Tellurium,selenium and cobalt enrichment in Neoproterozoic black shales,Gwna Group,UK: Deep marine trace element enrichment during the Second Great Oxygenation Event

Black shales of the late Neoproterozoic Gwna Group (570–580 Ma), UK, contain enrichments of tellurium (Te), selenium (Se) and cobalt (Co) relative to average shale compositions. The Te and Co enrichments bear comparison with those of ferromanganese crusts in the modern deep ocean. Gwna Group deposition coincides with the Second Great Oxidation Event, which had a significant effect on trace element fixation globally. Selenium and Te concentrations within these black shales indicate increased continental weathering rates, high biological productivity and corresponding increases in atmospheric O₂ concentrations. Cobalt, nickel (Ni) and arsenic (As) enrichments in this succession are secondary mineralisation phases. Demand for many of the trace elements found enriched in the Gwna Group black shales make their mechanisms of accumulation, and variations through the geological record, important to understand, and suggests that new resources may be sought based on black shale protoliths from this period.     

Hafnium/rare earth element fractionation in the sedimentary system and crustal recycling into the Earth's mantle

Among long-lived radioactive parent-daughter element pairs, the ratio Lu/Hf is strongly fractionated relative to constant Sm/Nd in the Earth's sedimentary system. This is caused by high resistance to chemical weathering of the mineral zircon (Zr,Hf)SiO₄. Zircon-bearing sandy sediments on and near continents have very low Lu/Hf, while deep-sea clays have up to three times the chondritic Lu/Hf ratio. Turbidity currents mechanically carry the low-Lu/Hf sandy material onto the ocean floor. The results are important for the crust-to-mantle recycling discussion, where most recycled materials would be subducted oceanic sediments. Such sediment should be capable of explaining the HfNd mantle isotopic variation by mixing with peridotite, but in fact any average pelagic sediment has Nd/Hf and Lu/Hf too high to allow mixing curves to pass through the Hf/Nd isotopic array. The array could only be reproduced by subduction of turbidite sandstone with pelagic sediment in the approximate ratio 1.2 to 1, and by maintaining a good mixture between the two components. At least today, turbidites are available for subduction only at locations quite different and distant from those where pelagic sediments may be recycled; furthermore, mantle isotopic variation shows that the mantle often cannot mix itself well enough to homogenize these widely-separated sedimentary components to the degree required. The Lu/Hf fractionations place a severe restriction on the ability of recycled sediments to explain mantle isotopic patterns.     

Investigations on cosmic-ray-produced nuclides in iron meteorites, 3. Exposure ages,meteoroid sizes and sample depths determined by mass spectrometric analyses of potassium and rare gases

Three physical quantities define the essentials of the cosmic ray exposure history of a sample of an iron meteorite: (1) the cosmic ray exposure age T, (2) the pre-atmospheric “size” S of the irradiated body, and (3) the location, i.e. the “depth” D, of the samples within the body. To establish these quantities for a given sample three independent quantities must be determined experimentally. In the present work T is ascertained by the ⁴¹K/⁴⁰K method and the ⁴He and ²¹Ne concentrations (C₄ and C₂₁) are measured by the isotope dilution method. Signer and Nier's evaluation of the rare gas distribution in the meteorite Grant and the measured exposure age for this meteorite provide the relationships allowing to ascertain for any meteorite the quantities S and D from the ²¹Ne production rate (P₂₁ = C₂₁/T) and the ⁴He/²¹Ne ratio.Earlier measurements have provided data on the isotopic composition of potassium in 74 different iron meteorites. New rare gas measurements are reported for some 40 samples. Results on the age, size and depth are obtained for almost 60 samples. These data suggest that Signer and Nier's model is well suited for describing not only the rare gas distribution in a single selected meteorite (Grant) but also the exposure histories of the great majority of all irons. For a few samples, however, secondary breakups of the meteoroid and a two- or multiple-stage irradiation must be invoked. Further measurements are proposed for testing and, possibly, refining the still somewhat uncertain relationships between the abundances of cosmogenic nuclides and the quantities T, S, and D in very large meteorites.Histograms are presented showing the age distributions for irons of different chemical groups and of different size ranges.The feasibility and the relative merits of other methods for the determination of T, S, and D are discussed.     

Near-future changes in storm surges along the Atlantic Iberian coast

Natural Hazards - Decadal predictions bridge the gap between the short-term weather/seasonal forecasts and the long-term climate projections. They target the reproduction of large-scale weather...     

Production of Drinking Water from Highly Contaminated Surface Waters: Removal of Organic,Inorganic, and Microbial Contaminants Applying Mobile Membrane Filtration Units

In military out of area missions of the Bundeswehr, it can be necessary to produce drinking water even from highly polluted surface waters containing a variety of organic, inorganic, and microbiological contaminants. Thus, mobile drinking water purification systems must be able to remove such contaminants as far as possible to meet the requirements of the German and European drinking water regulation/directive. Presently, two novel drinking water purification units applying membrane filtration undergo intensive long‐term trials carried out by the Bundeswehr. If these trials positively proof the functionality of these units and their ability to remove all possible contaminants they shall substitute so far available devices which use large amounts of chemicals and charcoal filtration for water purification.In the course of a research project, the functionality of the new devices and their efficacy to remove high amounts of algae, microbes, and organic and inorganic pollutants are additionally tested in “worst‐case” field studies. In September 2000, the first mobile drinking water purification unit was tested at the Teltowkanal in Berlin, Germany.This canal was chosen because it carries high burdens of municipal sewage effluents. The results from the fatigue test confirmed the ability of the water purification unit to reduce the concentrations of all contaminants meeting the maximum tolerance levels set by the German/European drinking water regulation.The pre‐filtration device was very effective in removing algae and solid particles to protect the membranes from clogging and to enable an almost maintenance‐free operation. Residues of pharmaceuticals and some other organic contaminants have almost totally been removed from the surface water where they were detected at individual concentrations up to the μg/L‐level.     

Compound summer temperature and precipitation extremes over central Europe

Theoretical and Applied Climatology - Reliable knowledge of the near-future climate change signal of extremes is important for adaptation and mitigation strategies. Especially compound extremes,...