Ramifications of high in-situ temperatures for laboratory testing and inferred stress states of unlithified sediments – A case study from the Nankai margin     

Andre Hüpers  Stefan KreiterAchim J. Kopf 《Marine and Petroleum Geology》2010

The recovery of drill cores involves changes in pressure and temperature conditions, which inevitably alter the mechanical properties of unlithified sediments. While expansion from unloading after core recovery is well studied, the effects from cooling on standard geotechnical tests are commonly neglected. Along the central portion of the Nankai margin sediments were recovered from high in-situ temperatures of up to 110 °C during IODP Leg 190. So far, the interpretation of the consolidation state of the Lower Shikoku Basin facies (LSB) entering the accretionary Nankai margin is ambiguous. Results from laboratory consolidation tests at room temperature show high pre-consolidation stresses. These were interpreted as hardening caused by cementation, while the field-based porosity vs. depth trend points towards normal consolidation. As an explanation for this discrepancy, the change of the mechanical properties by cooling from in-situ to laboratory conditions is proposed. In this paper, the results of a thermo-mechanical model are compared to published field data. This comparison suggests that the observed hardening is at least partially an artefact from cooling during core recovery, and that the strata may be considered normally consolidated to slightly overconsolidated. The latter can be explained by minor cementation or the influence of secondary consolidation. The results suggest that cooling from high in-situ temperatures may be important for the interpretation of the consolidation state of other sedimentary successions elsewhere.  相似文献   

Effect of bed surface roughness on longitudinal dispersion in artificial open channels     

Marcus Schulz  Jan Priegnitz  Jörg Klasmeier  Stefan Heller  Stefan Meinecke  Michael Feibicke 《水文研究》2012,26(2):272-280

In several empirical and modelling studies on river hydraulics, dispersion was negatively correlated to surface roughness. In this study, it was aimed to investigate the influence of surface roughness on longitudinal dispersion under controlled conditions. In artificial flow channels with a length of 104 m, tracer experiments with variations in channel bed material were performed. By use of measured tracer breakthrough curves, average flow velocity, mean longitudinal dispersion, and mean longitudinal dispersivity were calculated. Longitudinal dispersion coefficients ranged from 0·018 m² s^?1 in channels with smooth bed surface up to 0·209 m² s^?1 in channels with coarse gravel as bed material. Longitudinal dispersion was linearly related to mean flow velocity. Accordingly, longitudinal dispersivities ranged between 0·152 ± 0·017 m in channels with smooth bed surface and 0·584 ± 0·015 m in identical channels with a coarse gravel substrate. Grain size and surface roughness of the channel bed were found to correlate positively to longitudinal dispersion. This finding contradicts several existing relations between surface roughness and dispersion. Future studies should include further variation in surface roughness to derive a better‐founded empirical equation forecasting longitudinal dispersion from surface roughness. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Extreme storms in Malmö, Sweden     

Lars Bengtsson  Stefan Milloti 《水文研究》2010,24(24):3462-3475

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A personal perspective on future paths for remote sensing to proceed in earthquake science     

Stefan Dech 《Natural Hazards》2013,68(1):197-198

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Spatial patterns of groundwater‐lake exchange – implications for acid neutralization processes in an acid mine lake     

Christiane Neumann  Julia Beer  Christian Blodau  Stefan Peiffer  Jan H. Fleckenstein 《水文研究》2013,27(22):3240-3253

Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m^‐2 d^‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m^‐2 d^‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g^‐1 d^‐1) compared to alternating sites (<220 nmol g^‐1 d^‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

North Atlantic climate impact on early late‐glacial climate oscillations in the south‐eastern Alps inferred from a multi‐proxy lake sediment record     

Roland Schmidt  Kaarina Weckström  Stefan Lauterbach  Richard Tessadri  Kerstin Huber 《第四纪科学杂志》2012,27(1):40-50

High‐resolution multi‐proxy analyses of a sediment core section from Lake Jeserzersee (Saissersee) in the piedmont lobe of the Würmian Drau glacier (Carinthia, Austria) reveal pronounced climatic oscillations during the early late glacial (ca. 18.5–16.0k cal a BP). Diatom‐inferred epilimnetic summer water temperatures show a close correspondence with temperature reconstructions from the adjacent Lake Längsee record and, on a hemispheric scale, with fluctuations of ice‐rafted debris in the North Atlantic. This suggests that North Atlantic climate triggered summer climate variability in the Alps during the early late glacial. The expansion of pine (mainly dwarf pine) between ca. 18.5 and 18.1k cal a BP indicates warming during the so‐called ‘Längsee oscillation’. The subsequent stepwise climate deterioration between ca. 18.1 and 17.6k cal a BP culminated in a tripartite cold period between ca. 17.6 and 16.9k cal a BP with diatom‐inferred summer water temperatures 8.5–10 °C below modern values and a shift from wet to dry conditions. This period probably coincides with a major Alpine glacier advance termed the Gschnitz stadial. A warmer interval between ca. 16.9 and 16.4k cal a BP separates this cold phase from a second, shorter and less pronounced cold phase between ca. 16.4 and 16.0k cal a BP, which is thought to correlate with the Clavadel/Senders glacier advance in the Alps. The following temperature increase, coupled with wet (probably snow‐rich) conditions, caused the expansion of birch during the transition period to the late glacial interstadial. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Inversion for Range-Dependent Sediment Compressional-Wave-Speed Profiles From Modal Dispersion Data     

Rajan  S. D. Becker  K. M. 《Oceanic Engineering, IEEE Journal of》2010,35(1):43-58

A perturbative inversion method for estimating sediment compressional-wave-speed profiles from modal travel-time data is extended to include range-dependent environments. The procedure entails dividing a region into range-independent sections and obtaining estimates of the sediment properties for each region. Inversion results obtained using synthetic data show that range-dependent properties can be obtained if an experiment is designed to include multiple source/receiver combinations. This approach is applied to field data collected during the 2006 Shallow Water Experiment (SW06). The sediment compressional-wave-speed profiles resulting from analysis of the field data are evaluated by comparing acoustic fields predicted based on the inversion to acoustic fields measured during a different experiment conducted in the same region. The model is also compared to seismic reflection survey data collected during SW06. Resolution and variance estimated for the inversion results are also presented.   相似文献   

Satellite-based prediction of rainfall interception by tropical forest stands of a human-dominated landscape in Central Sulawesi,Indonesia     

Jens Nieschulze  Stefan Erasmi  Johannes Dietz  Dirk Hölscher 《Journal of Hydrology》2009,364(3-4):227-235

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East-Central Europe's changing energy landscapes: a place for geography     

Stefan Bouzarovski 《Area》2009,41(4):452-463

Energy developments in the post-Communist states of Eastern and Central Europe (ECE) have a major impact on global energy security and sustainability, thanks to this region's key geographical position between the energy-exporting states of the former Soviet Union, on the one hand, and the energy-importing states of Western and Southern Europe, on the other. At the same time, post-socialist reforms of energy industries in this region provide unique insights into the complex relations of power, economic transformation and spatial inequality that govern energy production and consumption. This paper therefore aims to provide an initial look at some of the theoretical and policy issues that underpin the emergent 'geographies' of energy reform in ECE, as well as their embeddedness in relations of power stemming from organisational, infrastructural and economic inequalities in the region. It employs an analysis of local news reports, policy papers and statistical data to examine the intricate institutional networks and spatial formations that have governed the energy transformation process. In broader terms, the paper aims to emphasise the important role that human geography can play in making sense of the territorial differences and frictions that have emerged during the post-socialist reform process, while challenging the idea of a 'neat' neoliberal transition from a centrally planned to a market-based mode of energy regulation .  相似文献   

Functioning of intertidal flats inferred from temporal and spatial dynamics of O<Subscript>2</Subscript>, H<Subscript>2</Subscript>S and pH in their surface sediment   总被引：1，自引：1，他引：0  

Stefan Jansen  Eva Walpersdorf  Ursula Werner  Markus Billerbeck  Michael E Böttcher  Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332

In this article, we describe the dynamics of pH, O₂ and H₂S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment. In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms, as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this way create specific niches for various types of microorganisms.  相似文献