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41.
碳酸盐风化碳汇与森林碳汇的对比——碳汇研究思路和方法变革的必要性 总被引:1,自引:1,他引:1
目前,全球碳循环研究主要集中在海洋碳汇以及陆地土壤和植被碳汇,而对岩石风化碳汇仅考虑地质长时间尺度的硅酸盐风化作用,而认为碳酸盐风化在长时间尺度上对碳汇无贡献。然而,碳酸盐相对于硅酸盐有快得多的溶解速度,且对全球变化(特别是气候和CO2变化)的响应迅速,同时由于生物作用和人为活动的影响,使得碳酸盐风化碳汇的能力需要重新评价。最新的研究发现,由碳酸盐溶解、全球水循环及水生生物光合利用溶解无机碳共同作用,即水-岩-气-生相互作用形成的大气碳汇,远远大于之前只估计了河流输运的无机碳汇,其量级与森林碳汇量相当,因此有必要对传统的碳汇研究思路和方法进行某些变革,这有可能为解决所谓的全球“碳失汇”问题找到一条出路。 相似文献
42.
Both the system of plate motions and the global gravity field or the geoid are now so precisely known that it seems worthwhile to look for quantitative relationships. Some aspects, such as the general occurrence of positive gravity and geoid anomalies in regions of plate convergence, have long been known. Our aim is to describe the gravitational field in terms of plate-kinematic parameters and we present a preliminary step in this direction: for four plates (Pacific, Nazca, Indian, American) we have computed the correlation of the Gem 8 geoid heights (with reference to an ellipsoid of 1/298.255 ellipticity) with distance from the poles of motion and distance from the axes in an “absolute” frame. The geoid tends first to drop from the ridge axes to at least 10° distance and then to rise toward the convergence zones. This trend is strongest for the Indian plate in collision with Eurasia, is smaller, but very clear for the oceanic Pacific and Nazca plates, and is not developed for the American plate which does not subduct. We did not find a consistent relationship for the geoid with distance from the pivots. A possible interpretation of the results is the return flow of the large-scale mantle circulation. 相似文献
43.
Unnaturally high hydraulic gradients below dam sites enhance dissolutional widening of fractures in limestone. A model is
presented which suggests that under unfavorable conditions, leakage rates could become unbearably high during the lifetime
of the dam. At the beginning when water is impounded, leakage rates are low and increase slowly. A positive feedback loop,
however, causes a sudden dramatic increase of leakage within a few years. Deep grouting becomes necessary to prevent such
failures. Inefficiencies in grouting may leave some open fractures in the grouting curtain. These fractures widen faster than
pathways below the grouting curtain, and reduce the effect of the grouted region located below. Therefore, open fractures
act in a similar way as reduction of the grouting depth. 相似文献
44.
Cosmas Kongnyuy Shang Muharrem Satir Emmanuel Nkonguin Nsifa Jean-Paul Liégeois Wolfgang Siebel Heiner Taubald 《International Journal of Earth Sciences》2007,96(5):817-841
We present a geochemical and isotopic study that, consistent with observed field relations, suggest Sangmelima late Archaean
high-K granite was derived by partial melting of older Archaean TTG. The TTG formations are sodic-trondhjemitic, showing calcic
and calc-alkalic trends and are metaluminous to peraluminous. High-K granites in contrast show a potassic calc-alkaline affinity
that spans the calcic, calc-alkalic, alkali-calcic and alkalic compositions. The two rock groups (TTG and high-K granites)
on the other hand are both ferroan and magnesian. They have a similar degree of fractionation for LREE but a different one
for HREE. Nd model ages and Sr/Y ratios define Mesoarchaean and slab-mantle derived magma compositions respectively, with
Nb and Ti anomalies indicating a subduction setting for the TTG. Major and trace element in addition to Sr and Nd isotopic
compositions support field observations that indicate the derivation of the high-K granitic group from the partial melting
of the older TTG equivalent at depth. Geochemical characteristics of the high-K granitic group are therefore inherited features
from the TTG protolith and cannot be used for determining their tectonic setting. The heat budget required for TTG partial
melting is ascribed to the upwelling of the mantle marked by a doleritic event of identical age as the generated high-K granite
melts. The cause of this upwelling is related to linear delamination along mega-shear zones in an intracontinental setting. 相似文献
45.
Żelaźniewicz Andrzej Dörr Wolfgang Bylina Paweł Franke Wolfgang Haack Udo Heinisch Helmut Schastok Janina Grandmontagne Klaus Kulicki Cyprian 《International Journal of Earth Sciences》2004,93(5):773-781
We report U–Pb single zircon ages from three pre-Variscan granitoids in the NE part of the Bohemian Massif. The Platerówka granodiorite from the Lausitz-Izera Unit, the Polish Sudetes, has been dated at 533±9 Ma. The Bitouchov granite form the SW part of the South Krkonoe Unit, the Czech Sudetes, gave an age of 540+11/–10 Ma, and the Wdroe granodiorite in the Fore-Sudetic Block yielded 548±9 Ma. All these latest Vendian/Early Cambrian granitoids represent the post-tectonic expression of a late Proterozoic Cadomian orogenic cycle and demonstrate the eastward extent of the Cadomian basement into the Variscan orogen. Granodiorites of similar age have so far been reported from Brittany and especially from the Saxo-Thuringian Terrane to the NE and SW of the Elbe Fault Zone. We conclude that the Saxo-Thuringian Terrane extends across the Elbe and Sudetic Marginal Fault Zones into the Fore-Sudetic Block. 相似文献
46.
47.
Wolfgang Friedrich Müller Yusof Vojdan-Shemshadi Horst Pentinghaus 《Physics and Chemistry of Minerals》1987,14(3):235-237
Transmission electron microscopic study of synthetic CaAl2Ge2O8-feldspar revealed two types of antiphase domains: type “b”-antiphase domains with the displacement vector 1/2 [110] and type “c”-antiphase domains with the displacement vector 1/2 [111]. The “b”-domains were on the order of 0.1 μm in size, while the “c”-domains displayed wall to wall distances mostly between 0.1 and 1 μm. The formation of the two types of antiphase domains is due to reductions in translational symmetry associated with the phase transitions \(C\bar 1 \to I\bar 1 \to P\bar 1\) . The antiphase domain textures of CaAl2Ge2O8-feldspar are very similar to the textures found in natural and synthetic anorthite, CaAl2Si2O8. 相似文献
48.
Peter Müller-Wolfskeil Dipl.-Geol. Prof. Dr. Wolfgang Zacher 《International Journal of Earth Sciences》1984,73(1):321-335
Zusammenfassung Eine Neuuntersuchung der Tektonik in den Vilser Alpen und im Hochvogelgebiet, wo die Frage seit langer Zeit diskutiert wird, ob dort die Allgäu- und Lechtal-Decke getrennte Einheiten bilden, oder stratigraphisch untrennbar zusammenhängen, erbrachte eine eindeutige Entscheidung für den Deckenbau. Der Verlauf der Deckengrenze konnte zwischen Hochvogel und Hohenschwangauer Alpen präzisiert werden. Der interne Falten- und Schuppenbau der Lechtal-Decke hat nirgends zur Bildung von tektonisch tieferen Teildekken geführt, die internen Verschuppungen besitzen nur ein geringes Ausmaß.
A new investigation of the tectonics in the Vilser Alps and in the Mt. Hochvogel area where since a long time a discussion was going on if the thrust sheets of Allgäu and Lechtal-Decke are separate units or connected by stratigraphic sequences, a definite decision could be made in favour of the nappe structure in this part of the Northern Calcareous Alps. The internal structure of the Lechtal-Decke thrust sheet is characterized by local imbricate structure which originate from sheared folds.
Résumé On a dicuté depuis longtemps dans les Vilser Alpen et dans la région du Mont Hochvogel le problème, si les nappes de Allgäu et Lechtal-Decke sont des unités separées ou qu'ils forment une partie inséparable par des séquences stratigraphiques. Une nouvelle examen de la tectonique a affirmé la structure de nappes dans cette région des Alpes Calcaires du Nord. La structure intérieure de la nappe de Lechtal-Decke est caracterisée par une structure écaillée locale, qui se developpe de plis cisaillés.
, - , . - . . ; .相似文献
49.
Sandra Freiboth Holger Class Rainer Helmig Tobias Graf Wolfgang Ehlers Viktoria Schwarz Christos Vrettos 《Computational Geosciences》2009,13(3):281-300
Multiphase flow processes in unsaturated cohesive soils are often affected by deformation due to swelling and shrinking as
a result of varying water contents. This paper presents a model concept which is denoted ‘phenomenological’ in terms of the
processes responsible for soil deformation, since the effects of deformation on flow and transport are only considered by
constitutive relations that allow an adaptation of the hydraulic properties. This new model is validated in a detailed intercomparison
study with two state-of-the-art models that are capable of explicitly describing the processes relevant for the deformation.
A ‘numerical experiment’ with a state-of-the-art reference model is used to produce ‘measurement data’ for an inverse-modelling-based
estimation of the model input parameters for the phenomenological concept. 相似文献
50.
Ekaterina Vasyukova Wolfgang Uhl Fuad Braga Claudia Simões Tânia Baylão Klaus Neder 《Environmental Earth Sciences》2012,65(5):1587-1599
Drinking water production at three waterworks was evaluated with respect to variable weather conditions in the Brasília Distrito
Federal. Results of the investigation revealed that seasonal variations in rainfall play an important role in influencing
the quality of the surface water sources used for drinking water production in the district. In most surface sources, particles
and apparent colour are likely to originate from erosion during rain events. This represents the primary challenge facing
waterworks, notably when the raw water qualities of the sources to be treated at one facility differ by one order of magnitude,
as well significantly varying from one season to the next. Treatment efficiencies in terms of turbidity, apparent colour and
dissolved organic carbon (DOC) removal were evaluated. Drinking water quality was found to be significantly influenced by
raw water quality at all considered treatment plants. With regard to DOC removal, treatment was most efficient in waterworks
which treated raw water with high percentages of biopolymers and humics. Most dissolved organics were removed by coagulation.
Finally, conclusions are drawn on how to better cope with challenges facing drinking water production in a tropical climate.
The first of these recommendations is the introduction of online turbidity and dissolved organic matter monitoring in order
to optimise the coagulation process for the removal of these two parameters. A combination of different coagulants could also
be considered for this process. Additional more sophisticated improvements to process stability, such as determination of
floc characteristics, introduction of artificial neural networks or the eventual upgrade of the treatment train using membrane
filtration, are also suggested. 相似文献