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111.
Anna E. Nelson John L. Smellie Michael J. Hambrey Mark Williams Maryline Vautravers Ulrich Salzmann John M. McArthur Marcel Regelous 《Quaternary Science Reviews》2009,28(27-28):3138-3160
Detailed sedimentological and microtextural analyses of newly-discovered late Neogene diamictites and other coarse-grained facies, mostly sandwiched between hyaloclastite of the James Ross Island Volcanic Group and Cretaceous sandstone and mudstone, indicate deposition mainly by glacigenic debris flows. The deposits on James Ross Island (northern Antarctic Peninsula) constrain the depositional setting, ice–bed dynamics and regional palaeoclimate. The sequences on James Ross Island vary in age but are mainly late Miocene and Pliocene. Unlike Neogene sedimentary sequences elsewhere in Antarctica, those on James Ross Island are unusually well-dated by a combination of 40Ar/39Ar and 87Sr/86Sr analyses on fresh interbedded lavas and pristine bivalve molluscs, respectively. The Sr isotopic ages of the debris flows cluster around 4.74, 4.89, 5.44, 5.78, and 6.31 Ma and probably date relatively warm periods in the northern Antarctic Peninsula region, when the bivalves lived under ice-poor or seasonally ice-free conditions. The bivalves are often remarkably well-preserved, lack adhering lithified sediment and, in at least two locations, are large, mainly unfragmented and sometimes articulated, suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier. These fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods, or “interglacials”, of the late Miocene and Pliocene. The James Ross Island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally. The high volume of glacigenic sediment delivery implicit in the James Ross Island successions indicates that a series of dynamic ice fronts crossed the region during the late Miocene and Pliocene epochs. Associated evidence, in the form of clast abrasion (including striations and faceting) and bedrock erosion, is indicative of basal sliding and subglacial sediment deformation active at the ice–bed interface and wet-based temperate or polythermal regimes, prior to remobilisation. The evidence further suggests two local ice caps on James Ross Island during the warm periods, as well as ice-overriding by the Antarctic Peninsula Ice Sheet from the west and northwest. 相似文献
112.
G��raldine Guerri Jean-Baptiste Daban Sylvie Robbe-Dubois Richard Douet Lyu Abe Jacques Baudrand Marcel Carbillet Anthony Boccaletti Philippe Bendjoya Carole Gouvret Farrokh Vakili 《Experimental Astronomy》2011,30(1):59-81
SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets whose first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The principal aim of this paper is to report the first laboratory experiment of the ALC designed for the SPHERE instrument. The performance and sensitivity of the optical configuration was first numerically studied with an end-to-end approach (see the results in paper I subtitled ??Detailed numerical study??). Made confident by the results, we then tested a prototype on an infrared coronagraphic bench. We measured the transmission profiles of the apodizer prototype and the coronagraphic performance of the apodized Lyot coronagraph in Y, J, and H bands. The coronagraph sensitivity to lateral and longitudinal misalignments of its three main components (apodizer, coronagraphic mask and Lyot stop) was finally studied in H band. We can conclude that the prototype meets the SPHERE technical requirements for coronagraphy. 相似文献
113.
The entrainment of material is a common process in debris-flow behaviour and can strongly increase its total volume. However, due to the complex nature of the process, the exact mechanisms of entrainment have not yet been solved. We analysed geomorphological and topographical data collected in 110 reaches of 17 granular debris flows occurred in the Pyrenees and the European Alps. Four governing factors (sediment availability, channel-bed slope, channel cross section shape and upstream-contributing area) were selected and defined for all the 110 reaches. One dataset of the resulting database was used to develop two models to estimate the erosion rates based on the governing factors: a formula derived from multiple linear regression (MLR) analysis and a decision tree (DT) obtained from J48 algorithm. The models obtained using these learning techniques were validated in another independent dataset. In this validation set, the DT model revealed better results. The models were also implemented in a torrent (test set), where the total debris-flow volume was known and two empirical methods (available in literature) were applied. This test revealed that both MLR and DT predict more accurately the final volume of the event than the empirical equations for volume prediction. Finally, a general DT was proposed, which includes three governing factors: sediment availability, channel-bed slope and channel cross section shape. This DT may be applied to other regions after adapting it regarding site-specific characteristics. 相似文献
114.
Bojan Nikolic Paul Alexander Garret Cotter Malcolm Longair Marcel Clemens 《Astrophysics and Space Science》2003,284(2):573-576
We present preliminary results of recent spatially resolved mid infrared (Mid-IR) spectroscopy with the MICHELLE instrument
on UKIRT of NGC 7469, observed as part of a larger programme to study a sample of starburst and AGN in the Mid-IR.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
115.
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
116.
Roshanka Ranasinghe Cilia Swinkels Arjen Luijendijk Dano Roelvink Judith Bosboom Marcel Stive DirkJan Walstra 《Coastal Engineering》2011
The recently developed Morphological Acceleration Factor (MORFAC) approach for morphodynamic upscaling enables numerical model simulations of coastal evolution at decadal to millennial time scales. Primarily due to the massive increase in modeling time scales it affords, the MORFAC approach is now standard in state-of-the-art commercially available coastal morphodynamic modeling suites. However, the general validity of the MORFAC concept for coastal applications has not yet been comprehensively investigated. Furthermore, a robust and objective method (as opposed to the subjective and inelegant trial and error method) for the a priori determination of the highest MORFAC that is suitable for a given simulation (i.e. critical MORFAC) does not currently exist. This communication presents some initial results of an ongoing, long-term study that attempts to rigorously and methodically investigate the limitations and strengths of the MORFAC approach. Based on the results of a strategically designed numerical modeling exercise using the morphodynamic model Delft3D, two main outcomes are presented. First, the main dependencies and sensitivities of the MORFAC approach to fundamental forcing conditions and model parameters are elucidated. Second, a criterion based on the Courant–Friedrichs–Levy (CFL) condition for bed form propagation that maybe used as a guide to determine the critical MORFAC a priori is proposed. 相似文献
117.
118.
Both climate change and river rehabilitation projects induce changes in floodplain sedimentation. Notably along the lower River Rhine, the sediment deposition patterns and rates are subject to change. To assess the magnitude of these changes, we developed the MoCSED model, a floodplain sedimentation model within a geographical information system for the lower Rhine River. We based MoCSED on the ‘method of characteristics’ (MoC), a particle tracking method that minimizes numerical dispersion. We implemented the MoCSED model in the PCRaster dynamic modelling language. The model input comprises initial suspended sediment concentrations, water levels, flow velocities, and longitudinal and transverse dispersivities. We used a combination of the Krone and Chen concepts to calculate the subsequent sedimentation (SED routine). We compared the model results with sediment trap data for the Bemmel floodplain along the Dutch Waal River during the 2003 inundation. This comparison showed that MoCSED was able to simulate the pattern of sediment deposition. In addition, the model proved to be an improvement in comparison with a conventional raster‐based floodplain sedimentation model for the lower River Rhine. In future, MoCSED may serve well to study the impact of a changing discharge regime due to climate change and floodplain rehabilitation plans on deposition of sediments. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
119.
We investigate sources of both dissolved and particulate organic carbon in the St Lawrence River from its source (the Great Lakes outlet) to its estuary, as well as in two of its tributaries. Special attention is given to seasonal interannual patterns by using data collected on a bi‐monthly basis from mid‐1998 to mid‐2003. δ13C measurements in dissolved inorganic carbon, dissolved organic carbon (DOC) and particulate organic carbon (POC), as well as molar C : N in particulate organic matter (POM), are used to bring insight into the dynamic between aquatic versus terrigenous sources. In addition, 14C activities of DOC were measured at the outlet of the St Lawrence River to its estuary to assess a mean age of the DOC exported to the estuary. In the St Lawrence River itself, aquatically produced POC dominates terrestrially derived POC and is depleted in 13C by approximately 12‰ versus dissolved CO2. In the Ottawa River, the St Lawrence River's most important tributary, the present dataset did not allow for convincing deciphering of POC sources. In a small tributary of the St Lawrence River, aquatically produced POC dominates in summer and terrestrially derived POC dominates in winter. DOC seems to be dominated by terrestrially derived organic matter at all sampling sites, with some influence of DOC derived from aquatically produced POC in summer in the St Lawrence River at the outlet of the Great Lakes and in one of its small tributaries. The overall bulk DOC is relatively recent (14C generally exceeding 100% modern carbon) in the St Lawrence River at its outlet to the estuary, suggesting that it derives mainly from recent organic matter from topsoils in the watershed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
120.
Using pressure fields classified by the SANDRA algorithm, this study investigates the changes in the relationship between North Atlantic/European sea level pressure (SLP) and gridded European winter (DJF) temperature and precipitation back to 1750. Important changes in the frequency of the SLP clusters are found, though none of them indicating significant long-term trends. However, for the majority of the SLP clusters a tendency toward overall warmer and partly wetter winter conditions is found, most pronounced over the last decades. This suggests important within-type variations, i.e. the temperature and precipitation fields related to a particular SLP pattern change their characteristics over time. Using a decomposition scheme we find for temperature and precipitation that within-type-related variations dominate over those due to changed frequencies of the SLP clusters: Approximately 70% (60%) of European winter temperature (precipitation) variations can be explained by within-type changes, most strongly expressed over Eastern Europe and Scandinavia. This indicates that the current European winter warming cannot be explained by changed frequencies of the SLP patterns alone, but to a larger degree by changed characteristics of the patterns themselves. Potential sources of within-type variations are discussed. 相似文献