1,720,959 research outputs found
Coral reefs of the Indo-Pacific and changes in global Holocene
Full text linkThe key to understanding the future impact of the anthropogenic combustion of fossil fuels on the climate system, is to fully understand the complex feedback loops within the natural Earth system. One natural climate feedback that has been proposed is the Coral Reef Hypothesis whereby significant increases in coral reef growth may have contributed to the deglacial increase in atmospheric CO2 observed in the ice core records. This thesis examines the role of coral reefs in the oceanic carbonate budget and global carbon cycle both spatially and temporally during the Holocene. Using the most comprehensive reef area estimate to date, a conservative estimate of cumulative CaCO3 accumulation within coral reefs globally from 10 kyr BP to present is 7970 Gt. This estimate includes a temporal and spatial view of reef CaCO3 accumulation during the Holocene and represents coral reefs alone, whereas previous budgets have included wider neritic carbonate facies. This mass of reefal CaCO3 accumulation would have made approximately 2100 Gt CO2 available for release to the atmosphere over the Holocene.Radiocarbon dating of coral obtained from new drill cores from Rodrigues (Southwest Indian Ocean), Lizard Island and MacGillivray Reef (Northern Great Barrier Reef (NGBR)), helps to reveal the spatial and temporal pattern of Holocene CaCO3 accumulation within these reefs and contributes to the dataset compiled to calculate the global mass balance of coral reef carbonate. The new data presented here demonstrates that the reefs at Rodrigues, like those at Reunion and Mauritius only reached a mature state (reached sea level) by 2 to 3 ka – thousands of years later than most of the reefs in the Australasian region. The windward margins at Lizard Island and MacGillivray Reef started growing ca 6.7 and 7.6 cal kyr BP respectively directly on an assumed granite basement and reached sea level approximately 4 and 5.6 cal kyr BP respectively. The leeward margin at MacGillivray Reef was initiated by 8.2 cal kyr BP directly on a granite basement, only reaching sea level relatively recently between 260 and 80 cal yr BP. The absence of Pleistocene reefal deposits indicates the possibility that the shelf in this region may have subsided relative to modern day sea level by at least 15 m since the last interglacial (125 ka).The role of the calcareous green alga Halimeda in the marine carbonate budget is still unknown both spatially and temporally for the Holocene. Here a quantification of the carbonate mass within the ribbon reefs and Halimeda bioherms on the outer shelf of the NGBR is presented. It is estimated that Halimeda bioherms contain at least as much (possibly 400 % more) CaCO3 sediment than the adjacent ribbon reefs within the NGBR province
Holocene evolution of the granite based Lizard Island and MacGillivray Reef systems, Northern Great Barrier Reef
No full textRadiocarbon dating of seven drill cores from both the windward Lizard Island fringing reef and the windward and leeward margins of MacGillivray platform reef, Northern Great Barrier Reef Province, reveal the Holocene evolution of these two mid shelf coral reefs. The windward margin at Lizard Island started growing approximately 6,700 calendar years before present (cal yr BP) directly on an assumed granite basement and approached present day sea level approximately 4,000 cal yr BP. Growth of the windward margin at MacGillivray Reef was initiated by 7,600 cal yr BP and approached present day sea level by approximately 5,600 cal yr BP. The leeward margin at MacGillivray was initiated by 8,200 cal yr BP also directly on an assumed granite basement, but only approached sea level relatively recently, between 260 and 80 cal yr BP. None of the cores penetrated the Holocene-Pleistocene unconformity. The absence of Pleistocene reefal deposits, at 15 m depth in the cores from MacGillivray Reef, raises the possibility that the shelf in this region has subsided relative to modern day sea level by at least 15 m since the last interglacial [125,000 years ago (ka)]
Coral Reef sedimentation on Rodrigues and the Western Indian Ocean and its impact on the carbon cycle
No full textCoral reefs in the southwest Indian Ocean cover an area of ca. 18530 km2 compared with a global reef area of nearly 300000 km2. These regions are important as fishing grounds, tourist attractions and as a significant component of the global carbon cycle. The mass of calcium carbonate stored within Holocene neritic sediments is a number that we are only now beginning to quantify with any confidence, in stark contrast to the mass and sedimentation rates associated with pelagic calcium carbonate, which have been relatively well defined for decades. We report new data that demonstrate that the reefs at Rodrigues, like those at Réunion and Mauritius, only reached a mature state (reached sea level) by 2-3 ka: thousands of years later than most of the reefs in the Australasian region. Yet field observations show that the large lagoon at Rodrigues is already completely full of carbonate detritus (typical lagoon depth less than 1 m at low spring tide). The presence of aeolian dunes at Rodrigues indicates periodic exposure of past lagoons throughout the Pleistocene. The absence of elevated Pleistocene reef deposits on the island indicates that the island has not been uplifted. Most Holocene reefs are between 15 and 20 m in thickness and those in the southwest Indian Ocean appear to be consistent with this observation. We support the view that the CO2 flux associated with coral-reef growth acts as a climate change amplifier during deglaciation, adding CO2 to a warming world. southwest Indian Ocean reefs could have added 7-10% to this global flux during the Holocene. <br/
Significance of Halimeda bioherms to the global carbonate budget based on a geological sediment budget for the Northern Great Barrier Reef, Australia
Full text linkSince the correlation between carbon dioxide (CO2) levels and global temperatures was established in the ice core records, quantifying the components of the global carbon cycle has become a priority with a view to constraining models of the climate system. The marine carbonate budget is still not adequately constrained and the quantitative significance of the calcareous green alga Halimeda still remains particularly poorly understood. Previously, it has been suggested that Halimeda bioherms on the shelf of the Great Barrier Reef may contain a volume of carbonate equal to or greater than that contained within the shelf edge coral reefs. This study uses published datasets to test this hypothesis in the Northern Great Barrier Reef (NGBR) province. It is estimated that Halimeda bioherms on the outer shelf of the NGBR contain at least as much (and up to four times more) CaCO3 sediment as the adjacent ribbon reef facies. Globally, if these findings are even only partially applicable, the contribution of shallow water carbonate sediments to the global carbon budget based on coral reefs alone is currently substantially underestimated
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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