On the background photochemistry of tropospheric ozone   总被引：3，自引：0，他引：3  

PAUL J. CRUTZEN  MARK G. LAWRENCE  ULRICH PÖSCHL 《Tellus. Series B, Chemical and physical meteorology》1999,51(1):123-146

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Reduction of biosphere life span as a consequence of geodynamics   总被引：1，自引：0，他引：1  

S. FRANCK  A. BLOCK  W. VON BLOH  C. BOUNAMA  H. J. SCHELLNHUBER  Y. SVIREZHEV 《Tellus. Series B, Chemical and physical meteorology》2000,52(1):94-107

The long‐term co‐evolution of the geosphere–biospere complex from the Proterozoic up to 1.5 billion years into the planet's future is investigated using a conceptual earth system model including the basic geodynamic processes. The model focusses on the global carbon cycle as mediated by life and driven by increasing solar luminosity and plate tectonics. The main CO₂ sink, the weathering of silicates, is calculated as a function of biologic activity, global run‐off and continental growth. The main CO₂ source, tectonic processes dominated by sea‐floor spreading, is determined using a novel semi‐empirical scheme. Thus, a geodynamic extension of previous geostatic approaches can be achieved. As a major result of extensive numerical investigations, the "terrestrial life corridor", i.e., the biogeophysical domain supporting a photosynthesis‐based ecosphere in the planetary past and in the future, can be identified. Our findings imply, in particular, that the remaining life‐span of the biosphere is considerably shorter (by a few hundred million years) than the value computed with geostatic models by other groups. The "habitable‐zone concept" is also revisited, revealing the band of orbital distances from the sun warranting earth‐like conditions. It turns out that this habitable zone collapses completely in some 1.4 billion years from now as a consequence of geodynamics.  相似文献   

湖南会同寒武纪早期有机碳同位素地层学研究          下载免费PDF全文

王丹  凌洪飞  ULRICH Struck  姚素平  李达  卫炜  魏广祎 《高校地质学报》2016,22(2):274

寒武纪早期是地球海洋环境与生命演化的关键时期,但目前扬子东南缘深水相区的早寒武纪地层尚缺乏系统、精确 的地层对比工作。该文选取湖南省怀化地区会同钻孔剖面（深水相区） 的留茶坡组硅质岩、小烟溪组黑色页岩为研究对 象,进行了高分辨的有机碳同位素（δ13Corg） 地层对比,结果在会同剖面自下而上识别出四个正漂移（P1、P2、P3和P4） 与两个负漂移（N1和N2）,结合其他剖面的生物化石记录和锆石U-Pb年龄资料,将会同剖面有机碳同位素与湖南其他 剖面,以及和云南和三峡等地浅水相区剖面的有机碳、无机碳同位素曲线进行对比,认为扬子东南缘埃迪卡拉系-寒武 系界线在湖南深水相区可放置于留茶坡组上部较大的有机碳同位素负漂移（Basal Cambrian Carbon isotope Excursion, BACE） 出现的位置,但由于钻孔深度不够,所以该负漂移未在会同剖面获得,而P1、P2和P3分别对应于寒武系的ZHUCE （ZHUjiaqing Carbon isotope Excursion,第二阶）、CARE （Cambrian Arthropod Radiation isotope Excursion,第三阶） 和MICE（MIngxinsi Carbon Isotope Excursion,第四阶） 正漂移,N1 和N2 分别对应于寒武系的SHICE （SHIyantou Carbon isotope Excursion,第二阶） 和AECE（Archaeocyathid Extinction Carbon isotope Excursion,第四阶） 负漂移,因此会同剖面留茶坡组顶部至小烟溪组底部属于寒武系第二阶,小烟溪组下部属于寒武系第三阶,而小烟溪组中-上部属于寒武系第四阶,而顶 部是否达到第四阶顶部尚无法确认。碳同位素的负漂移可能是海侵时期上升流水体将底层富含12C还原水体带至浅水地区所 致,并分别与埃迪卡拉动物群、小壳化石动物群和古杯动物的灭绝密切相关;而在生物繁盛时期,海洋初级生产力升高, 有机质埋藏增加,导致碳同位素的正漂移。  相似文献   

Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis   总被引：2，自引：1，他引：1  

P. HASALOVÁ  K. SCHULMANN  O. LEXA  P. &#;TÍPSKÁ  F. HROUDA  S. ULRICH  J. HALODA  P. TÝCOVÁ 《Journal of Metamorphic Geology》2008,26(1):29-53

A detailed field study reveals a gradual transition from high‐grade solid‐state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular, foliation‐parallel bodies of nebulitic migmatite within the eastern part of the Gföhl Unit (Moldanubian domain, Bohemian Massif). The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well‐equilibrated banded microstructure by crystallization of new interstitial phases (Kfs, Pl and Qtz) along feldspar boundaries and by resorption of relict feldspar and biotite. The grain size of all felsic phases decreases continuously, whereas the population density of new phases increases. The new phases preferentially nucleate along high‐energy like–like boundaries causing the development of a regular distribution of individual phases. This evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases. To explain these data, a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation. In this model, infiltrating melt passes pervasively along grain boundaries through the whole‐rock volume and changes completely its macro‐ and microscopic appearance. It is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation. The melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding, indicating that the melt distribution was controlled by the deformation of the solid framework. The microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms. The migmatite microstructures developed by granular flow accompanied by melt‐enhanced diffusion and/or melt flow. However, an AMS study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains.  相似文献   

Expert system for the selection of methods to calculate design flood flows     

EDUARDO A. VARAS  MARCELO VON CHRISMAR 《水文科学杂志》2013,58(6):739-749

Abstract

This paper presents an expert system to help select the best method to estimate design flood flows for civil engineering works based upon the procedures available, the nature and characteristics of the basin and existing hydrological records. The system presents the user with a list of possible methods ranked in descending grade order and optionally presents explanations which support the selected choices. Ordering is achieved using the knowledge base provided by the expert. The system recommends procedures for both preliminary estimates and final designs. The system also constitutes a valuable aid for junior engineers and experienced hydrologists in the selection of methods. Its conceptual structure can be easily generalized to treat other problems of a similar nature in the field of hydrology and water resources.  相似文献   

Retrieval of aerosol optical thickness for desert conditions using MERIS observations during the SAMUM campaign     

By TILMAN DINTER  WOLFGANG VON HOYNINGEN-HUENE  JOHN P. BURROWS  ALEXANDER KOKHANOVSKY  EIKE BIERWIRTH  MANFRED WENDISCH  DETLEF MÜLLER  RALPH KAHN  MOHAMMED DIOURI 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):229-238

Approximately 30% of the land surface is arid, having desert or semi-desert conditions. Aerosol originating from these regions plays a significant role in climate and atmospheric chemistry of the atmosphere. Retrieving aerosol properties from space-borne platforms above desert conditions, where the surface reflectance is usually very bright, is a challenging task. The proportion of the surface to top of atmosphere (TOA) reflectance can reach values over 90%, especially for wavelength above 500 nm. For these reasons detailed knowledge of aerosol and surface optical properties from these regions is required to separate atmosphere from intrinsically bright surfaces.
An approach to retrieve aerosol properties over arid and semi-arid regions based on the Bremen Aerosol Retrieval (BAER) has been developed and validated within the Dust Aerosol Retrievals from Space-Born Instruments (DREAMS) Project, which is part of the Saharan Mineral Dust Experiment ( SAMUM, 2006 ). Combining measurements of the backscattered radiation from the Medium Resolution Imaging Spectrometer (MERIS) instrument aboard Environmental Satellite (ENVISAT) and ground-based measurements in Morocco in radiation closure experiments yields the aerosol optical properties of mineral dust at selected locations.  相似文献   

THE INFLUENCE OF RIPARIAN VEGETATION COVER ON DIFFUSE LATERAL SEDIMENT CONNECTIVITY AND BIOGEOMORPHIC PROCESSES IN A MEDIUM‐SIZED AGRICULTURAL CATCHMENT,AUSTRIA     

RONALD E. POEPPL  MARGRETH KEILER  KIRSTEN VON ELVERFELDT  IRENE ZWEIMUELLER  THOMAS GLADE 《Geografiska Annaler: Series A, Physical Geography》2012,94(4):511-529

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Temporal and spatial sedimentation rate variabilities in the eastern Gotland Basin, the Baltic Sea     

CHRISTIAN CHRISTIANSEN  HELMAR KUNZENDORF  KAY-CHRISTIAN EMEIS  RUDOLF ENDLER  ULRICH STRUCK  THOMAS NEUMANN  VADIM SIVKOV 《Boreas: An International Journal of Quaternary Research》2002,31(1):65-74

The present study examines sedimentation rates in the eastern Gotland Basin using a variety of methods that reveal considerable heterogeneity in the rates, both spatially and temporally. High-resolution seismic recordings and correlation with long sediment cores indicate increased thickness of strata and higher sedimentation rates (0.75 mm a -1 ) in the eastern part of the basin than in the western part (0.23 mm a -1 ) since the Littorina transgression some 8000 14 C years BP. This difference is apparently a consequence of a counterclockwise near-bottom circulation in the basin with periodically high current speeds that cause winnowing on the steep SE slope of the basin and differential settling of sediments in areas of low current speeds. On shorter time scales, recent sediment accumulation rates based on radiometric dating ( 210 Pb) are in general twice as high as those observed 25 years ago using the same method. The higher modern rates, compared to those of the 1970s, may partly be due to increased eutrophication, as more carbon is buried in the sediment, and partly due to increased erosion in shallow water areas. However, strong lateral variations are evident. The average sediment accumulation rates vary between 119 and 340 g m -2 a -1 (corresponding to sedimentation rates of 2.1-2.5 mm a -1 ) in the deepest part of the basin. Very high rates (6100 g m -2 a -1 , corresponding to sedimentation rates of 30 mm a -1 ) are observed on an intraslope basin site (offshore Latvia) at a water depth of only 70 m. The radiometrically determined sediment accumulation rates are up to three times higher than those estimated from average water column concentrations of suspended matter and from sediment trap flux rates. The discrepancy suggests that sedimentation in the deep basin may have a substantial contribution from near-bottom lateral transport.  相似文献   

An efficient and accurate representation of complex oceanic and biospheric models of anthropogenic carbon uptake   总被引：6，自引：2，他引：6  

FORTUNAT JOOS  MICHELE BRUNO  ROGER FINK  ULRICH SIEGENTHALER  THOMAS F. STOCKER  CORINNE LE QUÉRÉ  JORGE L. SARMIENTO 《Tellus. Series B, Chemical and physical meteorology》1996,48(3):397-417

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FLARE MULTI-LINE 2D-SPECTROSCOPY     

MEIN  P.  MEIN  N.  MALHERBE  J.-M.  HEINZEL  P.  KNEER  F.  VON UEXKULL  M.  STAIGER  J. 《Solar physics》1997,172(1-2):161-170

A small flare was observed at the Teide Observatory on October 5, 1994. Simultaneous data were obtained at the German Vacuum Tower Telescope (VTT) with the MSDP spectrograph providing high-resolution imaging spectroscopy in two chromospheric lines, and the Gregory Coudé Telescope (GCT) providing information about the magnetic field. Basic flare characteristics are:The area of the flare kernel ( 2 x 2 arc sec) is similar in H and Caii 8542 Å.The early phase of the flare is characterized by a blue asymmetry in H and a red one in Caii 8542 Å line.The evolutions of line profiles are different; the red asymmetry observed in the Caii line is detected a few seconds later in H.The maximum asymmetry of the Caii line does not coincide with the maximum brightness.The flare occurs in a region of a strong horizontal gradient of the line-of-sight component of the magnetic field.Brightness and asymmetry in H and Caii are discussed in the context of standard flare models and velocity fields. Our observations suggest that a magnetic reconnection could occur at low levels of the solar atmosphere.  相似文献