1,721,210 research outputs found
Tasman leakage in a fine-resolution ocean model
No full textTasman leakage, the westward flow of thermocline waters south of Australia from the Pacific to the Indian Ocean, is one of the lesser-studied of the inter-ocean exchanges. Here, some of the properties of the Tasman leakage are inferred from Lagrangian particles integrated using the three-dimensional velocity fields of the 1/10 degree resolution OFES model. The mean Tasman leakage in this model is 4.2 Sv, with a standard deviation of 4.3 Sv. The heat flux associated with this leakage lies in the range 0.08–0.18 PW. There is large variability in the Tasman leakage on both sub-weekly and inter-annual scales, but no trend over the 1983–1997 period. Despite the large weekly variability, with peaks of more than 20 Sv, it appears that less than half of the Tasman leakage is carried within eddies
Empirical Lagrangian parametrization for wind-driven mixing of buoyant particles at the ocean surface
Full text linkTurbulent mixing is a vital component of vertical particulate transport, but ocean global circulation models (OGCMs) generally have low-resolution representations of near-surface mixing. Furthermore, turbulence data are often not provided in OGCM model output. We present 1D parametrizations of wind-driven turbulent mixing in the ocean surface mixed layer that are designed to be easily included in 3D Lagrangian model experiments. Stochastic transport is computed by Markov-0 or Markov-1 models, and we discuss the advantages and disadvantages of two vertical profiles for the vertical diffusion coefficient Kz. All vertical diffusion profiles and stochastic transport models lead to stable concentration profiles for buoyant particles, which for particles with rise velocities of 0.03 and 0.003 m s−1 agree relatively well with concentration profiles from field measurements of microplastics when Langmuir-circulation-driven turbulence is accounted for. Markov-0 models provide good model performance for integration time steps of Δt≈30 s and can be readily applied when studying the behavior of buoyant particulates in the ocean. Markov-1 models do not consistently improve model performance relative to Markov-0 models and require an additional parameter that is poorly constrained
Biofouled Microplastics Particle Data
No full textParticle data for the paper "Modelling submerged biofouled microplastics and their vertical trajectories" in Copernicus Biogeosciences
Closing the marine plastic mass budget: Using observational data to inform numerical models
No full textPlastic waste is causing a high amount of pollution in the ocean. A lot of plastic pollution remains afloat, and accumulates in the subtropical gyres, in the so called `floating garbage patches’. It is not well known where most of the marine plastic pollution actually comes from: is it for example originating from rivers, coastlines, or from fishing activity? Furthermore, it is relatively unknown which processes `remove’ plastic pollution from the surface of the ocean over time. A part of the plastic pollution ends up on the coastlines, starts to sink down after some time (e.g. under the influence of biofouling), or fragments into smaller particles. Current estimates of the amount of plastic pollution that is floating in the ocean are much lower than the estimated amount of plastic pollution entering the ocean every year. This thesis is written within the TOPIOS project (Tracking Of Plastics In Our Seas), where we attempt to resolve this discrepancy. In order to estimate the marine plastic mass budget, we combine numerical simulations of the ocean with observational measurements of plastic concentrations. One way to do this is by using statistical models. We use a regression method (random forests) to estimate the total amount of litter on the Dutch North Sea coastline. Using a beach cleanup dataset from The North Sea Foundation, we train a model to predict the amount of beach litter as a function of various environmental variables (e.g. conditions related to the weather, ocean currents, tides). This model is used to extrapolate the amount of litter along the entire Dutch North Sea coastline (about 16,500-31,200 kilograms in total). Observational data of plastic concentrations can also be used to calibrate unknown parameters in numerical models of the ocean currents. We do one such analysis for the Mediterranean Sea, and a more extended analysis for plastic pollution on a global scale. One important conclusion is that the total amount of plastic pollution in the global ocean is likely much higher than previously expected: roughly 3,000,000 tonnes (3 billion kilograms). Previous research, with estimated quantities of roughly 250,000 tonnes, mainly used net measurements to calibrate the numerical models. These kind of net measurements are likely to miss larger objects, which contribute to most of the marine plastic mass. In our analysis we additionally use data of larger plastic objects from visual observations (both from the open ocean and from beaches), and net measurements from the water column for the model calibration. We estimate that a relatively large part of marine plastics sinks down over time (for example due to growth of algae). Fragmentation of plastics plays an important role: most of the plastic items found in the ocean are small fragments originating from larger objects. We estimate that beaches contain about 2% of the global marine plastic mass. We estimate that the input of plastic pollution is much lower than previously expected, and that residence times of plastic items in the marine environment are higher than previously anticipated
The connected ocean: comparing inter-ocean transport at the surface and at depth
Full text linkThe oceans form a global network of inter-connected basins, with currents transporting a range
of tracers such as heat and pollution between them. Although the ocean dynamics play a key
role in determining transport between basins, the basins are de ned by arbitrary geographical
borders rather than physical connections. This thesis proposes a method of detecting dynamical
boundaries and applies it to the ocean surface and interior. To achieve this, probabilistic
models are used to summarise the transport described by vast datasets of water-following
trajectories. Such models, known as Markov Chain models, have previously been used to map
the distribution of plastic pollution yet are known to induce an artificial dispersion. First,
a sensitivity analysis of the effect of model parameters on artificial dispersion is performed,
to determine the optimal model set-up. Next, a global dataset of observed trajectories is
used to detect dynamic transport barriers in two key areas of inter-ocean surface exchange: the
Agulhas Current system and the North Atlantic inter-gyre transport barrier. Connectivity maps
are introduced as maps of tracer destinations which highlight dynamical segregation between
regions. For example, these are used to identify the source region for Agulhas Leakage and one-way
equator-ward transport across the Gulf Stream. Using a new method to extract geostrophic
motion from a trajectory dataset, the geostrophic contribution to inter-basin transport can
be identified. Finally, connectivity maps are produced for the ocean interior using virtual
particles released along isopycnals in the eddy-permitting ORCA025 ocean circulation model.
The change in connectivity, in the two study regions, between two target isopycnals is the first
step in creating a 3D border of the ocean basins. New basin definitions are then explained
by transport processes relevant to the region. Future work should establish the link between
dynamical boundaries and the distribution of heat and pollution.Open Acces
Global simulations of marine plastic transport show plastic trapping in coastal zones.
Full text linkGlobal coastlines potentially contain significant amounts of plastic debris, with harmful implications for marine and coastal ecosystems, fisheries and tourism. However, the global amount, distribution and origin of plastic debris on beaches and in coastal waters is currently unknown. Here we analyze beaching and resuspension scenarios using a Lagrangian particle transport model. Throughout the first 5 years after entering the ocean, the model indicates that at least 77% ofpositively buoyant marine plastic debris (PBMPD) released from land-based sources is either beached or floating in coastal waters, assuming no further plastic removal from beaches or the ocean surface. The highest concentrations ofbeached PBMPD are found in Southeast Asia, caused by high plastic inputs from land and limited offshore transport, although the absolute concentrations are generally overestimates compared to field measurements. The modeled distribution on a global scale is only weakly influenced by local variations in resuspension rates due to coastal geomorphology. Furthermore, there are striking differences regarding the origin of the beached plastic debris. In some exclusive economic zones (EEZ), such as the Indonesian Archipelago, plastic originates almost entirely from within the EEZ while in other EEZs, particularly remote islands, almost all beached plastic debris arrives from remote sources. Our results highlight coastlines and coastal waters as important reservoirs ofmarine plastic debris and limited transport ofPBMPD between the coastal zone and the open ocean
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
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