is most commonly limiting in upwelling regions, and both nutrients are frequently co-limiting in regions in between the nitrogen and iron limited systems. Manganese can be co-limiting with iron in parts of the Southern Ocean, whilst phosphate and cobalt can be co-/serially limiting in some settings. Overall, an analysis of experimental responses showed that phytoplankton net growth can be significantly enhanced through increasing the number of different nutrients supplied, regardless of latitude, temperature, or trophic status, implying surface seawaters are often approaching nutrient co-limitation. Assessments of nutrient deficiency based on seawater nutrient concentrations and nutrient stress diagnosed via molecular biomarkers showed good agreement with experimentally-assessed nutrient limitation, validating conceptual and theoretical links between nutrient stoichiometry and microbial ecophysiology
- …
