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MICHAEL ZECH ANDREI ANDREEV ROLAND ZECH STEFANIE MÜLLER ULRICH HAMBACH MANFRED FRECHEN WOLFGANG ZECH 《Boreas: An International Journal of Quaternary Research》2010,39(3):540-550
Zech, M., Andreev, A., Zech, R., Müller, S., Hambach, U., Frechen, M. & Zech, W.: Quaternary vegetation changes derived from a loess‐like permafrost palaeosol sequence in northeast Siberia using alkane biomarker and pollen analyses. Boreas, Vol. 39, pp. 540–550. 10.1111/j.1502‐3885.2009.00132.x. ISSN 0300‐9483 Alkane biomarker and pollen data were obtained from a 15‐m‐high and probably c. 240‐kyr‐old loess‐like permafrost palaeosol sequence (‘Tumara Palaeosol Sequence’, TPS) in northeast Siberia. The alkane results were corrected for degradation effects by applying an end‐member model and were evaluated by comparing them with the palynological results. The two data sets are generally in good agreement and suggest that the lower part of the TPS developed mainly under larch forests, whereas the upper part of the sequence reflects the expansion of mammoth steppes during the Weichselian glaciation and finally reforestation during the Lateglacial and the early Holocene. For the lower part of the TPS, the palaeoclimatic interpretation according to modern analogue methods would indicate warm, interglacial conditions, but this is at odds with the climate chronostratigraphy based on a multi‐proxy palaeopedological approach and numeric dating. Provided that the correlation of the discussed stratigraphic unit with the Late Saalian glaciation and the Marine Oxygen Isotope Stage 6 is correct, our results suggest that temperature was not a limiting factor for tree growth at that time. Furthermore, it seems very likely that it was not mainly temperature changes but rather increasing aridity and continentality during the course of the last glacial that favoured the expansion of the mammoth steppe. 相似文献
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Dust mobilization and transport in the northern Sahara during SAMUM 2006 – a meteorological overview
By PETER KNIPPERTZ ALBERT ANSMANN DIETRICH ALTHAUSEN DETLEF MÜLLER MATTHIAS TESCHE EIKE BIERWIRTH TILMAN DINTER THOMAS MÜLLER WOLFGANG VON HOYNINGEN-HUENE KERSTIN SCHEPANSKI MANFRED WENDISCH BERND HEINOLD KONRAD KANDLER REAS PETZOLD LOTHAR SCHÜTZ INA TEGEN 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):12-31
The SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5-km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper-level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut-off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples. 相似文献
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Earlier modelling studies have shown the difficulty of accurately simulating snowmelt infiltration into frozen soil using the hydraulic model approach. Comparison of model outputs and field measurements have inferred the occurrence of rapid flow even during periods when the soil is still partly frozen. A one-dimensional, physically based soil water and heat model (SOIL) has been complemented with a new two-domain approach option to simulate preferential flow through frozen layers. The ice is assumed to be first formed at the largest water filled pore upon freezing. Infiltrating water may be conducted rapidly through previously air-filled pores which are not occupied by ice. A minor fraction of water is slowly transferred within the liquid water domain, which is absorbed by the solid particles. A model validation with field measurements at a location in the middle-east of Sweden indicated that the two-domain approach was suitable for improving the prediction of drainage during snowmelting. In particular, the correlation between simulated and observed onset of drainage in spring was improved. The validation also showed that the effect of the high flow domain was highly sensitive to the degree of saturation in the topsoil during freezing, as well as to the hydraulic properties at the lower frost boundary regulating the upward water flow to the frozen soil and ice formation. 相似文献
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作为从出山口至入海河口直线距离仅约20 km的短途河流,小凌河下游地区及相邻潮间带表层发育了砾石质冲洪积扇、曲流河道滞留相-点状砂坝-泛滥平原与洼地、贝壳砾石海滩、盐沼、开放潮坪下部与中上部等一系列沉积环境。通过沉积地层学、年代地层学及新构造等方面的综合研究,1)将中、晚全新世地层划分为7个年代地层单元,2)发现了夏-西周、元末-明初两道年龄分别约为2 050～650 BC和1 350 AD的古海岸线,3)确立了春秋、中唐-北宋初、"小冰期"结束以来3次小凌河沉积期,最有可能发育的时间进一步限定在约650～400 BC(第1期)、约700～1 000 A(D第2期)和1 850 AD以来(第3期),4)提出了NW向与NE向构造加剧小凌河下游曲流发育的假说。 相似文献
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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
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
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A core from the southern mesotrophic basin of Lake George, New York, shows enrichment in the concentration of trace elements near its top. By contrast, a core from the northern oligotrophic basin shows, with the exception of manganese, an almost constant trace-element concentration throughout the core. Man's activities in the watershed surrounding the southern basin are responsible for enrichment in the trace-element concentration of newly deposited bottom sediments. Increase in trace-element concentration is not paralleled by increase in organic-carbon concentration. 相似文献