Snow cornice dynamics as a control on plateau edge erosion in central Svalbard     

Markus Eckerstorfer  Hanne H. Christiansen  Stephan Vogel  Lena Rubensdotter 《地球表面变化过程与地形》2013,38(5):466-476

Snow cornices grow extensively on leeward edges of plateau mountains in central Svalbard. A dominant wind direction, a snowdrift source area and a sharp slope transition largely control the formation of snow cornices in a barren peri‐glacial landscape. Seasonal snow cornice dynamics control bedrock weathering and erosion in sedimentary bedrock on the Gruvefjellet plateau edge in the valley Longyeardalen. Air, snow and ground temperature sensors, as well as automatic time‐lapse cameras on a leeward facing plateau edge were used to study seasonal cornice dynamics. These techniques allowed for monitoring of cornice accretion, deformation and collapse/melting in great detail. The active layer of the top plateau edge is characterized by high moisture content due to rain before freeze‐up in autumn and cornice meltdown during spring thaw. Thus frost weathering there can be very efficient in this otherwise cold and dry environment. Within the first autumn snowstorms, a vertical fully developed cornice was in place (190 cm thick). The backwall surface beneath the thickest part of the cornice remained in the ice segregation ‘frost cracking window’ for almost nine months. Highly weathered rock material from the plateau edge is thus incorporated into the cornice during cornice accretion. Brittle snow deformation leads to the opening of cornice tension cracks between the cornice mass and the snowpack on the plateau. These cracks are a prerequisite for cornice collapses, and often trigger cornice fall avalanches on the slope beneath. In these open cornice tension cracks, weathered rock debris, plucked from the plateau edge, can be visible, demonstrating the erosional property of the cornices. The cornice will either collapse or melt, resulting in suspended sediment transport downslope by cornice fall avalanche or release as rock fall respectively. Therefore, cornices both promote and trigger high weathering rates on Gruvefjellet, and thus control presently the development of the rockwall free faces and the talus cones. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Erratum to: Garnet and spinel in fertile and depleted mantle: insights from thermodynamic modelling     

Luca?ZibernaEmail author  Stephan?Klemme  Paolo?Nimis 《Contributions to Mineralogy and Petrology》2014,168(2):1036

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Spatial Variability of Stable Isotope Ratios in Oysters (Crassostrea gigas) and Primary Producers Along an Estuarine Gradient (Bay of Brest, France)     

Violette Marchais  Gauthier Schaal  Jacques Grall  Anne Lorrain  Caroline Nerot  Pierre Richard  Laurent Chauvaud 《Estuaries and Coasts》2013,36(4):808-819

This study aimed at characterizing the diet of the oyster Crassostrea gigas along an estuarine gradient in the Bay of Brest (France), through stable isotope (δ¹³C and δ¹⁵N) measurements in primary producers and wild oysters. The contribution of different potential food sources to the diet of C. gigas was estimated at high spatial resolution (over a gradient of 40 km with samplings every 2 km) to identify ecological transition zones and highlighted the dominance of resuspended biofilm in oysters diet. Although the different primary producers did not display any obvious pattern along the estuarine gradient, the stable isotope signatures of C. gigas differed among estuarine, inner Bay, and open sea sites. In particular, a striking ¹⁵N depletion pattern was found along the gradient which allowed to identify seven homogeneous groups. Moreover, some unexpected values found at two stations within the estuary revealed localized anthropogenic disturbances. Overall, our results suggest that suspension feeders might be better indicators of ecosystem functioning than primary producers and reflect the different ecological processes occurring along estuarine gradients, including localized anthropogenic inputs. We suggest that the usefulness of suspension feeders as indicators of ecosystem functional typology lies in the dominance of benthic material in their diet, which results in locally occurring processes being reflected in oysters’ stable isotope ratios.  相似文献   

Application of the water balance model J2000 to estimate groundwater recharge in a semi-arid environment: a case study in the Zarqa River catchment, NW-Jordan   总被引：1，自引：0，他引：1  

Stephan Schulz  Christian Siebert  Tino Rödiger  Marwan M. Al-Raggad  Ralf Merz 《Environmental Earth Sciences》2013,69(2):605-615

Pollution and overexploitation of scarce groundwater resources is a serious problem in the Zarqa River catchment, Jordan. To estimate this resource’s potential, the amount and spatial distribution of groundwater recharge was calculated by applying the hydrological model J2000. The simulation period is composed of daily values gathered over a 30-year period (July 1977 to June 2007). The figure finally obtained for estimated groundwater recharge of the Zarqa River catchment is 105 × 10⁶ m³ per year (21 mm a^?1). This is 19 % higher than the value previously assumed to be correct by most Jordanian authorities. The average ratio of precipitation to groundwater recharge is 9.5 %. To directly validate modelled groundwater recharge, two independent methods were applied in spring catchments: (1) alteration of stable isotope signatures (δ¹⁸O, δ²H) between precipitation and groundwater and (2) the chloride mass balance method. Recharge rates determined by isotopic investigations are 25 % higher, and recharge rates determined by chloride mass balance are 9 % higher than the modelled results for the corresponding headwater catchments. This suggests a reasonably modelled safe yield estimation of groundwater resources.  相似文献   

Organic sedimentary deposits in Titan’s dry lakebeds: Probable evaporite     

Jason W. Barnes  Jacob Bow  Jacob Schwartz  Robert H. Brown  Jason M. Soderblom  Alexander G. Hayes  Graham Vixie  Stéphane Le Mouélic  Sebastien Rodriguez  Christophe Sotin  Ralf Jaumann  Katrin Stephan  Laurence A. Soderblom  Roger N. Clark  Bonnie J. Buratti  Kevin H. Baines  Philip D. Nicholson 《Icarus》2011,216(1):136-140

We report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near Titan’s north pole in observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We show evidence that the deposits are evaporitic, making Titan just the third known planetary body with evaporitic processes after Earth and Mars, and is the first that uses a solvent other than water.  相似文献   

OSS (Outer Solar System): a fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt     

B. Christophe  L. J. Spilker  J. D. Anderson  N. André  S. W. Asmar  J. Aurnou  D. Banfield  A. Barucci  O. Bertolami  R. Bingham  P. Brown  B. Cecconi  J. -M. Courty  H. Dittus  L. N. Fletcher  B. Foulon  F. Francisco  P. J. S. Gil  K. H. Glassmeier  W. Grundy  C. Hansen  J. Helbert  R. Helled  H. Hussmann  B. Lamine  C. L?mmerzahl  L. Lamy  R. Lehoucq  B. Lenoir  A. Levy  G. Orton  J. Páramos  J. Poncy  F. Postberg  S. V. Progrebenko  K. R. Reh  S. Reynaud  C. Robert  E. Samain  J. Saur  K. M. Sayanagi  N. Schmitz  H. Selig  F. Sohl  T. R. Spilker  R. Srama  K. Stephan  P. Touboul  P. Wolf 《Experimental Astronomy》2012,34(2):203-242

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Stellar intensity interferometry: Prospects for sub-milliarcsecond optical imaging     

Dainis Dravins  Stephan LeBohec  Hannes Jensen  Paul D. Nuñez 《New Astronomy Reviews》2012,56(5):143-167

Using kilometric arrays of air Cherenkov telescopes at short wavelengths, intensity interferometry may increase the spatial resolution achieved in optical astronomy by an order of magnitude, enabling images of rapidly rotating hot stars with structures in their circumstellar disks and winds, or mapping out patterns of nonradial pulsations across stellar surfaces. Intensity interferometry (once pioneered by Hanbury Brown and Twiss) connects telescopes only electronically, and is practically insensitive to atmospheric turbulence and optical imperfections, permitting observations over long baselines and through large airmasses, also at short optical wavelengths. The required large telescopes (～10 m) with very fast detectors (～ns) are becoming available as the arrays primarily erected to measure Cherenkov light emitted in air by particle cascades initiated by energetic gamma rays. Planned facilities (e.g., CTA, Cherenkov Telescope Array) envision many tens of telescopes distributed over a few square km. Digital signal handling enables very many baselines (from tens of meters to over a kilometer) to be simultaneously synthesized between many pairs of telescopes, while stars may be tracked across the sky with electronic time delays, in effect synthesizing an optical interferometer in software. Simulated observations indicate limiting magnitudes around m_V = 8, reaching angular resolutions ～30 μarcsec in the violet. The signal-to-noise ratio favors high-temperature sources and emission-line structures, and is independent of the optical passband, be it a single spectral line or the broad spectral continuum. Intensity interferometry directly provides the modulus (but not phase) of any spatial frequency component of the source image; for this reason a full image reconstruction requires phase retrieval techniques. This is feasible if sufficient coverage of the interferometric (u, v)-plane is available, as was verified through numerical simulations. Laboratory and field experiments are in progress; test telescopes have been erected, intensity interferometry has been achieved in the laboratory, and first full-scale tests of connecting large Cherenkov telescopes have been carried out. This paper reviews this interferometric method in view of the new possibilities offered by arrays of air Cherenkov telescopes, and outlines observational programs that should become realistic already in the rather near future.  相似文献   

Recommendation for the discrimination of human-related and natural seismicity   总被引：1，自引：1，他引：0  

T. Dahm  D. Becker  M. Bischoff  S. Cesca  B. Dost  R. Fritschen  S. Hainzl  C. D. Klose  D. K��hn  S. Lasocki  Th. Meier  M. Ohrnberger  E. Rivalta  U. Wegler  Stephan Husen 《Journal of Seismology》2013,17(1):197-202

Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology.  相似文献   

The Lance Insertion Retardation meter (LIRmeter): an instrument for in situ determination of sea floor properties—technical description and performance evaluation     

Sebastian Stephan  Norbert Kaul  Heinrich Villinger 《Marine Geophysical Researches》2012,33(3):209-221

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Microstructure characteristics during hydrate formation and dissociation revealed by X-ray tomographic microscopy     

Stephan A. Klapp  Frieder Enzmann  Peter Walz  Thomas Huthwelker  Jürgen Tuckermann  J.-Oliver Schwarz  Thomas Pape  Edward T. Peltzer  Rajmund Mokso  David Wangner  Federica Marone  Michael Kersten  Gerhard Bohrmann  Werner F. Kuhs  Marco Stampanoni  Peter G. Brewer 《Geo-Marine Letters》2012,32(5-6):555-562

Despite much progress over the past years in fundamental gas hydrate research, frontiers to the unknown are the early beginning and early decomposition of gas hydrates in their natural, submarine environment: gas bubbles meeting ocean water and forming hydrate, and gas starting to escape from the surface of a hydrate grain. In this paper we report on both of these topics, and present three-dimensional microstructure results obtained by synchrotron radiation X-ray cryo-tomographic microscopy (SRXCTM). Hydrates can precipitate when hydrate-forming molecules such as methane exceed solubility, and combine with water within the gas hydrate stability zone. Here we show hydrate formation on surfaces of bubbles from different gas mixtures and seawater, based on underwater robotic in situ experiments in the deep Monterey Canyon, offshore California. Hydrate begins to form from the surrounding water on the bubble surfaces, and subsequently grows inward into the bubble, evidenced by distinct edges. Over time, the bubbles become smaller while gas is being incorporated into newly formed hydrate. In contrast, current understanding has been that hydrate decomposition starts on the outer surface of hydrate aggregates and grains. It is shown that in an early stage of decomposition, newly found tube structures connect well-preserved gas hydrate patches to areas that are dissociating, demonstrating how dissociating areas in a hydrate grain are linked through hydrate that is still intact and will likely decompose at a later stage.