Palaeoflood activity and climate change over the last 1400 years recorded by lake sediments in the north‐west European Alps     

B. Wilhelm  F. Arnaud  P. Sabatier  O. Magand  E. Chapron  T. Courp  K. Tachikawa  B. Fanget  E. Malet  C. Pignol  E. Bard  J. J. Delannoy 《第四纪科学杂志》2013,28(2):189-199

A high‐resolution sedimentological and geochemical study of a high‐altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352 m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800–1300) and the current period of global warming. On a multi‐decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi‐centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multi‐decadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The system CaO-Al2O3-SiO2-H2O: new phase equilibria data,some calculated phase relations,and their petrological applications     

Niranjan D. Chatterjee  Wilhelm Johannes  Hans Leistner 《Contributions to Mineralogy and Petrology》1984,88(1-2):1-13

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Enhancement of stream-sediment geochemical anomalies in Belgium and France by selective extractions and mineral separations     

H. Martin  E. Wilhelm  L. Laville-Timsit  P. Lecomte  F. Sondag  P. Warnant 《Journal of Geochemical Exploration》1984,20(2):179-203

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Post-drilling destabilization of temperature profile in borehole Yaxcopoil-1, Mexico     

Jan Šafanda  Philipp Heidinger  Helmut Wilhelm  Vladimír Čermák 《Hydrogeology Journal》2007,15(2):423-428

As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10^?11 m². This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region.  相似文献   

Time-dependent thermal state of the lithosphere in the foreland of the Eastern Carpathians bend. Insights from new geothermal measurements and modelling results     

C. Demetrescu  H. Wilhelm  M. Tumanian  S.B. Nielsen  A. Damian  V. Dobric&#;  M. Ene 《Geophysical Journal International》2007,170(2):896-912

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Leaching and differential recrystallization of metamict zircon under experimental hydrothermal conditions   总被引：14，自引：0，他引：14  

Thorsten Geisler  Marcus Ulonska  Helmut Schleicher  Robert T. Pidgeon  Wilhelm van Bronswijk 《Contributions to Mineralogy and Petrology》2001,141(1):53-65

We report results of hydrothermal experiments on four alluvial zircons from Sri Lanka, which cover a wide range of radiation damage, at 450 °C and 1.3 kbar for 744 h with 2 M CaCl₂ solution as reactive fluid. After the hydrothermal treatment, the most metamict samples show micrometer-thick reaction rims, which surround apparently unreacted zircon, as revealed by cathodoluminescence (CL) and Nomarski differential interference contrast (NDIC) images. These rims have sharp, curved, and transgressive boundaries with unreacted zircon and are, in some cases, spread out along cracks. The thickness of reaction rims increases with increasing cumulated !-dosage of the starting materials. The reaction rims are strongly enriched in Ca (up to 7000 ppm) and a water species and depleted in radiogenic Pb, Zr, and Si, as revealed by electron microprobe analyses. A significant Th loss from the reaction rims was detected in the case of the most metamict sample, whereas U remained in the structure. FT-infrared spectrometry and X-ray diffraction measurements revealed that the bulk run products were recrystallized. Using micro-Raman spectrometry, we were able to demonstrate that differential recrystallization took place. The reaction rims are strongly recrystallized, whereas the unreacted grain interiors underwent only minor recrystallization. Recrystallization of the rims is accompanied by an enhancement of the integral CL intensity. It is suggested that recrystallization in the reaction rims was catalyzed by water infiltration and ion exchange and prevented significant congruent zircon dissolution under the given experimental conditions. Previous zircon studies have shown that (1) a transgressive morphology, (2) a reduced Th-U ratio, and (3) an enhanced CL emission are also characteristics of rims in zircons from high-grade metamorphic rocks. Based on these similarities between natural and experimentally produced rims, it is suggested that leaching-catalyzed recrystallization is an important alteration process in zircon under wet geological conditions and can account for many complex core-rim structures found in natural zircons. Furthermore, the strong enrichment of Ca in the reaction rims supports previous assumptions that high Ca concentrations in natural zircons are of secondary origin. It is suggested that lower U-Pb concordia intercept ages obtained from single-phase zircons with high Ca contents date a leaching event.  相似文献   

Historical record of polycyclic aromatic hydrocarbons (PAH) and heavy metals in floodplain sediments from the Rhine River (Hessisches Ried, Germany)     

Tilman Gocht  Klaus-Martin Moldenhauer  Wilhelm Püttmann 《Applied Geochemistry》2001,16(15):301

The depth-related content of polycyclic aromatic hydrocarbons (PAH) and heavy metals was determined for two soil profiles (i.e. one Fluvisol and one Gleyic Cambisol) which developed in sediments from floodplains located at an old meander of the Rhine river. The meander had been cut off from the main river in 1829. The separation of the meander from the main river caused a change in sediment deposition (i.e. from sand to silt) which is clearly visible in the soil-profiles. Since that time, approximately 100 cm of sediments have accumulated due to temporary flooding of the area. Each soil profile was separated into 18 samples. The samples were analysed for their content of PAH after solvent extraction. Additionally, several trace elements (Co, Ni, Cd, Pb, Zn, Cr and Cu) were determined in the same sample set, and depth-related concentration profiles for both PAH and trace elements were developed. The distribution patterns of PAH with more than 3 condensed rings did not provide any evidence for PAH biodegradation or vertical transport after deposition of the sediments. Thus, in the case of PAH, the historical record can be derived not only from subhydric sediments but also from floodplain sediments. It was not possible to distinguish between atmospheric and fluvial input of PAH into the sediments from the observed distribution patterns due to the same origin of PAH from pyrolytic processes. A source determination of the PAH was not possible except for perylene, for which biogenic formation can be assumed. A comparison of the results shows that the depth-related PAH and trace element concentrations display similar trends over most of the total profiles. In the uppermost section of the profiles, the concentration of most trace elements declines whereas the PAH concentration remains high. This indicates the presence of different sources for PAH and trace elements in the last decades.  相似文献   

Versuch einer Begründung für den Wandel in der qualitativen und quantitativen Zusammensetzung des Fischbestandes im Bodensee während der letzten 60 Jahre und eine Bewertung der Besatzmassnahmen     

Wilhelm Nümann 《Aquatic Sciences - Research Across Boundaries》1973,35(2):206-238

Statistics for all important fish for the past 60 years and the management measures taken, together with the scientific results, have been evaluated, in order to recognize the development trend and the success or failure of the measures. Although total yields have increased by 500%, the catches for some species i.e. pike, pike-perch and lake trout, have decreased in the past 15 years in spite of enormous measures. The possible reasons are discussed. Cannibalism and decimation through rapacious fish regulate the yield and cause oscillations. Therefore studies on the biology of fish must rather consider the correlations between the single species. For good management, it is more important to plant alevins than fry.

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Meinem Mitarbeiter Heinz Quoss danke ich recht herzlich für die Zusammenstellung der einzelnen statistischen Werte und für die zahlreichen Berechnungen.  相似文献   

Euv Spectroscopy of the Sunspot Region Noaa 7981 Using Soho – II. Velocities and Line Profiles     

Brynildsen  N.  Brekke  P.  Fredvik  T.  Haugan  S. V. H.  Kjeldseth-Moe  O.  Maltby  P.  Harrison  R. A.  Pike  C. D.  Rimmele  T.  Thompson  W. T.  Wilhelm  K. 《Solar physics》1998,179(2):279-312

We have studied the dynamics in the sunspot transition region between the chromosphere and the corona and investigated the extension of the flow field into the corona. Based on EUV spectra of a medium size sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER on SOHO, we derive line-of-sight velocities and study the line profiles for a series of emission lines.The flow field in the low corona is found to differ markedly from that in the transition region. In the transition region the relative line-of-sight velocity shows an upflow in the umbra and relatively large areas with downflow that cover part of the penumbra. The spatial extent of these areas with upflow and downflow increases with increasing temperature in the transition region, but the whole flow field changes character as the temperature increases from the upper transition region to the low corona. Based on a calibration of the SUMER wavelength scale we find that the entire sunspot transition zone appears to be moving downwards towards the chromosphere. The relation between this finding and the general tendency for transition-region lines to show a net red shift is discussed.Several of the transition-region spectral line profiles are observed to show two line components with Gaussian shape and line-of-sight velocities that differ markedly. Several of the line profiles that are composed of two spectral line components occur close to the dividing line between up- and downflow. A discussion of this observation is presented. In small regions with spatial extent of a few arc sec we detect enhanced continuum emission underlying explosive events. The similarities between explosive events with continuum emission and the moustaches observed in H close to sunspots are so striking that we are tempted to introduce the notation transition-region moustaches.  相似文献   

Eo-alpine metamorphism in the uppermost unit of the Cretan nappe system — Petrology and geochronology     

Eberhard Seidel  Martin Okrusch  Hans Kreuzer  Helmut Raschka  Wilhelm Harre 《Contributions to Mineralogy and Petrology》1981,76(3):351-361

The uppermost unit of the Cretan nappe system consists of ophiolites on the top, and an ophiolitic mélange at the base.Among the various constituents of the mélange, there are slices of low-P/high-T metamorphics. They form a variegated series consisting of tholeiitic ortho-amphibolites, para-amphibolites, andalusite and sillimanite-cordierite-garnet bearing mica schists, calcsilicate rocks, and marbles. The metamorphic sequence is locally intruded by early tectonic magmatites of gabbroic, dioritic and granitic composition. Critical mineral assemblages lead to a maximum temperature of about 700° C reached during metamorphism, at a total pressure of 4–5 kilobars. K — Ar dating on 6 hornblendes, 7 biotites and 1 muscovite yielded cooling ages of 75–66 m.y. and confirmed earlier results according to which the metamorphism and related magmatism took place in Late Cretaceous times.In order to evaluate the age relationships between the hightemperature metamorphics within the ophiolitic mélange and the ophiolites, hornblendes from ultramafic and mafic rocks of the ophiolite complex were dated by the K — Ar method. Hornblende from one schistose hornblendite forming a constituent of the ophiolites proper yielded 156 m.y. and thus provides a middle Jurassic minimum age for the formation of this piece of oceanic lithosphere. Four hornblendes of calc-alkaline gabbrodiorite dikes within the ophiolite complex gave distinctly lower K — Ar dates of about 140 m.y.. The dikes probably intruded after the detachment of the ophiolites in an island-arc or continental-margin environment.As a consequence, the high-temperature metamorphics and related intrusives in the ophiolitic mélange of Crete are genetically unrelated to the overlying ophiolites. The paleogeographic position of the crystalline terrane, slices of which are now incorporated into the ophiolitic mélange is still open to discussion.  相似文献