Zum 80. Geburtstag von Hermann Heynig     

Dr.Lothar Tuscher 《Limnologica》2003,33(4):355-358

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Impact of precipitation seasonality changes on isotopic signals in polar ice cores: a multi-model analysis   总被引：1，自引：0，他引：1  

G. Krinner  M. Werner 《Earth and Planetary Science Letters》2003,216(4):525-538

For Central Greenland, water isotope analysis indicates a temperature difference of about 10°C since the Last Glacial Maximum (LGM). However, borehole thermometry and gas diffusion thermometry indicate that LGM surface temperatures were about 20°C colder than today. Two general circulation model studies have shown that changes in the seasonal precipitation timing in Central Greenland might have caused a warm bias in the LGM water isotope proxy temperatures, and that this bias could explain the difference in the estimated paleotemperatures. Here we present an analysis of a number of atmospheric general circulation model simulations mostly done within the framework of the Paleoclimate Modeling Intercomparison Project. The models suggest that the seasonal cycle of precipitation and surface mass balance over Central Greenland at the LGM might have been very different from today. This supports the idea that the accuracy of the water isotope thermometry at the LGM in Greenland might be compromised as a result of a modified surface mass balance seasonality. However, the models disagree on the amplitude and sign of the bias. For Central East Antarctica, a strong seasonality effect on the LGM isotopic signal is not simulated by any of the analyzed models. For the mid-Holocene (6 kyr BP) the models suggest relatively weak isotope paleothermometry biases linked to changes in the surface mass balance seasonality over both ice sheets.  相似文献   

Testing a model for predicting the timing and location of shallow landslide initiation in soil‐mantled landscapes     

M. Casadei  W. E. Dietrich  N. L. Miller 《地球表面变化过程与地形》2003,28(9):925-950

The growing availability of digital topographic data and the increased reliability of precipitation forecasts invite modelling efforts to predict the timing and location of shallow landslides in hilly and mountainous areas in order to reduce risk to an ever‐expanding human population. Here, we exploit a rare data set to develop and test such a model. In a 1·7 km² catchment a near‐annual aerial photographic coverage records just three single storm events over a 45 year period that produced multiple landslides. Such data enable us to test model performance by running the entire rainfall time series and determine whether just those three storms are correctly detected. To do this, we link a dynamic and spatially distributed shallow subsurface runoff model (similar to TOPMODEL) to an in?nite slope model to predict the spatial distribution of shallow landsliding. The spatial distribution of soil depth, a strong control on local landsliding, is predicted from a process‐based model. Because of its common availability, daily rainfall data were used to drive the model. Topographic data were derived from digitized 1 : 24 000 US Geological Survey contour maps. Analysis of the landslides shows that 97 occurred in 1955, 37 in 1982 and ?ve in 1998, although the heaviest rainfall was in 1982. Furthermore, intensity–duration analysis of available daily and hourly rainfall from the closest raingauges does not discriminate those three storms from others that did not generate failures. We explore the question of whether a mechanistic modelling approach is better able to identify landslide‐producing storms. Landslide and soil production parameters were ?xed from studies elsewhere. Four hydrologic parameters characterizing the saturated hydraulic conductivity of the soil and underlying bedrock and its decline with depth were ?rst calibrated on the 1955 landslide record. Success was characterized as the most number of actual landslides predicted with the least amount of total area predicted to be unstable. Because landslide area was consistently overpredicted, a threshold catchment area of predicted slope instability was used to de?ne whether a rainstorm was a signi?cant landslide producer. Many combinations of the four hydrological parameters performed equally well for the 1955 event, but only one combination successfully identi?ed the 1982 storm as the only landslide‐producing storm during the period 1980–86. Application of this parameter combination to the entire 45 year record successfully identi?ed the three events, but also predicted that two other landslide‐producing events should have occurred. This performance is signi?cantly better than the empirical intensity–duration threshold approach, but requires considerable calibration effort. Overprediction of instability, both for storms that produced landslides and for non‐producing storms, appears to arise from at least four causes: (1) coarse rainfall data time scale and inability to document short rainfall bursts and predict pressure wave response; (2) absence of local rainfall data; (3) legacy effect of previous landslides; and (4) inaccurate topographic and soil property data. Greater resolution of spatial and rainfall data, as well as topographic data, coupled with systematic documentation of landslides to create time series to test models, should lead to signi?cant improvements in shallow landslides forecasting. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Petrology and Geochemistry of the Volcanic Rocks Dredged from the Geophysicist Seamount in the Kurile Basin: Evidence for the Existence of Thinned Continental Crust     

Igor A. Tararin  Eugeniy P. Lelikov  Reinhard Werner 《Gondwana Research》2003,6(4):757-765

Dredged samples from the Geophysicist seamount volcano in the northeastern part of the Kurile Basin include volcanic and volcanoclastic rocks ranging from basalt to andesite. The rocks have geochemical features typical of high-K island-arc calc-alkaline volcanism. They are enriched in LILE and depleted in Zr, Ti, Nb, Ta and Y. The chondrite-normalized REE patterns are characterized by enrichment of LREE similar to those of island-arc lava from the submarine volcanoes of rear-arc zone of the Kurile Island Arc. The volcanic rocks have a wide range of ⁸⁷Sr/⁸⁶Sr ratios (0.70287-0.70652), varying ¹⁴³Nd/¹⁴⁴Nd and Pb isotopic ratios. Their trace-element compositions and Sr-Nd-Pb isotope signatures may be explained by a small addition of crustal continental component to mantle-derived magmas that suggest the existence of thinned continental basement under the eastern part of the Kurile Basin.  相似文献   

A numerical study of barotropic vortex motion near a large-scale mountain range with application to the motion of tropical cyclones approaching the Sierra Madre     

Dr. J. A. Zehnder  M. J. Reeder 《Meteorology and Atmospheric Physics》1997,64(1-2):1-19

Summary The motion of an idealized vortex near a large-scale mountain range is examined by numerically integrating the single-layer shallow-water equations on an equatorial beta plane. Modification of the asymmetric circulation by divergent vorticity generation as the air is forced across the ridge greatly affects the motion of the vortex. Attention is focused on the role of the vortex structure, the mountainrange width and orientation, and the stratification of the model atmosphere in influencing the motion of the vortex. A scale analysis is used to explain the sensitivity of the vortex track to changes in the model's external parameters. The sensitivity of the model vortex track to the slope and orientation of the mountain range is used to help explain some features of the observed tracks of hurricanes that make landfall on the east coast of Mexico.With 14 Figures  相似文献   

A Mid Cretaceous origin for the Galápagos hotspot: volcanological, petrological and geochemical evidence from Costa Rican oceanic crustal segments     

F. Hauff  K. Hoernle  H.-U. Schmincke  R. Werner 《International Journal of Earth Sciences》1997,86(1):141-155

The Quepos, Nicoya and Herradura oceanic igneous terranes in Costa Rica are conspicuous features of a Mid to Late Cretaceous regional magmatic event that encompasses similar terranes in Central America, Colombia, Ecuador and the Caribbean. The Quepos terrane (66?Ma), which consists of ol-cpx phyric, tholeiitic pillow lavas overlain by highly vesicular hyaloclastites, breccias and conglomerates, is interpreted as an uplifted seamount/ocean island complex. The Nicoya (～90?Ma) and Herradura terranes consist of fault-bounded sequences of sediments, tholeiitic volcanics (pillow lavas and massive sheet flows) and plutonic rocks. The volcanic rocks were emplaced at relatively high eruption rates in moderate to deep water, possibly forming part of an oceanic plateau. Major and trace element data from Nicoya/Herradura tholeiites indicate higher melting temperatures than inferred for normal mid-ocean-ridge basalts (MORB) and/or a different source composition. Sr–Nd–Pb isotopic ratios from all three terranes are distinct from MORB but resemble those from the Galápagos hotspot. The volcanological, petrological and geochemical data from Costa Rican volcanic terranes, combined with published age data, paleomagnetic results and plate tectonic reconstructions of this region, provide strong evidence for a Mid Cretaceous (～90Ma) age for the Galápagos hotspot, making it one of the oldest known, active hotspots on Earth. Our results also support an origin of the Caribbean Plate through melting of the head of the Galápagos starting plume.  相似文献   

Experimental determination of the solubility of Au in silicate melts     

Dr. A. Borisov  Dr. H. Palme 《Mineralogy and Petrology》1996,56(3-4):297-312

Summary We report here new data on the solubility of Au in silicate melts of anorthite-diopside eutectic composition at a wide range of oxygen fugacities, from pure oxygen to 10^–8 atm, and at a temperature range of 1300 °C to 1480 °C. Because experiments were done with metal loops at temperatures above the Au-melting temperature, PdAu-metal-alloys had to be used. Pd-solubility data derived from the same set of experiments agree with earlier data obtained from experiments with pure Pd-metal (Borisov et al., 1994a). The results of the present experiments show that Pd-solubilities are by a factor of 2 to 6 higher than Au-solubilities. Both, Au and Pd solubilities decrease with decreasing oxygen fugacity. At oxygen fugacities below the iron-wiistite buffer (IW) Au solubility increases with decreasing fO₂ probably reflecting formation of Au-silicides at such reducing conditions. Compared to Pd, Au has higher activity coefficients in Fe-metal and lower solubility in silicate melts. This leads to similar metal-silicate partition coefficients for both elements. At a temperature of 1350 °C and an oxygen fugacity corresponding to IW-2 D^Au (met/sil) is about 2.5 · 10⁷ and D^Pd (met/sil) about 1.6 · 10⁷. Thus similar behavior is expected during metal separation in planetary bodies including core formation in the Earth. The metal/silicate partition coefficient of Ir is, however, by several orders of magnitudes higher (Borisov and Palme, 1995a). Equilibration with chondritic metal will therefore lead to grossly non-chondritic Pd/Ir or Au/Ir ratios in coexisting silicate phases. Chondritic ratios are thus indicative of the presence of unfractionated meteoritic components. Samples from the upper mantle of the Earth, for example, reflect the admixture of a late unfractionated (chondritic) veneer (e.g.,Kimura et al., 1974;Jagoutz et al., 1979).Solubilities of Pd and Au in silicate melts are much higher than the contents in terrestrial basalts implying that the abundances of these two elements are not buffered by residual PGE- and Au-containing alloys. The most likely process for fractionating PGEs in terrestrial magmas are mineral-melt (e.g., olivine/melt) equilibria.

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Experimentelle Bestimmung der Löslichkeit von Au in Silikatschmelzen

Zusammenfassung In der vorliegenden Arbeit wird über die Ergebnisse der Bestimmung der Löslichkeit von Au in Silikatschmelzen mit der Zusammensetzung des Anorthit-Diopsid Eutektikums berichtet. Die Versuche wurden mittels Metallschlaufe über einen weiten Sauerstoffpartialdruckbereich, von reinem Sauerstoff bis zu 10^–8 atm und in einem Temperaturbereich von 1300 °C bis 1480 °C, durchgeführt. Da diese Temperaturen jedoch den Au-Schmelzpunkt überschreiten, wurde mit AuPd-Legierungen gearbeitet. Die Ergebnisse der dadurch zusätzlich erhaltenen Pd-Versuche stimmen mit früher bestimmten, mit reinen Pd-Schlaufen durchgeführten Pd-Löslichkkeiten überein (Borisov et al., 1994a). Die auf reine Metalle zurückgerechneten Löslichkeiten von Pd sind um einen Faktor 2 bis 6 mal höher als die entsprechenden Au-Löslichkeiten. Die Löslichkeiten beider Metalle nehmen mit abnehmendem Sauerstoffpartialdruck ab. Unter noch stärker reduzierenden Bedingungen (Eisen-Wüstit Gleichgewicht) nimmt die Löslichkeit von Au jedoch zu. Dies könnte auf die Bildung von Au-Siliziden zurückzuführen sein.Im Vergleich zu Pd sind die Aktivitätskoeffizienten von Au in metallischem Eisen höher, die Löslichkeiten in Silikatschmelzen jedoch niedriger. Das führt zu ähnlichen Metall/Silikat Verteilungskoeffizienten von Au und Pd. Bei einer Temperatur von 1350 °C und einer Sauerstoffugazität von IW-2 ergeben sich für D^Au (met/sil) 2.5 · 10⁷ und für D^Pd (met/sil) 1.6* 10⁷. Der Metall/Silikat-Verteilungskoeffizient von Ir ist jedoch unter den gleichen Bedingungen um mehrere Größenordnungen höher (Borisov andPalme, 1995a). Ein chondritisches Pd/Ir- oder Au/Ir-Verhältnis kann also auf die Anwesenheit einer unfraktionierten chondritischen Komponente zurückgeführt werden. Dies gilt beispielsweise für Proben aus dem oberen Erdmantel. Hier handelt es sich vermutlich um Zumischung einer späten chondritischen Akkretionskomponente, die sich nicht mehr mit einer metallischen Phase (Kern) ins Gleichgewicht gesetzt hat (z.B.Kimura et al., 1974,Jagoutz et al., 1979).Die Löslichkeiten von Pd und Au in Silikatschmelzen sind wesentlich höher als ihre Gehalte in basaltischen und komatiitischen Laven. Dies bedeutet, daß Au und Pd in Schmelzen aus dem Erdmantel nicht durch residuale Au- und/oder Pd-haltige Metall phasen bestimmt sind. Gleichgewichte zwischen Schmelze und Mineralen (z.B. Olivin) sind die wahrscheinlichsten Fraktionierungsmechanismen für Platingruppenelemente in terrestrischen Magmen.

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With 5 Figures  相似文献   

Policy concerns in Bulgarian food distribution     

Rene Mueller Dr.  James Mueller Dr. 《GeoJournal》1996,38(2):167-174

The Bulgarian food distribution system, like those of its Central and East European neighbours, lags behind the West in critical performance areas. Previous research quantified Central and East European food distribution deficiencies on the basis of a five factor model. This study investigates the attitudes of 250 Bulgarian consumers using these same five factors: food processing, quality, cost, availability and retailing. The findings show that the Bulgarian food distribution system does not satisfy consumer wants as well as do systems in other former communist countries in four of the five factors. At the same time, Bulgarian consumers are more satisfied than UK and US consumers in the system's ability to make some foods available. The study also shows that Bulgarian consumers who use privatised shops perceive the system more positively than those who use state and cooperative outlets. The implications of these and other findings are discussed in terms of critical policy concerns for government and industry stakeholders.  相似文献   

Witwatersrand iron-formations and their significance for gold genesis and the composition limits of orthoamphibole     

Dr. H. E. Frimmel 《Mineralogy and Petrology》1996,56(3-4):273-295

Summary In the West Rand Group of the 3.07–2.71 Ga old Witwatersrand Supergroup, South Africa, a series of banded iron-formations occur. They are of chemical origin and were deposited in an offshore shelf environment. The coarser-grained, in places pyrite-bearing, and partly auriferous metasedimentary rocks forming the bulk of the Witwatersrand Supergroup are regressive. The iron-formations, however, were deposited during transgression. The presence of allogenic pyrite in the fluviatile metaconglomerates and that of magnetite and, in places, haematite in the marine iron-formations suggests a lower pH and higher sulfur activity for the Archaean meteoric environment than for recent hydrothermal fluids on the ocean floor. Post-depositional alteration of the Witwatersrand rocks includes burial metamorphism at temperatures between 300 and 350 °C and pressures around 2.5 kbar, and multiple hydrothermal inflitration events at slightly lower temperatures, coeval with the brittle deformation of the basin fill during the deposition of the Transvaal Supergroup and the Bushveld Vredefort events.Additional thermal metamorphic overprint of the iron-formations around the Vredefort Dome caused the growth of orthoamphiboles. They show a wide range of compositions between ferro-anthophyllite and ferrous alumino-gedrite, suggesting that the crest of the solvus curve for Fe-rich orthoamphiboles is below 500 °C.Chlorite and amphibole compositions, and the presence of Fe-oxide-bearing horizons between pyrite-bearing ones indicate that the fluid composition during post-depositional alteration was largely controlled by the bulk rock composition of the infiltrated stratigraphic horizons and not by some external source.

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Zusammenfassung Die West Rand Group innerhalb der 3.07–2.71 Milliarden Jahre alten Witwatersrand Supergroup, Südafrika, führt eine Reihe von Magnetit- und Hämatit-haltigen Eisenformationen. Diese sind chemischen Ursprungs und wurden in einem flachmarinen Schelfmilieu abgelagert. Der überwiegende Teil der Witwatersrand Abfolge, bestehend aus klastischen, verschiedentlich Pyrit-führenden und teilweise goldhaltigen Metasedimentgesteinen, kann regressiven Phasen zugeschrieben werden. Die Eisenformationen wurden hingegen während transgressiven Phasen abgelagert. Aufgrund des Auftretens allogener Pyrite in den fluviatilen Konglomeratlagen und von Magnetit und Hämatit in den marinen Eisenformationen lassen sich für den meteorischen Bereich im Archaikum niedrigere pH-Werte und höhere Schwefelfugazität ableiten als für rezente submarine hydrothermale Fluide. Post-diagenetische Alterationsprozesse sind der Versenkungsmetamorphose mit Temperaturen zwischen 300 und 350 °C und Drucken um 2.5 kbar sowie etwas niedriger temperierten hydrothermalen Fluiden zuzuschreiben, die als Folge der inkompetenten Deformation der Beckenfüllung in diese während mehrer Stadien infiltrierten. Infiltration hydrothermaler Fluide während der Ablagerung der Transvaal Supergroup (2.55 Ga) und während des Bildung der Vredefort Struktur (2.0 Ga) sind durch Altersdaten belegt.Zusätzliche thermische Metamorphose der Fe-reichen Pelite und Eisenformationen im Bereich der Vredefort Struktur führte zur Bildung von Orthoamphibolen, deren Zusammensetzung von Anthophyllit bis zu Fe-reichem Alumino-Gedrit reicht. Dies läßt darauf schließen, daß die Solvuskurve für Fe-reiche Orthoamphibole unterhalb von 500 °C liegt.Die Zusammensetzung der Chlorite und Amphibole sowie das Auftreten von Fe-Oxid-führenden Horizonten in den generall Pyrit-reichen Metasedimentgesteinen gestatten die Annahme, daß die post-diagenetische Fluidzusammensetzung hauptsächlich durch die jeweilige Zusammensetzung der infiltrierten Gesteinshorizonte und nicht durch eine externe Quelle bestimmt wurde.

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With 8 Figures  相似文献   

A low plain between arcadia and agronomy: Ippolito Nievo and the Friulan landscape     

Prof.  Dr. Francesco Vallerani 《GeoJournal》1996,38(1):87-97

An analysis of the historical and cultural context of a large number of literary works illuminates the concept of landscape, a recurrent theme in contemporary humanistic geography. In this context, the works of Ippolito Nievo present an opportunity to look closer at the socio-economic circumstances of his time while also offering suggestive interpretative elements about the attitudes held concerning the wetlands of the lower Friulan plain.  相似文献