Climate and atmospheric history of the past 420,000 years from the Vostok ice core,

Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial-interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years. The late Quaternary period (the past one million years) is punctuated by a series of large glacial-interglacial changes with cycles that last about 100,000 years (ref. 1). Glacial-interglacial climate changes are documented by complementary climate records 1,2 largely derived from deep sea sediments, continental deposits of flora, fauna and loess, and ice cores. These studies have documented the wide range of climate variability on Earth. They have shown that much of the variability occurs with periodicities corresponding to that of the precession, obliquity and eccentricity of the Earth's orbit 1,3 . But understanding how the climate system responds to this initial orbital forcing is still an important issue in palaeoclimatology, in particular for the generally strong ϳ100,000-year (100-kyr) cycle. Ice cores give access to palaeoclimate series that includes local temperature and precipitation rate, moisture source conditions, wind strength and aerosol fluxes of marine, volcanic, terrestrial, cosmogenic and anthropogenic origin. They are also unique with their entrapped air inclusions in providing direct records of past changes in atmospheric trace-gas composition. The ice-drilling project undertaken in the framework of a long-term collaboration between Russia, the United States and France at the Russian Vostok station in East Antarctica (78Њ S, 106Њ E, elevation 3,488 m, mean temperature −55 ЊC) has already provided a wealth of such information for the past two glacial-interglacial cycles [4][5][6][7][8][9] Here we present a series of detailed Vostok records covering this ϳ400-kyr period. We show that the main features of the more recent Vostok climate cycle resemble those observed in earlier cycles. In particular, we confirm the strong correlation between atmospheric greenhouse-gas concentrations and Antarctic temperature, as well as the strong imprint of obliquity and precession in most of the climate time series. Our records reveal both similarities and differences between the successive interglacial periods. They suggest the lead of Antarctic air temperature, and of atmospheric greenhousegas concentrations, with respect to global ice volume and Greenland air-temperature changes during glacial terminations. The ice record The data are shown in Figs 1, 2 and 3 (see Supplementary Information for the numerical data). They include the deuterium content of the ice (dD ice , a proxy of local temperature change), the dust content (desert aerosols), the concentration of sodium (marine aerosol), and from the entrapped air the greenhouse gases CO 2 and CH 4 , and the d 18 O are defined in the legends to Figs 1 and 2, respectively.) All these measurements have been performed using methods previously described except for slight modifications (see The detailed record of dD ic

Nanotechnology : the Next Industrial Revolution ?

The essence of nanotechnology is the ability to work at the molecular level, atom by atom, to create large structures with fundamentally new properties. Nanostructures offer a new paradigm for materials manufacture by submicron-scale self-organization and self-assembly to create entities from the “bottom up” rather than the “top down” method. Nanometer structures will foster a revolution not only in information technology hardware but also in advances healthcare, therapeutics, diagnostics, environment and energy

On the atomic configuration of EL2

The atomic configuration of the EL2 defect in its stable state has been determined as an arsenic antisite defect associated with an arsenic interstitial at a next nearest neighbour site. The metastable EL2 state is tentatively assigned to an arsenic pair defect at a gallium lattice site (As-As ) Ga.La configuration atomique du défaut EL2 dans son état stable est attribuée à un complexe composé d'un antisite d'arsenique et d'un interstitiel d'arsenique en position de deuxième voisin. Les propriétés de l'état métastable peuvent être décrites dans un modèle d'une paire d'arsenique (As-As )Ga à un site gallium

Coherent Isotope History of Andean Ice Cores over the Last Century

[1] Isotope records from Andean ice cores provide detailed and high-resolution climate information on various time scales. However, the relationship between these valuable isotope records and local or regional climate remains poorly understood. Here we present results from two new drillings in Bolivia, from the Illimani and the Sajama ice caps. All four high altitude isotope signals in the Andes now available (Huascaran, Quelccaya, Illimani and Sajama) show near identical decadal variability in the 20th century. Comparison with general circulation model results and meteorological data suggest that the Andean high altitude records are primarily controlled by precipitation variability over the Amazon basin

CAPTURE CROSS-SECTIONS OF DEEP LEVELS IN SUPERLATTICES

La spectroscopie de transitoires de capacité peut être utilisée pour caractériser les super-réseaux et les défauts qu'ils contiennent. Ici nous décrivons la mesure de section de capture d'électrons sur des niveaux profonds introduits par irradiation d' électrons. La variation du taux de capture avec la température indique que cette capture se produit par émission multiphonon, dont les caractéristiques peuvent être prédites en prenant en compte la structure de bande du super-réseau.Transient capacitance spectroscopy can be used to characterize superlattices and the defects they contain. Here, we describe the measurement of electron capture cross-sections of deep levels introduced by electron irradiation. The variation of the capture rate versus temperature indicates that this capture occurs through a multiphonon emission process whose characteristics can be predicted in taking into account the superlattice band structure

Charge-injection mechanisms in semiconductor nanoparticles analyzed from force microscopy experiments

International audienc

Electrostatic force microscopy of individuallt charged silicon nanoparticles

International audienc