Using paleoclimate proxy-data to select optimal realisations in an ensemble of simulations of the climate of the past millennium   总被引：1，自引：0，他引：1  

Hugues Goosse  Hans Renssen  Axel Timmermann  Raymond S. Bradley  Michael E. Mann 《Climate Dynamics》2006,27(2-3):165-184

We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale.  相似文献   

Thermodynamics and environmental constraints make the biosphere predictable – a response to Volk     

Axel Kleidon 《Climatic change》2007,85(3-4):259-266

In his critique of Kleidon (Clim Change 66:271–319, 2004), Volk (Clim Change 85:3–4, 2007) concludes that maximum entropy production (MEP) has no great relevance for biological evolution and the time history of life on Earth. I think that most of his points are not justified but rather reflect (a) a lack of appreciation of the central importance of entropy production as the “universal currency” that measures what keeps systems working, including the biosphere, (b) a misunderstanding of how biotic activity is embedded in the global entropy budget, and (c) a lack of distinction between optimal environmental conditions that maximize productivity and result from environmental tradeoffs versus optimal function of organisms to some internal tradeoffs. The examples that he uses to support his conclusions show flaws in that these mostly discuss single environmental effects and immediate system responses. Optimal environmental conditions, however, requires at least two effects that result in a trade-off, so it is not surprising that his examples seem to contradict optimality and MEP. And the immediate response of a system to change can be very different than the response in steady state, for which MEP applies. This is specifically important to be considered in the context of the “cheater” problem. In summary, I do not think that Volk makes convincing arguments that contradict MEP, although I certainly agree that there is a lot more work to be done to fully recognize the great importance that thermodynamics and MEP play in shaping the Earth’s biosphere and its evolutionary history.  相似文献   

Rapakivi granites     

Axel Müller 《Geology Today》2007,23(3):114-120

Rapakivi granites, especially the famous rapakivis from southern Finland, are some of the most attractive building and decorative stones, used world-wide because of their striking textures and beautiful colours. But rapakivi granites are more than just building material, they have also been studied scientifically for over 100 years to try to explain the formation of their plagioclase-mantled alkali feldspar ovoids, the rapakivi feldspars which are responsible for the unique texture of the rock. Despite all the work which has been done on them, the formation of this distinctive texture is still not fully understood. Rapakivi granite complexes are not just a 'pretty face', they are also associated with important tin deposits in Rondônia and Amazonas in Brazil.  相似文献   

U-Pb-Hf isotopic data from detrital zircons in late Carboniferous and Mid-Late Triassic sandstones,and also Carboniferous granites from the Tauride and Anatolide continental units in S Turkey: implications for Tethyan palaeogeography     

Timur Ustaomer  Petek Ayda Ustaömer  Alastair H. F. Robertson  Axel Gerdes 《International Geology Review》2020,62(9):1159-1186

ABSTRACT

Zircons from Carboniferous sandstones (three samples) and Mid-Late Triassic sandstones (four samples) from the Tauride and Anatolide continental units were analysed for U-Pb-Hf isotopes. For comparison, zircons were also analysed from Carboniferous granites of the Afyon Zone, Anatolides (three samples). A NE African/Arabian source is inferred for both the Carboniferous sandstones of the Taurides (Alada?) and the Anatolides (Konya Complex). In contrast, the Carboniferous Karaburun Melange is characterised by a NW African provenance. A prominent Devonian population occurs in the Carboniferous Karaburun Melange, characterised by mainly positive ε_Hf(t) values that differ significantly from those of the Devonian granites of the Sakarya continental crustal unit (Pontides). Middle-Late Triassic Tauride sandstones include minor Palaeozoic and Early Mesozoic zircons. In contrast, Devonian and Carboniferous zircons are relatively abundant in Late Triassic sandstones of the Karaburun Peninsula. The Hf isotopic compositions of 25 Carboniferous-aged zircons from three samples of Mid-Late Triassic sandstone and one of Late Carboniferous age (one sample) overlap with the ε_Hf(t) values of Carboniferous arc-type granites in the Anatolides. Taking account of the available U-Pb and Lu-Hf isotopic data from comparative crustal units, the Devonian zircon populations from the melanges in the Karaburun Peninsula and the Konya Complex are inferred to have a westerly source (e.g. granitic rocks of Aegean region or central Europe). A tectonic model is proposed in which Palaeozoic Tethys sutured during the late Carboniferous in the west (Aegean region westwards), leaving an eastward-widening oceanic gulf in which sandstone turbidites accumulated, including Devonian zircons.  相似文献   

Design of feedback-controlled wide-band seismographs with respect to undesired side-effects     

Christian Teupser  Axel Plešinger 《Physics of the Earth and Planetary Interiors》1979,18(2):58-63

Various modifications of a displacement-sensing seismometer controlled by negative first-order low-pass, first-order high-pass and second-order high-pass feedback are analysed. Undesired side-effects of the frequency-limited feedback on the response of the closed-loop system are investigated. Rules for “optimum tuning” of systems with a flat-displacement or flat-velocity response in a desired period range are given.  相似文献   

Summary report of the researches in Sweden on volcanic and related phenomena during the period 1933–1936     

Axel Gavelin 《Bulletin of Volcanology》1937,1(1):117-118

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The complex X-ray spectrum of the isolated neutron star RBS1223     

Axel D. Schwope  Valeri Hambaryan  Frank Haberl  Christian Motch 《Astrophysics and Space Science》2007,308(1-4):619-623

We present a first analysis of a deep X-ray spectrum of the isolated neutron star RBS1223 obtained with XMM-Newton. Spectral data from four new monitoring observations in 2005/2006 were combined with archival observations obtained in 2003 and 2004 to form a spin-phase averaged spectrum containing 290 000 EPIC-pn photons. This spectrum shows higher complexity than its predecessors, and can be parameterised with two Gaussian absorption lines superimposed on a blackbody. The line centers, E ₂≃2E ₁, could be regarded as supporting the cyclotron interpretation of the absorption features in a field B∼4×10¹³ G. The flux ratio of those lines does not support this interpretation. Hence, either feature might be of truly atomic origin.   相似文献   

In situ U–Pb dating of micro-baddeleyite by secondary ion mass spectrometry     

Axel K. Schmitt  Kevin R. Chamberlain  Susan M. Swapp  T. Mark Harrison 《Chemical Geology》2010,269(3-4):386-395

We introduce a technique for U–Pb dating of baddeleyite using secondary ion mass spectrometry (SIMS) in situ analysis of ng-mass crystals that cannot be efficiently extracted by conventional mineral separation techniques. Average ²⁰⁷Pb/²⁰⁶Pb ages for Precambrian baddeleyite crystals are within < 0.3% of the respective isotope dilution thermal ionization mass spectrometry (ID-TIMS) ages. ²⁰⁶Pb/²³⁸U ratios are corrected for instrumental fractionation calibrated through linear regression in a Pb/U relative sensitivity vs. UO₂⁺/U⁺ calibration plot. Calibration is performed on separated baddeleyite crystals (～ 100–200 μm in maximum dimension) mounted in random crystallographic orientation. ²⁰⁶Pb/²³⁸U ages for baddeleyite from Duluth gabbro (FC4b) and Kovdor are accurate within 1–2% when averaging 15–30 individual spot analyses and relative sensitivities calibrated on Phalaborwa baddeleyite. The relative difference of ²⁰⁶Pb/²³⁸U between large crystals and micro-baddeleyite from FC4b is within ～ 1%. Comparison between silicate glass and baddeleyite, as well as replicate analysis of the same grains in different orientations relative to the incidence direction of the primary beam support previous evidence for bias in Pb/U sensitivity in baddeleyite due to variable crystal orientations. We successfully utilized oxygen flooding and a UO₂⁺/U⁺-based calibration to significantly reduce orientation dependent bias.  相似文献   

In situ U–Pb SIMS (IN-SIMS) micro-baddeleyite dating of mafic rocks: Method with examples     

Kevin R. Chamberlain  Axel K. Schmitt  Susan M. Swapp  T. Mark Harrison  Norbert Swoboda-Colberg  Wouter Bleeker  Tony D. Peterson  Charles W. Jefferson  Andrei K. Khudoley 《Precambrian Research》2010

An in situ U–Pb SIMS (IN-SIMS) method to date micro-baddeleyite crystals as small as 3 μm is presented with results from three samples that span a variety of ages and geologic settings. The method complements ID-TIMS geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation. X-ray mapping and BSE imaging are used to locate target grains in thin section, followed by SIMS analysis on a CAMECA ims 1270, using the field aperture in the transfer column to screen out ions from host phases. Internal age precisions for the method are anticipated to range from 0.1% for Precambrian rocks to 3–7% for Phanerozoic rocks. Results establish a 2689 ± 5 Ma age for mafic dikes in the Wyoming craton, USA, a 1540 ± 30 Ma age for a subaerial lava flow from the Thelon Basin of northern Canada, and a 457 ± 34 Ma age for mafic dikes in the platform sequence of southeastern Siberia. The method is ideal for relatively non-destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples.  相似文献   

New constraints on the auriferous Witwatersrand sediment provenance from combined detrital zircon U–Pb and Lu–Hf isotope data for the Eldorado Reef (Central Rand Group,South Africa)     

Nikola Koglin  Armin Zeh  Hartwig E. Frimmel  Axel Gerdes 《Precambrian Research》2010

Combined U–Pb and Lu–Hf isotope analyses of detrital zircon grains from the auriferous Eldorado Reef conglomerate, upper Central Rand Group, reveal new insights into the provenance of the sediments and thus, by implication, possibly also into that of the gold. Most of the detrital zircon grains, which are of magmatic origin, yielded Mesoarchaean ages clustering around 2.94 and 3.06 Ga. A subordinate zircon population gave ages with maxima at 3.28 and 3.44 Ga. The Mesoarchaean zircon grains mostly show super-chondritic ?Hf_t of up to +5.2, whereas the Palaeoarchaean zircon grains have nearly chondritic composition with ?Hf_t between −1.3 and +2.0. The new dataset of the Mesoarchaean zircon populations provides the first unambiguous evidence of the formation of juvenile crust not only at 3.06 but also at 2.94 Ga. As the analysed zircon grains are from the ruditic fraction, they must be derived from a comparatively proximal source in close vicinity to the Central Rand Basin. Based on currently available data, this source was most likely a magmatic arc that existed at the northern edge of the Witwatersrand Block at 3.06 Ga. An additional source might be the 2.94 Ga magmatic rocks of the Kraaipan Greenstone Belt that occurs to the west of the Witwatersrand Block. The minor fraction of Palaeoarchaean zircon grains in the Eldorado Reef perhaps stem from sources that are isotopically similar to the Barberton Greenstone Belt and the Limpopo Belt but were more proximal to the Central Rand Basin.  相似文献