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Dendrochronologically dated changes in the limit of pine in northernmost Finland during the past 7.5 millennia 总被引:3,自引:0,他引:3
SAMULI HELAMA MARKUS LINDHOLM MAURI TIMONEN MATTI ERONEN 《Boreas: An International Journal of Quaternary Research》2004,33(3):250-259
Postglacial changes in the occurrence of Scots pine in northernmost Finland and adjacent areas are indicated in data sets of megafossils dated to an accuracy of 1 year using analysis of tree rings. After adjustment for land uplift, results in the altitudinal and latitudinal extent and in the structure of the pine limit are compared in the context of megafossil and pollen evidence from Fennoscandia, the Kola Peninsula and Scotland. Temporal changes in tree density at the forest limit are estimated from chronology sample size. The record from the subregion of Enontekio shows a long-term retreat of pine, corresponding to summer cooling caused by orbital forcing. This long-term trend is superposed by shorter-term fluctuations, which is consistent with other proxy evidence of pine. An abrupt decline in the forest limit occurred during the first millennium BC in two major steps, with no indication of high-altitude pine germination between 800 BC and AD 100. The subregions of Inari and Utsjoki show significant fluctuations at the forest limit in tree density only. 相似文献
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Bianca KETTRUP Alexander DEUTSCH Markus OSTERMANN Pierre AGRINIER 《Meteoritics & planetary science》2000,35(6):1229-1238
Abstract— The 65 Ma Chicxulub impact structure, Mexico, with a diameter of ~180 km is the focus of geoscientific research because of its link to the mass extinction event at the Cretaceous‐Tertiary (K/T) boundary. Chicxulub, now buried beneath thick post‐impact sediments, is probably one of the best‐preserved terrestrial impact structures known. Because of its inaccessibility, only limited samples on the impact lithologies from a few drill cores are available. We report major element and Sr‐, Nd‐, O‐, and C‐isotopic data for Chicxulub impact‐melt lithologies and basement clasts in impact breccias of drill cores C‐1 and Y‐6, and for melt particles in the Chicxulub ejecta horizon at the K/T boundary in Beloc, Haiti. The melt lithologies with SiO2 ranging from 58 to ~63 wt% show significant variations in the content of Al, Ca, and the alkalies. In the melt matrix samples, δ13C of the calcite is about ?3%o. The δ18O values for the siliceous melt matrices of Y‐6 samples range from 9.9 to 12.4%o. Melt lithologies and the black Haitian glass have rather uniform 87Sr/86Sr ratios (0.7079 to 0.7094); only one lithic fragment displays 87Sr/86Sr of 0.7141. The Sr model ages TSrUR for most lithologies range from 830 to 1833 Ma; unrealistic negative model ages point to an open Rb‐Sr system with loss of Rb in a hydrothermal process. The 143Nd/144Nd ratios for all samples, except one basement clast with 143Nd/144Nd of 0.5121, cluster at 0.5123 to 0.5124. In an ?Nd‐?Sr diagram, impactites plot in a field delimited by ?Nd of ?2 to ?6, and ?Sr of 55 to 69. This field is not defined by the basement lithologies described to occur as lithic clasts in impact breccias and Cretaceous sediments. At least one additional intermediate to mafic precursor component is required to explain the data. 相似文献
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STEPHAN GRUBER MARKUS EGLI ISABELLE GÄRTNER‐ROER MARTIN HOELZLE 《Geografiska Annaler: Series A, Physical Geography》2012,94(2):177-182
Gruber, S., Egli, M., Gärtner‐Roer, I. and Hoelzle, M., 2012. Preface: The mountain cryosphere – a holistic view on processes and their interactions. Geografiska Annaler: Series A, Physical Geography, ??, ??–??. doi :10.1111/j.1468‐0459.2012.00468.x 相似文献
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Zircons from Syros, Cyclades, Greece--Recrystallization and Mobilization of Zircon During High-Pressure Metamorphism 总被引:27,自引:1,他引:27
TOMASCHEK FRANK; KENNEDY ALLEN K.; VILLA IGOR M.; LAGOS MARKUS; BALLHAUS CHRIS 《Journal of Petrology》2003,44(11):1977-2002
Zircons were studied from high-pressure/low-temperature metamorphosedmeta-igneous lithologies from Syros. These rocks carry severalzircon generations related to each other by dissolutionreprecipitationprocesses. One generation is pristine zircon that shows growthzoning, relatively elevated contents of trivalent cations andhigh Th/U ratios. The other end-member is a skeletal zircongeneration with negligible trivalent cation contents and lowTh/U ratios ( 相似文献
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By SAMUEL HAMMER FELIX VOGEL MARKUS KAUL INGEBORG LEVIN 《Tellus. Series B, Chemical and physical meteorology》2009,61(3):547-555
The hydrogen-to-carbon monoxide (H2 /CO) emission ratio of anthropogenic combustion sources was determined from more than two years of quasi-continuous atmospheric observations in Heidelberg (49°24' N, 8°42' E), located in the polluted Rhein-Neckar region. Evaluating concurrent mixing ratio changes of H2 and CO during morning rush hours yielded mean molar H2 /CO ratios of 0.40 ± 0.06, while respective results inferred from synoptic pollution events gave a mean value of 0.31 ± 0.05 mole H2 /mole CO. After correction for the influence of the H2 soil sink on the measured ratios, mean values of 0.46 ± 0.07 resp. 0.48 ± 0.07 mole H2 /mole CO were obtained, which are in excellent agreement with direct source studies of traffic emissions in the Heidelberg/Mannheim region (0.448 ± 0.003 mole H2 /mole CO). Including results from other European studies, our best estimate of the mean H2 /CO emission ratio from anthropogenic combustion sources (mainly traffic) ranges from 0.45 to 0.48 mole H2 /mole CO, which is about 20% smaller than the value of 0.59 mole H2 /mole CO which is frequently used as the basis to calculate global H2 emissions from anthropogenic combustion sources. 相似文献
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By BERNADETT WEINZIERL REAS PETZOLD MICHAEL ESSELBORN MARTIN WIRTH KATHARINA RASP KONRAD KANDLER LOTHAR SCHÜTZ PETER KOEPKE MARKUS FIEBIG 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):96-117
The Saharan Mineral Dust Experiment (SAMUM) was conducted in May/June 2006 in southern Morocco. As part of SAMUM, airborne in situ measurements of the particle size distribution in the diameter range 4 nm < D p < 100 μm were conducted. The aerosol mixing state was determined below D p < 2.5 μm. Furthermore, the vertical structure of the dust layers was investigated with a nadir-looking high spectral resolution lidar (HSRL). The desert dust aerosol exhibited two size regimes of different mixing states: below 0.5 μm, the particles had a non-volatile core and a volatile coating; larger particles above 0.5 μm consisted of non-volatile components and contained light absorbing material. In all cases, particles larger than 10 μm were present, and in 80% of the measurements no particles larger than 40 μm were present. The abundance of large particles showed almost no height dependence. The effective diameter D eff in the dust plumes investigated showed two main ranges: the first range of D eff peaked around 5 μm and the second range of D eff around 8 μm. The two ranges of D eff suggest that it may be inadequate to use one average effective diameter or one parametrization for a typical dust size distribution. 相似文献