Hydrodynamics of the Lake of Geneva

Air-flow works on the lake's water body which results in winddriven water circulation and wind waves This is a summary of work done by LHYDREP on the physical limnological aspect of the Leman. General information on the basin of the Leman is given in chapter 1. Subsequently in chapter 2 the measuring programme is presented, discussing the measuring positions, the measuring installations and the instruments used of the three campaigns. The data obtained during these campaigns are subsequently interpreted. In chapter 3 the atmospheric dynamics over the lake is discussed. It deals mainly with the mechanical energy transfer process which is represented here (as usually) by the drog coefficient, C_y. It is shown that the airflow velocity, the fetch Reynolds number and the air stability play important roles. In chapter 4 the hydrodynamics of the lake is presented. Predictions of numerical hydrodynamical models of steady-state circulation (chapter 4.2), of storm surges and of seiches (chapter 4.3) and of inertial currents (chapter 4.4) are compared with available data of the Leman during the homogeneous season. In addition a preliminary study of wind waves (chapter 4.5) is given.     

Salinity detection and associated behavior in the dungeness crab,Cancer magister

Dungeness crabs, Cancer magister, showed the same antennular flicking response to brief (<2 min) salinity fluctuations as they have previously shown in detecting chemical food cues during other studies. The threshold concentrations at which 50% of the crabs detected the salinity changes were 29.9‰ and 32.7‰ or 96% and 105% of ambient seawater (31.0‰). At the maximum salinity changes used, other behaviors accompanied the flicking response. In a second experiment where salinity rose or fell continuously, two previously undescribed behaviors, pulsing and closure, occurred. In pulsing, crabs showed a rapid coordinated opening and closing of the outer maxillipeds with rapid beating of the maxillipedal flagellae. In closure, crabs stopped all overt activity, retracted their appendages and tightly closed the buccal cavity with the outer maxillipeds. Under increasing salinity crabs exhibited pulsing at 34.9‰ or 113% of ambient seawater and closure at 36.2‰ or 117% of ambient. Under decreasing salinity crabs showed pulsing at 23.2‰ or 75% of ambient seawater and closure at 15.5‰ or 50% of ambient.     

Determination of O3-, CO- and PM10-transport in the metropolitan area of São Paulo, Brazil through synoptic-scale analysis of back trajectories

Summary This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the Metropolitan Area of S?o Paulo (MASP). Air-mass back trajectories from June to August of 1999 were calculated using a three-dimensional kinematic trajectory model and grouped into trajectory clusters. Correlations of individual trajectory clusters with O₃, CO and PM₁₀ concentrations were determined. In this model, trajectories were obtained using the means of the three wind velocity components (U, V and W). The three-dimensional wind field was derived from the Regional Atmospheric Modeling System, and downscaling was employed. Coarse and fine nested grids (64-km and 16-km horizontal resolution, respectively) were used. Every 12 h (at 00 and 12 UTC), a back-trajectory ensemble, using the 64-km grid, was calculated for five defined endpoints at intervals of 0.5° N, S, E and W of the MASP (λ = 23° 33′S, ϕ = 46° 45′W), that last endpoint being centered in the MASP. To analyze cluster trajectories, the five trajectory ensembles from each day were allocated into one of four clusters (northeast, southeast, southwest or northwest quadrant) based on the origin of the trajectory over 4 days. Days on which all five trajectories originated from the same quadrant were classified as “core” days. Core day concentrations of CO, O₃ and PM₁₀ during the study period were evaluated. The results show that, during the study period, air-mass back trajectories in the MASP originated from all four quadrants: northeast (32%), southeast (12%), southwest (19%) and northwest (37%). Our analysis of back-trajectory clusters in the MASP suggests a transport to ambient air of O₃ precursors and O₃ from the northeast region, which is associated with agricultural activities involving biomass burning.     

Crustal structure of mainland China from deep seismic sounding data

Since 1958, about ninety seismic refraction/wide angle reflection profiles, with a cumulative length of more than sixty thousand kilometers, have been completed in mainland China. We summarize the results in the form of (1) a new contour map of crustal thickness, (2) fourteen representative crustal seismic velocity–depth columns for various tectonic units, and, (3) a Pn velocity map. We found a north–south-trending belt with a strong lateral gradient in crustal thickness in central China. This belt divides China into an eastern region, with a crustal thickness of 30–45 km, and a western region, with a thickness of 45–75 km. The crust in these two regions has experienced different evolutionary processes, and currently lies within distinct tectonic stress fields. Our compilation finds that there is a high-velocity (7.1–7.4 km/s) layer in the lower crust of the stable Tarim basin and Ordos plateau. However, in young orogenic belts, including parts of eastern China, the Tianshan and the Tibetan plateau, this layer is often absent. One exception is southern Tibet, where the presence of a high-velocity layer is related to the northward injection of the cold Indian plate. This high-velocity layer is absent in northern Tibet. In orogenic belts, there usually is a low-velocity layer (LVL) in the crust, but in stable regions this layer seldom exists. The Pn velocities in eastern China generally range from 7.9 to 8.1 km/s and tend to be isotropic. Pn velocities in western China are more variable, ranging from 7.7 to 8.2 km/s, and may display azimuthal anisotropy.     

Topographic analysis of Devana Chasma, Venus: implications for rift system segmentation and propagation

Devana Chasma is a rift system on Venus formed in association with the Beta Regio and Phoebe Regio volcanic highlands, which are interpreted as mantle plumes. We present a new analysis of a 2500-km-long segment of Devana. Based on the rift topography, the horizontal extension across the rift boundary faults is 3–9 km. This is a lower bound on the total rift extension because the altimetry does not resolve the topographic relief across the numerous faults that are visible in radar images of the rift floor. The total extension across Devana is approximately 20 km, similar in magnitude to continental rift systems on Earth. Rift flank elevations are up to 3.1 km in the regions nearest the mantle plumes and decay strongly with increasing distance from the plumes, indicating a strong thermal component to the rift flank topography, unlike the situation usually reported for terrestrial rifts. As on Earth, there is also a flexural uplift component to the flank topography. Rift depths are up to 2.5 km below the surrounding plains, with considerable along-strike variability. There is a 600 km lateral offset along Devana Chasma near the mid-point between the two mantle plumes. Devana most likely formed as two distinct rifts due to the horizontal stresses created by outflow from the upwelling plumes. The offset zone formed as a result of the interaction between the two rift tips, which requires that upwelling at the two mantle plumes overlapped in time.     

Effects of mechanical layering on volcano deformation

The migration and accumulation of magma beneath volcanoes often causes surface displacements that can be measured by geodetic techniques. Usually, deformation signals are explained using models with uniform mechanical properties. In this paper, we study surface displacements due to magma chamber inflation, using heterogeneous finite element models. We first present a systematic analysis of the influence of mechanical layering, showing that the stiffness contrast significantly affects the entity and the pattern of vertical and radial displacements. Second, as an example we apply the models to interpret ground displacements at Darwin volcano (Galápagos Islands) as revealed by InSAR data in the period 1992–1998. The considered models suggest that geodetic data interpreted using homogeneous models leads to underestimation of the source depth and volume change. Thus, we propose correction factors for the source parameters estimated by homogeneous models, in order to consider a range of variation due to mechanical layering as analysed in this study. The effect of the mechanical heterogeneities affects the correct understanding of geodetic data and also influences the evaluation of a volcanic hazard potential.     

Rare earth elements as tracers of sediment contamination by phosphogypsum in the Santos estuary,southern Brazil

In the Cubatão region, southern Brazil, sediments are transported by several rivers from the Serra do Mar Ridge into the Santos estuary. Fertilizer plants have been operating along the margins of one of these rivers (Mogi River) producing a large volume of phosphogypsum, which is stockpiled in nearby areas. Surface sediments of the Mogi River were sampled upstream and downstream in relation to the point where the effluents of the phosphogypsum piles flow into the drainage system. In the vicinity of this point one sediment core was collected. Results show that REE, Ba, Zr and Th concentrations in the non-contaminated sediments are of the same order as those present in the upper continental crust. The contaminated samples present a composition affected by that of the phosphogypsum, marked by a higher concentration of these elements and a stronger degree of REE fractionation. These phosphogypsum characteristics are inherited from the Catalão igneous phosphate ore and were moderately modified by the industrial process of phosphoric acid production. The phosphogypsum signal decreases rapidly downstream, pointing to a limited area of influence of the stacks. The deepest sediments of the core are also free of contamination, representing a time interval prior to the deposition of phosphogypsum wastes on the banks of the estuary.