Simulation of local atmospheric dynamics in the coastal region of Dunkerque

The structure of the lower troposphere has been studied during the sea-breeze and post sea-breeze events in an industrialized coastal area of the North Sea. Atmospheric dynamics and dispersion of pollutants in the lower troposphere have been analyzed by the experimental results of the 3D nonhydrostatic Meso-NH model in Dunkerque area (51°N, 2.20°E), in the north of France. The simulations were verified and extended by data of the measurement campaign. Ground-based remote sensing systems (lidar and sodar), surface meteorology and air quality network stations data have been employed. We illustrate the different pollution scenarios and breeze structure by the analysis of Lagrangian tracers and back trajectories.     

A sensitive method for measuring atmospheric concentrations of sulfur dioxide

A new sensitive method for measuring atmospheric concentrations of sulfur dioxide is presented. Samples are obtained using the mist chamber, which collects highly water-soluble gases with high efficiency, and concentrates them in a small volume of water. Particles are removed from the sampled air stream with a teflon filter, before it enters the mist chamber. After collection, the pH of the water is raised above pH 10 using sodium carbonate, then hydrogen peroxide (H₂O₂) is added to oxidize sulfur that may be present in the sulfur (IV) oxidation state, to sulfate. After a reaction time of at least 16 hours, the sulfate concentration is measured by ion chromatography. From the sulfate concentration, the water volume used in the mist chamber, and the volume of air sampled, the atmospheric concentration of SO₂ is computed. The method is not sensitive to other atmospheric sulfur gases such as DMS, SC₂, H₂S, COS, or MSH. The estimated overall precision of the method is 10%. The detection limit at the present stage of technique development is approximately 20 ppt (parts per trillion, or 10^-12 mol · mol^-1) for a 45 minute sampling time, with lower concentrations being detectable with lower precision.     

Adoption of flood-related preventive behaviours by people having different risks and histories of flooding

Natural Hazards - The increase in the frequency of floods, which is a projected consequence of climate change, can have wide-ranging health and economic impacts. To cope with these floods and to...     

Effects of sedimentary interfaces on fracture pattern,linkage, and cluster formation in peritidal carbonate rocks

The permeability of a reservoir is particularly dependent upon the proportion of its fractures that penetrate or are arrested at interfaces such as contacts and discontinuities. Here we report on fracture penetration and fracture arrest in Lower Cretaceous peritidal deposits exposed in the Pizzicoli Quarry, Gargano Promontory, southern Italy. We measured more than 2000 fractures, in the field and using LIDAR data, of which 564 fractures from the field and 518 from LIDAR studies are the focus of this paper. Fracture arrest/deflection and penetration depend much on the effects of peritidal cycle interfaces such as paleosol horizons, laminated carbonate mudstones, and stylonodular horizons. The laminated mudstones have the greatest effect; 63–99% of the fractures are deflected or arrested at such interfaces, whereas 63–90% are deflected/arrested at paleosols, and 20–35% at stylonodular horizons. In the mudstones, many fractures are arrested at thin, internal laminae, such that few penetrate the entire laminated layer, and fewer still the boundaries between the layers. Paleosol interfaces deflect/arrest more than 60% of all fractures. However, when small-offset fractures above and below paleosols are regarded as penetrating, they are evenly spaced (non-clustered), so that fracture-related fluid transport may occur across the entire paleosol. Stylonodular horizons deflect/arrest and split some fractures, but generally have little effect compared with the other types of interfaces. We present three main mechanisms for fracture deflection and/or arrest: (1) the fracture-induced tensile stress ahead of its tip, referred to as the Cook-Gordon debonding mechanism; (2) rotation of the principal stresses at and across the interface, resulting in the formation of stress barriers; and (3) large elastic mismatch (particularly as regards Young’s moduli) between layers across an interface. All these mechanisms are likely to have operated during fracture propagation and arrest in the carbonate rocks of the Pizzicoli Quarry.     

Indentation of a continent with a built-in thickness change: experiment and nature

Orogens oblique to the direction of plate convergence are currently attributed to obliquity between the margins of one or both of the sutured continents to their direction convergence. We use a single analogue experiment and natural examples to illustrate a potential additional factor: variations in strength of the indented continent at a high angle to the convergence direction. The wavelengths of structures in laterally shortened lithosphere depend on the strength of the most competent layers. Lateral variations in crustal thickness must therefore lead to structures oblique to any applied lateral compression.

An analogue experiment was performed to explore this phenomenon. A two-layer ‘indented continent’ was modelled by a brittle upper crust of sand above a lower crust of high-viscosity polymer floating on a single layer of low-viscosity syrup representing the mantle. The well-known strike-slip structures allowing lateral escape to distant weak boundaries were hindered by lateral boundaries in front of the indenter. This allowed us to focus on the effects of a thickness change built into the ‘indented continent’ along a zone parallel to the direction in which a vertical rigid wall advancing at a steady rate represented the indenter. Vertical escape led to an ‘orogenic belt’ oblique to the advancing wall; this obliquity influences subsequent lateral escape. Model scaling and interpretations are based on Extended Thin Sheet Approximation (ETSA) and standard theories of faulting.

Four sectors of the Alpine–Himalayan orogen (Iran, Tunisia, the Eastern Alps and the Himalaya) are oblique to the continental convergence direction, and we point to thickness changes at high angles to the suture that may account for this geometry. As crustal thicknesses north of oblique sectors of the Himalayas are not yet known, we speculate on them.

We infer from the main difference between our experiment and all our examples chosen from nature that vertical orogenic escape was oblique to our model suture but can be parallel to natural sutures.     

Composition and distribution of larval fishes in New Jersey high marshes

The surface of the salt marsh is an important, but largely unrecognized, site for fish reproduction and larval growth. In an attempt to determine the composition and distribution of fishes utilizing these habitats, we sampled larval and juvenile fish with plankton nets, dip nets, and traps at a variety of microhabitats (tidal and nontidal ponds and ditches and the marsh surface) in three New Jersey high marshes. Two of the three marshes had been altered for mosquito control. During April to September 1980, we collected over 2,400 larvae and juveniles. All study sites were dominated by the larvae of the resident killifishes (Fundulus heteroclitus, Cyprinodon variegatus, F. luciae, andLucania parva) and less commonlyMenidia beryllina. However, the occurrence and abundance of each species varied with microhabitat. Larval production in all three marshes peaked during June–July, but extended from May until September. In most instances juveniles of the dominant fishes had microhabitat preferences similar to the larvae. High marshes may be more important for fish production than previously recognized because they serve as nursery areas for the resident killifishes.     

187Re,recyclingR-process elements through stars,and the age of the Galaxy

The enhanced -decay rate of ionized¹⁸⁷Re in stars has been studied within the context of a detailed numerical model of the production ofr-process elements and their recycling through stars during the course of galactic evolution. It is concluded that the enhanced decay rate does not significantly reduce the Re-Os chronometer age for the Galaxy. Consequently, the¹⁸⁷Re -decay half-life and the neutron cross-section ratio (¹⁸⁶Os)/(¹⁸⁷Os) remain as the significant uncertainties in this chronology. Unlike the uncertainties in other chronologies, both are amenable to laboratory measurements.     

New Early Permian paleomagnetic results from the Brive basin (French Massif Central) and their implications for Late Variscan tectonics

In order to assess the structural evolution of the Brive basin and the Paleozoic activity of surrounding major faults in the French Massif Central, we carried out a paleomagnetic study on Early Permian rocks from this basin. Positive-fold tests and solely reversed polarities indicate that the characteristic remanent magnetization is likely to be primary. Early Permian tilt-corrected site mean declinations vary from 207°–167° indicating that the Brive basin experienced internal vertical-axis rotations. On the contrary, Late Permian paleomagnetic site means exhibit a circular Fisherian distribution showing no relative rotations. Detailed analyses of Permian paleomagnetic data from five contemporaneous basins of the French Massif Central reveal that these basins share the same equatorial paleolatitude with stable Europe throughout the Permian. However, in Early Permian, three of the five basins experienced differential rotations. The Saint-Affrique basin not only suffered internal deformation during the Early Permian, but the basin as a whole underwent a full-scale counterclockwise vertical-axis block rotation with respect to stable Europe. As a consequence, paleomagnetic data from similar late orogenic basins have to be thus carefully considered for establishment of Apparent Polar Wander paths.