1,722,120 research outputs found
Macroalgal photophysiology in the intertidal zone on Tromsøya
No full textMacroalgal physiology in the winter spring transition was analysed variable fluorescence tools. Estimates include quantum yield and the parameters alpha and maximum rates for electron transport rate versus irradiance curve fits. The species included: Pelvetia canaliculate, Fucus spiralis, Fucus vesiculosus, Ascophyllum nodosum and Fucus serratus
Microbial diversity and ecology in the coastal Arctic seasonal ice zone
Full text linkMarine microbes are crucial for the marine food web and carbon cycle. Algae are the main source of organic matter in the oceans with algae blooms triggering reoccurring bacterial succession patterns. Bacteria can recycle nutrients from organic matter coming from land or algae, fueling regenerated primary production. Terrestrial freshwater inputs can have substantial impacts on Arctic marine microbes via import of nutrients, organic matter, and sediments, and via changing the marine hydrography. The aims of this PhD thesis are i) to summarize the current knowledge about microbial ecology in the Arctic seasonal ice zone, ii) to study the effects of terrestrial inputs from rivers and glaciers on the microbial food web over different seasons, and iii) to dive into algae-bacteria interactions with a focus on the importance of regenerated production.
We provide evidence that subglacial upwelling is an important process in a tidewater glacier-influenced fjord on Svalbard in spring, a previously understudied season. Subglacial upwelling lead to increased surface water nutrients, a stratified surface layer, and brackish sea ice. At the glacier front, microbial communities were significantly different compared to a sea-ice edge reference site. Phytoplankton primary production was two orders of magnitude higher at the glacier site compared to the reference site, due to upwelling related nutrient inputs and potentially also stratification and a thinner snow cover. During the spring freshet and in summer we investigated the impacts of river runoff on bacterial and archaeal communities with detailed considerations of environmental drivers. We found significant differences between bacterial communities during the spring freshet and late summer, mainly controlled by the concentrations and properties of dissolved organic matter, nutrient concentrations, and fjord hydrography. We recreated major algal spring bloom dynamics in an experimental study with algae-bacteria co-cultures. I used the experimental data to extend a commonly used dynamic algal growth model improving the modeling of multi-nutrient limitations and bacterial remineralisation. The work within this thesis demonstrates that microbial communities and functions are highly regulated by environmental constraints in the coastal seasonal ice zones
Arctic marine microbial ecology during the Svalbard Polar Night
Full text linkThis study investigated the presence and activity of the components of the microbial food web (sepcifically viruses, heterotrophic bacteria and nanoflagellates, and autotrophic Cyanobacteria and pico-nanoflagellates) in the waters around the Svalbard archipelago (Norway) during the polar night period. The study focused on two major questions – are there differences in the community composition in different water masses? And, are there significant changes occurring during the polar night period? Two cruises in January and November 2017 with a total of 11 stations offered the opportunity to test these hypotheses. Flow cytometry was used to determine cell abundances in the uppermost 100m of the water column, and 8 serial dilution experiments were conducted to estimate their growth and grazing rates. All studied organism groups occurred in all samples in low abundances in both January and November. Comparison to the hydrographic regime revealed strong linkages between community structure and hydrography with higher abundances in Atlantic Water samples. Heterotrophic nanoflagellates and autotrophic pico-nanoplankton were markedly less present in January, whereas bacteria and viruses displayed steady concentrations in both months. This supported the hypothesis of succession in the microbial network throughout the polar night, and the possible role of mixotrophy and resting stages are discussed. No significant growth or grazing was detected in the experiments, which could be caused e.g. by low substrate availability and resting strategies. This study demonstrated that all members of the microbial food web organisms persists throughout the polar night in the major water masses around Svalbard. Future studies using alternative approaches are suggested to further study these processes during times of low activity
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
Seasonal abundance and activity of sympagic meiofauna in Van Mijenfjorden, Svalbard
Full text linkThe importance of landfast ice as a nursery and breeding ground for Arctic marine invertebrates was studied in Van Mijenfjorden (77°N, 15/16°W), southwestern Svalbard from March to May 2017. The collection of first-year ice cores with stations along a depth gradient allowed the investigation of both temporal and spatial differences in sympagic meiofauna community composition and abundance. Furthermore, water column samples were retrieved to examine the strength of sympagic-pelagic coupling. Overall, 13 taxa were identified from the ice and 15 taxa from the water column with low abundances of dominant ice fauna in the water samples. Total sympagic metazoan abundance peaked in late April with over 25,000 ind m-2, due to the reproduction of ice-associated nematodes. Throughout spring the presence of sexually mature nematodes and eggs supported the notion that sea ice in Van Mijenfjorden, especially at the main station (vMF/Mn – 50 m water depth), served as a breeding and reproductive ground to ice nematodes
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
- …
