1,720,984 research outputs found
Sources and fluxes of hydrothermal heat, chemicals and biology within a segment of the Mid-Atlantic Ridge
No full textWe have conducted a segment-wide study of the chemical, biological and thermal effects of hydrothermal activity, in a bathymetrically enclosed, 50-km-long segment of the Mid-Atlantic Ridge, at 29°N. Our study involved long-term monitoring of bottom current speeds and temperatures coupled with ‘snap-shot' surveys of the concentrations of hydrothermal shrimp, manganese and particulate plumes occupying the water column enclosed by the axial valley. These data are combined with the calculated volume transport rates for the segment and the results compared with the heat and manganese flux from the Broken Spur vent field, located in the center of the segment. Our current meter data show that the basin-like bathymetry acts to restrict and control flow of water. Warm and shallow water, exported from the segment, is replaced by colder and deeper water. Water column profiles showed an increase in temperature of the water within the ‘Broken Spur' segment, compared with background stations located outside the ridge axis. The average refresh rate for the water column enclosed by the segment was found to be about 262 days. From these data, we calculate that the segment-wide flux of juvenile shrimp is 20×106 individuals per year. We show that the flux of manganese (exported at a rate of 5–6 mol/s) is matched by input from high-temperature effluent discharge at the Broken Spur vent field. We also calculate that the minimum average heat flux exported from the segment is about 275 MW. Of this, more than 90% is pervasively dissipated throughout the segment floor by conductively heated sea water, or simple thermal conduction, that carries little or no manganese to the water column. The remaining 10% or less of the heat flux results from localized, manganese-rich, high-temperature hydrothermal venting.<br/
Detection of an unusually large hydrothermal event plume above the slow-spreading Carlsberg Ridge: NW Indian Ocean
Full text linkAbout 90% of Earth's volcanism occurs along the global mid-ocean ridge system. Here, sporadic volcanic and tectonic activity is thought to cause cataclysmic release of hydrothermal fluids, forming event plumes. Each plume often contains as much hydrothermal effluent and heat as chronic hydrothermal venting from a typical vent site discharges during a year. To date, only a few event plumes have been detected, and only above intermediate-rate spreading ridges in the Pacific. Here, we report the first evidence for an unusually large event plume that originated from the slow-spreading (3 cm/yr full-rate) Carlsberg Ridge in the NW Indian Ocean. At 70 km long, up to 4540 km3 in volume and with up to 24 × 1016 J of excess heat, this event plume was substantially larger than previous ones and demonstrates that dispersion of hydrothermal heat and biological products from slow spreading ridges may be more significant and effective than hitherto imagined
Submarine hydrothermal venting on the southern Kermadec volcanic arc front (offshore New Zealand): location and extent of particle plume signatures
No full textLetters to Nature: Hydrothermal activity along the southwest Indian Ridge
No full textTwenty years after the discovery of sea-floor hot springs, vast stretches of the global mid-ocean-ridge system remain unexplored for hydrothermal venting. The southwest Indian ridge is a particularly intriguing region, as it is both the slowest-spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the Atlantic and Pacific oceans2. A recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest-spreading ridge sections, thus impeding migration and enhancing faunal diversity2. Here, however, we report evidence of hydrothermal plumes at six locations within two 200-km-long sections of the southwest Indian ridge indicating a higher frequency of venting than expected. These results suggest that fluxes of heat and chemicals from slow-spreading ridges may be greater than previously thought and that faunal migration along the southwest Indian ridge may serve as an important corridor for gene-flow between Pacific and Atlantic hydrothermal fields
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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