Changes in the South Pacific Convergence Zone in IPCC AR4 future climate projections   总被引：1，自引：0，他引：1  

Josephine R. Brown  Aurel F. Moise  Francois P. Delage 《Climate Dynamics》2012,39(1-2):1-19

The response of the South Pacific Convergence Zone (SPCZ) to climate change is examined using simulations from 16 coupled climate models under the A2 emission scenario carried out for the Intergovernmental Panel on Climate Change Fourth Assessment Report. Characteristics of the austral summer SPCZ in the late twenty-first century are compared with the late twentieth century: the orientation and latitude of the SPCZ precipitation band; the area and intensity of precipitation within the SPCZ; and the eastern extent of the SPCZ. Changes in the SPCZ position are examined using a simple linear fit to the band of maximum precipitation and using a “pattern matching” technique. Both techniques find no consistent shift in the slope or mean latitude of the austral summer SPCZ. However, many models simulate a westward shift in the eastern edge of the SPCZ in austral summer, with reduced precipitation to the east of around 150°W. The westward contraction of the SPCZ is associated with a strengthening of the trade winds in the southeast Pacific and an increased zonal sea surface temperature gradient across the South Pacific. The majority of models simulate an increase in the area of the SPCZ and in mean and maximum precipitation within the SPCZ, defined by a 6?mm/day precipitation threshold, consistent with increased moisture convergence in a warmer climate. Changes in the SPCZ response to ENSO are examined using ENSO precipitation composites. The SPCZ has a reduced slope and is shifted towards the equator in the A2 multi-model mean El Ni?o composite.  相似文献   

The effect of ground ice on the Martian seasonal CO₂ cycle     

Robert M. Haberle  Francois Forget  James Schaeffer  Nora J. Kelly 《Planetary and Space Science》2008,56(2):251-255

The mostly carbon dioxide (CO₂) atmosphere of Mars condenses and sublimes in the polar regions, giving rise to the familiar waxing and waning of its polar caps. The signature of this seasonal CO₂ cycle has been detected in surface pressure measurements from the Viking and Pathfinder landers. The amount of CO₂ that condenses during fall and winter is controlled by the net polar energy loss, which is dominated by emitted infrared radiation from the cap itself. However, models of the CO₂ cycle match the surface pressure data only if the emitted radiation is artificially suppressed suggesting that they are missing a heat source. Here we show that the missing heat source is the conducted energy coming from soil that contains water ice very close to the surface. The presence of ice significantly increases the thermal conductivity of the ground such that more of the solar energy absorbed at the surface during summer is conducted downward into the ground where it is stored and released back to the surface during fall and winter thereby retarding the CO₂ condensation rate. The reduction in the condensation rate is very sensitive to the depth of the soil/ice interface, which our models suggest is about 8 cm in the Northern Hemisphere and 11 cm in the Southern Hemisphere. This is consistent with the detection of significant amounts of polar ground ice by the Mars Odyssey Gamma Ray Spectrometer and provides an independent means for assessing how close to the surface the ice must be. Our results also provide an accurate determination of the global annual mean size of the atmosphere and cap CO₂ reservoirs, which are, respectively, 6.1 and 0.9 hPa. They also indicate that general circulation models will need to account for the effect of ground ice in their simulations of the seasonal CO₂ cycle.  相似文献   

The concentration and isotopic composition of hydrogen,carbon and nitrogen in carbonaceous meteorites     

Francois Robert  Samuel Epstein 《Geochimica et cosmochimica acta》1982,46(1):81-95

Concentrations and isotopic compositions were determined for H₂, N₂ and C extracted by stepwise pyrolysis from powdered meteorites, from residues of meteorites partially dissolved with aqueous HF, and from residues of meteorites reacted with HF-HCl solutions. The meteorites treated were the carbonaceous chondrites, Orgueil, Murray, Murchison, Renazzo and Cold Bokkeveld. Data determined for whole rock samples are in approximate agreement with previously published data. Acidification of the meteorites removed the inorganic sources of H₂, so that H₂ in the HF-HCl acid residues came primarily from insoluble organic matter, which makes up 70–80% fraction of the total carbon in carbonaceous meteorites. The δD in the organic matter differs markedly from previously determined values in organic matter in meteorites. The δD values of organic matter from acid residues of C1 and C2 carbonaceous chondrites range from +650 to + 1150%. The acid residues of the Renazzo meteorite, whose total H₂ has a δD of +930‰, gave a δD value of +2500‰. Oxidation of the HF-HCl residue with H₂O₂ solution removes the high δD and the low δ¹⁵N components. The δ¹³C values range between ?10 and ?21 and δ¹⁵N values range between +40 and ?11. The δ¹⁵N of Renazzo is unusual; its values range between +150 and ?190.There is good correlation between δD and the concentration of H₂ in the acid residues, but no correlation exists between δD, δ¹³C and δ¹⁵N in them. A simple model is proposed to explain the high δD values, and the relationships between δD values and the concentration of H₂. This model depends on the irradiation of gaseous molecules facilitating reaction between ionic molecules, and indicates that an increase in the rate of polymerization and accumulation of organic matter on grains would produce an increase in the deuterium concentration in organic matter.  相似文献   

The chemistry of magmatic gases from Erta'Ale,Ethiopia     

Werner F Giggenbach  Francois Le Guern 《Geochimica et cosmochimica acta》1976,40(1):25-30

The chemical composition of the gases emitted from a hornito close to the active lava lake of Erta'Ale, Ethiopia, as derived from chemical analyses on 18 samples collected on 23 January 1974, was found to be (in mol-%): H₂O: 79.4, CO₂: 10.4, total S: 7.36, HCl: 0.42, H₂: 1.49, N₂: 0.18, Ar: 0.001, CO: 0.46, and COS: 0.009. Thermodynamic considerations, based on the equilibria CO₂ + H₂ ? CO + H₂O and CO₂ + 3H₂ + SO₂ ? COS + 3H₂O show that the analytical values represent the equilibrium composition of a gas mixture at the measured temperature of around 1130°C under close to the surface pressure conditions. Comparison of the Erta'Ale gas emissions with those from other volcanoes suggests a close similarity in their chemical composition. This similarity is considered to be due to common processes governing the release of gaseous species from a magma.  相似文献   

Mapping ethnic diversity in highland Northern Vietnam     

Jean Michaud  Sarah Turner  Yann Roche 《GeoJournal》2002,57(4):305-323

In this paper we initially present a critical review of a range of ethnological maps produced over the last 130 years for highland northern Vietnam. In particular we illustrate the many difficulties faced when trying to represent mosaics of ethnic highland minority groups on two dimensional maps. Such historical maps included no attempts to bring topographic details into the picture, an idea that would have been virtually impossible anyway, given the cartographic technologies at the time. Yet by not including such details or not representing them clearly, a partial image of these populations has been created that, over time, has become a standardised representation. Therefore, as a more systematic approach to the analysis of these highland minority groups, we present recent attempts to create more functional maps and models for the northern Vietnam province of Lao Cai, using modern cartographic techniques and geographic information systems. Utilising tools such as digital cartography and digital elevation models a wealth of information can be gained which has the potential, amongst other possible uses, to allow for a greater understanding and sensitivity regarding ethnic minority groups in Northern Vietnam, and their use of the local environment. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Subsidence and strike-slip tectonism of the upper continental slope off Manzanillo, Mexico     

William L. Bandy  Franois Michaud  Jacques Bourgois  Thierry Calmus  Jrme Dyment  Carlos A. Mortera-Gutirrez  Jose Ortega-Ramírez  Bernard Pontoise  Jean-Yves Royer  Bertrand Sichler  Marc Sosson  Mario Rebolledo-Vieyra  Florence Bigot-Cormier  Oscar Díaz-Molina  Angel D. Hurtado-Artunduaga  Guillermo Pardo-Castro  Corrine Trouillard-Perrot 《Tectonophysics》2005,398(3-4):115-140

The direction of convergence between the Rivera and North American plates becomes progressively more oblique (in a counter-clockwise sense as measured relative to the trench-normal direction) northwestward along the Jalisco subduction zone. By analogy to other subduction zones, the forces resulting from this distribution of convergence directions are expected to produce a NW moving, fore-arc sliver and a NW–SE stretching of the fore-arc area. Also, a series of roughly arc parallel strike-slip faults may form in the fore-arc area, both onshore and offshore, as is observed in the Aleutian arc.In the Jalisco subduction zone, the Jalisco block has been proposed to represent such a fore-arc sliver. However, this proposal has encountered one major problem. Namely, right-lateral strike-slip faulting within the fore-arc sliver, and between the fore-arc sliver and the North American plate, should be observed. However, evidence for the expected right-lateral strike-slip faulting is sparse. Some evidence for right-lateral strike-slip faulting along the Jalisco block–North American plate boundary (the Tepic–Zacoalco rift system) has been reported, although some disagreement exists. Right-lateral strike-slip faulting has also been reported within the interior of the Jalisco block and in the southern Colima rift, which forms the SE boundary of the Jalisco block.Threefold, multi-channel seismic reflection data were collected in the offshore area of the Jalisco subduction zone off Manzanillo in April 2002 during the FAMEX campaign of the N/O L'Atalante. These data provide additional evidence for recent strike-slip motion within the fore-arc region of the Jalisco subduction zone. This faulting offsets right-laterally a prominent horst block within the southern Colima rift, from which we conclude that the sense of motion along the faulting is dextral. These data also provide additional evidence for recent subsidence within the area offshore of Manzanillo, as has been proposed.  相似文献   

Tantalite in Suzhou Granite：mineralogy and Geological Implications     

王汝成  林承毅等 《中国地球化学学报》1997,16(4):353-358

Tantalite,occurring as intergranular tabular crystals,was reported for the first time in the Suzhou granite.Electron microprobe analyses show that it is rich in W and Ti,with a Ta/(Ta Nb) ratio ranging from 0.5 to 0.73 and a Mn(Mn Fe) ratio between 0.20 and 0.40.It is structurally distinct from isomorphic tapiolite by a remarked Ag Raman peak at 880cm^-1.The associated zircon is striking by significant enrichment of Hf,with the HfO2 content amounting up to 35%-40%,The discovery of tantalite suggests that the Suzhou granite should be classified as a S-type granite instead of A-type as considered previously.  相似文献   

Brood patch temperature during provocation of common eiders in Ny-Ålesund, Svalbard     

Francois Criscuolo  Michel Gauthier-Clerc  Yvon Le  Maho Geir W. Gabrielsen 《Polar research》2001,20(1):115-118

In this short note we describe the behaviour and body changes of three incubating female common eiders ( Somateria mollissima ) during provocation made by humans approaching the nest. The study site was near the settlement of Ny-Ålesund, Svalbard. Temperture transmitters were implanted subcutaneously at the brood patch and data recorded using a VHF receiver. We found that the female experiment exhibited a passive defence response ("freezing"), accompanied by a significant drop in brood patch temperature (0.6 °C) during provocation; this temperature drop lasted for 5 minutes. These accord with other studies of the physiological changes which the passive defence response in birds and other animals.  相似文献   

Marcel Bertrand et „l'orogenèse programmée”     

Professeur Francois Ellenberger 《International Journal of Earth Sciences》1983,72(2):757-757

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Comparative high-resolution chemostratigraphy of the Bonarelli Level from the reference Bottaccione section (Umbria-Marche Apennines) and from an equivalent section in NW Sicily: Consistent and contrasting responses to the OAE2   总被引：1，自引：0，他引：1  

Giovanna Scopelliti  Rodolfo Neri  Francois Baudin 《Chemical Geology》2006,228(4):266-285

The Bonarelli Level (BL) from the upper Cenomanian portion of the reference Bottaccione section (central Italy) is characterized by the presence of black shales containing high TOC concentrations (up to 17%) and amounts of CaCO₃ near to zero. In the absence of carbonate and, consequently, of relative carbon- and oxygen-isotopic data, the elemental geochemistry revealed to be a very useful tool to obtain information about the palaeoclimatic and palaeoceanographic evolution of the Tethys Ocean during the OAE2. Based on several geochemical proxies (Rb, V, Ni, Cr, Si, Ba), the BL is interpreted as a high-productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle. The enrichment factors of peculiar trace metals (Zn, Cd, Pb, Sb, Mo, U) provide further insight about the H₂S activity at the seafloor during the organic-rich sediment deposition and permitted us to evaluate the use of Ba as palaeoproductivity tracer in conditions of high rate of sulphate reduction.By comparing geochemical records from the reference Bottaccione section (central Italy) with those previously obtained for the coeval Calabianca section (northwestern Sicily), different degrees of oceanic anoxia were delineated and ascribed to different abundance and type (degradable or refractory) of organic matter, which are limiting factors in the bacterial sulphate reduction reactions and in subsequent euxinic conditions at seafloor in the Tethys realm. Based on a ciclostratigraphic approach, consistent fluctuations at 100 ky scale in the chemostratigraphic signals from the two sections are inferred to be expression of a strong orbital-climatic forcing driving changes in the oceanic environment during the BL deposition.  相似文献