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71.
Marion Sautier Roger Martin-Clouaire Robert Faivre Michel Duru 《Climatic change》2013,120(1-2):341-355
Research aiming to reduce the vulnerability of agricultural systems to climate variability and change requires practical appraisal of their climatic exposure. We propose a method to map local climatic conditions over a given period to a set of productivity and management-related indicators that are specific to grassland-based livestock systems. Our method based on a reference system balances herbage production and feed requirements over a long period (≥ 30 years) and provides boundaries for productivity-defined seasons and indicators for surplus or shortage of herbage at seasonal and annual scales. This exposure-assessment method was applied to five climatically contrasting locations in south-western France. The trends and variability of the exposure indicators were analysed for past (1980–2010) and future (2035–2065) periods, considering the A1B scenario of the IPCC. Despite high year-to-year variability and the heterogeneity of the climatic situations studied, we show that climate change can modify the boundaries of productivity-defined seasons and seasonal herbage surplus or shortage. Moreover, the exposure indicators succeed in detecting climate-induced changes and distinguishing situations where a classical exposure indicator, such as annual forage production, could not. The exposure indicators highlight the forage productivity and the timing of production associated with local climatic conditions. These features fit the temporal scale at which farmers consider farm management and are highly suitable for identifying adaptation strategies that reduce the vulnerability of grassland-based livestock systems. 相似文献
72.
C. C. Kuranz R. P. Drake T. L. Donajowski K. K. Dannenberg M. Grosskopf D. J. Kremer C. Krauland D. C. Marion H. F. Robey B. A. Remington J. F. Hansen B. E. Blue J. Knauer T. Plewa N. Hearn 《Astrophysics and Space Science》2007,307(1-3):115-119
We present data from recent high-energy-density laboratory experiments designed to explore the Rayleigh–Taylor instability
under conditions relevant to supernovae. The Omega laser is used to create a blast wave structure that is similar to that
of the explosion phase of a core-collapse supernova. An unstable interface is shocked and then decelerated by the planar blast
wave, producing Rayleigh–Taylor growth. Recent experiments were performed using dual, side-on, x-ray radiography to observe
a 3D “egg crate” mode and an imposed, longer-wavelength, sinusoidal mode as a seed perturbation. This paper explores the method
of data analysis and accurately estimating the position of important features in the data. 相似文献
73.
Marion Ferrat Dominik J. Weiss Stanislav Strekopytov Hongyun Chen Youbin Sun Ryuji Tada 《Geochimica et cosmochimica acta》2011,75(21):6374-6399
The Asian Monsoon forms an important part of the earth’s climate system, yet our understanding of the past interactions between its different sub-systems, the East Asian and Indian monsoons, and between monsoonal winds and other prevailing wind currents such as the Westerly jet, is limited, particularly in central Asia. This in turn affects our ability to develop climate models capable of accurately predicting future changes in atmospheric circulation patterns and monsoon intensities in Asia. Provenance studies of mineral dust deposited in terrestrial settings such as peat bogs can address this problem directly, by offering the possibility to examine past deposition rates and wind direction, and hence reconstruct past atmospheric circulation patterns. However, such studies are challenged by several issues, most importantly the identification of proxies that unambiguously distinguish between the different potential dust sources and that are independent of particle size. In addition, a single analytical method that is suitable for sample preparation of both dust source (i.e. desert sand, soil) and receptor (i.e. dust archive such as peat or soil profiles) material is desirable in order to minimize error propagation derived from the experimental and analytical work. Here, an improved geochemical framework of provenance tracers to study atmospheric circulation patterns and palaeomonsoon variability in central Asia is provided, by combining for the first time mineralogical as well as major and trace elemental (Sc, Y, Th and the rare earth elements) information on Chinese (central Chinese loess plateau, northern Qaidam basin and Taklamakan, Badain Juran and Tengger deserts), Indian (Thar desert) and Tibetan (eastern Qinghai-Tibetan Plateau) dust sources.Quartz, feldspars and clay minerals are the major constituents of all studied sources, with highly variable calcite contents reflected in the CaO concentrations. Chinese and Tibetan dust sources are enriched in middle REE relative to the upper continental crust and average shale but the Thar desert has a REE signature distinctly different from all other dust sources. There are significant differences in major, trace and REE compositions between the coarse and fine fractions of the surface sands, with the finest <4 μm fraction enriched in Al2O3, Fe2O3, MnO, MgO and K2O and the <32 μm fractions in Sc, Y, Th and the REE relative to the coarse fractions. The <4 μm fraction best represents the bulk REE geochemistry of the samples. The provenance tracers Y/∑REE, La/Er, La/Gd, Gd/Er, La/Yb, Y/Tb, Y/La, Y/Nd and to a certain extent the europium anomaly Eu/Eu∗ (all REE normalized to post-Archean Australian shale, PAAS) are particle size-independent tracers, of which combinations of Y/∑REE, La/Yb, Y/Tb, Y/La and Eu/Eu∗ can be used to distinguish the Thar desert, the Chinese deserts, the Chinese loess plateau and the Tibetan soils. Their independence upon grain size means that these tracers can be applied to the long-range provenance tracing of Asian dust even when only bulk samples are available in the source region. Combinations of La/Th, Y/Tb, Y/∑REE, Sc/La and Y/Er distinguish the Tibetan soils from the Chinese loess plateau and the Chinese deserts. La/Th and notably Th/∑REE isolate the signature of the Badain Juran desert and the combination of Sc/La and Y/Er that of the Taklamakan desert. The similarity in all trace and REE-based provenance tracers between the northern Qaidam basin and Tengger desert suggests that these two deposits may have a common aeolian source. 相似文献
74.
Zhengle Chen Jian Liu Hongliang Gong Fengbin Han Stephanie Marion Briggs Enjiu Zheng Guo Wang 《Tectonophysics》2011,497(1-4):45-56
The Dingshan area located in the northern part of the Junggar Basin of northwestern China is a significant prospect area for sandstone-type uranium deposits in China, where mainly Cenozoic rocks were deposited. The Cenozoic strata can be divided into four units according to the prior data and our own field observation. Sedimentary studies indicate that most Cenozoic strata were deposited under a hot and arid climate in a continental environment. The sedimentary facies are alluvial-fan, meandering-fluvial, and fluvio-lacustrine. Field investigation and interpretation of satellite images suggest that Cenozoic tectonics in the area is characterized by reactivation of early deep-seated thrusts, resulting in extensional fractures and formation of many small depressions in the shallow crustal level. Measurement of joint orientations suggests that regional shortening direction trends in north–south in the middle Pleistocene as indicated by the ESR (Electronic Spin Resonance) age of 0.1–0.4 Ma obtained from fault gouge and gypsum deposits. A four-stage sedimentation-tectonic evolution model of the northern Junggar Basin during the Late Cenozoic can be established based on reconstruction of sedimentary filling processes and Cenozoic tectonic movements. We suggest that landform evolution and groundwater movement are controlled by active tectonics, indicating that Late Cenozoic tectonic activities may also play important roles in the formation of sandstone-type uranium deposits. Therefore, a new metallogenic model for sandstone-type uranium deposits is proposed. 相似文献
75.
Marion Michael 《Australian Journal of Earth Sciences》2013,60(3):211-222
Graphs of the yearly number of volcanoes in eruption from 1900 through 1968 for 21 volcanic areas of the circum‐Pacific belt show fluctuations with statistically significant amplitudes in eight of the areas, and some indication of auto‐correlation and periodicity in 14 of them. Thus, in a total of 16 out of the 21 areas studied, these volcanic pulses appear to be statistically significant. They are best defined in the New Guinea‐Solomons area, Santa Cruz‐New Hebrides‐Matthew Island area, and the West Indies where the numbers of volcanoes in eruption have significant fluctuations in amplitude, are auto‐correlated and tend to be periodic. The periods (around 17 years) of the western Pacific areas are, with few exceptions, much less than those of the eastern Pacific areas suggesting an overall first‐order cause for these volcanic fluctuations which, in each area, seem to be due to the volcanoes’ responding to regional stress pulses. These may be caused by variations in stress owing to sea‐floor spreading on the East Pacific Rise, the dichotomy of periods being due to a different mantle‐flow regime on either side of it, resulting from the proximity of the Rise to the eastern Pacific margin. An examination of the years for which the maximum or one less than the maximum number of volcanoes are in eruption suggests that large pulses of volcanic activity tend to migrate southwards. There are six main pulses in the western Pacific and three in the eastern. The latter are better‐defined and more widely spaced in time. The pulse occurring in the first decade of this century is simultaneous on both sides of the Pacific, a reflexion of the global tectonic instability of this period. The reason for this southward migration of the volcanic pulses is not yet known. It may be a strain‐release phenomenon. 相似文献
76.
Uwe Hoffmann Christoph Breitkreuz Karel Breiter Sergey Sergeev Klaus Stanek Marion Tichomirowa 《International Journal of Earth Sciences》2013,102(1):73-99
Nine SHRIMP U/Pb ages on zircon and two Pb/Pb single zircon ages have been determined from Late Paleozoic volcanic rocks from Saxony and northern Bohemia. Samples came from the Teplice-Altenberg Volcanic Complex, the Meissen Volcanic Complex, the Chemnitz Basin, the Döhlen Basin, the Brandov-Olbernhau Basin, and the North Saxon Volcanic Complex. The Teplice-Altenberg Volcanic Complex is subdivided into an early Namurian phase (Mikulov Ignimbrite, 326.8 ± 4.3 Ma), thus older than assumed by previous studies, and a late caldera-forming phase (Teplice Ignimbrite, 308.8 ± 4.9 Ma). The age of the latter, however, is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint. The Leutewitz Ignimbrite, product of an early explosive volcanic episode of the Meissen Volcanic Complex yielded an age of 302.9 ± 2.5 Ma (Stephanian A). Volcanic rocks intercalated in the Brandov-Olbernhau Basin (BOB, 302 ± 2.8 Ma), Chemnitz Basin (CB, 296.6 ± 3.0 Ma), Döhlen Basin (DB, 296 ± 3.0 Ma), and the North Saxon Volcanic Complex (NSVC, c. 300–290 Ma) yielded well-constrained Stephanian to Sakmarian ages. The largest Late Paleozoic ignimbrite-forming eruption in Central Europe, the Rochlitz Ignimbrite, has a well-defined middle Asselian age of 294.4 ± 1.8 Ma. Ages of palingenic zircon revealed that the Namurian-Westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous Paleozoic geodynamic phases. The Precambrian inherited ages support the chronostratigraphic structure assumed for the Saxo-Thuringian Zone of the Variscan Orogen. The present results help to improve the chronostratigraphic allocation of the Late Paleozoic volcanic zones in Central Europe. At the same time, the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the Variscan Orogeny. 相似文献
77.
The environment is impacted by natural and anthropogenic disturbances that occur at different spatial and temporal scales, and that lead to major changes and even disequilibria when exceeding the resiliency capacities of the ecosystem. With an annual mean flow of 1700 m3 s−1, the Rhône River is the largest of the western Mediterranean basin. Its annual solid discharges vary between 2 and 20 Mt, with flood events responsible for more than 70% of these amounts. 相似文献
78.
79.
Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO4 and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O2) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O2) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO4 and water was observed over a pH range of 0–2 only at 50 °C, whereas no exchange occurred at lower temperatures over a period of 8 a. The calculated half-time of the exchange rate for 50 °C (pH = 0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions (T 25 °C, pH 3) for decades.Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O2 to pyrite surface sites. The sorption of molecular O2 is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO4. The calculated bulk contribution of atmospheric O2 in the dissolved SO4 reached up to 50% during initial oxidation stages (first 5 days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100 days. Based on the direct incorporation of molecular O2 in the early-formed sulfates, chemisorption and electron transfer of molecular O2 on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10 days, the O of all newly-formed sulfates originates only from water, indicating direct interaction of hydroxyls from water with S at the anodic S pyrite surface site. Then, the role of molecular O2 is as proposed in previous studies: acting as electron acceptor only at the cathodic Fe pyrite surface site for oxidation of Fe(II) to Fe(III). 相似文献
80.
B. Carpentier P. Ungerer I. Kowalewski C. Magnier J.P. Courcy A.Y. Huc 《Organic Geochemistry》1996,24(12):1115-1139
Oil-gas phase equilibria is likely to represent one of the main causes of observed compositional heterogeneities in fields. Our research has been focused mainly on the light C14-hydrocarbons fraction and can be divided into two parts. The first part was performed with a fluid mixture of a Middle East crude oil and a synthetic gas, and includes PVT experiments, high resolution-gas chromatography (HR-GC) and 13C gas chromatography-combustion-isotopic ratio mass spectrometry (GC-C-IR-MS) analyses. Our observations show that under a given set of PT conditions there is a preferential separation of aromatics into the oil phase and isoalkanes into the gas phase. Moreover, the data from 13C GC-C-IRMS suggest a small isotopic fractionation between the two phases, with the gas being relatively isotopically lighter. The second part is theoretical, and uses Equation of State (EOS) calculations which successfully simulate the previous experiment. 相似文献