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Life on the margin: implications of ocean acidification on Mg-calcite, high latitude and cold-water marine calcifiers
No full textFuture anthropogenic emissions of CO2 and the resulting ocean acidification may have severe consequences for marine calcifying organisms and ecosystems. Marine calcifiers depositing calcitic hard parts that contain significant concentrations of magnesium, i.e. Mg-calcite, and calcifying organisms living in high latitude and/or cold-water environments are at immediate risk to ocean acidification and decreasing seawater carbonate saturation because they are currently immersed in seawater that is just slightly supersaturated with respect to the carbonate phases they secrete. Under the present rate of CO2 emissions, model calculations show that high latitude ocean waters could reach undersaturation with respect to aragonite in just a few decades. Thus, before this happens these waters will be undersaturated with respect to Mg-calcite minerals of higher solubility than that of aragonite. Similarly, tropical surface seawater could become undersaturated with respect to Mg-calcite minerals containing ?12 mole percent (mol%) MgCO3 during this century. As a result of these changes in surface seawater chemistry and further penetration of anthropogenic CO2 into the ocean interior, we suggest that (1) the magnesium content of calcitic hard parts will decrease in many ocean environments, (2) the relative proportion of calcifiers depositing stable carbonate minerals, such as calcite and low Mg-calcite, will increase and (3) the average magnesium content of carbonate sediments will decrease. Furthermore, the highest latitude and deepest depth at which cold-water corals and other calcifiers currently exist will move towards lower latitudes and shallower depth, respectively. These changes suggest that anthropogenic emissions of CO2 may be currently pushing the oceans towards an episode characteristic of a ‘calcite sea.
Clues from current high CO2 environments on the effects of ocean acidification on CaCO3 preservation
No full textAcidification of surface seawater owing to anthropogenic activities has raised serious concerns on its consequences for marine calcifying organisms and ecosystems. To acquire knowledge concerning the future consequences of ocean acidification (OA), researchers have relied on incubation experiments with organisms exposed to future seawater conditions, numerical models, evidence from the geological record, and recently, observations from aquatic environments exposed to naturally high CO2 and low pH, e.g., owing to volcanic CO2 vents, upwelling, and groundwater input. In the present study, we briefly evaluate the distribution of dissolved CO2–carbonic acid parameters at (1) two locations in the Pacific and the Atlantic Ocean as a function of depth, (2) a mangrove environment in Bermuda, (3) a seasonally stratified body of water in a semi-enclosed sound in Bermuda, and (4) in temporarily isolated tide pools in Southern California. We demonstrate that current in situ conditions of seawater pCO2, pH, and CaCO3 saturation state (?) in these environments are similar or even exceed the anticipated changes to these parameters in the open ocean over the next century as a result of OA. The observed differences between the Pacific and Atlantic Oceans with respect to seawater CO2–carbonic acid chemistry, preservation of CaCO3 minerals, and the occurrence and distribution of deep-sea marine calcifiers, support the hypothesized negative effects of OA on the production and preservation of CaCO3 in surface seawater. Clues provided from shallow near-shore environments in Bermuda and Southern California support these predictions, but also highlight that many marine calcifiers already experience relatively high seawater pCO2 and low pH conditions
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
Global climatic change: Disturbance regimes and biospheric feedbacks of temperate and boreal forests
No full textDispelling 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
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