Characteristics of spectral aerosol optical depths over India during ICARB

Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from tshe adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent (α) remained significantly lower (～1) over the Arabian Sea compared to Bay of Bengal (BoB) (～1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of α, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in α over the BoB.     

Microstructural, chemical and textural records during growth of snowball garnet

The growth history of two populations of snowball garnet from the Lukmanier Pass area (central Swiss Alps) was examined through a detailed analysis of three-dimensional geometry, chemical zoning and crystallographic orientation. The first population, collected in the hinge of a chevron-type fold, shows an apparent rotation of 360°. The first 270° are characterized by spiral-shaped inclusion trails, gradual and concentric Mn zoning and a single crystallographic orientation, whereas in the last 90°, crenulated inclusion trails and secondary Mn maxima centred on distinct crystallographic garnet domains are observed. Microstructural, geochemical and textural data indicate a radical change in growth regime between the two growth sequences. In the first 270°, growth occurred under rotational non-coaxial flow, whereas in the last 90°, garnet grew under a non-rotational shortening regime. The second population, collected in the limb of the same chevron-type fold structure, is characterized by a spiral geometry that does not exceed 270° of apparent rotation. These garnet microstructures do not record any evidence for a modification of the stress field during garnet growth. Concentric Mn zoning as well as a single crystallographic orientation are observed for the entire spiral. Electron backscatter diffraction data indicate that nearly all central domains in the snowball garnet are characterized by one [001] axis oriented (sub-)parallel to the symmetry axis and by another [001] axis oriented (sub-)parallel to the orientation of the internal foliation. These features suggest that the crystallographic orientation across the garnet spiral is not random and that a relation exists among the symmetry axis, the internal foliation and the crystallographic orientation.     

Hydrochemical variation in the springs water between Jerusalem–Ramallah Mountains and Jericho Fault,Palestine

The spatial and temporal changes of the composition of the groundwater from the springs along the Wadi Qilt stream running from the Jerusalem–Ramallah Mountains towards the Jericho Plain is studied during the hydrological year 2006/2007. The residence time and the intensity of recharge play an important role in controlling the chemical composition of spring water which mainly depends on distance from the main recharge area. A very important factor is the oxidation of organics derived from sewage and garbage resulting in variable dissolved CO₂ and associated HCO₃ ⁻ concentration. High CO₂ yields lower pH values and thus under-saturation with respect to calcite and dolomite. Low CO₂ concentrations result in over-saturation. Only at the beginning and at the end of the rainy season calcite saturation is achieved. The degradation of dissolved organic matter is a major source for increasing water hardness. Besides dissolution of carbonates dissolved species such as nitrate, chloride, and sulfate are leached from soil and aquifer rocks together with only small amounts of Mg. Mg not only originates from carbonates but also from Mg–Cl waters are leached from aquifer rocks. Leaching of Mg–Cl brines is particularly high at the beginning of the winter season and lowest at its end. Two zones of recharge are distinguishable. Zone 1 represented by Ein Fara and Ein Qilt is fed directly through the infiltration of meteoric water and surface runoff from the mountains along the eastern mountain slopes with little groundwater residence time and high flow rate. The second zone is near the western border of Jericho at the foothills, which is mainly fed by the under-groundwater flow from the eastern slopes with low surface infiltration rate. This zone shows higher groundwater residence time and slower flow rate than zone 1. Groundwater residence time and the flow rate within the aquifer systems are controlled by the geological structure of the aquifer, the amount of active recharge to the aquifer, and the recharge mechanism. The results of this study may be useful in increasing the efficiency of freshwater exploitation in the region. Some precautions, however, should be taken in future plans of artificial recharge of the aquifers or surface-water harvesting in the Wadi. Because of evaporation and associated groundwater deterioration, the runoff water should be artificially infiltrated in zones of Wadis with high storage capacity of aquifers. Natural infiltration along the Wadis lead to evaporation losses and less quality of groundwater.     

Principles of geomechanical safety assessment for radioactive waste disposal in salt structures

Today, a large amount of knowledge is available concerning various sites of potential high active waste (HAW) repositories in salt media. Domal Zechstein salt formations have been examined at several sites in Germany. Extensive R&D work was initiated in the former Asse Salt Mine in order to explore the suitability of salt for waste isolation by laboratory tests, theoretical studies and in-situ tests with test results forming a technological base for future repository development.

Resulting from the inhomogeneity of salt structures the demanded safety of a permanent repository for radioactive wastes can be demonstrated only by a specific site analysis in which the entire system, “the geological situation, the repository, and the form and amount of the wastes” and their interrelationships are taken into consideration.

The site analysis has three essential tasks: (1) Assessment of the thermomechanical load capacity of the host rock, so that deposition strategies can be determined for the site; (2) Determination of the safe dimensions of the mine (e.g. stability of the caverns and safety of the operations); and (3) Evaluation of the barriers and the long-term safety analysis for the authorization procedure.

The geotechnical stability analysis is a critical part of the safety assessment. Engineering–geological study of the site, laboratory and in situ-experiments, geomechanical modelling, and numerical static calculations comprise such an analysis.

Within a scenario analysis — according to the multi-barrier principle, the geological setting is checked to be able to contribute significantly to the waste isolation over long periods. The assessment of the integrity of the geological barrier can only be performed by making calculations with geomechanical and hydrogeological models. The proper idealization of the host rock in a computational model is the basis of a realistic calculation of stress distribution and excavation damage effects. The determination of water permeability along discontinuities is necessary in order to evaluate the barrier efficiency of each host rock.

In this paper some important processes for the performance assessment are described, namely creep and fracturing, permeability and infiltration, and halokinesis and subrosion.

For the future, the role and contributions of geoscientific and rock mechanics work within the safety assessment issues (e.g. geomechanical safety indicators) must be identified in greater detail, e.g. considerations of geomechanical natural analogy for calibration of constitutive laws.     

Authigenic carbonates in methane seeps from the Norwegian sea: Mineralogy, geochemistry, and genesis

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active CH₄bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanetrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH₄ oxidation. Isotopically light carbon (δ¹³C_av =−28.9%0) of carbon dioxide produced during CH₄ oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (δ¹⁸O_av = 5%0) in carbonates is inherited from seawater sulfate. A rapid sulfate reduction (up to 12 mg S dm⁻³ day⁻¹) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this, carbonates can only be formed in surface sediments near the water-bottom interface. Authigenic carbonates occurring within sediments occur do notin situ. Salinity, as well as CO ₃ ²⁻ /Ca and Mg/Ca ratios, correspond to the field of nonmagnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. The radiocarbon age of carbonates is about 10000 yr.     

The chemical evolution of globular clusters

The sequence of events determining the initial stages of star formation is analyzed in framework of the self-enrichment scenario. The computations are based on a single-zone chemo-dynamical model. It is shown that the first episode of star formation was characterized by an initial mass function shifted toward massive stars (M ≥ 8M_⊙). We argue that the transition to a star formation with a normal (Salpeter) initial mass function was due to more efficient radiative cooling of the proto-globular cluster gas after its enrichment to a metallicity of Z ～ 0.02 Z_⊙ in agreement with those observed in globular clusters.     

Application of Deuterium Excess for Identification of Freshwater Sources in the Bays of Novaya Zemlya Archipelago

Doklady Earth Sciences - An isotopic–geochemical study was carried out for waters of Tsivolkii and Sedov bays (southeastern coast of the Novaya Zemlya Archipelago). The waters of these bays...