| 1. |
- Büchert, A., et al.
(författare)
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Dioxin contamination in food : Bayreuth, Germany, from September 28 to October 1, 2000
- 2001
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Ingår i: Environmental Science and Pollution Research. - : Ecomed Publishers. - 0944-1344 .- 1614-7499. ; 8:2, s. 84-88
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Tidskriftsartikel (refereegranskat)abstract
- Dioxin and PCB monitoring programs for food and feeding stuff in most countries of the world, including many European Countries are currently inadequate. Better control of food production lines and food processing procedures is needed to minimize entry of dioxin to the food chain and will help to avoid dioxin contamination accidents. This would also improve the ability to trace back a possible contamination to its source. European guidelines for monitoring programs should be established to ensure comparable and meaningful results. These guidelines should define the minimum requirements for the design of monitoring programs, analytical methods, and quality assurance.Though data from Northern Europe shows that the general population exposure to dioxin and PCB has decreased during the last ten years these compounds continue to be a risk of accidental contamination of the food chain. The most prominent recent example is the Belgian dioxin contamination of feeding stuff in 1999. The Belgian dioxin contamination was not detected due to dioxin monitoring programs but by their direct biological effects seen in animals. Four other cases of dioxin contamination have been detected in Europe since 1997 due to local monitoring programs. One of them (citrus pulp pellets 1998) was in a much larger scale than the Belgian dioxin contamination.The general population's exposure to dioxins and PCBs is still in the same range (1-4 pg WHO-TEQ/kg body weight and day) as the recently revised WHO tolerable daily intake (TDI). There is concern that short-term high level exposure to dioxins, furans, and PCB may cause biological effects on the human fetal development and further research is required.Further actions to control sources building on considerable advances already made in many countries may need to be supplemented by measures to prevent direct contamination of feeding stuff or food to reduce general population exposure further.
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| 2. |
- Muchowski, Julia, 1989-, et al.
(författare)
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Diapycnal Mixing Induced by Rough Small-Scale Bathymetry
- 2023
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 50:13
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Tidskriftsartikel (refereegranskat)abstract
- Diapycnal mixing impacts vertical transport rates of salt, heat, and other dissolved substances, essential for the overturning circulation and ecosystem functioning in marine systems. While most studies have focused on mixing induced by individual obstacles in tidal flows, we investigate the net effect of non-tidal flow over multiple small-scale (<1 km) bathymetric features penetrating a strongly-stratified density interface in a coastal region. We combine high-resolution broadband acoustic observations of turbulence microstructure with traditional shear microstructure profiling, to resolve the variability and intermittency of stratified turbulence related to the rough bathymetry. Scale analysis and acoustic imaging suggest that underlying mixing mechanisms are related to topographic wake eddies and breaking internal waves. Depth averaged dissipation rates (1.1 × 10−7 Wkg−1) and turbulent vertical diffusivities (7 × 10−4 m2s−1) in the halocline exceed reference values by two orders of magnitude. Our study emphasizes the importance of rough small-scale bathymetric features for the vertical transport of salt in coastal areas.
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| 3. |
- Arneborg, Lars, 1969, et al.
(författare)
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Gravity Current Dynamics and Entrainment - A Process Study Based on Observations in the Arkona Basin
- 2007
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Ingår i: journal of physical oceanography. ; 37, s. 2094-2113
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Tidskriftsartikel (refereegranskat)abstract
- A 19 hour time series of dissipation, stratification and horizontal velocities has been obtained for a dense gravity current flowing into the Arkona Basin in the western Baltic Sea. The observations are compared with one-dimensional, quasi-steady theory, where the gravity component in the flow direction is balanced by bottom friction, while that in the cross flow direction is balanced by the Coriolis force. The observations deviate from the theory in that the bottom shear stress is more than twice as large as that required to balance the gravity. Several reasons for this discrepancy are discussed. A 1D turbulence model is also compared with the observations. Profiles of velocity, stratification and dissipation rates generally show similar variations with depth as the observations, although the observed dissipation rates are somewhat larger than the modeled and the modeled transverse velocities are much larger than the observed. Subsequently, the model is used to investigate the variation of the entrainment parameter for a large range of Ekman and Froude numbers. Within the modeled parameter space, the entrainment parameter can be collapsed onto a curve that is an increasing function of both the Froude and the Ekman numbers. There is one puzzling result of the observations that differs from the model results and earlier observations, namely that the observed entrainment rate increases dramatically during the observation period, where the Froude number decreases slightly. Some reasons for this increase are discussed.
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| 4. |
- Burchard, H., et al.
(författare)
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Dynamics of medium-intensity dense water plumes in the Arkona Basin, Western Baltic Sea
- 2005
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Ingår i: Ocean Dynamics. - : Springer Science and Business Media LLC. - 1616-7341 .- 1616-7228. ; 55:5-6, s. 391-402
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the dynamics of medium-intensity inflow events over Drogden Sill into the Arkona Sea are investigated. Idealised model simulations carried out with the General Estuarine Transport Model suggest that most of the salt transport during such inflow events occur north of Kriegers Flak, a shoal with less than 20 in water depth Surrounded by water depths of more than 40 in. This assumption about the pathway is supported by recent ship-based observations in the Arkona Sea during a medium-intensity inflow event. The propagation of a saline bottom plume could be observed during several days after having passed Drogden Sill. In the area north of Kriegers Flak the plume was about 10 m thick, and propagated with more than 0.5 m s(-1) and a salinity of tip to 20 psu (with ambient water salinity being 8 psu) eastwards. Although the model simulations were idealised, the Structural agreement between the observation and model result was good, The structure and pathways of these medium-intensity inflow events are of specific interest due to the plans for erecting extensive offshore wind farms in the Arkona Sea which may under certain circumstances lead to increased entrainment of ambient water into the bottom Plumes.
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| 5. |
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| 6. |
- Umlauf, L., et al.
(författare)
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Dynamics of rotating shallow gravity currents passing through a channel. Part I: Observation of transverse structure
- 2009
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Ingår i: Journal of Physical Oceanography. ; 39, s. 2385-2401
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed data set describing a quasi-stationary bottom gravity current, approximately 10 m thick and 10 km wide, passing through a channel-like constriction in the Western Baltic Sea. The data include full-depth, synoptic, and highly resolved transects of stratification and turbulence parameters, as well as detailed velocity transects across the gravity current at different down-channel locations. Our velocity data reveal a persistent transverse circulation, creating a characteristic wedge-shaped density structure in the interface. A strong asymmetry was also found in the interior of the gravity current, where we observed the evolution of a dynamically significant transverse density gradient to the right of the down-channel flow. Spectral analysis of the near-bottom velocities showed a surprisingly strong contribution to the bottom stress from low-frequency motions with periods up to 30 minutes that are possibly related to internal wave effects. Cross-channel transects of shearmicrostructure were used to investigate the transverse variation of local entrainment rates and bottom stresses. These data indicate that frictional control is essential for this class of gravity currents that are characterized by subcritical Froude numbers, small entrainment, strong rotational effects, and small thickness compared to the bottom Ekman layer.
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| 7. |
- Umlauf, L., et al.
(författare)
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Dynamics of rotating shallow gravity currents passing through a channel. Part II: Analysis
- 2009
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Ingår i: Journal of Physical Oceanography. ; 39, s. 2402-2416
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Tidskriftsartikel (refereegranskat)abstract
- The physics of frictional control for channelized rotating gravity currents are analyzed using an extensive data set including hydrographic, current, and microstructure measurements from the Western Baltic Sea. Rotational effects in these gravity currents, characterized by Ekman numbers of the order of one and sub-critical Froude numbers, induce a complex transverse circulation that strongly affects the internal dynamics. The key component of this circulation is a geostrophically balanced transverse jet in the interface that modifies the entrainment process by (i) laterally draining the interface and (ii) providing additional interfacial shear comparable to the down-channel shear. The recirculation of mixed interfacial fluid into the interior distorts the internal density structure of the gravity current, and creates a thermal wind shear in the interior that is comparable to the observed shear. Using a theoretical model, this effect is shown to be responsible for the three-layer structure of the transverse velocity with the near-bottom velocity and stress directed opposite to the Ekman transport. Our analysis confirms the key assumption in available models for frictional control in rotating gravity currents: the transverse Ekman transport is balanced by the geostrophic transport due to the down-channel tilt of the interface.
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| 8. |
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