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41.
Camille Jourdain Nicolas Claude Pablo Tassi Florian Cordier Germain Antoine 《地球表面变化过程与地形》2020,45(5):1100-1122
Alpine gravel-bed rivers are dynamic systems that have been subjected to many anthropic alterations in the past centuries. Riparian vegetation development on previously bare sediment bedforms has been a common adjustment, raising important management issues in terms of flood risks and biodiversity. Many of these rivers are also channelized, and as a result present a pattern of alternate bars. Considering recent advances in numerical biomorphodynamic modeling, this study aims at exploring numerically the morphodynamics of alternate bars in the presence of riparian vegetation. To this end, a dynamic vegetation module has been implemented on top of an existing morphodynamic model, accounting for ecological processes of seed dispersal, seedling recruitment, growth, and mortality. Numerical simulations have been performed on a simplified reach of a gravel-bed river with free migrating alternate bars at initial state. In this work 96 scenarios have been simulated, each representing 50 years of channel evolution, with different flood regimes characterized by various peak discharges and flood durations. Yearly peak discharge variability is explicitly modeled in 48 scenarios. Model outcomes present two possible equilibrium biomorphodynamic behaviors: stationary vegetated bars, or free migrating bars in the case of frequent vegetation removal during floods. This binary behavior holds true when the stochasticity of annual peak discharges is represented, and for a wide range of parameter values included in vegetation dynamic modeling. Transient mobility of vegetated bars is observed in specific configurations where large sediment deposits deflect the flow field, eroding bar heads. Modeled bar wavelengths are in the range of values predicted for free bars by linear bar theory, and remain far from the theoretical values of hybrid, steady bars. The shift from unvegetated migrating bars to steady vegetated bars seems to show that in these simulations vegetation constitutes a hydraulic forcing, leading to a shift from free bars to forced bars, with a final configuration largely inherited from the initial state. © 2019 John Wiley & Sons, Ltd. 相似文献
42.
Martim A.B. Moulton Patrick A. Hesp Graziela Miot da Silva Camille Bouchez Muriel Lavy Guilherme B. Fernandez 《地球表面变化过程与地形》2019,44(2):459-470
Studies have shown that the impact of climate change, human and animal actions on coastal vegetation can turn stabilized dunes into active mobile dunes and vice versa. Yet, the driving factors that trigger vegetation changes in coastal dunes are still not fully understood. In the transgressive dunefields of the Younghusband Peninsula (south-east coast of South Australia) historical aerial photographs show an increase in vegetation cover over the last ~70 years. This study attempts to identify the causes of the changes in vegetation cover (1949 to 2017) observed in a typical section of the coastal dune systems of the Peninsula. Vegetation cover was first estimated for various years using the available historical aerial photography (long-term changes – 1949 to 2017) and recent satellite imagery (short-term annual changes – 2010 to 2017) for the area, and then results were discussed against the observed changes in climatic variables and rabbit density, factors that could have played a role in this transformation. Results of long-term changes show that the vegetation cover has increased significantly from 1949 to 2017, from less than 7% vegetation cover to almost 40%, increasing dune stabilization and forming parabolic dune systems. Periods with the largest growth in vegetation cover (1952-1956 and 2009-2013) coincide with a significant decline in rabbit numbers. Rabbit density was found to be the primary factor linked to the rapid vegetation growth and stabilization of the dunefield, for both decadal long-term (last 68 years) and annual short-term changes (last 8 years). Other factors such as changes in rainfall, aeolian sediment transport, land use practices, and the introduction of invasive plants have apparently played a limited to negligible role in this stabilization process. © 2018 John Wiley & Sons, Ltd. 相似文献
43.
Camille Litty Fritz Schlunegger Naki Akçar Pierre Lanari Marcus Christl Christof Vockenhuber 《地球表面变化过程与地形》2019,44(5):991-1003
Sediment accumulation can occur in response to a change in either tectonic or climatic driving forces. Here, we explore these controls on the deposition of the Lima Conglomerate, Peru. We use a combination of quantitative methods to explore the age of sediment accumulation, the provenance of the material and the paleo-erosion rates recorded by these deposits. Isochron burial dating with cosmogenic 10Be and 26Al yield an age of c. 500 ka for the base (490 ± 70 ka) and the uppermost sample situated c. 30 m higher upsection (490 ± 80 ka). Results of paleo-erosion rate estimates with concentrations of in situ 10Be show a c. 60% increase from 105 ± 10 mm ka-1 for the base to 169 ± 14 mm ka-1 for the uppermost sample. Finally, provenance tracing with in situ U/Pb ages on detrital zircon implies that the material has been derived from the entire drainage basin. The combination of results suggests that sediment accumulation occurred in response to an erosional pulse, which affected the entire basin within a short time interval. Because 10Be data represents a large spatial record of erosion, we exclude the possibility where a breakout of a lake or a focused release of material in response to earthquakes, were responsible for the large material flux. Instead, the erosional pulse was likely to have occurred at the scale of the entire basin, supporting the idea of a larger-scale, most likely climate driven control. In this context, the accumulation age of c. 500 ka falls into an orbital cycle fostering the emerging picture in the literature that sediment routing in the Andes have most likely been driven by climate and cyclic changes. We suggest that the Andean mountain range offers an ideal laboratory to explore the erosional history in relation to climate patterns, at least in Peru. © 2018 John Wiley & Sons, Ltd. 相似文献
44.
Olivine dissolution in molten silicates: An experimental study with application to chondrule formation 
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下载免费PDF全文 Mg‐rich olivine is a ubiquitous phase in type I porphyritic chondrules in various classes of chondritic meteorites. The anhedral shape of olivine grains, their size distribution, as well as their poikilitic textures within low‐Ca pyroxene suggest that olivines suffer dissolution during chondrule formation. Owing to a set of high‐temperature experiments (1450–1540 °C) we determined the kinetics of resorption of forsterite in molten silicates, using for the first time X‐ray microtomography. Results indicate that forsterite dissolution in chondrule‐like melts is a very fast process with rates that range from ~5 μm min?1 to ~22 μm min?1. Forsterite dissolution strongly depends on the melt composition, with rates decreasing with increasing the magnesium and/or the silica content of the melt. An empirical model based on forsterite saturation and viscosity of the starting melt composition successfully reproduces the forsteritic olivine dissolution rates as a function of temperature and composition for both our experiments and those of the literature. Application of our results to chondrules could explain the textures of zoned type I chondrules during their formation by gas‐melt interaction. We show that the olivine/liquid ratio on one hand and the silica entrance from the gas phase (SiOg) into the chondrule melt on the other hand, have counteracting effects on the Mg‐rich olivine dissolution behavior. Silica entrance would favor dissolution by maintaining disequilibrium between olivine and melt. Hence, this would explain the preferential dissolution of olivine as well as the preferential abundances of pyroxene at the margins of chondrules. Incipient dissolution would also occur in the silica‐poorer melt of chondrule core but should be followed by crystallization of new olivine (overgrowth and/or newly grown crystals). While explaining textures and grain size distributions of olivines, as well as the centripetal distribution of low‐Ca pyroxene in porphyritic chondrules, this scenario could also be consistent with the diverse chemical, isotopic, and thermal conditions recorded by olivines in a given chondrule. 相似文献
45.
Camille Clerc Philippe Boulvais Yves Lagabrielle Michel de Saint Blanquat 《International Journal of Earth Sciences》2014,103(1):141-163
Brecciated and fractured peridotites with a carbonate matrix, referred to as ophicalcites, are common features of mantle rocks exhumed in passive margins and mid-oceanic ridges. Ophicalcites have been found in close association with massive peridotites, which form the numerous ultramafic bodies scattered along the North Pyrenean Zone (NPZ), on the northern flank of the Pyrenean belt. We present the first field, textural and stable isotopic characterization of these rocks. Our observations show that Pyrenean ophicalcites belong to three main types: (1) a wide variety of breccias composed of sorted or unsorted millimeter- to meter-sized clasts of fresh or oxidized ultramafic material, in a fine-grained calcitic matrix; (2) calcitic veins penetrating into fractured serpentine and fresh peridotite; and (3) pervasive substitution of serpentine minerals by calcite. Stable isotopic analyses (O, C) have been conducted on the carbonate matrix, veins and clasts of samples from 12 Pyrenean ultramafic bodies. We show that the Pyrenean ophicalcites are the product of three distinct genetic processes: (1) pervasive ophicalcite resulting from relatively deep and hot hydrothermal activity; (2) ophicalcites in veins resulting from tectonic fracturing and cooler hydrothermal activity; and (3) polymictic breccias resulting from sedimentary processes occurring after the exposure of subcontinental mantle as portions of the floor of basins which opened during the mid-Cretaceous. We highlight a major difference between the eastern and western Pyrenean ophicalcites belonging, respectively, to the sedimentary and to the hydrothermal types. Our data set points to a possible origin of the sedimentary ophicalcites in continental endorheic basins, but a post-depositional evolution by circulation of metamorphic fluids or an origin from relatively warm marine waters cannot be ruled out. Finally, we discuss the significance of such discrepancy in the characteristics of the NPZ ophicalcites in the frame of the variable exhumation history of the peridotites all along the Pyrenean realm. 相似文献
46.
Lique Camille Johnson Helen L. Plancherel Yves Flanders Robert 《Climate Dynamics》2015,45(5-6):1235-1252
Climate Dynamics - The impact of climate warming on the ocean near Greenland is investigated with a high resolution coupled global climate model. The ocean around Greenland exhibits a strong... 相似文献
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Climate Dynamics - Biosphere–atmosphere interactions play a very important role in modulating regional climate. To capture these bi-directional interactions, a dynamic vegetation model, the... 相似文献
48.
Camille Rivard Emmanuelle Montargès-Pelletier Delphine Vantelon Manuel Pelletier Chithra Karunakaran Laurent J. Michot Frédéric Villieras Nicolas Michau 《Physics and Chemistry of Minerals》2013,40(2):115-132
In the context of radioactive waste repository in geological formation, kaolinite-metallic iron interaction in chlorine solution was conducted in batch experiments, under anoxic conditions at 90 °C during 9 months. After a mineralogical characterization at a global scale, products were analyzed at the micrometer and nanometer scales by X-ray absorption spectroscopic techniques (XAS and STXM). Absorption at Al, Si and Fe edges was investigated to have a complete overview of the distribution and status of constituting elements. Whereas Si K-edge results do not evidence significant evolution of silicon status, investigations at Al K-edge and Fe L-edges demonstrate variations at aggregate and particle scales of IVAl:VIAl and Fe2+:Fe3+ ratios. Spectroscopic data evidence the systematic crystallization of Fe-serpentines onto the remaining particles of kaolinite and the absence of pure species (kaolinite or Fe-serpentines). Combination of spatially resolved spectroscopic analyses and TEM-EDXS elemental distribution aims to calculate unit cell formulae of Fe-serpentines layers and abundance of each species in mixed particles. For most of the investigated particles, results reveal that the variations of particles composition are directly linked to the relative contributions of kaolinite and Fe-berthierine in mixed particles. However, for some particles, microscale investigations evidence crystallization of two other Fe-serpentines species, devoid of aluminum, cronstedtite and greenalite. 相似文献
49.
The link between the Atlantic Multidecadal Oscillation (AMO) and low-frequency changes of the Atlantic Meridional Overturning Circulation (AMOC) is investigated in three historical and five control simulations with different climate models. An AMOC intensification is followed by a positive AMO phase in each case, but the time lag and the strength of the AMO–AMOC link depend on the model and the type of simulation. In historical simulations, the link is sensitive to the method used to remove the influence of external and anthropogenic forcing from the sea surface temperature (SST) before defining the AMO. Subtracting the regression onto the global mean SST leads to better correlations between the AMO and the AMOC than linear or quadratic detrending, or removing the global mean SST, but a dynamical filter based on linear inverse modeling (LIM) yields even slightly higher correlations. The LIM filter, which decomposes the SST field into non-orthogonal normal modes that may have a physical interpretation, allows investigating whether removing Pacific links from SST improves the AMOC–AMO correlation. In several cases, there is a small improvement when removing the links to the El Niño Southern Oscillation, but the correlation becomes weaker in one historical simulation, so no firm conclusion can be drawn. Additionally removing the modes associated with the Pacific decadal variability strongly degrades the representation of AMOC changes by the AMO in one model, and it tends to reduce the AMOC–AMO correlation in most others, reflecting the strong relation between the Pacific and the Atlantic at decadal scales. The LIM-based filter is finally applied to observed SSTs, confirming that the AMO amplitude is smaller and its recent positive phase weaker than when the global effects are represented by a linear trend. When the global signal is removed, the observed AMO leads the Pacific Decadal Oscillation, but does not significantly lag it, as suggested earlier, stressing the need to carefully remove global changes when investigating low-frequency interbasin connections. 相似文献
50.
Why do people not learn from flood disasters? Evidence from Vietnam’s northwestern mountains 总被引：4，自引：2，他引：2
Iven Schad Petra Schmitter Camille Saint-Macary Andreas Neef Marc Lamers La Nguyen Thomas Hilger Volker Hoffmann 《Natural Hazards》2012,62(2):221-241
This article explores how the causes and impacts of a flood event as perceived by local people shape immediate responses and future mitigation efforts in mountainous northwest Vietnam. Local flood perception is contrasted with scientific perspectives to determine whether a singular flood event will trigger adjustments in mitigation strategies in an otherwise rarely flood-affected area. We present findings from interdisciplinary research drawing on both socioeconomic and biophysical data. Evidence suggests that individual farmers?? willingness to engage in flood mitigation is curbed by the common perception that flooding is caused by the interplay of a bundle of external factors, with climatic factors and water management failures being the most prominent ones. Most farmers did not link the severity of flooding to existing land use systems, thus underlining the lack of a sense of personal responsibility among farmers for flood mitigation measures. We conclude that local governments cannot depend on there being a sufficient degree of intrinsic motivation among farmers to make them implement soil conservation techniques to mitigate future flooding. Policy makers will need to design measures to raise farmers?? awareness of the complex interplay between land use and hydrology and to enhance collective action in soil conservation by providing appropriate incentives and implementing coherent long-term strategies. 相似文献