Input sensitivity study of a stratospheric photochemistry model

A general technique for calculating the sensitivities, uncertainties and overall imprecision of a model to a set of input parameters is described and applied to the calculation of CFM induced stratospheric ozone depletion. The input data set used is reaction rates and the technique highlights those that most need further study in the laboratory. The convolution of individual uncertainties to obtain an overall imprecision gives good agreement with the results of Monte-Carlo calculations using the same model.A paper presented at the IAGA/IAMAP Joint Assembly at Seattle, Washington, USA. 22 August–3 September 1977.     

Concentration and size variation of condensation nuclei at Mawson,Antarctica

Condensation nucleus (CN) concentrations have been measured at Mawson (67.6°S, 62.9°E) since mid 1981. Weekly median concentrations have an annual cycle with a maximum of around 300 to 400 cm^-3 in summer and a minimum of a few tens of particles per cm^-3 in winter. In this respect Mawson behaves very much like an Antarctic continental location. Preliminary measurements of the size distribution of CN particles taken over a nine month period suggest a seasonal change in typical particle radius from around 0.01 m in winter to around 0.04 m in summer. Diurnal variation in the CN concentration is generally very weak and does not show any systematic relation to the pronounced diurnal variation in wind-speed at Mawson.Department of Science, Antarctic Division     

The restoration of thrust systems and displacement continuity around the Mont Blanc massif,NW external Alpine thrust belt

Foreland-propagating external thrust belts may be considered as essentially plane strain phenomena so that displacements can be correlated throughout their linked, three-dimensional fault geometry. This approach has been applied to part of the northwest external French-Swiss Alps, around the Mont Blanc basement massif. Imbricates of basement and cover sequences on the SW margin of this massif restore to a width in excess of 77 km with an implicit shortening of at least 67 km. These displacements can be correlated with those in the neighbouring Helvetic nappes by transferring movements, via lateral branch lines, onto the Mont Blanc thrust. By reappraising thrust geometries, the Helvetic/Ultrahelvetic nappe complex has been restored to a width of 114 km to the ESE of the Aiguilles Rouges basement massif. Displacements on the internal (SE) margin of the Mont Blanc massif, estimated by balanced sections and a restoration of the Ultrahelvetic klippen in the sub-alps, exceed 59 km. Thrust continuity, incorporating the restorations of nappes and imbricate geometries around the Mont Blanc massif, is illustrated on a crude, restored branch-line map which also serves as a preliminary palaeogeographic reconstruction. External thrust systems, to the east of the external Belledonne/Aiguilles Rouges massif, restore to a width of at least 140 km in the footwall to the Frontal Pennine thrust.     

Direct-Push Electrical Conductivity Logging for High-Resolution Hydrostratigraphic Characterization

Fine-scale hydrostratigraphic features often play a critical role in controlling ground water flow and contaminant transport. Unfortunately, many conventional drilling- and geophysics-based approaches are rarely capable of describing these features at the level of detail needed for contaminant predictions and remediation designs. Previous work has shown that direct-push electrical conductivity (EC) logging can provide information about site hydrostratigraphy at a scale of relevance for contaminant transport investigations in many unconsolidated settings. In this study, we evaluate the resolution and quality of that information at a well-studied research site that is underlain by highly stratified alluvial sediments. Geologic and hydrologic data, conventional geophysical logs, and particle-size analyses are used to demonstrate the capability of direct-push EC logging for the delineation of fine-scale hydrostratigraphic features in saturated unconsolidated formations. When variations in pore-fluid chemistry are small, the electrical conductivity of saturated media is primarily a function of clay content, and hydrostratigraphic features can be described at a level of detail (<2.5 cm in thickness) that has not previously been possible in the absence of continuous cores. Series of direct-push EC logs can be used to map the lateral continuity of layers with non-negligible clay content and to develop important new insights into flow and transport at a site. However, in sand and gravel intervals with negligible clay, EC logging provides little information about hydrostratigraphic features. As with all electrical logging methods, some site-specific information about the relative importance of fluid and sediment contributions to electrical conductivity is needed. Ongoing research is directed at developing direct-push methods that allow EC logging, water sampling, and hydraulic testing to be done concurrently.     

Simulation Assessment of Direct Push Injection Logging for High-Resolution Aquifer Characterization

Direct push injection logging (DPIL) has become one of the most widely used approaches for obtaining vertical profiles of hydraulic conductivity (K) in environmental site investigations. Despite its widespread use, however, there has been no rigorous analysis of the underlying physical processes that take place during DPIL or how the approach would perform under different hydrogeological and operating conditions. We address these issues through a series of numerical simulations. Results show that the ratio of DPIL injection rate over pressure can be used for direct determination of K when K is >10⁻⁶ m/s. When K is <10⁻⁶ m/s and specific storage (Ss) is >10⁻³/m, the ratio becomes increasingly sensitive to Ss; in that case, additional information on Ss is needed for reliable K estimation. For unconsolidated formations of moderate K or higher, the ratio of injection rate over pressure should provide a reasonable K estimate when Ss is <10⁻³/m. Although water injection at previous depths during continuous DPIL has only a small impact on the pressure response measured at the current injection depth, probe advancement can have a significant impact when K and Ss are small. Consequently, in fine-grained materials, the advancement-generated pore water pressure increase can comprise a large portion of the measured pressure response. To diminish the impact of probe advancement in such materials, advancement speed should be kept as low as possible (e.g., 0.5 cm/s).     

Isotope geochemistry of drainage from an acid mine impaired watershed,Oakland, California

Oxidation of sulfides at the Leona Heights Sulfur Mine has resulted in the liberation of acid, SO₄ and metals to Leona Creek. Previous research at the site has indicated Fe(II) oxidation at rates faster than would be predicted by abiotic oxidation alone, particularly in the segment of stream between the Adit and Leona Street sample stations. In order to assess the mechanisms responsible for sulfide oxidation, samples were collected for isotopic analysis of water and SO₄, the results of which were used to develop a stoichiometric isotope-balance model. This exercise indicated that the percentage of water-derived oxygen in SO₄ increased spatially from between 56% and 64% at the Adit to between 71% and 72% at Leona Street, illustrating that increased sulfide oxidation via Fe(III) was occurring within, or as water flows over, the waste rock, relative to water emanating directly from the former mine. The incorporation of water-derived oxygen in SO₄ during pyrite oxidation is a process controlled by Fe oxidizing bacteria such as A. ferrooxidans at low pH. The role of bacteria was further supported by estimates of the rate constant for Fe oxidation between sampling stations, yielding values that were approximately 10⁶ faster than abiotic Fe oxidation alone. Stable isotopic analysis of water further indicates a close correlation of adit spring water to the local meteoric water line, while ³H data indicate a groundwater apparent age, or time of travel from its primary zone of recharge, of <5–18 a. Additionally, the δ³⁴S data, in conjunction with reported albitized feldspars within the Leona Rhyolite host rock, indicate a magmatic origin of ore sulfur, contrary to previous interpretations at the site.