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By HEATHER D. GRAVEN † BRITTON B. STEPHENS THOMAS P. GUILDERSON TERESA L. CAMPOS DAVID S. SCHIMEL J. ELLIOTT CAMPBELL RALPH F. KEELING 《Tellus. Series B, Chemical and physical meteorology》2009,61(3):536-546
Measurements of Δ14 C in atmospheric CO2 are an effective method of separating CO2 additions from fossil fuel and biospheric sources or sinks of CO2 . We illustrate this technique with vertical profiles of CO2 and Δ14 C analysed in whole air flask samples collected above Colorado, USA in May and July 2004. Comparison of lower tropospheric composition to cleaner air at higher altitudes (>5 km) revealed considerable additions from respiration in the morning in both urban and rural locations. Afternoon concentrations were mainly governed by fossil fuel emissions and boundary layer depth, also showing net biospheric CO2 uptake in some cases. We estimate local industrial CO2 :CO emission ratios using in situ measurements of CO concentration. Ratios are found to vary by 100% and average 57 mole CO2 :1 mole CO, higher than expected from emissions inventories. Uncertainty in CO2 from different sources was ±1.1 to ±4.1 ppm for addition or uptake of −4.6 to 55.8 ppm, limited by Δ14 C measurement precision and uncertainty in background Δ14 C and CO2 levels. 相似文献
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Sedimentologists recognize that development of a fine‐resolution, truly three‐dimensional analytical tool is essential if the internal structure of an opaque material is to be examined. This paper therefore seeks to: (i) test the viability of magnetic resonance imaging for sedimentological research; and (ii) investigate fine‐sediment infiltration into gravel beds. The results of six experiments are analysed quantitatively using Image J post‐processing software. Data indicate that magnetic resonance imaging‐based measurements of particle axes and volumes are comparable with standard laboratory techniques. Furthermore, the technique permits visualization and analysis of differences in the pattern of fine‐sediment infiltration (median particle diameter, d) into a framework of gravel (median particle diameter, D). Data clearly illustrate a siltation process for samples of D/d = 34 and a sealing process for samples of D/d = 7 where the seal is restricted to a depth equal to 2D. This pore‐scale visualization is valuable to the understanding of hydraulic–sediment–habitat interactions. 相似文献
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CLARENCE KIDSON DAVID D. GILBERTSON JOHN R. HAYNES ALAN HEYWORTH CLEDWYN E. HUGHES ROBIN C. WHATLEY 《Boreas: An International Journal of Quaternary Research》1978,7(4):215-228
Sands and gravels underlain by silts and clays, known as the Burtle Beds, from the Somerset Levels of South West England have been examined in a specially excavated pit. The Mollusca, Foraminifera and the Ostracoda, and the sparse macroscopic plant remains included in the deposit, all indicate a prgressive marine transgression in which water temperatures obtained approximating to those of the present sea in the adjacent Bristol Channel. The deposits are shown to be estuarine/marine near shore and intertidal sediments of interglacial age. Radiometric assays and studies of palaeomagnetism have failed to indicate clearly which interglacial marine transgressive phase is involved. Geomorphological considerations supported to some extent by the Ostracoda suggest that a last interglacial (Ipswichian) age is more likely than an earlier (Hoxnian?) date. Estimates of the height of sea levels involved are, of necessity, based on evidence which cannot be regarded as wholly reliable. Having regard to the environmental conditions indicated by the included fauna, and making allowance for post depositional erosion, it is suggested that mean sea level at the height of the ‘Burtle’ transgression was between 9 and 12 m above that of the present (O. D.). Assuming a similar tidal range to that of today, a MHWST (Mean High Water of Spring Tides) level of between 15 and 18 m above O. D. is indicated 相似文献
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Alpine valley heads on the Antarctic Peninsula 总被引：1，自引：0，他引：1
Landform assemblages may be useful for elucidating glaciological changes in West Antarctica. Numerous nunataks in the Antaretic Peninsula are highly dissected by alpine valley heads (corries, cirque-headed valleys, etc.). It is believed that these have been cut by wet-based mountain glaciation before and during the build up of the ice-sheet. though the smallest ones may have formed later at times when the ice-sheet was insufficiently thick to submerge them. Dimensions of the features suggest that the main alpine glaciation was in the Miocene. Morphometric analysis of 1663 alpine valley heads has been based on satellite imagery, concentrating on regional variations in frequency, size and orientation. Length of alpine glaciation is believed to be an important control of size. Orientation is believed to have been influenced by palaeoclimate as well as topography. During early, more marginal glaciations poleward and lee-side sites were occupied by corrie glaciers, with more windward sites being added as glaciation intensified, followed by northerly orientations under more recent polar conditions. Comparisons have also been made with other morphometric studies of corries in Antarctica and elsewhere. 相似文献
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Abstract— Analytical scanning electron microscopy has been used to investigate the surface textures and compositions of newly exposed shatter cones from the 1.85 Ga Sudbury impact structure, Canada. Unusual surface microstructures are observed at the micron scale, including silicate melt smears, melt fibres and melt splats. Silicate and Ni-rich spherules up to 5 μm in diameter adorn earlier-formed surface features, and we interpret these to be condensates formed due to shock-induced vaporization of the shatter cone surfaces. The development of striations on the shatter cones is attributed to shock-related fracture and slip. Formation of melts and spherules indicates that the highest ranks of shock metamorphism (Stages IV and V) were realized, but only on a very localized scale. Shatter cone surfaces are, therefore, likely sites for the development of high-pressure polymorphs and, if the chemistry is appropriate, fullerenes. As such, they may be equivalent to “Type A” pseudotachylytes and shock veins in meteorites. 相似文献
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This paper deals with the experimental activity carried out in the field of flood monitoring at the Civil Engineering Department of Florence University (Italy) in cooperation with EOSAT (USA) and Eurimage (Italy). The aim of the study is to research the possibilities of satellite data utilization to aid in modelling of the hydrological behaviour of a river basin and monitoring flood emergencies. The area selected for the study is the Fucecchio Marsh (Tuscany, Italy), in which flooding events are very frequent. This paper describes the results of the study, with particular reference to the use of Landsat TM data to estimate soil water content, and the use of ERS SAR data to analyse flash flood events. © 1997 John Wiley & Sons, Ltd. 相似文献
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JESSICA TROFIMOVS JODIE K. FISHER HEATHER A. MACDONALD PETER J. TALLING R. STEPHEN J. SPARKS MALCOLM B. HART CHRISTOPHER W. SMART GEORGES BOUDON CHRISTINE DEPLUS JEAN‐CHRISTOPHE KOMOROWSKI ANNE LE FRIANT STEVEN G. MORETON MELANIE J. LENG 《Sedimentology》2010,57(3):735-759
Bioclastic flow deposits offshore from the Soufrière Hills volcano on Montserrat in the Lesser Antilles were deposited by the largest volume sediment flows near this active volcano in the last 26 kyr. The volume of these deposits exceeds that of the largest historic volcanic dome collapse in the world, which occurred on Montserrat in 2003. These flows were most probably generated by a large submarine slope failure of the carbonate shelf comprising the south‐west flank of Antigua or the east flank of Redonda; adjacent islands that are not volcanically active. The bioclastic flow deposits are relatively coarse‐grained and either ungraded or poorly graded, and were deposited by non‐cohesive debris flow and high density turbidity currents. The bioclastic deposit often comprises multiple sub‐units that cannot be correlated between core sites; some located just 2 km apart. Multiple sub‐units in the bioclastic deposit result from either flow reflection, stacking of multiple debris flow lobes, and/or multi‐stage collapse of the initial landslide. This study provides unusually precise constraints on the age of this mass flow event that occurred at ca 14 ka. Few large submarine landslides have been well dated, but the slope failures that have been dated are commonly associated with periods of rapid sea‐level change. 相似文献
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