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81.
Larisa A. Savelieva Andrei A. Andreev Raphael Gromig Dmitry A. Subetto Grigory B. Fedorov Volker Wennrich Bernd Wagner Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):349-360
The new pollen record from the upper 12.75 m of a sediment core obtained in Lake Ladoga documents regional vegetation and climate changes in northwestern Russia over the last 13.9 cal. ka. The Lateglacial chronostratigraphy is based on varve chronology, while the Holocene stratigraphy is based on AMS 14C and OSL dates, supported by comparison with regional pollen records. During the Lateglacial (c. 13.9–11.2 cal. ka BP), the Lake Ladoga region experienced several climatic fluctuations as reflected in vegetation changes. Shrub and grass communities dominated between c. 13.9 and 13.2 cal. ka BP. The increase in Picea pollen at c. 13.2 cal. ka BP probably reflects the appearance of spruce in the southern Ladoga region at the beginning of the Allerød interstadial. After c. 12.6 cal. ka BP, the Younger Dryas cooling caused a significant decrease in spruce and increase in Artemisia with other herbs, indicative of tundra‐ and steppe‐like vegetation. A sharp transition from tundra‐steppe habitats to sparse birch forests characterizes the onset of Holocene warming c. 11.2 cal. ka BP. Pine forests dominated in the region from c. 9.0 to 8.1 cal. ka BP. The most favourable climatic conditions for deciduous broad‐leaved taxa existed between c. 8.1 and 5.5 cal. ka BP. Alder experiences an abrupt increase in the local vegetation c. 7.8 cal. ka BP. The decrease in tree pollen taxa (especially Picea) and the increase in herbs (mainly Poaceae) probably reflect human activity during the last 2.2 cal. ka. Pine forests have dominated the region since that time. Secale and other Cerealia pollen as well as ruderal herbs are permanently recorded since c. 0.8 cal. ka BP. 相似文献
82.
Lasse Hjuler Christiansen Andrea Capolei John Bagterp Jørgensen 《Computational Geosciences》2017,21(3):411-426
The uncertainties related to long-term forecasts of oil prices impose significant financial risk on ventures of oil production. To minimize risk, oil companies are inclined to maximize profit over short-term horizons ranging from months to a few years. In contrast, conventional production optimization maximizes long-term profits over horizons that span more than a decade. To address this challenge, the oil literature has introduced short-term versus long-term optimization. Ideally, this problem is solved by a posteriori multi-objective optimization methods that generate an approximation to the Pareto front of optimal short-term and long-term trade-offs. However, such methods rely on a large number of reservoir simulations and scale poorly with the number of objectives subject to optimization. Consequently, the large-scale nature of production optimization severely limits applications to real-life scenarios. More practical alternatives include ad hoc hierarchical switching schemes. As a drawback, such methods lack robustness due to unclear convergence properties and do not naturally generalize to cases of more than two objectives. Also, as this paper shows, the hierarchical formulation may skew the balance between the objectives, leaving an unfulfilled potential to increase profits. To promote efficient and reliable short-term versus long-term optimization, this paper introduces a natural way to characterize desirable Pareto points and proposes a novel least squares (LS) method. Unlike hierarchical approaches, the method is guaranteed to converge to a Pareto optimal point. Also, the LS method is designed to properly balance multiple objectives, independently of Pareto front’s shape. As such, the method poses a practical alternative to a posteriori methods in situations where the frontier is intractable to generate. 相似文献
83.
Manfred F. Buchroithner Guido Ehlert Bernd Hetze Horst Kohlschmidt Nikolas Prechtel 《Pure and Applied Geophysics》2014,171(6):1077-1087
Mountain-rescue operations require rapid response whilst also ensuring the security of the rescue teams. Rescuing people in a big rock-face is even more difficult if night or fog prevent sight. The paper presents a technical solution to optimally support, under these aggravated conditions, the location of the casualties and the navigation of the rescue team(s) in a rock-face from a coordination station. In doing so, standard components like a smartphones with GPS functionality, a data communication on a client–server basis and VR visualisation software have been adapted to the specific requirements. Remote support of the navigation in steep rocky terrain requires a highly accurate wall model which permits the local experts of the coordination station to dependably estimate geometry and structure of the rock along the rescue route and to convey necessary directives to the retrieval team. Based on terrestrial laser-scans from different locations, such a model has been generated for the mighty Dachstein South Face (Austria) and texturised with digital photographs. Over a twelve-month period, a transdisciplinary team of the Dresden University of Technology (Informatics, Electrical Engineering, Cartography) developed and integrated the various technical modules of the mountain-rescue support-system (digital rock-face model, optimised GPS data transmission between mobile device, server and client, data filtering, and dynamic visualisation component). In summer 2011 the proper functioning of the prototype was demonstrated in a rescue exercise under foggy dusk conditions. 相似文献
84.
Tobias Dürig Fabio Dioguardi Ralf Büttner Pierfrancesco Dellino Daniela Mele Bernd Zimanowski 《Bulletin of Volcanology》2012,74(4):895-902
Brittle magmatic fragmentation plays a crucial role in explosive eruptions. It represents the starting point of hazardous
explosive events that can affect large areas surrounding erupting volcanoes. Knowing the initial energy released during this
fragmentation process is fundamental for the understanding of the subsequent dynamics of the eruptive gas-particle mixture
and consequently for the forecasting of the erupting column’s behavior. The specific kinetic energy (SKE) of the particles
quantifies the initial velocity shortly after the fragmentation and is therefore a necessary variable to model the gas-particle
conduit flow and eruptive column regime. In this paper, we present a new method for its determination based on fragmentation
experiments and identification of the timings of energy release. The results obtained on compositions representative for basaltic
and phonolitic melts show a direct dependence on magma material properties: poorly vesiculated basaltic melts from Stromboli
show the highest SKE values ranging from 7.3 to 11.8 kJ/kg, while experiments with highly vesiculated samples from Stromboli
and Vesuvius result in lower SKE values (3.1 to 3.8 kJ/kg). The described methodology presents a useful tool for quantitative
estimation of the kinetic energy release of magmatic fragmentation processes, which can contribute to the improvement of hazard
assessment. 相似文献
85.
Dirk Enters Hermann Behling Christoph Mayr Lydie Dupont Bernd Zolitschka 《Journal of Paleolimnology》2010,44(1):265-277
Environmental changes of the last 9,300 years were reconstructed by geochemical and pollen analyses of a 14-m-long, laminated
sediment core from Lago Aleixo, south-eastern Brazil. Fossil pollen assemblages indicate open savannah vegetation (campo cerrado)
and gallery forests until approximately 6,900 cal. BP. During that time, siderite laminae were deposited under anoxic conditions
at the lake bottom. Then, increased rainfall and a shorter annual dry period allowed gallery forests and semi-deciduous forests
to expand, leading to more closed cerrado vegetation. High-intensity rainfall events during this period are recorded as peaks
in K and Ti concentrations. The sediment facies during this period consists of alternating layers of diatoms and minerogenic
matter. C/N ratios imply that algae and perhaps soils, too, were the main contributors to sediment organic matter. Biogenic
silica and δ13Corg variations indicate increasing primary productivity, which was related to higher nutrient flux from intensified leaching
of soils, as shown by rising K/Al ratios. Around 800 cal. BP, a closed, semi-deciduous forest developed under present-day
climate conditions. Slope stabilization diminished erosion processes in the catchment and caused reduced input of minerogenic
matter into the basin. Human impact is evident in the topmost homogeneous sediments, as removal of the stabilizing forest
cover amplified soil erosion. The continuous trend to more humid conditions during the Holocene probably reflects increased
influence of the Amazon Basin as a moisture source. We conclude that the Lago Aleixo sediment archive was a sensitive recorder
of environmental dynamics in tropical South America, which were mainly controlled by changes in precipitation patterns. 相似文献
86.
Elena Dunca Harry Mutvei Peter Göransson Carl-Magnus Mörth Bernd R. Schöne Martin J. Whitehouse Mikael Elfman Susanne P. Baden 《International Journal of Earth Sciences》2009,98(1):3-17
Shells of Arctica islandica collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak (Swedish West Coast) were used to monitor local climate variations and the influence of human activities on the local environment. For this purpose, we analysed the growth, structure and chemical composition of these shells and compared them with shells collected from Kiel Bay, Norway and Iceland. The growth rate of the studied shells registers an NAO periodicity of ca 8 years. However, the observed signal is weak because of other environmental interferences that are either of natural or anthropogenic origin. For example, the oxygen isotope ratios show temperature fluctuation, but also the influx of low salinity water. Higher contents of S, N, Cu, Zn, As, Cd and P in shell portions formed during the last century are related to human activities such as mining and industrial development. Our study indicates that in order to use Arctica shells as archives of climate change it is necessary to study the full range of environmental data that is recorded in the shells by using a multi element and isotope approach in combination with different analytical techniques including investigation of growth rates and shell structure. 相似文献
87.
Niels Nielsen Viggo Hansen Kaj Hansen Kr. M. Jensen Sten Folving Sofus Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):101-118
Meyer, Marlene: Settlement Patterns and Land-use in Northern Ghana—A Study of the Changes during the period 1963–1991 based on Historical Surveys and recent SPOT-images. Geografisk Tidsskrift 92:101–104. Copenhagen 1992. A study by Hunter (1966) describes how large areas along the Red Volta River bank, have been abandoned due to river blindness. The mapping of current land-use status and settlements patterns, using multispectral SPOT-satellite images, shows how the border of settlements continue to retreat, whereas new land is being reclaimed for bush fields in the abandoned areas. 相似文献
88.
Birger Ulf Hansen Ole Humlum Niels Nielsen Dorte P. Lundqvist Ditte L. Jansen Christian Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):93-109
An automatic meteorological station has been operating at the Arctic Station (69°15'N, 53°31'W) in West Greenland since 1990. This paper summarises meteorological parameters during 2002, including snow cover, ground temperatures and active layer development, and air temperatures at the Station during the last 12 years are compared to large scale trends during the last century. A compilation of 93 sedimentation rate determinations based on 210Pb dating has been carried out for the North Sea-Baltic Sea transition area from a database containing 165 determinations carried out by Danish institutions. In the depositional parts of the area sedimentation rates generally range 25–6403 g m?2 y?1. An extreme rate of 13351 g m?2 y?1 is observed on a station in the Skagerrak. Sedimentation rates significantly increase with depth indicating that the Skagerrak and northern parts of the Kattegat as well as the deep basins in the Baltic Sea act as depocentres for fine-grained sediments. Apparently, sedimentation rates have increased in recent years. 相似文献
89.
Alexandre Raphael Cabral Bernd Lehmann Miguel Tupinambá Michael Wiedenbeck Michael Brauns 《Journal of Geochemical Exploration》2011
The Palaeo-Mesoproterozoic metasiliciclastic rocks of the southern Serra do Espinhaço, Minas Gerais, Brazil, are host to historically important alluvial deposits of diamonds and gold. Detrital gold grains often comprise Au–Pd–Pt intermetallic compounds, with low Ag contents, which contain inclusions of tourmaline and titaniferous hematite (up to ~ 6 wt.% TiO2). The latter minerals connect the alluvial mineralisation to the rutile–hematite–quartz veins and tourmalinisation observed in the quartzitic country rocks of the alluvial gravel. The quartzite (Sopa-Brumadinho Formation of lacustrine to fan-deltaic origin) is affected by pervasive B metasomatism with F-bearing tourmaline replacing the recrystallised quartz fabric. The tourmaline belongs to the alkali group, with Mg/(Mg + Fe) and X/(X + Na) ratios in the ranges from 0.5 to 0.7 and 0.18 to 0.29, respectively, where X represents vacancies in the X site. Boron-isotopic values of tourmaline vary from ~ 1 to − 10.4‰ δ11B. The B-isotope range, in conjunction with the Na–Mg-rich tourmaline composition, and the widespread occurrence of tourmalinite in the Sopa-Brumadinho Formation suggest a derivation from non-marine evaporitic brines. Brines are capable of transporting otherwise immobile Ti and explain, under oxidising conditions, the fractionation of Ag from Pd to precipitate palladiferous gold with extremely high Pd/Ag ratios. Zirconium-in-rutile and Ti-in-quartz temperatures for a variety of hematite-rich veins suggest episodic vein emplacement over a temperature range from around 500 °C to ~ 350 °C. Cross-cutting relationships and episodic vein emplacement indicate a late-Brasiliano age. 相似文献
90.
Axel Müller Bernd Leiss Klaus Ullemeyer Karel Breiter 《International Journal of Earth Sciences》2011,100(7):1515-1532
The lattice-preferred orientation (LPOs) of two late-Variscan granitoids, the Meissen monzonite and the Podlesí dyke granite,
were determined from high-resolution time-of-flight neutron diffraction patterns gained at the diffractometer SKAT in Dubna,
Russia. The results demonstrate that the method is suitable for the LPO analysis of polyphase, relatively coarse-grained (0.1–6 mm)
rocks. The Meissen monzonite has a prominent shape-preferred orientation (SPO) of the non-equidimensional minerals feldspar,
mica and amphibole, whereas SPO of the Podlesí granite is unapparent at the hand-specimen scale. The neutron diffraction data
revealed distinct LPOs in both granitoids. The LPO of the non-equidimensional minerals feldspar, mica and amphibole developed
mainly during magmatic flow. In the case of the Meissen monzonite, the magmatic flow was superimposed by regional shear tectonics,
which, however, had no significant effect on the LPOs. In both samples, quartz shows a weak but distinct LPO, which is atypical
for plastic deformation and different in the syn-kinematic Meissen monzonite and the post-kinematic Podlesí granite. We suggest
that, first of all, the quartz LPO of the Meissen monzonite is the result of oriented growth in an anisotropic stress field.
The quartz LPO of the Podlesí granite, which more or less resembles a deformational LPO in the flattening field of the local
strain field, developed during magmatic flow, whereby the rhombohedral faces of the quartz crystals adhered to the (010) faces
of aligned albite and to the (001) faces of zinnwaldite. Due to shape anisotropy of their attachments, the quartz crystals
were passively aligned by magmatic flow. Thus, magmatic flow and oriented crystal growth are the major LPO-forming processes
in both granitoids. For the Meissen monzonite, the solid-state flow was too weak to cause significant crystallographic re-orientation
of the minerals aligned by magmatic flow. Finally, the significance of our results for the evaluation of the regional tectonic
environment during magma emplacement is discussed. The discussion on the regional implications of the more methodologically
oriented results provides the basis for future, more regionally aimed studies in view of the fabric characteristics of such
plutons and their developing mechanisms. 相似文献