European temperature records of the past five centuries based on documentary/instrumental information compared to climate simulations     

Eduardo Zorita  Anders Moberg  Lotta Leijonhufvud  Rob Wilson  Rudolf Brázdil  Petr Dobrovolný  Jürg Luterbacher  Reinhard Böhm  Christian Pfister  Dirk Riemann  Rüdiger Glaser  Johan Söderberg  Fidel González-Rouco 《Climatic change》2010,101(1-2):143-168

Two European temperature reconstructions for the past half-millennium, January-to-April air temperature for Stockholm (Sweden) and seasonal temperature for a Central European region, both derived from the analysis of documentary sources and long instrumental records, are compared with the output of climate simulations with the model ECHO-G. The analysis is complemented by comparisons with the long (early)-instrumental record of Central England Temperature (CET). Both approaches to study past climates (simulations and reconstructions) are burdened with uncertainties. The main objective of this comparative analysis is to identify robust features and weaknesses in each method which may help to improve models and reconstruction methods. The results indicate a general agreement between simulations obtained with temporally changing external forcings and the reconstructed Stockholm and CET records for the multi-centennial temperature trend over the recent centuries, which is not reproduced in a control simulation. This trend is likely due to the long-term change in external forcing. Additionally, the Stockholm reconstruction and the CET record also show a clear multi-decadal warm episode peaking around AD 1730, which is absent in the simulations. Neither the reconstruction uncertainties nor the model internal climate variability can easily explain this difference. Regarding the interannual variability, the Stockholm series displays, in some periods, higher amplitudes than the simulations but these differences are within the statistical uncertainty and further decrease if output from a regional model driven by the global model is used. The long-term trend of the CET series agrees less well with the simulations. The reconstructed temperature displays, for all seasons, a smaller difference between the present climate and past centuries than is seen in the simulations. Possible reasons for these differences may be related to a limitation of the traditional ‘indexing’ technique for converting documentary evidence to temperature values to capture long-term climate changes, because the documents often reflect temperatures relative to the contemporary authors’ own perception of what constituted ‘normal’ conditions. By contrast, the amplitude of the simulated and reconstructed inter-annual variability agrees rather well.  相似文献   

Laterally constrained inversion of helicopter-borne frequency-domain electromagnetic data     

Bernhard Siemon  Esben Auken  Anders Vest Christiansen 《Journal of Applied Geophysics》2009,67(3):259-268

Helicopter-borne frequency-domain electromagnetic (HEM) surveys are used for fast high-resolution, three-dimensional resistivity mapping. Standard interpretation tools are often based on layered earth inversion procedures which, in general, explain the HEM data sufficiently. As a HEM system is moved while measuring, noise on the data is a common problem. Generally, noisy data will be smoothed prior to inversion using appropriate low-pass filters and consequently information may be lost.For the first time the laterally constrained inversion (LCI) technique has been applied to HEM data combined with the automatic generation of dynamic starting models. The latter is important because it takes the penetration depth of the electromagnetic fields, which can heavily vary in survey areas with different geological settings, into account. The LCI technique, which has been applied to diverse airborne and ground geophysical data sets, has proven to be able to improve the HEM inversion results of layered earth structures. Although single-site 1-D inversion is generally faster and — in case of strong lateral resistivity variations — more flexible, LCI produces resistivity — depth sections which are nearly identical to those derived from noise-free data.The LCI results are compared with standard single-site Marquardt–Levenberg inversion procedures on the basis of synthetic data as well as field data. The model chosen for the generation of synthetic data represents a layered earth structure having an inhomogeneous top layer in order to study the influence of shallow resistivity variations on the resolution of deep horizontal conductors in one-dimensional inversion results. The field data example comprises a wide resistivity range in a sedimentary as well as hard-rock environment.If a sufficient resistivity contrast between air and subsurface exists, the LCI technique is also very useful in correcting for incorrect system altitude measurements by using the altitude as a constrained inversion parameter.  相似文献   

Propagation of the Storegga tsunami into ice‐free lakes along the southern shores of the Barents Sea     

Anders Romundset  Stein Bondevik 《第四纪科学杂志》2011,26(5):457-462

Deposits in coastal lakes in northernmost Norway reveal that the Storegga tsunami propagated well into the Barents Sea ca. 8100–8200 years ago. A tsunami deposit – found in cores from five coastal lakes located near the North Cape in Finnmark – rests on an erosional unconformity and consists of graded sand layers and re‐deposited organic remains. Rip‐up clasts of lake mud, peat and soil suggest strong erosion of the lake floor and neighbouring land. Inundation reached at least 500 m inland and minimum vertical run‐up has been reconstructed to 3–4 m. In this part of the Arctic coastal lakes are usually covered by >1 m of solid lake ice in winter. The significant erosion and deposition of rip‐up clasts indicate that the lakes were ice free and that the ground was probably not frozen. We suggest that the Storegga slide and ensuing tsunami happened sometime in the summer season, between April and October. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Comment: Radiocarbon deglaciation chronology of the Thunder Bay,Ontario area and implications for ice sheet retreat patterns     

Anders E. Carlson  Peter U. Clark  Steven W. Hostetler 《Quaternary Science Reviews》2009,28(23-24):2546-2547

  相似文献   

Population-level genotyping of coat colour polymorphism in woolly mammoth (Mammuthus primigenius)     

Claire Workman  Love Dalen  Sergey Vartanyan  Beth Shapiro  Pavel Kosintsev  Andrei Sher  Anders Gotherstrom  Ian Barnes 《Quaternary Science Reviews》2011,30(17-18):2304-2308

Patterns in the spatial or temporal distribution of genotypes may be indicative of natural selection. Previous work on the woolly mammoth melanocortin-1 receptor (Mc1r) gene identified three polymorphic positions that suggest Pleistocene populations may have harboured both light- and dark-haired mammoths (Rompler et al., 2006, 313: 62). Here, we extend this work and present the first population-level analysis of a functional gene in an extinct species. We genotyped the Mc1r gene in 47 woolly mammoth samples excavated from sites across the central portion of the woolly mammoths’ former range to examine the extent of variation of this polymorphism through time and across space. Only one individual was found to be heterozygous, indicating that the frequency of the ‘light’ mutant allele was very low. We conclude that light-coloured woolly mammoths would have been very rare, and may even have been non-existent if the ‘light’ mutant allele was strongly selected against in its homozygotic form. With the increasing availability of large-scale sequencing technologies, population-level datasets capable of identifying local adaptation will become increasingly attainable.  相似文献   

Abundance of 17 trace elements in carbonaceous chondrites     

Urs Krähenbühl  John W. Morgan  R. Ganapathy  Edward Anders 《Geochimica et cosmochimica acta》1973,37(5):1353-1370

Seventeen trace elements (Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Rb, Re, Sb, Se, Te, Tl, U and Zn) were measured by neutron activation analysis in 8 C1 samples (1 Alais, 3 Ivuna, 4 Orgueil) and in 3 C2 samples (one each of Mighei, Murchison, Murray). The results show far less scatter than earlier literature data. The standard deviation of a single measurement from the mean of 8 C1 samples lies between 2 and 14 per cent, except for the following 4 elements: Au ±18 per cent, Ag ±22 per cent, Rb ±19 per cent and Br ±33 per cent. The first two probably reflect contamination and sample heterogeneity, the last two, analytical error. Apparently C1 chondrites have a far more uniform composition than some authors have claimed.The new data suggest significant revisions in cosmic abundance for the following elements (old values in parentheses): Zn 1250 (1500), Cd 1.51 (2.12), Ir 0.72 (0.43) atoms/10⁶ Si atoms. The Br value is also lower, 6.8 vs 20.6, but may be affected by analytical error.Relative to C1 chondrites, the C2 chondrites Mighei, Murchison and Murray are depleted in volatile elements by a factor of 0.508 ± 0.038, much more constant than indicated by oldor data. Ordinary chondrites also show a more uniform depletion relative to the new C1 data. The mean depletion factor of Sb, F, Cu, Ga, Ge, Sn, S, Se, Te and Ag is 0.227 ± 0.027 in H-chondrites. This constancy further strengthens the case for the two-component model of chondrite formation.  相似文献   

Lunar crater Copernicus: search for debris of impacting body at Apollo 12 site     

John W. Morgan  R. Ganapathy  J.C. Laul  Edward Anders 《Geochimica et cosmochimica acta》1973,37(1):141-154

In an attempt to characterize meteoritic material at the Apollo 12 site, 4 KREEP concentrates from soil 12033 have been analyzed by neutron activation analysis. These contain a meteoritic component in which siderophile Ir, Re and Sb are depleted by about a factor of 2, while volatile Se, Zn, Ag and Bi are depleted by a factor of more than 5 relative to Au. This pattern does not closely resemble any major chondrite or iron meteorite group, but is very similar to that observed in high-alkali samples from Apollo 14. The meteoritic component in KREEP at both sites is therefore predominantly derived from Imbrian ejecta. However, a second, small component of primitive composition seems to be present in Apollo 12 KREEP, judging from the slight, uniform enrichments in Ir, Re, Sb, Se and Zn relative to Au. This component does not seem to be due to micrometeorites. If it is attributed to the Copernican projectile, the crater Copernicus may have been formed by a cometary nucleus, 4 km in diameter, with an impact velocity of 30–40 km/sec. These conclusions depend critically on the assumption that the meteoritic component in Apollo 12 KREEP is representative of the entire impact.  相似文献   

Chemical fractionations in meteorites—VI. Accretion temperatures of H-, LL- and E-chondrites,from abundance of volatile trace elements     

J.C. Laul  R. Ganapathy  Edward Anders  John W. Morgan 《Geochimica et cosmochimica acta》1973,37(2):329-357

Extending our earlier work on 11 L-chondrites, we have measured 9 volatile elements (Ag, Bi, Cs, In, Rb, Tl, Se, Cd, Zn) by neutron activation analysis in 11 LL- and 10 E-chondrites; the first 6 elements also in 22 H-chondrites. The observed fractionation patterns are consistent with theoretical condensation curves and hence were apparently established during condensation from the solar nebula. Ordinary chondrites seem to have accreted between 420 and 500°K at $\text{P ≈ 10}{}^{\mathrm{?5}}$ atm; enstatite chondrites, at 460 to 520°K and P ≈ 5 x? 10^?4 atm. The values for ordinary chondrites agree with O¹⁸-based temperatures by Onuma. et al. (1972) and with other characteristics such as Fe²⁺ content, presence of FeS and absence of Fe₃O₄.A few detailed trends were noted. Seven of the 54 meteorites seem to contain small amounts of a material enriched in Ag, Bi and especially T1; possibly a late condensate from a region depleted in metal. Silver shows considerable scatter, which suggests inhomogeneous distribution in the meteorites. Xenon correlates with In approximately as expected for equilibrium solubility, with some differences (petrologic type 3; E-chondrites) attributable to mineralogical factors. Meteorites of higher petrologic types are slightly deficient in Xe, probably due to gas losses during metamorphism. Cesium also appears to have been redistributed during metamorphism.Various features of the two-component model are critically examined in the light of the latest evidence. Apparently this model still is an adequate approximation of reality.  相似文献   

How well do we know “Cosmic” abundances?     

Edward Anders 《Geochimica et cosmochimica acta》1971

Five lines of evidence suggest that Cl chondrites closely approximate the condensable fraction of primordial solar-system matter: continuity of isotopic and elemental abundance trends, agreement with solar and cosmic-ray abundances, fractionation patterns among chondrites, and absence of chondrules. Maximum differences between Cl abundances and true solar-system abundances are estimated as factors of 2–5 for individual elements and a factor of 1.5 or less for groups of 10 or more elements.  相似文献   

Land degradation,natural resources and local knowledge in the sahel zone of Burkina Faso   总被引：4，自引：0，他引：4  

Per Lindskog  Anna Tengberg 《GeoJournal》1994,33(4):365-375

This paper proposes a conceptual model that integrates physical and ecological aspects with human aspects of land degradation through a multidisciplinary approach. The model was applied at the local level in a case study in northern Burkina Faso. Assessments of the degradation of the vegetation cover from aerial photographs and a satellite image were analysed in the framework of the model. Another input to the model was results from interviews and field visits with peasants living in the area.The local knowledge of the physical symptoms of land degradation and of the physical variables, eg rainfall and wind, is very close to the scientific logic. However, people do not generally see the links between these variables and the symptoms. Likewise, they do not perceive land degradation to be influenced in any way by human actions. Instead, the cause of land degradation is attributed to God, Allah. Thus, an important field of intervention for governments and development agencies should be to make people aware of their role in land management.  相似文献