1,720,990 research outputs found
Is the Earth currently in a Global tidal maximum? 500 Ma of coupled tectonic and tidal modelling
No full textEarth’s continents in the present day are the dispersed fragments of the former supercontinent Pangea which existed from 330 - 180 Ma. In around 200 - 250 Myr, following the progression of the current supercontinent cycle, the Earth’s continents will reform into another supercontinent. The supercontinent cycle is closely linked to the Wilson cycle which describes the life cycle of oceans as they form, grow, shrink, and eventually close. As oceans grow and shrink with theWilson cycle the tides within them are affected. The present day North Atlantic ocean, which formed as a result of the breakup of Pangea, is resonant with the M2 tide, causing macrotidal (>4m) tidal amplitudes and strengthening the global M2 tidal dissipation rate to 2.5 TW. Is this a unique occurrence in the present supercontinent cycle or is the tide periodically buoyed by resonance in ocean basins because of geometry changes brought about by the progression of the Wilson cycle? Here we will reconstruct predictions of the progression of the current supercontinent cycle into the future (+250 Ma) with GPlates which we will then use as a boundary condition for tidal modelling at 20 Myr intervals with OTIS (Oregon state Tidal Inversion Software). We present four unique scenarios of the Earth’s future, each arguing a different style of supercontinent formation. In all scenarios of the future, we find that the Atlantic continues to widen over the next 25 Myrs, causing the tide within it to weaken as resonance is lost. However, we find several other occurrences of tidal resonance during the future scenarios, which causes tidal dissipation rates to increase to 70 – 250% of the present-day value. This periodic increase in tidal amplitudes and dissipation affects the evolution of the Earth-Moon system over geological time and has implications for ocean circulation, climate and the ocean’s ability to host and support life in the past and future.Instituto Dom Luiz, grant no. IF/00702/201
Is the Earth currently in a Global tidal maximum? 500 Ma of coupled tectonic and tidal modelling
No full textEarth’s continents in the present day are the dispersed fragments of the former supercontinent Pangea which existed from 330 - 180 Ma. In around 200 - 250 Myr, following the progression of the current supercontinent cycle, the Earth’s continents will reform into another supercontinent. The supercontinent cycle is closely linked to the Wilson cycle which describes the life cycle of oceans as they form, grow, shrink, and eventually close. As oceans grow and shrink with theWilson cycle the tides within them are affected. The present day North Atlantic ocean, which formed as a result of the breakup of Pangea, is resonant with the M2 tide, causing macrotidal (>4m) tidal amplitudes and strengthening the global M2 tidal dissipation rate to 2.5 TW. Is this a unique occurrence in the present supercontinent cycle or is the tide periodically buoyed by resonance in ocean basins because of geometry changes brought about by the progression of the Wilson cycle? Here we will reconstruct predictions of the progression of the current supercontinent cycle into the future (+250 Ma) with GPlates which we will then use as a boundary condition for tidal modelling at 20 Myr intervals with OTIS (Oregon state Tidal Inversion Software). We present four unique scenarios of the Earth’s future, each arguing a different style of supercontinent formation. In all scenarios of the future, we find that the Atlantic continues to widen over the next 25 Myrs, causing the tide within it to weaken as resonance is lost. However, we find several other occurrences of tidal resonance during the future scenarios, which causes tidal dissipation rates to increase to 70 – 250% of the present-day value. This periodic increase in tidal amplitudes and dissipation affects the evolution of the Earth-Moon system over geological time and has implications for ocean circulation, climate and the ocean’s ability to host and support life in the past and future.Instituto Dom Luiz, grant no. IF/00702/201
Oceanographic conditions during Manta trawls in the South Atlantic Ocean with Bark Europa in autumn 2023
No full textSurface ocean microplastic samples were collected in the South Atlantic and analysed. Trawls were conducted onboard the Bark Europa, a traditional three-masted, square-rigged Barque while under sail. The data was collected in autumn 2023 over 10 trawl locations from Cape Town (South Africa) to Montevideo (Uruguay). Surface water samples were collected using a Manta trawl (mouth area: 40.5 cm², mesh size: 500 µm; cod end: 333 µm), towed three consecutive times for ~30 minutes at each station. Environmental conditions such as sea state, wind speed, and wind direction were recorded. Three samples were collected at each site, except for one location where only one trawl was conducted due to environmental conditions. This dataset describes these environmental conditions. The trawls were monitored and adjusted to ensure smooth sampling outside the vessel's wake zone. Microplastic samples collected during the study were processed using a series of stacked sieves (5 mm, 1mm, 0.3mm) and rinsed with filtered fresh water. Particles with largest dimension over 1 mm were visually identified (removed if not polymer), and everything smaller was collected. Samples were then chemically purified and investigated via stereoscopy , followed by ATR-FTIR spectroscopy in the laboratory to identify the polymer types of the microplastics. Cross-contamination was minimized through procedural blanks, samples of potential contamination and careful equipment handling. The microplastic particles collected were also categorized by shape (film, foam, fragment, line, microfiber, microbead, industrial pellet) and colour
Microplastic particle characteristics during Manta trawls in the South Atlantic Ocean with Bark Europa in autumn 2023
No full textSurface ocean microplastic samples were collected in the South Atlantic and analysed. Trawls were conducted onboard the Bark Europa, a traditional three-masted, square-rigged Barque while under sail. The data was collected in autumn 2023 over 10 trawl locations from Cape Town (South Africa) to Montevideo (Uruguay). Surface water samples were collected using a Manta trawl (mouth area: 40.5 cm², mesh size: 500 µm; cod end: 333 µm), towed three consecutive times for ~30 minutes at each station. Environmental conditions such as sea state, wind speed, and wind direction were recorded. Three samples were collected at each site, except for one location where only one trawl was conducted due to environmental conditions. The trawls were monitored and adjusted to ensure smooth sampling outside the vessel's wake zone. Microplastic samples collected during the study were processed using a series of stacked sieves (5 mm, 1mm, 0.3mm) and rinsed with filtered fresh water. Particles with largest dimension over 1 mm were visually identified (removed if not polymer), and everything smaller was collected. Samples were then chemically purified and investigated via stereoscopy , followed by ATR-FTIR spectroscopy in the laboratory to identify the polymer types of the microplastics. Cross-contamination was minimized through procedural blanks, samples of potential contamination and careful equipment handling. The microplastic particles collected were also categorized by shape (film, foam, fragment, line, microfiber, microbead, industrial pellet) and colour
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
Internal tide driven tracer transport across the continental slope
Get PDFThe role of the internal tide in driving tracer transport across the continental slope is examined using simplified layered theory, channel model experiments and observational diagnostics of near shelf‐edge moorings. The effect of the internal tide is interpreted in terms of its Stokes' drift, which is separated into two distinct components: a bolus component, driven by the co‐variance of layer thickness and the velocity; and a shear component, driven by the velocity following the movement of an interface. For a three layer ocean, in the model experiments and observations, the onshore propagation of an internal tide drives a Stokes' transport directed onshore in the surface and the bottom layers, and directed offshore in the pycnocline. This reversing structure is due to the bolus component dominating near the boundaries, while the shear component dominates at the pycnocline. In the observational diagnostics, the Stokes' transport is not cancelled by the Eulerian transport, which is mainly directed along bathymetric contours. The Stokes' drift of the internal tide then provides a systematic on shelf tracer transport if there is a tracer sink on the shelf, carried in the surface or bottom layers. Conversely, the tracer transport is directed offshore if there is a tracer source on the shelf with plumes of shelf tracer expected to be carried offshore along the pycnocline. This tracer transport as a result of the internal tide is diagnosed for heat, salt and nitrate. The depth‐integrated nitrate flux is directed onto the shelf supplying nutrients to the productive shelf seas
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
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