1,721,082 research outputs found
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
Aeolian Iron and Its Contribution to Phytoplankton Production in McMurdo Sound, Southwest Ross Sea, Antarctica
No full textEach summer the waters in McMurdo Sound (Lat. 77.5ºS; Long. 165ºE), south-western (SW) Ross Sea encounter vast phytoplankton blooms. This phenomenon is stimulated by the addition of bio-available iron (Fe) to an environment where phytoplankton growth is otherwise Fe-limited. One possible source of such Fe is aeolian sand and dust (ASD) which accumulates on sea ice and is released into the ocean during the summer melt season.
The amount of bio-available Fe (i.e. the amount of Fe immedately accessible to phytoplankton) potentially supplied to the ocean by ASD depends on a number of factors including; the ASD flux into the ocean, its particle size distribution and Fe content. However, none of these parameters are well constrained in the SW Ross Sea region and, as a result, the significance of this Fe source in the biogeochemical cycle of phytoplankton growth remains to be quantified.
This study focuses on an area (7400 km²) of Southern McMurdo Sound, one of the few areas where direct sampling of ASD that has accumulated on sea ice is possible. To evaluate the flux and solubility of Fe contained in ASD into McMurdo Sound, the mass accumulation rate and particle size of 70 surface snow samples and 3 shallow (3 m) firn cores from the nearby McMurdo Ice Shelf covering the period 2000 - 2008 have been analysed. Selected samples were also measured for total and soluble Fe, Sr and Nd isotopic ratios and mineralogy as a guide to Fe-fertilisation potential and provenance, respectively.
Mass and particle size data show an exponential decrease in mass accumulation rate (from 26.00 g m⁻² yr⁻¹ to 0.70 g m⁻² yr⁻¹) and a decrease in modal particle size (from 130 to 69 μm) over a distance of 120 km from Southern McMurdo Sound northwards to Granite Harbour. Both these trends are consistent with ASD being dispersed northwards across the sea ice by southerly storms from an area of the McMurdo Ice Shelf, where submarine freezing and surface ablation have resulted in a surface covered with debris from the sea floor, known as the 'dirty ice' or 'debris bands' (Lat. 77.929ºS; Long. 165.505ºE) in Southern McMurdo Sound. This assertion is further supported by the Sr and Nd isotopic signature of ASD
matching local source rocks and the presence of vesicular glass of Southern McMurdo Sound in all samples which also points to the debris bands as the origin of ASD in McMurdo Sound.
Bio-available Fe is extremely difficult to quantify hence Fe solubility was used as an approximation in this thesis. Analysis of both total (i.e. particulate and soluble) and the percentage of soluble Fe in the 0.4 - 10 μm dust size fraction (i.e. the fraction most likely to become bio-available) by solution ICP-MS shows a narrow range of values; 3.84 ± 1.99 wt % and 9.42 ± 0.70 % respectively. Combining these values with mass accumulation rate estimates for the particles 0.4 - 10 μm in size, gives an annual soluble Fe flux for the region 500 km² north of the debris bands in McMurdo Sound of 0.55 mg m⁻² yr⁻¹ (9.89 μmol m⁻² yr⁻¹), with spatial variability largely determined by differences in mass accumulation rate.
These fluxes are at least an order of magnitude greater than predicted in global dust deposition models for the Southern Ocean and measured in snow samples from East Antarctica. Furthermore, these values exceed the Fe threshold, estimated as 0.2 nM (Boyd and Abraham, 2001), required for phytoplankton growth following the simple dust-biota model of Boyd et al. (2010) and assuming the release of captured ASD in snow is instantaneous. Whilst not constrained in the present study, ASD sourced from the debris bands may be sufficiently widely dispersed, particularly during storm years, to contribute to Fe-fertilisation up to 1200 km from Southern McMurdo Sound.
Short, ~10 year long, firn core records of mass accumulation and methylsuphonate concentration, a proxy for phytoplankton productivity, shows a close correspondence between the two during particularly stormy years. Whilst not demonstrating a cause-and-effect relationship, this observation suggests coastal ice cores may contain an important record of the interplay between climate, dust supply, Fe-fertilisation of near shore waters and phytoplankton productivity on decadal and longer timescales
Sedimentary Processes and the Holocene Development of Palmyra Atoll, Equatorial Pacific Ocean
No full textCoral atolls are unique landforms in that they are the physical manifestations of the interplay between both biological and geological processes. Prominent amongst these processes is the ability of the reef organisms to produce CaCO3 and its subsequent erosion and dispersal as sediment. Overriding controls on this process are organic productivity, wave energy, and relative sea level. The development and stability of atolls are thus critically dependent on the balance between several processes which may change over time. Atolls are regarded as being particularly vulnerable to environmental change.
This study investigates the Holocene geological history of Palmyra atoll, at 5°52’N 162°04’W, in the northern Line Islands. Beachrock is used as an indicator of (a) paleo-sea level and (b) paleo-shoreline conditions from clasts trapped within the beachrock matrix. The study also models annual CaCO3 production and hydrodynamic conditions at the sea bed to provide an integrated assessment of the past and present sedimentary processes and reef island development at Palmyra Atoll. The atoll is currently the focus of intensive scientific study by the Palmyra Atoll Research Consortium and is particularly suited to this study because of the reduced human presence. This allows the examination of the relationship between beachrock, islet development and other processes, in an environment lacking ongoing anthropogenic development.
Beachrock was found at 10 locations at Palmyra Atoll and yielded 14C ages ranging from 1249 to 105 cal. yrs BP. Typically, the beachrock contains mostly coral and algal clasts and is thought to form in the intertidal zone. Continual wetting and drying throughout a tidal cycle results in the precipitation of marine phreatic cements, which thus, indicate paleo-shorelines and sea level elevation. The production of CaCO3 sediment at Palmyra was estimated using reef habitat zones from Hopley (1996) and suggests that the most productive areas are reef terraces and the reef edge. An estimate total of 91,500 tonnes of CaCO3 is produced annually on the reefs, although only approximately 9 % of this becomes sediment that remains on the reef islands.
Hydrodynamic processes were modelled using the SWAN model, a bathymetric grid from NOAA, and bottom conditions estimated from other studies. Input parameters were determined using a 13 year WAVEWATCHIII hindcast model of the wave climate for the central Pacific, as well as estimations of extreme wave events. Sediment transport was inferred from the modelled bed shear stress and these results show that to form most of the beachrock outcrops on Palmyra extremely strong wave action must be coupled with a higher sea level in order to allow the propagation of wave energy across the reef to some of the island shorelines.
Integration of all results suggests that growth of the reef islands at Palmyra Atoll was initiated as the sea level fell from the mid-Holocene Highstand, 1-2 m above present mean sea level. The islands subsequently grew progressively eastward, forming 3-4 island chains which strike north or northeast. The beachrock that formed on these island provided protection from later wave erosion. Despite limitations caused by lack of climatic and other environmental data due to the isolation of the study area, results are reliable and highlight the application of beachrock as a proxy for past climates and sea levels
Ice dynamics and ocean productivity during the Late Miocene, offshore Wilkes Land, East Antarctica
No full textThe middle Miocene Climatic Transition (~14 Ma) is commonly interpreted to represent the significant advance of the East Antarctic Ice Sheet (EAIS), and the transition to a hyper-arid climate and a stable polar-styled ice sheet. However, an increasing number of studies provide evidence for continued instability and abundant meltwater processes influencing the low-lying margins of the EAIS during the Late Miocene (~11.6-5.3 Ma). The history of the EAIS during this period remains ambiguous due to the sparse number of records, and those that do exist have poor age resolution. This thesis investigates Integrated Ocean Drilling Program Site U1361 (64°24.5°S 143°53.1°E), located on the lowermost continental rise of the Wilkes Land margin. It aims to assess the variability of the EAIS and associated changes in palaeoceanography offshore one of the largest marine-based sectors of East Antarctica, the Wilkes Subglacial Basin, and to establish if the EAIS was responding to orbital forcings during the Late Miocene.
The study period (~11.7 to 10.8 Ma) contains six intervals of nannofossil-rich mudstones, interbedded with laminated mudstones and diatom-rich mudstones. Nannofossils are absent elsewhere in core U1361A, which covers the past ~14 Ma. To identify the sedimentary and depositional processes which influenced this anomalous interval of calcareous biological productivity, a high-resolution record (using ~450 samples) of Iceberg Rafted Debris (IBRD), grain size analysis and bulk geochemistry XRF analysis have been developed.
A lithofacies scheme has been established and used to provide an interpretation of the shifting sedimentary processes through time. Repeating cycles of faintly laminated mudstones were interpreted to represent the influence of bottom current activity on overbank turbidites, that spill onto a channel leeve, during glacial periods. The contouritic nature of the facies is likely associated with the low-relief channel-levee system at this time. Interglacial sedimentation is characterised by an increase in biogenic content, IBRD and bioturbation, with deposition occurring during biologically productive open marine conditions. Two types of biogenic productivity are present over the interval (silica and/or carbonate). The intervals of diatom-rich mud were interpreted to be associated with enhanced upwelling of Circumpolar Deep Water (CDW). While, the nannofossil-rich mudstones suggest a significantly warmer climate, with coccolithophore production proposed to represent the influence of meltwater and shifting Southern Ocean frontal systems, acting to restrict nutrient upwelling and increase water temperatures.
Nannofossil-rich muds are only present for a short interval (700 kyr), suggesting that the anomalous depositional environment between ~11.7 to 11.0 Ma was potentially related to the significant retreat and surface meltwater processes at the EAIS margin. Interglacial sedimentation at Site U1361 is also accompanied by an increase in grain size (i.e. silt), interpreted to represent oceanic current intensification which acts to restrict the deposition of finer material, relative to glacial intervals. This intensification of ocean current strength may have resulted in increased heat delivery to the EAIS margin triggering a terrestrial based ice sheet, and the delivery of nutrients stimulating marine productivity.
Spectral analysis of the mean grain size (MGS) and IBRD Mass Accumulation Rate (MAR) records revealed that during the Late Miocene (~11.7 to 10.8 Ma), the ice sheet was paced by ~100 kyr eccentricity cycles, and a low frequency ~20 kyr processional component. This is consistent with two Late Miocene ¹⁸O records that are also paced by eccentricity, suggesting that the Antarctic Ice Sheet was contributing a significant signal to the global ¹⁸O record during this interval of the Late Miocene. However, the presence of nannofossil suggests a warmer world, rather than the colder climate state that are often inferred to lead to eccentricity/precession variability. A recent hypothesis proposed by Levy et al., (2019) invokes that a warmer climate may lead to surface melt processes which at high latitudes are dominated by eccentricity/precession. Although this style of climate is commonly thought to have occurred prior to ~14 Ma in East Antarctica, the evidence presented in this study suggests such a state existed at the Wilkes Land margin until at least ~11.0 Ma
(Table T5) Silicon, aluminium and calcium oxide composition of ODP Hole 172-1063D bulk sediments
No full text(Table T5) Silicon, aluminium and calcium oxide composition of ODP Hole 172-1063D bulk sediment
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