Methane in the southern North Sea: Sources, spatial distribution and budgets   总被引：3，自引：0，他引：3  

Maik Grunwald  Olaf Dellwig  Melanie Beck  Joachim W. Dippner  Jan A. Freund  Cora Kohlmeier  Bernhard Schnetger  Hans-Jürgen Brumsack 《Estuarine, Coastal and Shelf Science》2009,81(4):445-456

Measurements of methane (CH₄) so far have always shown supersaturation in the entire North Sea relative to the atmospheric partial pressure and the distribution of surface CH₄ reveals a distinct increase towards the shore. Since North Sea sediments presumably are an insignificant source for CH₄ the coastal contribution via rivers and tidal flats gains in importance.In this work, CH₄ data from the River Weser, the back barrier tidal flats of Spiekeroog Island (NW Germany), and the German Bight are presented. Results from the River Weser are compared to other rivers draining into the German Bight. Measurements in the tidal flat area of Spiekeroog Island highlight this ecosystem as an additional contributor to the overall CH₄ budget of the southern North Sea. A tidally driven CH₄ pattern is observed for the water column with maximum values during low tide. Tidal flat sediments turn out to be the dominating source because pore waters discharged during low tide are highly enriched in CH₄. In contrast, the freshwater contribution to the tidal flats by small coastal tributaries has almost no impact on water column CH₄ concentrations. The CH₄ level seems to be disturbed irregularly by wind forcing due to elevated degassing and prevention of advective flow when tidal flats remain covered by water.Based on our data, two model calculations were used to estimate the impact of tidal flats on the CH₄ budget in the German Bight. Our results demonstrate that the back barrier tidal flats of the east Frisian Wadden Sea contribute CH₄ in an order of magnitude between the Wash estuary and River Elbe and thus have to be considered in budget calculations.  相似文献   

Reply to “comment on solute carbon and carbon segregation in magnesium oxide single crystals — A secondary ion mass spectrometry study” by I.S.T. Tsong and U. Knipping     

Friedemann Freund 《Physics and Chemistry of Minerals》1986,13(4):280-280

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Equal Spacing of Strike-Slip Faults     

A. M. Merzer  R. Freund 《Geophysical Journal International》1976,45(1):177-188

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Buckling of Strike-Slip Faults-in a Model and in Nature     

A. M. Merzer  R. Freund 《Geophysical Journal International》1975,43(2):517-530

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应力激活电流与软化岩石     

Freund F T  Hoenig S A  Braun A  Dahlgren R P  Momayez M  Chu J J  米琦 《国际地震动态》2011,(1):104-109

当岩石受到机械应力作用时,隐藏的电子缺陷就被激活.这种激活会产生通过释放高移动性的缺陷电子使岩石电导率增加的电子空穴对,相当于O~2-点阵中存在的O-,叫做正空穴,用符号h˙表示.这种电荷载体h˙能够从受到应力作用的岩石中扩散到周围未受应力作用的岩石中.阻止h˙流出改变了岩石的力学属性:使它们得到软化和弱化.进行中的研...  相似文献   

Toward a unified solid state theory for pre-earthquake signals   总被引：3，自引：0，他引：3  

Friedemann Freund 《Acta Geophysica》2010,58(5):719-766

Many different non-seismic pre-earthquake signals have been reported but there is great uncertainty about their origin, their correlation to each other and to the impending seismic event. The discovery of stress-activated electric currents in rocks provides a possible explanation. Stresses activate electronic charge carriers, namely defect electrons in the oxygen anion sublattice, equivalent to O⁻ in a matrix of O²⁻, also known as positive holes. These charge carriers pre-exist in unstressed rocks in a dormant, electrically inactive state as peroxy links, O₃Si-OO-SiO₃, where two O⁻ are tightly bound together. Under stress dislocations sweep through the mineral grains causing the peroxy links to break. Positive holes, thus generated, flow down stress gradients, constituting an electric current with attendant magnetic field variations and EM emissions. The positive holes accumulate at the surface, creating electric fields, strong enough to field-ionize air molecules. They also recombine leading to a spectroscopically distinct IR emission seen in laboratory experiments and night-time infrared satellite images. In addition positive holes interact with radon in the soil, affecting the radon emanation.  相似文献   

Dissolution of uranophane: An AFM, XPS, SEM and ICP study     

Michael Schindler  Michael Freund  Peter C. Burns 《Geochimica et cosmochimica acta》2009,73(9):2510-202

Dissolution experiments on single crystals of uranophane and uranophane-β, Ca(H₂O)₅[(UO₂)(SiO₃(OH)]₂, from the Shinkolobwe mine of the Democratic Republic of Congo, were done in an aqueous HCl solution of pH 3.5 for 3 h, in HCl solutions of pH 2 for 5, 10 and 30 min, and in Pb²⁺-, Ba-, Sr-, Ca- and Mg-HCl solutions of pH 2 for 30 min. The basal surfaces of the treated uranophane crystals were examined using atomic-force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Solutions after dissolution experiments on single crystals and synthetic powders were analysed with inductively coupled plasma-optical emission spectroscopy (ICP-OES) and mass spectroscopy (ICP-MS). The morphology of the observed etch pits (measured by AFM) were compared to the morphology, predicted on the basis of the bond-valence deficiency of polyhedron chains along the edges of the basal surface. Etch pits form in HCl solutions of pH 2. Their decrease in depth with the duration of the dissolution experiment is explained with the stepwave dissolution model, which describes the lowering of the surrounding area of an etch pit with continuous waves of steps emanated from the etch pit into the rest of the crystal surface. Hillocks form in an HCl solution of pH 3.5, and the chemical composition of the surface (as indicated by XPS) shows that these hillocks are the result of the precipitation of a uranyl-hydroxy-hydrate phase. Well-orientated hillocks form on the surface of uranophane in a SrCl₂-HCl solution of pH 2. They are part of an aged silica coating of composition Si₂O₂(OH)₄(H₂O)_n. An amorphous layer forms on the surface of uranophane in a MgCl₂-HCl solution of pH 2, which has a composition and structure similar to silicic acid. Small crystallites of uranyl-hydroxy-hydrate phases form on the surface of uranophane after treatment in Pb(NO₃)₂-HCl and BaCl₂-HCl solutions of pH 2. Dissolution experiments on synthetic uranophane powders show that in the early stage of the experiments, the dissolution rate of uranophane increase in the sequence Pb(NO₃)₂-HCl < BaCl₂-HCl < CaCl₂-HCl < HCl < SrCl₂-HCl < MgCl₂-HCl, indicating that the dissolution of uranophane is more enhanced in solutions containing divalent cations of small ionic radii and high Lewis acidity (Mg, MgCl⁺).  相似文献   

Effect of impurities on grain growth in synthetic calcite aggregates     

D. Freund  E. Rybacki  G. Dresen 《Physics and Chemistry of Minerals》2001,28(10):737-745

 We investigated grain growth of calcite aggregates fabricated from crushed natural single crystals with different impurity content. The total trace-element concentration of the starting powders varied from about 170 ppm to more than 930 ppm with Mn as the major component. Samples were produced by hot-isostatic pressing of the different powders at 300 MPa confining pressure at 600 °C for 2 h. The starting material for the anneals was dry and had a uniform microstructure with an average grain size of about 5 μm and a porosity of <2.1%. Three disks with Mn concentrations of 10, 350, and 670 ppm, respectively, were annealed in the same run at a confining pressure of 300 MPa, and temperatures between 700 and 900 °C for up to 20 h. Grain growth was fastest in samples with the highest Mn concentrations. A multivariable fit to the data yields grain-growth exponents of 2.0 ± 0.3 for samples with 10 ppm Mn and 2.3 ± 0.2 for those with 670 ppm Mn. The activation energies for grain growth vary from 99 ± 12 kJ mol⁻¹ to 147 ± 14 kJ mol⁻¹ for the respective calcite compositions. Received: 22 August 2000 / Accepted: 12 March 2001  相似文献   

Active faulting in the dead sea rift   总被引：8，自引：0，他引：8  

Z. Garfunkel  I. Zak  R. Freund 《Tectonophysics》1981,80(1-4):1-26

Manifestations of Late Quaternary and Holocene faulting were studied in a 500 km long segment of the Dead Sea transform (rift). Most prominent are left-slip faults, whose characteristic physiographic features are recognizable along most of the studied segment. Where these faults bend or are stepped to the left, rhomb-shaped grabens (or pull aparts) are produced, forming depressions. In the reverse situation compressional features such as pressure ridges, domes and folds form positive topographic features. Such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers. Normal faults, sub-parallel to the left slip faults, produce a trough-like valley along much of the Dead Sea transform, but are most prominent along the margins of the large rhomb-grabens, e.g., the Dead Sea trough. They apparently record a small component of transverse extension. Generally, their motion is slow: young slip did not occur along some segments during the last few 10⁴ y. Elsewhere throws of 10–20 m at least occurred in this period. The Dead Sea transform is seismically active. The instrumental and historic records indicate a seismic slip rate of 0.15–0.35 cm/y during the last 1000–1500 y, while estimates of the average Pliocene—Pleistocene rate are 0.7–1.0 cm/y. Either much creep takes place, or the slip rate varies over periods of a few 10³ y.  相似文献   

Structural and locational evolution of industry in Southern Europe     

Bodo Freund 《GeoJournal》1986,13(1):67-73

S European Industry is characterized by the importance of certain branches and by plant size. Traditional branches of consumer goods are dominated by the national bourgeoisie, intermediate goods by oligopolistic (state) enterprises, modern consumer and capital goods by multinational corporations. Industrialization was retarded for various social and physical reasons. For the locational pattern some factors had specific importance (diffusion, shipping traffic for supplies, deficient infrastructure, urbanisation economies, social structure). Economic nationalism and interventionism from the thirties to the late fifties had structural and locational effects. Subsequent opening led to important foreign investment with diverse locational consequences: the large majority of the market-orientated companies concentrated on big cities and induced industrial suburbanisation. Export-orientated plants, relatively often in Portugal, also decided for rural areas and provincial towns. Regional industrial policy which began weakly with fiscal allowances in the fifties and soon adopted the growth pole idea led to results remaining only far beyond expectations. International economic crisis has heavily stroken the countries which turned out to be very dependant.  相似文献