Schallausbreitung im Schlick     

Dipl.-Phys. Florian Schirmer 《Ocean Dynamics》1970,23(1):24-30

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Calcium isotope fractionation in calcite and aragonite   总被引：1，自引：0，他引：1  

Nikolaus Gussone  Florian Böhm  Martin Dietzel  Barbara M.A. Teichert  Gert Wörheide 《Geochimica et cosmochimica acta》2005,69(18):4485-4494

Calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite. Precipitation temperatures ranged from 0 to 28°C. Calcium isotope fractionation shows a temperature dependence in accordance with previous observations: 1000 · ln(α_cc) = −1.4 + 0.021 · T (°C) for calcite and 1000 · ln(α_ar) = −1.9 + 0.017 · T (°C) for aragonite. Within uncertainty the temperature slopes are identical for the two polymorphs. However, at all temperatures calcium isotopes are more fractionated in aragonite than in calcite. The offset in δ^44/40Ca is about 0.6‰. The underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals, or to different Ca reaction behavior at the solid-liquid interface. Recently, the observed temperature dependence of the Ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting (Lemarchand et al., 2004). We show that this mechanism can in principle also be applied to CaCO₃ precipitation in natural environments in normal marine settings. Following this model, Ca isotope fractionation in marine Ca carbonates is primarily controlled by precipitation rates. On the other hand the larger Ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates. The rate control model of Ca isotope fractionation predicts a strong dependence of the Ca isotopic composition of carbonates on ambient CO₃²⁻ concentration. While this model is in general accordance with our observations in marine carbonates, cultured specimens of the planktic foraminifer Orbulina universa show no dependence of Ca-isotope fractionation on the ambient CO₃²⁻ concentration. The latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water.  相似文献   

Wide-angle observations of ALP 2002 shots on the TRANSALP profile: Linking the two DSS projects     

Florian Bleibinhaus  Ewald Brückl  ALP Working Group 《Tectonophysics》2006,414(1-4):71

Dynamite shots of the crustal-scale refraction seismic project ALP 2002 were recorded by an array of 40 seismological three-component stations on the TRANSALP profile. These observations provide a direct link between the two deep seismic projects. We report preliminary results obtained from these data. In a first approach, we verified the TRANSALP refraction seismic velocity model computing travel times for several shots and comparing them to the new observations. The results generally confirm this model. Significant first-break travel time differences in and near the Tauern Window are explained by anisotropy. Large-scale features of the model, particularly the Moho structure, seem to be continuous towards the east. Travel time residuals of wide-angle reflections indicate a slight eastward dip component of the Adriatic Moho.  相似文献   

Lateral variations in sediment composition and bedding in Middle Triassic interplatform basins (Buchenstein Formation, southern Alps, Italy)     

Florian Maurer  Wolfgang Schlager 《Sedimentology》2003,50(1):1-22

ABSTRACT Hemipelagic deposits are widespread in Triassic sequences of the Alpine belt and provide important data for stratigraphy and the study of bedding rhythms. The area of the western and central Dolomites of northern Italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting. The Buchenstein Formation, the object of this study, was deposited in up to 1000 m deep, Middle Triassic interplatform basins, which extend over an area of 500 km² within the Dolomites. Excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated (anoxic) and bioturbated facies down to a bed scale, and show its relationship to coeval carbonate platforms. Correlation of lithostratigraphically well‐constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow‐water debris in the succession and is a function of the distance to coeval carbonate platform sources. In the laminated background deposit, thickness variations in limestones and marls parallel the thickness variations in ash layers, and were caused by local redeposition of sediment on the basin floor. Lateral persistence of laminae indicates that bottom currents were weak in the Buchenstein basin, but were able to redeposit mud in a significant way. In the area around Seceda and Geisler (western Dolomites), a lateral transition from dark‐grey laminated to grey bioturbated to red bioturbated facies is observed, which is probably linked to local relief with different oxygenation conditions on the sea floor. A comparison shows that decimetre‐scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis. Correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin, and decrease in thickness and contain less micrite towards the east, further away from the main shallow‐water areas. Nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin. These observations point to a platform source of lime mud in the Buchenstein basin.  相似文献   

Landslides and increased debris-flow activity: A systematic comparison of six catchments in Switzerland     

Florian Frank  Christian Huggel  Brian W. McArdell  Andreas Vieli 《地球表面变化过程与地形》2019,44(3):699-712

An increase in debris-flow frequency is expected in steep Alpine catchments after the occurrence of a large landslide, such as a rock avalanche. Herein we describe changes in debris-flow activity following increases in sediment availability due to landslides, or accelerated rock-glacier movement, for five catchments in the Swiss Alps, the Spreitgraben, Schipfenbach, Bondasca, Riascio, and Dorfbach catchments. Documentation on debris-flow activity is available from both before and after the landslide that generated the new sediment deposits. Data from nearby meteorological stations were used to explore possible changes in rainfall activity, and how the intensity and duration of rainfall events may have changed. In all cases there was a considerable increase in debris-flows frequency for one to eight years following the landslide. The annual number of days with debris-flow activity following the landslide was similar to that observed for the Illgraben catchment, where many such landslides occur annually. No clear change in precipitation totals preceding debris flows was apparent for the Riascio catchment, suggesting that the increase in frequency of debris flows is related to the increase in the amount of sediment that can be readily mobilized. In the two cases where rainfall data were available on an hourly basis, no systematic changes in the intensity or duration of rainfall related to debris-flow triggering were apparent, as shown by the close-clustering of storms on the intensity-duration plots. Following the sediment-generating event, an initial and sudden increase of the sediment yield was observed, followed by a decrease over time towards pre-disturbance values. The response of the catchments appears to be related to the amount of debris-flow activity prior to the landslide: sediment yield from catchments with frequent debris flows prior to the landslide activity did not increase as dramatically as in catchments where debris-flow activity was less common prior to the landslide. © 2018 John Wiley & Sons, Ltd.  相似文献   

Postglacial to Holocene landscape evolution and process rates in steep alpine catchments     

Florian Kober  Kristina Hippe  Bernhard Salcher  Reto Grischott  Raphael Zurfluh  Irka Hajdas  Lukas Wacker  Marcus Christl  Susan Ivy-Ochs 《地球表面变化过程与地形》2019,44(1):242-258

Climate change and high magnitude mass wasting events pose adverse societal effects and hazards, especially in alpine regions. Quantification of such geomorphic processes and their rates is therefore critical but is often hampered by the lack of appropriate techniques and the various spatiotemporal scales involved in these studies. Here we exploit both in situ cosmogenic beryllium-10 (¹⁰Be) and carbon-14 (¹⁴C) nuclide concentrations for deducing exposure ages and tracing of sediment through small alpine debris flow catchments in central Switzerland. The sediment cascade and modern processes we track from the source areas, through debris flow torrents to their final export out into sink regions with cosmogenic nuclides over an unprecedented five-year time series with seasonal resolution. Data from a seismic survey and a 90 m core revealed a glacially overdeepened basin, filled with glacial and paraglacial sediments. Surface exposure dating of fan boulders and radiocarbon ages constrain the valley fill from the last deglaciation until the Holocene and show that most of the fan existed in early Holocene times already. Current fan processes are controlled by episodic debris flow activity, snow (firn) and rock avalanches. Field investigations, digital elevation models (DEMs) of difference and geomorphic analysis agree with sediment fingerprinting with cosmogenic nuclides, highlighting that the bulk of material exported today at the outlet of the subcatchments derives from the lower fans. Cosmogenic nuclide concentrations steadily decrease from headwater sources to distal fan channels due to the incorporation of material with lower nuclide concentrations. Further downstream the admixture of sediment from catchments with less frequent debris flow activity can dilute the cosmogenic nuclide signals from debris flow dominated catchments but may also reach thresholds where buffering is limited. Consequently, careful assessment of boundary conditions and driving forces is required when apparent denudation rates derived from cosmogenic nuclide analysis are upscaled to larger regions. © 2018 John Wiley & Sons, Ltd.  相似文献   

Climate change effects on hydrological system conditions influencing generation of storm runoff in small Alpine catchments   总被引：1，自引：0，他引：1       下载免费PDF全文

Gertraud Meißl  Herbert Formayer  Klaus Klebinder  Florian Kerl  Friedrich Schöberl  Clemens Geitner  Gerhard Markart  David Leidinger  Axel Bronstert 《水文研究》2017,31(6):1314-1330

Floods and debris flows in small Alpine torrent catchments (<10 km²) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude–frequency relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. Three small Alpine catchments in different altitudes in Western Austria (Ruggbach, Brixenbach and Längentalbach catchment) were investigated by both field experiments and process‐based simulation. Rainfall–runoff model (HQsim) runs driven by localized climate scenarios (CNRM‐RM4.5/ARPEGE, MPI‐REMO/ECHAM5 and ICTP‐RegCM3/ECHAM5) were used in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On one hand, the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature‐controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high‐altitude catchment is less sensitive to climate change‐induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation‐related small proportion of sensitive areas. For the period 2071–2100, the number of days with critical antecedent soil moisture content will be significantly reduced to about 60% or even less in summer in all catchments. In contrast, the number of days with dried‐out litter layers causing hydrophobic effects will increase by up to 8%–11% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10%.  相似文献   

Evaluating debris-flow and anthropogenic disturbance on 10Be concentration in mountain drainage basins: implications for functional connectivity and denudation rates across time scales     

Francesco Brardinoni  Reto Grischott  Florian Kober  Corrado Morelli  Marcus Christl 《地球表面变化过程与地形》2020,45(15):3955-3974

We examine the sensitivity of ¹⁰Be concentrations (and derived denudation rates), to debris-flow and anthropogenic perturbations in steep settings of the Eastern Alps, and explore possible relations with structural geomorphic connectivity. Using cosmogenic ¹⁰Be as a tracer for functional geomorphic connectivity, we conduct sampling replications across four seasons in Gadria, Strimm and Allitz Creek. Sampling sites encompass a range of structural connectivity configurations, including the conditioning of a sackung, all assessed through a geomorphometric index (IC). By combining information on contemporary depth of erosion and sediment yield, disturbance history and post-LGM (Last Glacial Maximum) sedimentation rates, we constrain the effects of debris-flow disturbance on ¹⁰Be concentrations at the Gadria sites. Here, we argue that bedrock weakening imparted by the sackung promotes high depth of erosion. Consequently, debris flows recruit sediment beyond the critical depth of spallogenic production (e.g., >3 m), which in turn, episodically, due to predominantly muogenic production pathways, lowers ¹⁰Be concentration by a factor of 4, for at least 2 years. In contrast, steady erosion in Strimm Creek yields very stable ¹⁰Be concentrations through time. In Allitz Creek, we observe two- to fourfold seasonal fluctuations in ¹⁰Be concentrations, which we explain as the combined effects of water diversion and hydraulic structures on sediment mixing. We further show that ¹⁰Be concentration correlates inversely with the IC index, where sub-basins characterized by high concentrations (long residence times) exhibit low IC values (structurally disconnected) and vice versa, implying that, over millennial time scales a direct relation exists between functional and structural connectivity, and that the IC index performed as a suitable metric for structural connectivity. The index performs comparably better than other metrics (i.e., mean slope and mean normalized channel steepness index) previously used to assess topographic controls on denudation rates in active unglaciated ranges. In terms of landscape evolution, we argue that the sackung, by favouring intense debris-flow activity across the Holocene, has aided rapid postglacial reshaping of the Gadria basin, which currently exhibits a topographic signature characteristic of unglaciated debris-flow systems. © 2020 John Wiley & Sons, Ltd.  相似文献   

Where could catch shares prevent stock collapse?     

Florian K. Diekert  Anne Maria Eikeset  Nils Chr. Stenseth 《Marine Policy》2010

In a widely received study Costello and his colleagues found that catch shares give better stock persistence and higher catch for fishermen. The conclusions made by Costello et al. were further supported by Grafton and McIlgorm where they suggested a framework in order to determine the costs and benefits of separate ITQ management in seven Australian commonwealth fisheries, and what the alternatives should be if the net benefits do not justify ITQs. This raises the question why we do not see catch shares being used more often. We explore at a global scale which countries would have the potential to, and indeed do, fulfil the conditions necessary to implement such a management strategy.  相似文献   

Estimation of phase center corrections for GLONASS-M satellite antennas   总被引：3，自引：3，他引：0  

Florian Dilssner  Tim Springer  Claudia Flohrer  John Dow 《Journal of Geodesy》2010,84(8):467-480

Driven by the comprehensive modernization of the GLONASS space segment and the increased global availability of GLONASS-capable ground stations, an updated set of satellite-specific antenna phase center corrections for the current GLONASS-M constellation is determined by processing 84 weeks of dual-frequency data collected between January 2008 and August 2009 by a worldwide network of 227 GPS-only and 115 combined GPS/GLONASS tracking stations. The analysis is performed according to a rigorous combined multi-system processing scheme providing full consistency between the GPS and the GLONASS system. The solution is aligned to a realization of the International Terrestrial Reference Frame 2005. The estimated antenna parameters are compared with the model values currently used within the International GNSS Service (IGS). It is shown that the z-offset estimates are on average 7 cm smaller than the corresponding IGS model values and that the block-specific mean value perfectly agrees with the nominal GLONASS-M z-offset provided by the satellite manufacturer. The existence of azimuth-dependent phase center variations is investigated and uncertainties in the horizontal offset estimates due to mathematical correlations and yaw-attitude modeling problems during eclipse seasons are addressed. Finally, it is demonstrated that the orbit quality benefits from the updated GLONASS-M antenna phase center model and that a consistent set of satellite antenna z-offsets for GPS and GLONASS is imperative to obtain consistent GPS- and GLONASS-derived station heights.  相似文献