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排序方式: 共有142条查询结果,搜索用时 15 毫秒
71.
Katarina Gobo Massimiliano Ghinassi Wojciech Nemec Eivind Sjursen 《Sedimentology》2014,61(4):1086-1119
This study from the southern margin of the Gulf of Corinth documents a Late Pleistocene incised valley‐fill succession that differs from the existing facies models, because it comprises gravelly shoal‐water and Gilbert‐type deltaic deposits, shows strong wave influence and lacks evidence of tidal activity. The valley‐fill is at least 140 m thick, formed in 50 to 100 ka between the interglacials Marine Isotope Stage 9a and Marine Isotope Stage 7c. The relative sea‐level rise left its record both inside and outside the incised valley, and the age of the valley‐fill is estimated from a U/Th date of coral‐bearing deposits directly outside the palaeovalley outlet. Tectonic up‐warping due to formation of a valley‐parallel structural relay ramp contributed to the valley segmentation and limited the landward extent of marine invasions. The valley segment upstream of the ramp crest was filled with a gravelly alluvium, whereas the downstream segment accumulated fluvio‐deltaic deposits. The consecutive deltaic systems nucleated in the ramp‐crest zone, forming a bathymetric gradient that promoted the ultimate growth of thick Gilbert‐type delta. The case study contributes to the spectrum of conceptual models for incised valley‐fill architecture. Four key models are discussed with reference to the rates of sediment supply and accommodation development, and it is pointed out that not only similarity, but also all departures of particular field cases from these end‐member models may provide valuable information on the system formative conditions. The Akrata incised valley‐fill represents conditions of high sediment supply and a rapid, but stepwise development of accommodation that resulted from the spatiotemporal evolution of normal faulting at the rift margin and overprinted glacioeustatic signals. This study adds to an understanding of valley‐fill architecture and provides new insights into the Pleistocene tectonics and palaeogeography of the Corinth Rift margin. 相似文献
72.
In this work we consider when and how much liquid water during present climate is possible within the gullies observed on the surface of Mars. These features are usually found on poleward directed slopes. We analyse the conditions for melting of H2O ice, which seasonally condenses within the gullies. We follow full annual cycle of condensation and sublimation of atmospheric CO2 and H2O, accounting for the heat and mass transport in the soil. During the summer, once the facets of the gullies are exposed to the Sun the water ice can melt and evaporate. Two mid latitude locations in both hemispheres are considered. The model includes both the rough geometry of the gullies as well as the slope of the surface where the gullies appear. It is an extension of the model developed to calculate condensation of CO2 ice in troughs of different sizes, including polygonal features on Mars (Kossacki and Markiewicz, 2002, Icarus 160, 73; Kossacki et al., 2003, Planet. Space Sci. 51, 569). We have found, that water ice accumulated during winter can undergo transition to the liquid phase after complete sublimation of CO2 ice. The amount of liquid water depends on water content in the atmosphere and on the local wind speed. It is probably not enough to destabilise the slope and cause flow of the surface material. However, even the small amounts of liquid water predicted, can play an important role in surface chemistry, in increasing the cohesive strength of the soil's surface layer and possibly may have some exobiological implications. 相似文献
73.
Marcel Marchand Agustin Sanchez-ArcillaMaria Ferreira Jeremy GaultJosé A. Jiménez Marina MarkovicJan Mulder Leo van RijnAdrian St?nic? Wojciech SuliszJames Sutherland 《Ocean & Coastal Management》2011,54(12):859-866
The main objective of the Conscience project was to develop and test concepts, guidelines and tools for the sustainable management of erosion along the European coastline, based on the best available scientific knowledge and on existing practical experience. Four concepts are potentially capable of providing the nexus between scientific knowledge and management: coastal resilience, coastal sediment cell, favourable sediment status and strategic sediment reservoir. The project has tested the use of these concepts and found that they are useful, provided that they are positioned and linked within a logical structure that we shall call the Conscience “Frame of Reference”, defined in time and space and supported through data and monitoring. Practical experience in six coastal sites in Europe has shown that the use of this Frame of Reference together with these concepts can make management objectives explicit and transparent. It can therefore support the design of an appropriate, resilience based coastal erosion management practice. 相似文献
74.
In this work we estimate the minimum persistence time of subsurface ice in water rich sediment layers remaining after sublimation of a martian lake. We simulate sublimation of ice from layers of different granulations and thicknesses. Presented results assume insolation and atmospheric conditions characteristic for the present day southern Elysium, where data from Mars Express have identified surface features possibly indicating the very recent presence of a frozen body of water [Murray et al., 2005. Nature 434, 352-356]. The age of these features is estimated to be several million years. On this time scale, we find that most of the water ice must have sublimated away, however remnant ice at a few percent level cannot be excluded. This amount of water ice is sufficient for chemical cementation of the observed features and explains their relatively pristine appearance, without significant signs of erosion. 相似文献
75.
Wojciech W. Grabowski Joanna Slawinska Hanna Pawlowska Andrzej A. Wyszogrodzki 《Acta Geophysica》2011,59(6):1184-1204
This paper presents application of the EULAG model combined with a sophisticated double-moment warm-rain microphysics scheme to the model intercomparison case based on RICO (Rain in Cumulus over Ocean) field observations. As the simulations progress, the cloud field gradually deepens and a relatively sharp temperature and moisture inversions develop in the lower troposphere. Two contrasting aerosol environments are considered, referred to as pristine and polluted, together with two contrasting subgridscale mixing scenarios, the homogeneous and the extremely inhomogeneous mixing. Pristine and polluted environments feature mean cloud droplet concentrations around 40 and 150 mg?1, respectively, and large differences in the rain characteristics. Various measures are used to contrast evolution of macroscopic cloud field characteristics, such as the mean cloud fraction, the mean cloud width, or the height of the center of mass of the cloud field, among others. Macroscopic characteristics appear similar regardless of the aerosol characteristics or the homogeneity of the subgrid-scale mixing. 相似文献
76.
Anna Gotkowska‐Płachta Zofia Filipkowska Ewa Korzeniewska Wojciech Janczukowicz Beverly Dixon Iwona Gołaś Damian Szwalgin 《洁净——土壤、空气、水》2013,41(5):429-436
Experiments were conducted to study the airborne microbial contamination generated by a wastewater treatment plant (WWTP). Aerosol samples were collected simultaneously, by sedimentation and impact methods, from the area and the surroundings of the WWTP. Total colony forming units (CFUs) of heterotrophic bacteria (HPC), as well as members of the Enterobacteriaceae, staphylococci, enterococci, actinomycetes, and microscopic fungi were determined. Bacterial (HPC) concentrations ranged between 101 and 104 CFU/m3, fungi 0 and 104 CFU/m3. Higher numbers of HPC bacteria in air samples were observed in summer, fungi in autumn. The main emission of microorganisms to atmospheric air was from the mechanical sewage treatment devices of the WWTP. The facilities of the biological sewage treatment of the plant did not generate large amounts of bioaerosols. In the air obtained from the premises of the WWTP, 25 species of the Enterobacteriaceae were isolated (Salmonella spp., Klebsiella pneumoniae, Escherichia coli). At the fence and in the surroundings only Pantoea spp. were identified. This suggests that the sewage bacteria were mainly discharged in the area of the WWTP. The presence of enteric bacteria, especially Enterobacteriaceae reflects the level of air pollution with bioaerosols from sewage and is an important factor during monitoring the quality of the air around WWTPs. 相似文献
77.
Wojciech Tylmann Bernd Zolitschka Dirk Enters Christian Ohlendorf 《Journal of Paleolimnology》2013,50(4):487-503
Glacial landscapes of the Land of Great Masurian Lakes and Suwa?ki Lakelands in northeast Poland are characterized by very high abundance of lakes. These two areas were surveyed for lakes containing laminated sediments. Using bathymetry as a criterion, 60 small, deep lakes, representing preferred conditions for formation and preservation of lacustrine non-glacial varves, were selected for gravity coring. We found laminated sediments in 24 of the lakes, 15 in the Land of Great Masurian Lakes and 9 in the Suwa?ki Lakeland. Seven of these 24 sediment records were laminated in the topmost part only. Analysis of lake morphometric variables showed that the relation between surface area and maximum water depth can be used to identify lakes with laminated sediments. Most of the newly discovered lakes with laminated deposits have surface areas ≤0.3 km2 and maximum depths of 15–35 m. Multivariate statistical analysis (Linear Discriminant Analysis) of the lake dataset identified the morphological features of lake basins and their catchments that largely control preservation of laminated sediments. Microscopic and geochemical analyses revealed a biogenic (carbonaceous) type of lamination typical for lakes in northeast Poland. Such lakes are characterized by a spring-summer lamina that is rich in calcium carbonate and an autumn-winter lamina composed of organic and minerogenic detritus. This pattern may be modified by multiple periods of calcite deposition during a single year or substantial contribution of clastic material. Laminations and high sedimentation rates offer the possibility of high-resolution investigation of past climate and environmental changes through application of myriad biological, isotopic and geochemical proxies. 相似文献
78.
Marek Grad Rolf Mjelde Wojciech Czuba Aleksander Guterch the IPY Project Group 《Geophysical Prospecting》2012,60(5):855-869
Wide‐angle seismic data acquired by use of air‐guns and ocean bottom seismometers (OBS) contain strong direct water arrivals and multiples, generally considered as noise and thus not included in the modelling. However, a recent study showed that standard ray‐tracing modelling of the water multiples recorded off the Bear Island, North Atlantic, provided a reliable estimate of the velocity distribution in the water layer. Here, we demonstrate that including the amplitudes in the modelling provide valuable information about the VP contrast at the seafloor, as well as the VP/VS ratio and attenuation (QP) of the uppermost sediments. The VP contrast at the seafloor is estimated at about 250 m/s, within a precision of approximately ±30 m/s. The VP/VS ratio in the uppermost sedimentary layer is modelled in the range 2.25–2.50 and the QP factor is estimated at 1000 for the water, 30–50 for the uppermost layer and 40–50 for the second sedimentary layer. The values obtained for the sediments suggest a lithology dominated by silty clays, with porosity below average. 相似文献
79.
Wojciech Drzewiecki Piotr Wężyk Marcin Pierzchalski Beata Szafrańska 《Pure and Applied Geophysics》2014,171(6):867-895
In 2011 the Marshal Office of Ma?opolska Voivodeship decided to evaluate the vulnerability of soils to water erosion for the entire region. The quantitative and qualitative assessment of the erosion risk for the soils of the Ma?opolska region was done based on the USLE approach. The special work-flow of geoinformation technologies was used to fulfil this goal. A high-resolution soil map, together with rainfall data, a detailed digital elevation model and statistical information about areas sown with particular crops created the input information for erosion modelling in GIS environment. The satellite remote sensing technology and the object-based image analysis (OBIA) approach gave valuable support to this study. RapidEye satellite images were used to obtain the essential up-to-date data about land use and vegetation cover for the entire region (15,000 km2). The application of OBIA also led to defining the direction of field cultivation and the mapping of contour tillage areas. As a result, the spatially differentiated values of erosion control practice factor were used. Both, the potential and the actual soil erosion risk were assessed quantificatively and qualitatively. The results of the erosion assessment in the Ma?opolska Voivodeship reveal the fact that a majority of its agricultural lands is characterized by moderate or low erosion risk levels. However, high-resolution erosion risk maps show its substantial spatial diversity. According to our study, average or higher actual erosion intensity levels occur for 10.6 % of agricultural land, i.e. 3.6 % of the entire voivodeship area. In 20 % of the municipalities there is a very urgent demand for erosion control. In the next 23 % an urgent erosion control is needed. Our study showed that even a slight improvement of P-factor estimation may have an influence on modeling results. In our case, despite a marginal change of erosion assessment figures on a regional scale, the influence on the final prioritization of areas (municipalities) according to erosion control needs is visible. The study shows that, high-resolution satellite imagery and OBIA may be efficiently used for P-factor mapping and thus contribute to a refined soil erosion risk assessment. 相似文献
80.
Precise estimation of covariance parameters in least-squares collocation by restricted maximum likelihood 总被引:1,自引:0,他引:1
Precise estimates of the covariance parameters are essential in least-squares collocation (LSC) in the case of increased accuracy requirements. This paper implements restricted maximum likelihood (REML) method for the estimation of three covariance parameters in LSC with the Gauss-Markov second-order function (GM2), which is often used in interpolation of gravity anomalies. The estimates are then validated with the use of an independent technique, which has been often omitted in the previous works that are confined to covariance parameters errors based on the information matrix. The crossvalidation of REML estimates with the use of hold-out method (HO) helps in understanding of REML estimation errors. We analyzed in detail the global minimum of negative log-likelihood function (NLLF) in the estimation of covariance parameters, as well, as the accuracy of the estimates. We found that the correlation between covariance parameters may critically contribute to the errors of their estimation. It was also found that knowing some intrinsic properties of the covariance function may help in the scoring process. 相似文献