Lake Jezero v Ledvici (NW Solvenia) – changes in sediment records over the last two centuries     

Anton Brancelj  Milijan Šiško  Gregor Muri  Peter Appleby  Andrea Lami  Ewan Shilland  Neil L. Rose  Christian Kamenik  Stephen J. Brooks  John A. Dearing 《Journal of Paleolimnology》2002,28(1):47-58

Lake Jezero v Ledvici (NW Slovenia) is a 14 m deep mountain lake at an elevation of 1860 m, situated on limestone bedrock. It is an oligotrophic, alkaline and hard-water lake with a transparency of about 14 m and has suffered several times over recent centuries from strong earthquakes. In 1996 five sediment cores, between 35 and 45 cm long, were collected from the deepest part of the lake and analysed to reconstruct environmental changes over the last few centuries. The data indicate changes induced by pollution and climate change during the last two centuries similar to those in other European mountain and remote lakes. However, at this site earthquakes have also affected the lake and partly obscure the interpretation of the sediment record. From 1780 to 1890, sediment records show low abundance of diatoms and relatively high abundance of Cladocera. After 1890, the number of diatoms started to increase coinciding with a strong earthquake. From the beginning of the 20th century, concentrations of spheroidal carbonaceous particles (SCP), diatom valves and head capsules of chironomids gradually increased whilst in Cladocera the main difference observed was a change in the proportion of benthic taxa. After 1960, in parallel with a rise in air temperature, a further increase in accumulation rate of diatoms started, but there was a decrease in Cladocera.  相似文献   

pH changes in peralkaline late-magmatic fluids     

Gregor Markl  Lukas Baumgartner 《Contributions to Mineralogy and Petrology》2002,144(3):331-346

The 1.15-Ga-old Ilimaussaq intrusive complex in South Greenland shows an extensive fractionation trend from alkaline augite syenite to various varieties of strongly peralkaline, agpaitic nepheline syenites. The peralkaline nepheline-bearing syenites crystallized between ca. 900 and 450 °C at 1 kbar and they are cut by late-magmatic hydrothermal veins with nepheline-absent assemblages of albite + aegirine + analcime - sodalite - Na-Be-silicates (tugtupite, chkalovite, sørensenite) - ussingite (NaAlSi₃O₈*NaOH). Based on fluid inclusions and phase equilibria, these veins crystallized between 300 and 500 °C at 1 kbar. Textures indicate that the hydrothermal veins at least partly replaced earlier Ilimaussaq rocks. The occurrence of ussingite and tugtupite suggests that the late-magmatic fluids had strongly basic pH values. Speciation calculations show that the pH in fluids of the system Na-Al-Si-O-H-Cl mainly depends on the Na/Cl ratio and, to a lesser degree, on salinity and temperature. If the Na/Cl ratio is greater than 1, pH (at 400 °C and 1 kbar, where neutrality is about at pH 5) lies between 7 and 12. Because Na/Cl tends to decrease in the final stages of magmatism and during crystallization of the vein assemblage, pH of late-magmatic fluids generally should become more acidic, and only two processes can increase Na/Cl and, thus, pH: dissolution of a Cl-poor or Cl-free Na silicate or unmixing of an HCl-enriched vapour phase. Field observations and microtextures suggest that replacement reactions are responsible for the change to basic pH at least in some alteration assemblages. While replacement of 1 mol nepheline by 1 mol analcime would not alter the pH, the volume-conserving reaction 1.85  Ne + 2.3  H₂ O + 0.19  H₄ SiO₄ = 1.02  Anl + 0.83   Na⁺ + 0.83  Al(OH)₄^-1.85\;{\rm Ne} + 2.3\;{\rm H}_{\rm 2} {\rm O} + 0.19\;{\rm H}_{\rm 4} {\rm SiO}_4 = 1.02\;{\rm Anl} + 0.83\,\;{\rm Na}^ + + 0.83\;{\rm Al(OH)}_4^ - can be used to model the replacement process quantitatively, provided it occurred in a more or less closed system. Progress of this reaction leads to successively increasing pH of the fluid during fluid-rock interaction and stabilizes minerals such as ussingite and tugtupite. Transferring the two processes to a larger scale, it is proposed that the extreme 'hyper-agpaitic' assemblages at Ilimaussaq or at the Kola peninsula, which include copious amounts of very basic, water-soluble minerals such as trona, villiaumite or thermonatrite, are formed either in this way by autometasomatic reactions of late-magmatic fluids or melts (or supercritical fluid-melt-mixtures) with earlier crystallized rocks of the same plutonic complex or by large-scale vapour unmixing in the very final stages of magmatism.  相似文献   

Summer Floods in Central Europe – Climate Change Track?     

Zbigniew W. Kundzewicz  Uwe Ulbrich  Tim brücher  Dariusz Graczyk  Andreas Krüger  Gregor C. Leckebusch  Lucas Menzel  Iwona Pińskwar  Maciej Radziejewski  Małgorzata Szwed 《Natural Hazards》2005,36(1-2):165-189

In Central Europe, river flooding has been recently recognized as a major hazard, in particular after the 1997 Odra /Oder flood, the 2001 Vistula flood, and the most destructive 2002 deluge on the Labe/Elbe. Major recent floods in central Europe are put in perspective and their common elements are identified. Having observed that flood risk and vulnerability are likely to have grown in many areas, one is curious to understand the reasons for growth. These can be sought in socio-economic domain (humans encroaching into floodplain areas), terrestrial systems (land-cover changes – urbanization, deforestation, reduction of wetlands, river regulation), and climate system. The atmospheric capacity to absorb moisture, its potential water content, and thus potential for intense precipitation, are likely to increase in a warmer climate. The changes in intense precipitation and high flows are examined, based on observations and projections. Study of projected changes in intense precipitation, using climate models, for several areas of central Europe, and in particular, for drainage basins of the upper Labe/Elbe, Odra/Oder, and Vistula is reported. Significant changes have been identified between future projections and the reference period, of relevance to flood hazard in areas, which have experienced severe recent floodings.  相似文献   

A Simple In Vivo Fluorescence Method for the Selective Detection and Quantification of Freshwater Cyanobacteria and Eukaryotic Algae     

Jakub Gregor  Blahoslav Mar&#x;lek 《洁净——土壤、空气、水》2005,33(2):142-148

A method for the rapid detection of cyanobacteria (blue‐green algae) and their differentiation from eukaryotic algae in natural phytoplankton assemblages is presented. Fluorescence emission of photosynthetic pigments at 670 nm was measured using a microplate fluorescence reader when excited at two different wavelengths – 485 nm and 590 nm. The ratio of fluorescence excited at these wavelengths (590 nm/485 nm) was proportional to the ratio of cyanobacteria and eukaryotic algae, which was determined by the in situ spectrofluorometer for the phytoplankton quantification. The fluorescence intensity was equal to the total chlorophyll‐a content. These two fluorescence values can provide the first warning on a development of potentially toxic cyanobacteria in water.  相似文献   

Nutrient,heavy metal and organic pollutant composition of suspended and bed sediments in the Rhone River     

S. Santiago  R. L. Thomas  G. Larbaigt  C. Corvi  D. Rossel  J. Tarradellas  D. J. Gregor  L. McCarthy  J. P. Vernet 《Aquatic Sciences - Research Across Boundaries》1994,56(3):220-242

The environmental quality of the Rhone River (Switzerland-France) has been assessed with a geochemical survey of the pollutants bound to suspended sediments. Ten samples were collected between Lake Geneva and the Mediterranean Sea in Nobember 1989 by continuous flow centrifugation and analysed for grain size distribution, carbonate, organic C, N, forms of particulate P, trace metals, and organic compounds (chlorobenzenes, organochlorine pesticides, PCBs, and PAHs). Four bed sediment samples were also studied for comparative purposes. The suspended solids provide lower variance by parameter than the bed sediments and are clearly most suitable for synoptic monitoring.The Upper Rhone River carries a glacial derived sediment with a low nutrient content, the stretch from Geneva to Lyon provides a sediment dominated by carbonate, and in the Lower Rhone the organic matter and phosphorus are relatively increased, mainly due to wastewater effluents and to an industrial P source. High concentrations of metals and organic micropollutants downstream of Lyon indicate a multiple contamination in the Lower Rhone, whereas more specific inputs are located downstream of Geneva and Arles.The comparison with data from other polluted major systems, the Rhine, the Niagara and the Detroit rivers, shows on overall similarity confirming that the Rhone quality is degraded downstream of Lyon. The levels of particular concern are for Hg, DDT metabolites which reveal a recent release in the basin, PCBs with a likely high chlorine content, and PAHs.The statistical evaluation of the compositional variables indicates a limited number of well defined associations, suggesting that the contamination of the suspended sediments results from the combination of numerous and intermittent point and diffuse sources in the Rhone River basin.  相似文献   

Mesozoic volcanics of western sicily     

R. Catalano  B. d'Argenio  C. B. Gregor  A. E. M. Nairn  G. Nardi  P. Renda 《International Journal of Earth Sciences》1984,73(2):577-598

The Mesozoic lavas and minor intrusions in the thrust sheets of western Sicily have the following characteristics:

1. The lavas in the Triassic Mufara Formation in the north were broken into fragments which rotated independently within the incompetent strata that enclose them. This behavior is characteristic of igneous rocks found within the more internal (northerly) thrust units.
2. The Jurassic lavas in the more external (southerly) units have consistent directions which agree with those of the Ammonitico Rosso limestones in the same zone and lie about 30° clockwise from those of coeval autochthonous formations in Tunisia.Schult's presumed Cretaceous directions from Custonaci on the north coast (similar to those found in the Cretaceous Scaglia Rossa at Terrasini to the east byChannel et al., 1980) are rotated still more (140°) with respect to those of the autochthonous Iblean platform of SE Sicily. These differences are believed to reflect rotation of the thrust sheets during tectonic transport in Cenozoic times, the internal units being the most strongly rotated.
3. All the igneous rocks are highly altered: generally the original mineralogy cannot be completely determined. Relative abundances of some of the less mobile elements (Ti, Sr, Y) suggest that they are intraplate basalts.

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Iron isotope fractionation during hydrothermal ore deposition and alteration   总被引：4，自引：0，他引：4  

Gregor Markl  Friedhelm von Blanckenburg 《Geochimica et cosmochimica acta》2006,70(12):3011-3030

Iron isotopes fractionate during hydrothermal processes. Therefore, the Fe isotope composition of ore-forming minerals characterizes either iron sources or fluid histories. The former potentially serves to distinguish between sedimentary, magmatic or metamorphic iron sources, and the latter allows the reconstruction of precipitation and redox processes. These processes take place during ore formation or alteration. The aim of this contribution is to investigate the suitability of this new isotope method as a probe of ore-related processes. For this purpose 51 samples of iron ores and iron mineral separates from the Schwarzwald region, southwest Germany, were analyzed for their iron isotope composition using multicollector ICP-MS. Further, the ore-forming and ore-altering processes were quantitatively modeled using reaction path calculations. The Schwarzwald mining district hosts mineralizations that formed discontinuously over almost 300 Ma of hydrothermal activity. Primary hematite, siderite and sulfides formed from mixing of meteoric fluids with deeper crustal brines. Later, these minerals were partly dissolved and oxidized, and secondary hematite, goethite and iron arsenates were precipitated. Two types of alteration products formed: (1) primary and high-temperature secondary Fe minerals formed between 120 and 300 °C, and (2) low-temperature secondary Fe minerals formed under supergene conditions (<100 °C). Measured iron isotope compositions are variable and cover a range in δ⁵⁶Fe between −2.3‰ and +1.3‰. Primary hematite (δ⁵⁶Fe: −0.5‰ to +0.5‰) precipitated by mixing oxidizing surface waters with a hydrothermal fluid that contained moderately light Fe (δ⁵⁶Fe: −0.5‰) leached from the crystalline basement. Occasional input of CO₂-rich waters resulted in precipitation of isotopically light siderite (δ⁵⁶Fe: −1.4 to −0.7‰). The difference between hematite and siderite is compatible with published Fe isotope fractionation factors. The observed range in isotopic compositions can be accounted for by variable fractions of Fe precipitating from the fluid. Therefore, both fluid processes and mass balance can be inferred from Fe isotopes. Supergene weathering of siderite by oxidizing surface waters led to replacement of isotopically light primary siderite by similarly light secondary hematite and goethite, respectively. Because this replacement entails quantitative transfer of iron from precursor mineral to product, no significant isotope fractionation is produced. Hence, Fe isotopes potentially serve to identify precursors in ore alteration products. Goethites from oolitic sedimentary iron ores were also analyzed. Their compositional range appears to indicate oxidative precipitation from relatively uniform Fe dissolved in coastal water. This comprehensive iron isotope study illustrates the potential of the new technique in deciphering ore formation and alteration processes. Isotope ratios are strongly dependent on and highly characteristic of fluid and precipitation histories. Therefore, they are less suitable to provide information on Fe sources. However, it will be possible to unravel the physico-chemical processes leading to the formation, dissolution and redeposition of ores in great detail.  相似文献   

Probabilities in climate policy advice: a critical comment     

Gregor Betz 《Climatic change》2007,85(1-2):1-9

This essay explores as to whether probabilistic climate forecasting is consistent with the prerequisites of democratic scientific policy advice. It argues that, given the boundaries of our current knowledge, it is highly problematic to assign exact, unconditional probabilities to possible values of climate sensitivity. The range of possible–instead of probable–future climate scenarios is what climate policy should be based on.  相似文献   

A new linguistic quantifier knowledge-guided OWA approach for mineral prospectivity mapping: a case study of the Bavanat Region,Iran     

Reza Ghasemi  Behzad Tokhmechi  Gregor Borg 《Arabian Journal of Geosciences》2018,11(19):588

The main purpose of this study is to introduce a geographic information system (GIS)-based, multi-criteria decision analysis method for selection of favourable environments for Besshi-type volcanic-hosted massive sulphide (VHMS) deposits. The approach integrates two multi-criteria decision methods (analytical hierarchy process and ordered weighted averaging) and theory of fuzzy sets, within a GIS environment, to solve the problem of big suggested areas and missing known ore deposits in favourable environment maps for time and cost reduction. We doubled the fuzzy linguistic variables’ significance as a method to apply the arrange weights that the analytical hierarchy process (AHP)-ordered weighted averaging (OWA) hybrid procedure depends on. Another aim of this work is to assist mineral deposit exploration by modelling existing uncertainty in decision-making. Both AHP and fuzzy logic methods are knowledge-based, and they are affected by decision maker judgments. We used data-driven OWA approach in a hybrid method for solving this problem. We applied a new knowledge-guided OWA approach on data with changing linguistic variables according to the mineral system for VHMS deposits. Additionally, we used a vector-based method combination, which increased the precision of results. Results of knowledge-guided OWA showed that all of the mines and discovered deposits have been predicted with 100% accuracy in half of the size of the suggested area. To summarize, results improved the selection of possible target sites and increased the accuracy of results as well as reducing the time and cost, which will be used for field exploration. Finally, the hybrid methods with a knowledge-guided OWA approach have delivered more reliable results compared to exclusively knowledge-driven or data-driven methods. The study proved that expert knowledge and processed data (information) are critical important keys to exploration, and both of them should be applied in hybrid methods for reaching reliable results in mineral prospectivity mapping.  相似文献   

Centrifuge modelling of rainfall-induced slope failure in variably saturated soil     

Wang  Shun  Idinger  Gregor  Wu  Wei 《Acta Geotechnica》2021,16(9):2899-2916

Acta Geotechnica - This paper presents the results of centrifuge tests on rainfall-induced instabilities in variably saturated slopes. The roles of rainfall intensity and initial conditions, such...  相似文献