A strike‐slip core complex from the Najd fault system,Arabian shield

Metamorphic core complexes are usually thought to be associated with regional crustal extension and crustal thinning, where deep crustal material is exhumed along gently dipping normal shear zones oblique to the regional extension direction. We present a new mechanism whereby metamorphic core complexes can be exhumed along crustal‐scale strike‐slip fault systems that accommodated crustal shortening. The Qazaz metamorphic dome in Saudi Arabia was exhumed along a gently dipping jog in a crustal‐scale vertical strike‐slip fault zone that caused more than 25 km of exhumation of lower crustal rocks by 30 km of lateral motion. Subsequently, the complex was transected by a branch of the strike‐slip fault zone, and the segments were separated by another 30 km of lateral motion. Strike‐slip core complexes like the Qazaz Dome may be common and may have an important local effect on crustal strength.     

Pre-processing of a sample of multi-scene and multi-date Landsat imagery used to monitor forest cover changes over the tropics

In support to the Remote Sensing Survey of the global Forest Resource Assessment 2010, the TREES-3 project has processed more than 12,000 Landsat TM and ETM+ data subsets systematically distributed over the tropics. The project aims at deriving area estimates of tropical forest cover change for the periods 1990-2000-2005. The paper presents the pre-processing steps applied in an operational and robust manner to this large amount of multi-date and multi-scene imagery: conversion to top-of-atmosphere reflectance, cloud and cloud shadow detection, haze correction and image radiometric normalization. The results show that the haze correction algorithm has improved the visual appearance of the image and significantly corrected the digital numbers for Landsat visible bands, especially the red band. The impact of the normalization procedures (forest normalization and relative normalization) was assessed on 210 image pairs: in all cases the correlation between the spectral values of the same land cover in both images was improved. The developed automatic pre-processing chain provided a consistent multi-temporal data set across the tropics that will constitute the basis for an automatic object-based supervised classification.     

Risk acceptance criterion for tanker oil spill risk reduction measures

This paper is aimed at investigating whether there is ample support for the view that the acceptance criterion for evaluating measures for prevention of oil spills from tankers should be based on cost-effectiveness considerations. One such criterion can be reflected by the Cost of Averting a Tonne of oil Spilt (CATS) whereas its target value is updated by elaborating the inherent uncertainties of oil spill costs and establishing a value for the criterion’s assurance factor. To this end, a value of $80,000/t is proposed as a sensible CATS criterion and the proposed value for the assurance factor F = 1.5 is supported by the retrieved Protection and Indemnity (P&I) Clubs’ Annual Reports. It is envisaged that this criterion would allow the conversion of direct and indirect costs into a non-market value for the optimal allocation of resources between the various parties investing in shipping. A review of previous cost estimation models on oil spills is presented and a probability distribution (log-normal) is fitted on the available oil spill cost data, where it should be made abundantly clear that the mean value of the distribution is used for deriving the updated CATS criterion value. However, the difference between the initial and the updated CATS criterion in the percentiles of the distribution is small. It is found through the current analysis that results are partly lower than the predicted values from the published estimation models. The costs are also found to depend on the type of accident, which is in agreement with the results of previous studies. Other proposals on acceptance criteria are reviewed and it is asserted that the CATS criterion can be considered as the best candidate. Evidence is provided that the CATS approach is practical and meaningful by including examples of successful applications in actual risk assessments. Finally, it is suggested that the criterion may be refined subject to more readily available cost data and experience gained from future decisions.     

In situ rates of sulfate reduction in response to geochemical perturbations

Rates of in situ microbial sulfate reduction in response to geochemical perturbations were determined using Native Organism Geochemical Experimentation Enclosures (NOGEEs), a new in situ technique developed to facilitate evaluation of controls on microbial reaction rates. NOGEEs function by first trapping a native microbial community in situ and then subjecting it to geochemical perturbations through the introduction of various test solutions. On three occasions, NOGEEs were used at the Norman Landfill research site in Norman, Oklahoma, to evaluate sulfate-reduction rates in wetland sediments impacted by landfill leachate. The initial experiment, in May 2007, consisted of five introductions of a sulfate test solution over 11 d. Each test stimulated sulfate reduction with rates increasing until an apparent maximum was achieved. Two subsequent experiments, conducted in October 2007 and February 2008, evaluated the effects of concentration on sulfate-reduction rates. Results from these experiments showed that faster sulfate-reduction rates were associated with increased sulfate concentrations. Understanding variability in sulfate-reduction rates in response to perturbations may be an important factor in predicting rates of natural attenuation and bioremediation of contaminants in systems not at biogeochemical equilibrium.     

Physiological effects of hypercapnia in the deep-sea bivalve Acesta excavata (Fabricius, 1779) (Bivalvia; Limidae)

The option of storing CO₂ in subsea rock formations to mitigate future increases in atmospheric CO₂ may induce problems for animals in the deep sea. In the present study the deep-sea bivalve Acesta excavata was subjected to environmental hypercapnia (pHSW 6.35, PCO₂ = 33,000 μatm) corresponding to conditions reported from natural CO₂ seeps. Effects on acid–base status and metabolic rate were related to time of exposure and subsequent recovery. During exposure there was an uncompensated drop in both hemolymph and intracellular pH. Intracellular pH returned to control values, while extracellular pH remained significantly lower during recovery. Intracellular non-bicarbonate buffering capacity of the posterior adductor muscle of hypercapnic animals was significantly lower than control values, but this was not the case for the remaining tissues analyzed. Oxygen consumption initially dropped by 60%, but then increased during the final stages of exposure, which may suggest a higher tolerance to hypercapnia than expected for a deep-living species.     

Quantitative evaluation of soil processes using in situ-produced cosmogenic nuclides

In situ-produced cosmogenic nuclides provide a means for quantitative evaluation of a wide range of weathering and sediment transport processes. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments, they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins. Here, we review the systematics of cosmogenic nuclide production within the Earth's surface, and present field examples demonstrating the utilization of in situ-produced cosmogenic nuclides distributions for evaluation of a range of soil evolution processes. To cite this article: E.T. Brown et al., C. R. Geoscience 335 (2003).     

On the Effect of Thermally Induced Stresses in Failures of Some Rock Slopes in Rio de Janeiro, Brazil

Previous studies have indicated that many rock slope failures in Rio de Janeiro, Brazil, occur during relatively dry periods when there is little, if any, rainfall. In the present paper, we describe these events and propose possible mechanisms for their occurrence. It is believed that daily fluctuations in temperature may create thermally induced stresses of enough magnitude to propagate fractures already existing in the rock mass. Laboratory experiments were conducted in order to measure temperature variations in a fractured rock system. Using the experimentally obtained data, we carried out numerical analyses in order to verify whether temperature-related stresses were indeed able to propagate fractures existing in the rock mass. The results obtained indicate that cycles of temperature change over time, especially during the colder months of the year can indeed create stress conditions in the rock mass able to propagate existing non-persistent joints, and ultimately lead to failure of the rock slope.     

Experimental and numerical modelling of sedimentation in a rectangular shallow basin

Numerical simulation of flows in shallow reservoirs has to be checked for its consistency in predicting real flow conditions and sedimentation patterns. Typical flow patterns may exhibit flow separation at the inlet, accompanied by several recirculation and stagnation areas all over the reservoir surface. The aim of the present research project is to study the influence of the geometry of a reservoir on sediment transport and deposition numerically and experimentally, focusing on a prototype reservoir depth between 5 and 15 m as well as suspended sediment transport.
A series of numerical simulations is presented and compared with scaled laboratory experiments, with the objective of testing the sensitivity to different flow and sediment parameters and different turbulence closure schemes. Different scenarios are analyzed and a detailed comparison of preliminary laboratory tests and some selected simulations are presented.
The laboratory experiments show that suspended sediment transport and deposition are determined by the initial flow pattern and by the upstream and downstream boundary conditions. In the experiments, deposition in the rectangular basin systematically developed along the left bank, although inflow and outflow were positioned symmetrically along the centre of the basin. Three major horizontal eddies developed influencing the sediment deposition pattern. Although asymmetric flow patterns are privileged, a symmetric pattern can appear from time to time. This particular behaviour could also be reproduced by a two-dimensional depth-averaged flow and sediment transport model （CCHE2D）. The paper presents numerical simulations using different turbulence closure schemes （k-ε and eddy viscosity models）. In spite of the symmetric setup, these generally produced an asymmetric flow pattern that can easily switch sides depending on the assumptions made for the initial and boundary conditions. When using the laboratory experiment as a reference, the most reliable numerical results have been obtai     

The use of the log-normal distribution of individuals among species in monitoring zoobenthos in the northern Baltic archipelago

The log-normal distribution of individuals among species of shallow, brackish water benthos is compared to other, more commonly used methods. This method, the use of which was introduced in marine monitoring in 1979, has not previously been tested on macrobenthos of the northern Baltic Sea. The relevance of other indices are discussed in relation to the log-normal distribution. Based on samples from three localities (soft littoral benthos, soft bottom benthos and sand bottom benthos) it is shown that the log-normal distribution could well be used as an important tool in interpreting benthic data sets from low-saline waters with few macrozoobenthic species. It illustrates natural and anthropogenic changes on the zoobenthic communities more adequately than the other parameters calculated.     

Pressure variations in peat as a result of gas bubble dynamics

Transient high pore‐water pressures, up to 50 cm higher than ambient pressure, developed over the summer season at various depths in a shallow (1 m) fen peat. The excess pressures had a pattern of gradual increases and sharp drops, and their initiation and release typically corresponded to abrupt changes in atmospheric pressure. We conclude that these phenomena depend on gas bubbles (probably methane) generated by biological activity, both by clogging pores and by building up pressure as they grow. These transient and spatially discontinuous high‐pressure zones were found using pressure transducers in sealed (backfilled) pits, but not in piezometers open to the atmosphere. Piezometers may provide a conduit for the release of gas and pressure, thus rendering them unsuitable for measuring this phenomenon. Although the development of localized zones of high pressure causes erratic and unpredictable hydraulic gradients, we suggest that their effect on the flow of water or solutes is offset by the reduced permeability caused by the bubbles, which allows them to be sustained. These zones, however, probably deflect flows driven by the dominant hydraulic gradients. Furthermore, they may cause the peat volume to adjust (swell). The use and interpretation of traditional methods for estimating hydraulic head and conductivity in peat soils thus require great caution. Copyright © 2004 John Wiley & Sons, Ltd.