1,721,242 research outputs found
Testing the palaeoclimatic signal from peat bogs - temperature or precipitation forcing?
No full textThe aim of this project was to compare a peatland proxy climate record with a temperature reconstruction based on chironomids in the sediments of a nearby lake in an attempt to assess the degree to which the peat-based record reflects temperature changes. Peat-based palaeoclimatic proxies measure bog surface wetness, which depends upon effective precipitation (precipitation minus evapotranspiration), and previous work involving comparisons with Little Ice Age records, and the analysis of long documentary climate records, had suggested the hypothesis that the temperature signal is more coherent and is dominant over the spatially and temporally incoherent precipitation signal. A 3 metre peat core of from Walton Moss, Cumbria, was analysed for plant macrofossils, colorimetric humification, and testate amoebae, to yield three independent climate proxies. A 240 cm core of sediments from Talkin Tarn, nine km south of Walton Moss, was analysed for chironomid head capsules, and air temperatures were reconstructed using a mean July temperature transfer function. The cores were dated using AMS radiocarbon dates and an Icelandic tephra. The three proxy reconstructions from Walton Moss show coherent patterns of change over the last 3000 years. The plant macrofossil data show the profile to be sensitive to mire water table fluctuations, with the numerous occurrences of the hygrophilous Sphagnum section Cuspidata modelled as low DCA scores, indicating climatic deteriorations. The main climatic deteriorations identified from these proxy data occur between cal. 2900-2830 BP; 2630-2590 BP; 1730 BP; 1550-1400 BP; 1120 BP; 840 BP; 680BP; 500-400 BP, and 240-150 BP. The chironomids from the sediments of Talkin Tarn showed changing domination of various taxa over time, with over 50 taxa identified. The fossil data were modelled with a transfer function from 153 Norwegian lakes (S. Brooks & H. J. B. Birks, pers. comm.), producing a maximum range of reconstructed values between 14.8-12.6°C, with an RMSEP of 1.0592. The mud/water interface was not retained by the core, although the reconstructed temperature for the sample at 10 cm (closest to the modern day) is 14.8°C, an exact match with the present recorded 30 year average mean July temperature of 14.8°C for Talkin Tarn. The results indicate that the midges appear to have responded to fluctuations in past temperature, most notably around cal. 2500 BP, when there is a significant increase in the abundance of Tanytarsus lugens group indicating a relatively large decrease in temperature of over 2°C. Other notable fluctuations occur earlier in the Holocene, illustrated by the decline in temperature from 14.8 to 13.6°C between ca. cal. 5300 and 4550 BP, and the lowering of temperature by ca. 1.3°C between 2000 and 1500 BP. Although the general trend of temperature fluctuations can be reconstructed from the chironomid transfer function, the comparatively low sampling resolution of the chironomids (one sample every ca. 250 years) prevents detailed inferences being made with respect to the rates and magnitudes of change over time. However, it is significant that the age/depth model for Talkin Tarn dates the main temperature decline to around cal. 2600 BP. A well known climatic deterioration has been recorded from many bogs around this time, as well as from a chironomid reconstruction in the Cairngorms. The Walton Moss data also show a climatic deterioration at this time. The other major temperature decline in the chironomid-inferred temperature reconstruction matches a general trend within the mire water table reconstructions from the testate amoebae data. A 1.3°C drop in temperature at Talkin Tarn is associated with an initial 7.4 cm rise in water table depth at Walton Moss at cal. 1730 BP, and comparatively high water tables continue (with subtle fluctuations, as indicated by the other proxy reconstructions) until cal. 920 BP, when they fall to below 11 cm. This corresponds with a 1°C increase in temperature at Talkin Tarn between cal. 1090-830 BP, and could be an indication of climatic change associated with the Medieval Warm Period. Although the three proxy reconstructions from Walton Moss detect changes associated with the Little Ice Age, there is no such indication from the chironomid-inferred temperatures. This may be due to the low sampling resolution, or may reflect other changes in the lake catchment, such as anthropogenic activity. Human influence is indicated by an increase in pastoral pollen indicators towards the top of the fossil pollen spectra (S. Morriss, pers. comm). It may also be suggested that chironomids respond not only to the relatively small changes of temperature within the Holocene, but also to changes in the pH of the lake water. However, this should only be a possible factor in lakes with acid rock catchments (S. Brooks, pers.comm.) which is not the case at Talkin Tarn. This project was designed as a palaeoecological test of the hypothesis that changes in bog surface wetness are driven primarily by temperature, and this hypothesis has been upheld. The project has further demonstrated that chironomids can successfully detect small scale temperature changes during the Holocene, based upon the new 153-lake transfer function, which also successfully models the present July temperature. The use of three independent proxies on the same peat profile gives a firmer foundation for proxy climate reconstructions – although time-consuming it is to be recommended for critical applications. <br/
The climate of Scotland over the last 5000 years inferred from multiproxy peatland records: inter-site correlations and regional variability
No full textThe mid to late-Holocene climates of most of Scotland have been reconstructed from seven peat bogs located across north–south and east–west geographical and climatological gradients.The main techniques used for palaeoclimatic reconstruction were plant macrofossil, colorimetric humification, and testate amoebae analyses, which were supported by a radiocarbon-based chronology, aided by markers such as tephra isochrons and recent rises in pine pollen and in spheroidal carbonaceous particles (SCPs). Field stratigraphy was undertaken at each site in order to show that the changes detected within the peat profiles were replicable. Proxy climate records were reconstructed using detrended correspondence analysis (DCA) of the plant macrofossil data and a mean water tabledepth transfer function on the testate amoebae data. These reconstructions, coupled with the humification data, were standardised for each site and used to produce a composite record of bog surface wetness (BSW) from each site. The results show coherent wet and dry phases over the last 5000 years and suggest regional differences in climate across Scotland, specifically between northern and southern Scotland. Distinct climatic cycles are identified, all of which record a millennial-scale periodicity which can be correlated with previously identified marine and ice core Holocene cycles. The keyrole of the macrofossil remains of Sphagnum imbricatum, a taxon now extinct on many sites, is discussed in relation to the identified climatic shifts
Assessment, insight and awareness in design for users with special needs
No full textUser-Centred Design (UCD) has to take into account insight and awareness shown by potential users as a key part of the process. Other important factors (listed below) also depend upon insight and awareness
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
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