Outflows from Dynamo-Active Protostellar Accretion Discs     

Brigitta von Rekowski  Axel Brandenburg  Wolfgang Dobler  Anvar Shukurov 《Astrophysics and Space Science》2004,292(1-4):493-500

An axisymmetric model of a cool, dynamo-active accretion disc is applied to protostellar discs. Thermally and magnetically driven outflows develop that are not collimated within 0.1 AU. In the presence of a central magnetic field from the protostar, accretion onto the protostar is highly episodic, which is in agreement with earlier work.  相似文献   

Palaeontological and facial features of the Upper Jurassic Hochstegen Marble (Tauern Window, Eastern Alps)     

Wolfgang Kiessling 《地学学报》1992,4(2):184-197

Micropalaeontological, microscopic and mineralogical investigations of the ductily deformed and greenschist-facies metamorphic Hochstegen Marble in the Tauern Window shed new light on its stratigraphy and fades.
New radiolarian and sponge spicule discoveries have been made in cherty limestone marbles. They confirm previous age assignments and permit for the first time a more exact micropalaeontological age determination of early Tithonian for the upper parts of the marble. Forty morphotypes of radiolarians could be distinguished; in one sample a Fisher diversity index of 6 is reached indicating deeper marine conditions. The spicule fauna is also diverse and shows affinity to the S-German Malm. In respect to all the data it can be presumed that carbonate sedimentation of the Hochstegen Marble took place in a deeper marine environment at the southern margin of the European continent (Helvetic realm) during the whole Late Jurassic.  相似文献   

List of forthcoming papers     

Wolfgang Wenzel 《Astrophysics and Space Science》1993,201(1):153-153

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Offshore granulites from the Bay of Biscay margins: fission tracks constrain a Proterozoic to Tertiary thermal history     

Bernhard Fügenschuh  Nikolaus Froitzheim  Raymond Capdevila  Gilbert Boillot 《地学学报》2003,15(5):337-342

Zircon and apatite fission track ages were determined on granulites dredged along the Bay of Biscay margins. A sample from Ortegal Spur (Iberia margin) yielded 725 ± 67 Ma (zircon). A sample from Le Danois Bank (Iberia margin) yielded 284 ± 58 Ma (zircon), indicating post‐Variscan cooling. Apatite from this sample gave 52 ± 2 Ma, interpreted as final cooling after ‘Pyrenean’ thrust imbrication. Two other samples from Le Danois Bank have Early Cretaceous apatite ages (138 ± 7 and 120 ± 8 Ma), interpreted to result from exhumation during rifting. Finally, a granulite from Goban Spur (Armorican margin) gave 212 ± 10 Ma (apatite), coinciding with a precursory rifting phase. Together with published radiometric results, these data indicate a Precambrian high‐grade terrane at the site of the current margins. The distribution of the granulites on the seafloor reflects tectonic and erosional processes related to (a) Mesozoic rifting and (b) Early Tertiary incipient subduction of the Bay of Biscay beneath Iberia.  相似文献   

Our galaxy — A former seyfert?     

Wolfgang Kundt 《Astrophysics and Space Science》1987,129(1):195-201

A re-interpretation is offered for both the galactic center lobe and the high-velocity clouds in the galactic halo: the galactic center lobe is a 2-sided chimney for relativistic pair plasma emerging from the center of the Milky Way (=Sag A^*) and streaming as 2 jets through the halo. The channel walls of the flow serve as cold traps for the galactic fountain whenceHi clouds rain back into the disk.  相似文献   

Sulfur isotope measurement of sulfate and sulfide by high-resolution MC-ICP-MS   总被引：4，自引：0，他引：4  

Paul R. Craddock  Olivier J. Rouxel  Lary A. Ball  Wolfgang Bach   《Chemical Geology》2008,253(3-4):102-113

We have developed a technique for the accurate and precise determination of ³⁴S/³²S isotope ratios (δ³⁴S) in sulfur-bearing minerals using solution and laser ablation multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). We have examined and determined rigorous corrections for analytical difficulties such as instrumental mass bias, unresolved isobaric interferences, blanks, and laser ablation- and matrix-induced isotopic fractionation. Use of high resolution sector-field mass spectrometry removes major isobaric interferences from O₂⁺. Standard-sample bracketing is used to correct for the instrumental mass bias of unknown samples. Background on sulfur masses arising from memory effects and residual oxygen-tailing are typically minor (< 0.2‰, within analytical error), and are mathematically removed by on-peak zero subtraction and by bracketing of samples with standards determined at the same signal intensity (within 20%). Matrix effects are significant (up to 0.7‰) for matrix compositions relevant to many natural sulfur-bearing minerals. For solution analysis, sulfur isotope compositions are best determined using purified (matrix-clean) sulfur standards and sample solutions using the chemical purification protocol we present. For in situ analysis, where the complex matrix cannot be removed prior to analysis, appropriately matrix-matching standards and samples removes matrix artifacts and yields sulfur isotope ratios consistent with conventional techniques using matrix-clean analytes. Our method enables solid samples to be calibrated against aqueous standards; a consideration that is important when certified, isotopically-homogeneous and appropriately matrix-matched solid standards do not exist. Further, bulk and in situ analyses can be performed interchangeably in a single analytical session because the instrumental setup is identical for both. We validated the robustness of our analytical method through multiple isotope analyses of a range of reference materials and have compared these with isotope ratios determined using independent techniques. Long-term reproducibility of S isotope compositions is typically 0.20‰ and 0.45‰ (2σ) for solution and laser analysis, respectively. Our method affords the opportunity to make accurate and relatively precise S isotope measurement for a wide range of sulfur-bearing materials, and is particularly appropriate for geologic samples with complex matrix and for which high-resolution in situ analysis is critical.  相似文献   

Impact of nitrogenous fertilizers on carbonate dissolution in small agricultural catchments: Implications for weathering CO₂ uptake at regional and global scales   总被引：5，自引：0，他引：5  

Anne-Sophie Perrin  Anne Probst  Jean-Luc Probst 《Geochimica et cosmochimica acta》2008,72(13):3105-3123

The goal of this study was to highlight the occurrence of an additional proton-promoted weathering pathway of carbonate rocks in agricultural areas where N-fertilizers are extensively spread, and to estimate its consequences on riverine alkalinity and uptake of CO₂ by weathering. We surveyed 25 small streams in the calcareous molassic Gascogne area located in the Garonne river basin (south-western France) that drain cultivated or forested catchments for their major element compositions during different hydrologic periods. Among these catchments, the Hay and the Montoussé, two experimental catchments, were monitored on a weekly basis. Studies in the literature from other small carbonate catchments in Europe were dissected in the same way. In areas of intensive agriculture, the molar ratio (Ca + Mg)/HCO₃ in surface waters is significantly higher (0.7 on average) than in areas of low anthropogenic pressure (0.5). This corresponds to a decrease in riverine alkalinity, which can reach 80% during storm events. This relative loss of alkalinity correlates well with the content in surface waters. In cultivated areas, the contribution of atmospheric/soil CO₂ to the total riverine alkalinity (CO_{2 ATM-SOIL}/HCO₃) is less than 50% (expected value for carbonate basins), and it decreases when the nitrate concentration increases. This loss of alkalinity can be attributed to the substitution of carbonic acid (natural weathering pathway) by protons produced by nitrification of N-fertilizers (anthropogenic weathering pathway) occurring in soils during carbonate dissolution. As a consequence of these processes, the alkalinity over the last 30 years shows a decreasing trend in the Save river (one of the main Garonne river tributaries, draining an agricultural catchment), while the nitrate and calcium plus magnesium contents are increasing.We estimated that the contribution of atmospheric/soil CO₂ to riverine alkalinity decreased by about 7-17% on average for all the studied catchments. Using these values, the deficit of CO₂ uptake can be estimated as up to 0.22-0.53 and 12-29 Tg¹ yr⁻¹ CO₂ on a country scale (France) and a global scale, respectively. These losses represent up to 5.7-13.4% and only 1.6-3.8% of the total CO₂ flux naturally consumed by carbonate dissolution, for France and on a global scale, respectively. Nevertheless, this loss of alkalinity relative to the Ca + Mg content relates to carbonate weathering by protons from N-fertilizers nitrification, which is a net source of CO₂ for the atmosphere. This anthropogenic CO₂ source is not negligible since it could reach 6-15% of CO₂ uptake by natural silicate weathering and could consequently partly counterbalance this natural CO₂ sink.  相似文献   

Calcium isotope (δCa) fractionation along hydrothermal pathways, Logatchev field (Mid-Atlantic Ridge, 14°45′N)     

Marghaleray Amini  Anton Eisenhauer  Florian Böhm  Wolfgang Bach  Martin Rosner  Barbara Bock  Folkmar Hauff 《Geochimica et cosmochimica acta》2008,72(16):4107-4122

We investigate the Logatchev Hydrothermal Field at the Mid-Atlantic Ridge, 14°45′N to constrain the calcium isotope hydrothermal flux into the ocean. During the transformation of seawater to a hydrothermal solution, the Ca concentration of pristine seawater ([Ca]_SW) increases from about 10 mM to about 32 mM in the hydrothermal fluid endmember ([Ca]_HydEnd) and thereby adopts a δ^44/40Ca_HydEnd of −0.95 ± 0.07‰ relative to seawater (SW) and a ⁸⁷Sr/⁸⁶Sr isotope ratio of 0.7034(4). We demonstrate that δ^44/40Ca_HydEnd is higher than that of the bedrock at the Logatchev field. From mass balance calculations, we deduce a δ^44/40Ca of −1.17 ± 0.04‰ (SW) for the host-rocks in the reaction zone and −1.45 ± 0.05‰ (SW) for the isotopic composition of the entire hydrothermal cell of the Logatchev field. The values are isotopically lighter than the currently assumed δ^44/40Ca for Bulk Earth of −0.92 ± 0.18‰ (SW) [Skulan J., DePaolo D. J. and Owens T. L. (1997) Biological control of calcium isotopic abundances in the global calcium cycle. Geochim. Cosmochim. Acta61,(12) 2505-2510] and challenge previous assumptions of no Ca isotope fractionation between hydrothermal fluid and the oceanic crust [Zhu P. and Macdougall J. D. (1998) Calcium isotopes in the marine environment and the oceanic calcium cycle. Geochim. Cosmochim. Acta62,(10) 1691-1698; Schmitt A. -D., Chabeaux F. and Stille P. (2003) The calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance. Earth Planet. Sci. Lett. 6731, 1-16]. Here we propose that Ca isotope fractionation along the fluid flow pathway of the Logatchev field occurs during the precipitation of anhydrite. Two anhydrite samples from the Logatchev Hydrothermal Field show an average fractionation of about Δ^44/40Ca = −0.5‰ relative to their assumed parental solutions. Ca isotope ratios in aragonites from carbonate veins from ODP drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average δ^44/40Ca of −1.54 ± 0.08‰ (SW). The relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine Ca isotope budget, in particular with regard to ocean crust alteration.  相似文献   

Circulation in the Gulf of Aqaba (Red Sea) during winter—spring     

Riyad Manasrah  H. Uli Lass  Wolfgang Fennel 《Journal of Oceanography》2006,62(2):219-225

This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring 1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route. The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an internal tide wave (∼12 h period; 0.2 ms⁻¹ amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of about 5–8 km.  相似文献   

Quaternary geology of the Amazonian Lowland     

Georg Irion  Jens Müller  Jose Nunes de Mello  Wolfgang J. Junk 《Geo-Marine Letters》1995,15(3-4):172-178

The Quaternary history of the Amazon lowlands is characterized by deposition of sediments of Andean provenance and by the influences of changing sea levels. Areas well above the present water tables were not reached by Pleistocene high-water stages. These areas have been intensively weathered since the Tertiary, forming hard lateritic weathering horizons. These weathering horizons are best explained by the relatively constant, humid tropical climate throughout the Quaternary. In the western Amazonian Lowland, flood plains corresponding to the different Pleistocene sea-level heights were formed. During low sea level, erosion in the drainage areas increased and the water levels of the central Amazon River system were lowered. Valleys drowned and lakes formed in the lower reaches of rivers and creeks during high sea-level stages. These lakes (ria lakes) remained in the valleys with rivers having a low sediment load. Seismic profiling (3.5 kHz) in some of these lakes clearly showed deposits of the three last periods of Quaternary high sea-level stages.  相似文献