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排序方式: 共有224条查询结果,搜索用时 31 毫秒
91.
Benjun Wu Clinton P. Conrad Arnauld Heuret Carolina Lithgow-Bertelloni Serge Lallemand 《Earth and Planetary Science Letters》2008,272(1-2):412-421
Although subducting slabs undergo a bending deformation that resists tectonic plate motions, the magnitude of this resistance is not known because of poor constraints on slab strength. However, because slab bending slows the relatively rapid motions of oceanic plates, observed plate motions constrain the importance of bending. We estimated the slab pull force and the bending resistance globally for 207 subduction zone transects using new measurements of the bending curvature determined from slab seismicity. Predicting plate motions using a global mantle flow model, we constrain the viscosity of the bending slab to be at most ~ 300 times more viscous than the upper mantle; stronger slabs are intolerably slowed by the bending deformation. Weaker slabs, however, cannot transmit a pull force sufficient to explain rapid trenchward plate motions unless slabs stretch faster than seismically observed rates of ~ 10− 15 s− 1. The constrained bending viscosity (~ 2 × 1023 Pa s) is larger than previous estimates that yielded similar or larger bending resistance (here ~ 25% of forces). This apparent discrepancy occurs because slabs bend more gently than previously thought, with an average radius of curvature of 390 km that permits subduction of strong slabs. This gentle bending may ultimately permit plate tectonics on Earth. 相似文献
92.
François Bourrin Xavier Durrieu de Madron Serge Heussner Claude Estournel 《Continental Shelf Research》2008
A 1-year survey of sediment dynamics on the Têt inner-shelf in the south-western part of the Gulf of Lions was conducted as part of the EUROSTRATAFORM program (European Margin Strata Formation) from October 2004 to November 2005. Several bottom instruments (ADCP, wave gauge and altimeters) were deployed at 28 m water depth on the Têt prodelta to measure forcing responsible for sediment erosion and transport on the inner-shelf. 相似文献
93.
Joan Fabres Tommaso Tesi Jose Velez Fabian Batista Cindy Lee Antoni Calafat Serge Heussner Albert Palanques Stefano Miserocchi 《Continental Shelf Research》2008
To investigate the role of coastal canyons in the transfer of organic matter from the shelf to the slope and basin, we deployed sediment trap/current meter pairs at the head of five canyons in the Gulf of Lions (GoL) between November 2003 and May 2004. Analysis of organic carbon, biogenic silica, Corg isotopic composition, Corg/total nitrogen, chloropigments, and amino acids clearly shows the seasonal influence and effect of extreme meteorological events on the composition of collected particles. The sampling period was divided into three “scenarios”. The first corresponded to a large easterly storm and flood of the Rhone river during stratified water column conditions; the composition of material collected during this event was influenced by increased transfer of riverine and coastal particulate matter, with a lower Corg content. During the second “fall-winter” scenario, northern and northwestern winds blowing over the shelf caused cooling and homogenization of the shelf water column; particles collected at this time reflected the homogeneous source of particulate matter transported through canyons; particles sitting in the vicinity of canyon heads are most likely swept downslope by the general south-westward circulation. Organic tracers indicate a degraded origin for organic matter transported during this period. A third “spring” scenario corresponded to northern winds alternating with eastward windstorms that triggered and/or enhanced the cascading of dense waters accumulated on the bottom of the shelf due to previous cooling. These conditions occurred in conjunction with increased phytoplankton productivity in shelf surface waters. Organic matter advected mainly by dense shelf water cascading was fresher due to the transport of newly produced particles and a variable terrestrial fraction; this fraction depended on the proportion of resuspended material accumulated during previous high discharge periods that was involved in each transport pulse. The tight link shown between meteorological conditions and organic matter transport is important for continental margin geochemical studies as future changes in climatic conditions may lead to dramatic changes in carbon sequestration capability and in the ecosystems of deep margin environments. 相似文献
94.
Julien Ruffault Nicolas K. Martin-StPaul Serge Rambal Florent Mouillot 《Climatic change》2013,117(1-2):103-117
The Mediterranean area is one of the regions of the world where GCMs agree the most on precipitation changes due to climate change. In this study we aim to assess the impact of recent climate change on drought features of Mediterranean ecosystems in Southern France. Regional climatic trends for the 1971–2006 period are compared to drought trends based on a water balance model accounting for soil properties, vegetation structure and functioning. Drought, defined here as periods when soil water potentials drop below ??0.5 MPa, is described in terms of intensity, duration and timing, which are integrative of both climate variability and site conditions. Temporal trends in precipitation, temperature and solar radiation lead altogether to drier and warmer conditions over the region but with a high spatial heterogeneity; for similar climatic trends, a significant increase in drought intensity was detected in the wettest areas of the region, whereas drought intensity in the driest areas did not change. Indeed, in the wettest areas, we observed an earlier onset of drought by about 1 month, but a constant end of drought. In the driest areas of the region, we observed the same earlier onset of drought but combined with an earlier end of drought, thus leading to a shift of the dry season without increasing its duration. The definition of drought features both in terms of intensity but also of seasonal timing appears relevant to capture historical or forecasted changes in ecosystem functioning. Studies concerning climate change impacts on forested ecosystems should be interpreted with caution when using climate proxies alone. 相似文献
95.
The “optimal fingerprint” method, usually used for detection and attribution studies, requires to know, or, in practice, to
estimate the covariance matrix of the internal climate variability. In this work, a new adaptation of the “optimal fingerprints”
method is presented. The main goal is to allow the use of a covariance matrix estimate based on an observation dataset in
which the number of years used for covariance estimation is close to the number of observed time series. Our adaptation is
based on the use of a regularized estimate of the covariance matrix, that is well-conditioned, and asymptotically more precise,
in the sense of the mean square error. This method is shown to be more powerful than the basic “guess pattern fingerprint”,
and than the classical use of a pseudo-inverted truncation of the empirical covariance matrix. The construction of the detection
test is achieved by using a bootstrap technique particularly well-suited to estimate the internal climate variability in real
world observations. In order to validate the efficiency of the detection algorithm with climate data, the methodology presented
here is first applied with pseudo-observations derived from transient regional climate change scenarios covering the 1960–2099
period. It is then used to perform a formal detection study of climate change over France, analyzing homogenized observed
temperature series from 1900 to 2006. In this case, the estimation of the covariance matrix is only based on a part of the
observation dataset. This new approach allows the confirmation and extension of previous results regarding the detection of
an anthropogenic climate change signal over the country. 相似文献
96.
Study of the total lightning activity in a hailstorm 总被引:1,自引:0,他引:1
Joan Montany Serge Soula Nicolau Pineda Oscar van der Velde Pere Clapers Glria Sol Joan Bech D. Romero 《Atmospheric Research》2009,91(2-4):430-437
A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground. 相似文献
97.
98.
Why Is the Climate Forcing of Sulfate Aerosols So Uncertain? 总被引:2,自引:0,他引:2
l. IntroductionAlthough the aerosol has been recognized as an important factor which has innuence onthe past, present and future climate for a long time, it still has much uncertainty in assessingits climate forcing. The direct radiative forcing of sulfate aerosols has been estimated rangingfrom --0.3 W/ m2 to --0.9 W/ m2 in recent publications (Charlson et al., l992, Kiehl andBriegleb l993; Taylor and Penner 1994, Boucher and Anderson l995, Kieh1 and Rodhe l995;Chuang et al., l997, Penne… 相似文献
99.
Petrology and U/Pb geochronology of the Telohat migmatites,Aleksod, Central Hoggar,Algeria 总被引:6,自引:0,他引:6
Pierre Barbey Jean-Michel Bertrand Serge Angoua Danielle Dautel 《Contributions to Mineralogy and Petrology》1989,101(2):207-219
The Aleksod region is composed of metasedimentary rocks and large areas of biotite and hornblende-bearing migmatites. Anatexis
associated with the main deformation stages, occurred under high pressure and temperature conditions estimated at 13±2 Kbar
and 750±50° C. The bulk mineralogical composition of the Telohat migmatites shows that their protolith was granodioritic.
Internal structures of zircons and U-Pb data suggest a polyphased evolution, with a 2131±12 Ma age for the protolith and a
609±17 Ma age for the Pan-African tectono-metamorphic evolution, thus precluding any Kibaran event in the Aleksod area. Leucosomes
are richer in Sr and display lower Rb, Zr, Nb, Y, Th, U and REE contents than melanosomes wherein accessory phases are stored.
Eu contents are also lower in the leucosomes but in lesser proportion than the other rare earth's, leading to a significant
positive anomaly. Petrogenetic modelling accounting for accessory mineral phases clearly shows that the trace element contents
of leucosomes and melanosomes follow a distribution law consistent neither with equilibrium nor fractional melting. Their
trace element patterns are best explained by the model of disequilibrium melting, with mixing of a few residual phases. The
present results and previous Sr isotopic data as well raise the question of disequilibrium melting in anatexis of crustal
material
CRPG Contribution no 782 相似文献
100.
An harmonic analysis of limestone bed and marl interbed thicknesses of pelagic Berriasian-Barremian interval from the Angles area (SE France) shows that marly parts of the succession contain frequencies significantly different from calcareous ones. Some of the resulting periods are in the Milankovitch frequency band but many others are different from those predicted by the orbital theory. 相似文献