1,720,995 research outputs found
The effects of 20th century climatic perturbation on calcareous algae in the Santa Barbara Basin (California)
No full textDecadal- and interannual modes of atmosphere-ocean variability are well-known from instrumental observations in the Pacific region. These fluctuations are associated with the Pacific Decadal Oscillation (PDO) and greatly impact marine ecosystems along the California coastline. However, it is currently unclear how the effects of recent warming on different marine taxa may be similar or different from past PDO variations. The PDO has basin-wide effects on sea-surface temperature (SST) and thermocline slope that are similar to El Niño but on longer time scales. A laminated box core from the Santa Barbara anoxic Basin reveals that coccolithophore assemblage fluctuations can be related to climatic and paleoceanographic changes during the last century. In our study, the main oceanographic parameters controlling the distribution of coccolithophore assemblages are temperature and water stratification, since nitrate and phosphate are relatively high throughout the study period. Variations in abundance of two warm water affinity species (Florisphaera profunda and Umbilicosphaera sibogae) show different patterns with respect to the PDO and warming trend. U. sibogae reflects decadal-scale fluctuations associated with the PDO during the 20th century while F. profunda has relatively low abundances during a positive phase of the PDO from 1935-1945 but increases in abundance during the last two decades, in association with the warming trend. While variations in abundance of other species may also reflect the PDO, there appears to be an influence of the 20th century warming trend on some aspects of the coccolithophore assemblage shift during the last 20 years. We will discuss the coccolithophore response to the apparently superimposed anthropogenic effect
The effects of El Nino Events on Coccolithophore assemblages in the Santa Barbara Basin (California)
No full textEl Niño (EN) is a disruption of the ocean-atmosphere system in the tropical Pacific that has important consequences for global weather patterns. EN events are marked by years with an increase of sea-surface temperature, sea-level barometric pressure and rain fall along the California Margin. A laminated box core from the Santa Barbara anoxic Basin is used in this work to study the EN effect on primary productivity, in particular on coccolithophores in the California Borderland during the last 60 years. The EN events were defined by two indexes: Multivariate ENSO Index (MEI) from 1996 to 1950 and Southern Oscillation Index (SOI) from 1950 to 1939. In the box-core samples we can observe an increase of coccolithophore carbonate flux during the years following EN events (positive MEI and negative SOI). In particular, Gepyrocapsa oceanica flux abundance shows a strong positive correlation with strong EN events, like in 1965-66, 1982-83 and in 1997-98 (for 1997-98 from sediment trap experiment in the center of SBB). Significant sea-cliff erosion and storm damage occurred along the central coast of California during the 1982-83 and 1997-98 El Nino winters. We will discuss the coccolithophore response to El Nino events, also considering the minor chemical elemental changes in the surface water column. In our study, it appears that the main oceanographic parameter controlling the distribution of coccolithophore assemblages is temperature, since nitrate and phosphate are relatively high throughout the study period
Seasonal and interannual export production of coccolithophores in Cariaco Basin (Venezuela): tools for climatic variability
No full textCariaco Basin shows marked seasonal and interannual variations in hydrographic
properties and primary production. Partially isolated from the open Caribbean Sea
by a series of shallow sills, Cariaco Basin is anoxic below ̃250m water depth because
of restricted water exchange and high oxygen demand created by productive
conditions associated with seasonal upwelling along the southern Caribbean margin.
Moreover, the strength of the Northeast trade winds varies seasonally, because of the
annual migration of the Intertropical Convergence Zone (ITCZ), causing a significant
seasonal change in the surface waters of the Cariaco Basin. The combination of
high biogeochemical input and the lack of bioturbation at the bottom allow the deposition
of laminated sediments that exhibit high sedimentation rates. In this study
we track changes in coccolith export production and ecology in sediment trap samples
(10,30_N; 64,40_W; from November 1996 to October 1999) and laminated core
(CAR7-1) samples from Cariaco Basin, in order to monitor and understand climate
and ocean variability in the southern Caribbean region during the last 1000 years.
During a three-year sediment trapping project in Cariaco Basin significant changes
in coccolithophore fluxes occurred in response to changes in hydrography. Seasonal
coccolith fluxes are observed with flux maxima in late-fall and winter, when the hydrographic
conditions are relatively stable. In particular, coccolithophore patterns suggest
that these trends are driven by both annual and interannual changes in the upper water
column associated with El Niño conditions. The coccolith flux recorded in core
CAR7-1 was dominated by E. huxleyi, G. oceanica and F. profunda, the same species
that dominated the sediment trap samples.We will show the significant changes occuring
down-core, reflecting hydrographic and climatic variation in ITCZ position over
the Caribbean region. Moreover, C. leptoporus in this basin may indicate an increase in
cool water due to intensification in trade winds and upwelling intensity. Total coccolith
fluxes show evidence of centennial scale variability, suggesting solar modulatio
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
Dispelling 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
Sinking of coccolith carbonate and potential contribution to organic carbon ballasting in the deep ocean
No full textThere exists a great need to better understand the controls on organic carbon sequestration to the deep sea, by virtue of its role in modulating atmospheric CO2. Recent studies suggest that organic fluxes to the oceanic interior are higher in regions dominated by carbonate sedimentation, thus also concluding that relatively heavy carbonate particles are an effective mineral ballast for organic carbon. CO2 in the pelagic ocean is mainly mediated by foraminifera and coccolithophores, but the precise role of these carbonate producers as mineral ballast for organic carbon in the ocean has not yet been tested. Here we evaluate sediment-trap flux data from an array of 13 moorings (15 traps) situated in diverse conditions and with global coverage, all for organic carbon flux, calculated coccolith-carbonate flux, and fine fraction flux (when available). Discrepancies are recorded between the amount of carbonate fine fraction and calculated coccolith carbonate, and there is the need to determine the origin of the unknown CO2 in the fine fraction. The coccolith-carbonate flux magnitude is determined not only by the coccolith flux number but also by the carbonate mass of the key species. For example, very abundant coccolithophore species such as Emiliania huxleyi have a very low species-specific carbonate mass, and are therefore of lower carbonate flux significance than expected intuitively. Among the main coccolith carbonate species contributors in our sediment-trap sites are Calcidiscus leptoporus and Helicosphaera carteri, in that these are all relatively massive compared to their numerical abundances. We observed generally positive correlations between calculated coccolith carbonate and organic carbon daily fluxes, suggesting that on a global basis there is a ballasting mechanism at work, seemingly most efficiently with C. leptoporus in the carbonate-dominated North Atlantic. A fairly constant global relationship between annual fluxes of calculated coccolith carbonate and organic carbon implies some uniformity in the PIC/POC “rain ratio”. However, improvements in coccolith carbonate estimation are needed to not only understand this ratio currently, but also to help understand future sequestration of organic carbon to the oceanic interior
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