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Exploring the potential of tree-ring chronologies from the Trafoi Valley (Central Italian Alps) to reconstruct glacier mass balance 总被引：2，自引：0，他引：2
GIOVANNI LEONELLI MANUELA PELFINI PAOLO CHERUBINI 《Boreas: An International Journal of Quaternary Research》2008,37(1):169-178
Two tree-ring chronologies of stone pine ( Pinus cembra L.) and two of Norway spruce ( Picea abies Karst.) were constructed on the basis of data from three high-altitude sites in the Trafoi Valley (Central Alps, Italy) to test tree species sensitivity to climate at different sites and to explore the potential of the two species for reconstructing the mass balance of two glaciers in the same region (the Careser and Hintereis glaciers). Influence of climate on tree-ring growth and on glacier mass variations was tested by means of Pearson's correlation and response functions. At highest altitude sites, both species appeared to be sensitive to July temperatures, while stone pine also showed higher sensitivity than Norway spruce to previous winter precipitation. Comparing the dendrochronological and glaciological series, stone pine showed higher negative correlations with glacier mass balance series than Norway spruce. These different relationships reflect different species responses to climate, and stone pine is potentially useful in reconstructing past glacier mass balance in the Central Alps. Extreme climatic events induce different and even contrasting responses of tree-ring growth and glacier mass variations and may therefore bias tree-ring-based glacier mass balance reconstructions. 相似文献
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We present a simple algorithm to model the surface air temperature trends at the middle-high latitudes of the northern and southern hemispheres for the last century. Unlike previous approaches, based on the variation of the solar irradiance only, the algorithm here presented is the sum of one more external influence: the periodic variation of insolation due to the astronomical nutation of the Earth's axis. The model we present predicts the anticorrelated mean surface air temperature trends, measured at middle-high latitudes of the two hemispheres, during the period of low solar irradiance. According to Milankovitch, a change of the Earth's obliquity means a variation of insolation mainly at the middle-high latitudes; this variation takes opposite sign for northern and southern hemispheres. 相似文献
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The purpose of this report is to show a method of determining the top of a refractor departing from the times and slopes of the direct and inverse dromocrones. The method does not need topographical correction and can be applied without knowledge of the distance between the geophone and the shot point. These results having been obtained, the commonly accepted point of view is upset: instead of looking for two points on the surface corresponding to one point of the refractor, we try to etablish, starting with only one point from the surface, the two corresponding points from the top of the refractor. This method can be applied to isolated points and does not demand interpretative hypotheses of any kind, excluding the velocity evaluation of the overburden and of the refractor. The necessary calculations can be easily executed by means of a digital computer to which the dromocrone times and the distances between the geophones must be given. These calculations can also be executed by a person having no knowledge of refraction seismology. This report also examines the validity of the approximations involved in the method proposed. 相似文献
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A general perturbation–linearization scheme is proposed for the problem of data assimilation with an imperfect and nonlinear model, allowing for the application of the weak constraint representer method. The scheme is shown in discrete formalism for a generic model. An application example is given with computer‐generated data in the case of the Burgers equation. Discussion in reference to the assimilation example concerns: the rôle of the model error, seen as a forcing term in the dynamics; the rôle of representers as a posteriori error covariances; a comparison among different choices for a priori dynamic error variance and strong constraint assimilation. Weak and strong constraint methods are also compared in a forecasting experiment. 相似文献
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PAOLO GIACCARIA 《Geographical review》2012,102(3):293-315
The existing postcolonial literature privileges the British and French imperial/colonial history that mirrors the ongoing debate on the relationship among cosmopolitanism, universalism, and imperialism. These debates take for granted the Kantian and Hegelian hierarchy of European civilizations, hence marginalizing the southern shores of Europe and the broader Mediterranean space. Drawing on Mignolo's notion of “border thinking” and on Isin's account of the city as a “difference machine,” I address the issue of how imperialism, colonialism, and cosmopolitanism come together and relate to each other in the context of the Mediterranean (allegedly) cosmopolitan cities. In particular, cosmopolitanism is read as the outcome of the reciprocal adjustment of interior and exterior borders in the making of modernity/coloniality in the Mediterranean. Focusing on the Ottoman millet system, my main claim in this article is that cosmopolitanism worked as a peculiar dispositif within the urban difference machine, enabling the city to sustain the tension between different accounts of citizenship. 相似文献
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Exposure age dating and Equilibrium Line Altitude reconstruction of an Egesen moraine in the Maritime Alps, Italy 总被引：1，自引：0，他引：1
PAOLO ROBERTO FEDERICI DARRYL E. GRANGER MARTA PAPPALARDO ADRIANO RIBOLINI MATTEO SPAGNOLO ANDREW J. CYR 《Boreas: An International Journal of Quaternary Research》2008,37(2):245-253
Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10 Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10 Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present-day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas. 相似文献
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Rhodolith-bearing limestones as transgressive marker beds: fossil and modern examples from North Island, New Zealand 总被引：2，自引：0，他引：2
Rhodoliths are nodular structures composed mainly of the superimposed thalli of calcareous red algae. Because their development is controlled by an array of ecological parameters, rhodoliths are a valuable source of palaeoenvironmental information. However, despite their common use in palaeoecological reconstructions, the stratigraphic significance of rhodolith accumulations seldom has been addressed in detail. In a study of Cenozoic rhodolith‐bearing deposits from the North Island of New Zealand, rhodolithic units, usually of limited lateral extent, typically occur above major unconformities at the base of deepening upwards successions. Two types of transgressive rhodolith‐bearing deposits may be distinguished on the basis of texture and rhodolith internal structure: (i) type A deposits are clast‐supported rhodolithic rudstones containing abundant pebbles and cobbles reworked from the substrate, and are characterized by rhodoliths with a compact concentric to columnar internal structure and a high nucleus to algal cover ratio; (ii) type B deposits are rhodolithic floatstones with a matrix usually consisting of bryozoan fragments, benthic foraminifera and echinoid fragments or terrigenous silty fine sand. The rhodoliths of type B units usually have a loose internal framework with irregular to branched crusts. The two contrasting rhodolith‐bearing units are interpreted as characteristic facies of transgressive systems tract deposits, analogous to shell concentrations formed under conditions of low net sedimentation. Type A deposits are correlated with relatively high‐energy settings and/or narrow submerged palaeotopographic lows, whereas type B deposits are interpreted as forming in lower‐energy settings. The association between transgression and development of rhodolithic facies is confirmed by observations of a modern rhodolith production site at Whangaparaoa Peninsula in North Island, where algal nodules grow above a ravinement surface cut during the Holocene sea‐level rise, and also by a review of published fossil examples, many of which show stratigraphic and compositional attributes analogous to those of the New Zealand occurrences. The review indicates that transgressive rhodolith accumulations develop more commonly in, but are not restricted to, non‐tropical settings. It is suggested that a combination of factors, such as low net sedimentary input, nature of the substrate, sea‐level rise and inherited physiography contribute to determine the relationship between rhodolith‐bearing deposits and transgressive settings. 相似文献
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Abstract The effects induced on the climate by human activity have become a major issue for the new millennium. In order to arrive at sustainable conclusions it is necessary, first of all, to assess and quantify natural climatic changes. In general this is done by analysing available time series. In the case of historical hydrometeorological data sets, a comparative analysis with solar cycles is not usually conducted. This work, however, demonstrates that the effect of solar cycles observed at the Equator is also visible at middle and high latitudes with multiple periodicity of the basic solar frequency (roughly 11 years). This could well be due to the interaction between solar forcing and circulation mechanisms within the atmosphere, i.e. water-air-soil interactions coupled with anthropogenic forcing. This theory has been tested by comparing different types of historical data series with the River Po discharges and cyclic appearance of slime bloom in the Adriatic Sea. 相似文献