1,720,971 research outputs found
Significance of the Polar Frontal Zone for large-sized diatoms and new production during summer in the Atlantic sector of the Southern Ocean
No full textThe chlorophyll a (chl a) biomass and primary production of three phytoplankton size fractions were estimated in the Atlantic sector of the Southern Ocean from 12 December 1995 to 20 January 1996. Elevated concentrations of chl a, primary production, and contribution of microplankton (>20 ?m) coincided with dominance by large or long-chained diatoms (Thalassiothrix spp., Pseudonitzschia lineola, and Chaetoceros spp.) in the Polar Frontal Zone (PFZ, 49.5°S–52°S). Vertically resolved assimilation numbers (i.e. primary production normalized to chl a) and intrinsic growth rates of microplankton were much lower at high-biomass stations of the Northern Polar Frontal Zone (NPFZ) than in adjacent waters. Silicic acid appeared to be the proximal factor limiting the growth and yield of resident diatoms in the NPFZ. A carbon budget showed that, during the sampling period, diatom dominance at high-biomass sites was associated with near-steady-state conditions. This system exhibited a low POC sinking flux relative to total primary production, despite strong dominance by microplankton. South of 52°S, total chl a and primary production were generally low, but increased sharply in a mixed Phaeocystis-diatom bloom that extended from 61°S to 65°S in the Seasonal Ice Zone (SIZ). We estimated that the PFZ contributes from 37% to 67% of the total open-water new production in the Southern Ocean near the Greenwich meridian, depending on whether blooms occur or not in the SIZ.<br/
Zooplanktonpopulationen dreier nordatlantischer Schelfe Auswirkungen abiotischer und biotischer Faktoren
No full textTIB: RO 4719 (3) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Wandering whales? Relationship between whales and the sea ice environment in the Southern Ocean
Get PDFEach austral summer large baleen whales migrate into the Southern Ocean to feed on krill. The melting of sea ice leads to algal blooms which allow rapid growth and development of krill. In order to predict how baleen whales will respond to long-term changes in the physical environment, we need to understand the relationships between baleen whales, their prey and the physical environment. The spatial models in this thesis are based on visual observations by whale observers onboard ships in open waters.
The model analyses suggest that Antarctic minke whales are more often found close to the sea ice edge, continental shelf and frontal systems. Estimates show higher numbers of minke whales in regions that experienced more sea ice melting during austral spring and summer. These findings strongly suggest that the amount of sea ice cover, and especially its seasonal change, affects populations of minke whales at the regional scale.
For the Scotia Sea, different species of baleen whales may target different types of krill. Minke whales and humpback whales were more often found in waters inhabited by juvenile krill, while fin whales were more often found in deeper waters, inhabited by adult krill.
Improved understanding of whale behaviour will help us to better predict how baleen whales will respond to environmental change. We hardly know how far away baleen whales can detect krill swarms and how they forage in a three-dimensional environment. Recent advances in infrared detection and acoustic research are promising techniques to remedy this knowledge gap
Responses of seabirds, in particular prions (Pachyptila sp.), to small-scale processes in the Antarctic Polar Front
Get PDFSmall-scale distribution patterns of seabirds in the Antarctic Polar Front (APF) were investigated in relation to other biological, physical, and chemical features during the ANT-XIII/2 research cruise of R.V. Polarstern from December 1995 to January 1996. The APF is characterized by steep gradients in sea-surface temperature and salinity. Within the APF, gradient zones were closely associated with elevated levels of primary production, chlorophyll-a (chl-a) concentrations, and zooplankton densities. Even broad-billed prions (‘Pachyptila vittata-group’), which dominated the seabird community by 83% in carbon requirements, showed small-scale distributional patterns that were positively related to primary production, chl-a, and total zooplankton densities. The findings demonstrate a close, direct link between fine-scale physical processes in the APF and biological activity through several food web levels up to that of zooplankton-eating seabirds. Broad-billed prions appeared to forage on very small copepods (Oithona spp.) in close association with the front. Fish- and squid-eating predators showed poor correlations with small-scale spatial structures of the APF. However, in a wider band around the APF, most top predators did occur in elevated densities, showing gradual spatio-temporal diffusion of the impact of the APF on higher trophic levels.<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
- …
