Modelling centennial sediment waves in an eroding landscape – catchment complexity          下载免费PDF全文

Jeroen M. Schoorl  Arnaud J. A. M. Temme  Tom Veldkamp 《地球表面变化过程与地形》2014,39(11):1526-1537

Sediment flux dynamics in fluvial systems have often been related to changes in external drivers of topography, climate or land cover. It is well known that these dynamics are non‐linear. Recently, model simulations of fluvial activity and landscape evolution have suggested that self‐organization in landscapes can also cause internal complexity in the sedimentary record. In this contribution one particular case of self‐organization is explored in the Sabinal field study area, Spain, where several dynamic zones of sedimentation and incision are observed along the current river bed. Whether these zones can be caused by internal complexity was tested with landscape evolution model (LEM) LAPSUS (Landscape Process Modelling at Multi‐dimensions and Scales). During various 500 year simulations, zones of sedimentation appear to move upstream and downstream in eroding river channels (‘waves’). These waves are visualized and characterized for a range of model settings under constant external forcing, and the self‐organizing process behind their occurrence is analysed. Results indicate that this process is not necessarily related to simplifications in the model and is more generic than the process of bed‐armouring that has recently been recognized as a cause for complexity in LEM simulations. We conclude that autogenic sediment waves are the result of the spatial propagation in time of feedbacks in local transport limited (deposition) and detachment limited (erosion) conditions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Protostellar Collapse Induced by Compression     

Hennebelle Patrick  Belloche Arnaud  Whitworth Anthony  André Philippe 《Astrophysics and Space Science》2004,292(1-4):355-360

We present numerical simulations of the evolution of low-mass, isothermal, molecular cores which are subjected to an increase in external pressure. If the external pressure increases very slowly, the core approaches instability quite quasi-statically. However, for faster compressions, a compression wave is driven into the core (Hennebelle, P., Whitworth, A., Gladwin, P. and André, P.: 2003a MNRAS 340, 870). Quantitative comparisons with observational velocity and density profiles are presented. The consequences of this compression for the fragmentation of the cloud is investigated and discussed.  相似文献   

On the errors on Ω₀: Monte Carlo simulations of the EMSS cluster sample     

Jamila Oukbir  Monique Arnaud 《Monthly notices of the Royal Astronomical Society》2001,326(2):453-462

We perform Monte Carlo simulations of synthetic EMSS cluster samples, to quantify the systematic errors and the statistical uncertainties on the estimate of Ω₀ derived from fits to the cluster number density evolution and to the X-ray temperature distribution up to z =0.83 . We identify the scatter around the relation between cluster X-ray luminosity and temperature to be a source of systematic error, of the order of Δ_systΩ₀=0.09 , if not properly taken into account in the modelling. After correcting for this bias, our best Ω₀ is 0.66. The uncertainties on the shape and normalization of the power spectrum of matter fluctuations imply relatively large uncertainties on this estimate of Ω₀, of the order of Δ_statΩ₀=0.1 at the 1 σ level. On the other hand, the statistical uncertainties due to the finite size of the high-redshift sample are twice as small. Therefore, what is needed in order to improve the accuracy of Ω₀ estimates based on cluster number density evolution is a more reliable measure of the local temperature function and a better understanding of the cluster observed properties both in the local Universe and at high redshift, that is the relation between cluster mass, temperature and luminosity. This requires detailed observations of X-ray selected cluster samples, in comparison with hydrodynamic simulations including refined physics.  相似文献   

Sr and Nd isotopes as tracers of clastic sources in Lake Le Bourget sediment (NW Alps, France) during the Little Ice Age: Palaeohydrology implications     

Marie Revel-Rolland  Fabien Arnaud  Marc Desmet  Chantal Alibert 《Chemical Geology》2005,224(4):183-200

Geochemical methods (major elements and Sr, Nd isotopes) have been used to (1) characterize Lake Le Bourget sediments in the French Alps, (2) identify the current sources of the clastic sediments and estimate the source variability over the last 600 years. Major element results indicate that Lake Le Bourget sediments consist of 45% clastic component and 55% endogenic calcite. In addition, several individual flood levels have been identified during the Little Ice Age (LIA) on the basis of their higher clastic content (> 70%).Potential sources of Lake Le Bourget clastic sediments have been investigated from Sr and Nd isotope compositions. The sediments from the Sierroz River and Leysse River which are mainly derived from the Mesozoic Calcareous Massifs are characterised by lower ⁸⁷Sr/⁸⁶Sr ratios and slightly lower ?_Nd(0) ratios than the Arve River sediments which are derived from the Palaeozoic Mont-Blanc External Crystalline Massifs. The Rhône River appears to have been the main source of clastic sediments into the lake for the last 600 years, as evidenced by a similar Sr and Nd isotopic compositions analyzed in core B16 sediments (⁸⁷Sr/⁸⁶Sr = 0.719, ?_Nd(0) = − 10) and in the sediments of the Rhône River (⁸⁷Sr/⁸⁶Sr = 0.719, ?_Nd(0) = − 9.6).The isotopic signatures of flood events and background samples from core B16 in Lake Le Bourget are also similar. This indicates that prior to ∼ 1800, the inputs into the lake have remained relatively homogeneous with the proportion of clastic component mainly being a function of the palaeohydrology of the Rhone River. Early human modification (deforestation and agriculture) of the lake catchment before the 1800s appears to have had little influence on the source of clastic sediments.  相似文献   

Interactions between Volatile Reduced Sulfur Compounds and Metals in the Seine Estuary (France)     

Amandine Cozic  Eric Viollier  Jean-François Chiffoleau  Joël Knoery  Emmanuelle Rozuel 《Estuaries and Coasts》2008,31(6):1063-1071

Concentrations of volatile hydrogen sulfide (H₂S), carbonyl sulfide (OCS), methane thiol (MeSH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) in the Seine estuary (France) were investigated in spring 2005 using samples collected from the first meter beneath the surface. Levels of dissolved metals (Ag, Cd, Cu, Zn, Ni, Co, Pb), suspended particulate matter, and particular organic carbon were also assessed. Maximum concentrations were 0.80 nM for H₂S, 0.64 nM for OCS, 3.06 nM for MeSH, 11.06 nM for DMS, and 1.18 nM for DMDS, and different features were observed for the five volatile reduced sulfur compounds (VRSCs). Experiments were conducted to determine silver–VRSC conditional stability constants. Major interactions were observed between H₂S and Ag, which may partially account for the absence of volatile H₂S at the lowest salinities. OCS, MeSH, and DMS did not interact with Ag, as revealed by their insignificant K′ values. Variations in concentrations along the salinity gradient may be explained by the influence of phytoplanktonic compounds.  相似文献   

Sediments of Lake Vens (SW European Alps,France) record large-magnitude earthquake events     

Jade Petersen  Bruno Wilhelm  Marie Revel  Yann Rolland  Christian Crouzet  Fabien Arnaud  Elodie Brisset  Eric Chaumillon  Olivier Magand 《Journal of Paleolimnology》2014,51(3):343-355

We studied sediment cores from Lake Vens (2,327 m asl), in the Tinée Valley of the SW Alps, to test the paleoseismic archive potential of the lake sediments in this particularly earthquake-sensitive area. The historical earthquake catalogue shows that moderate to strong earthquakes, with intensities of IX–X, have impacted the Southern Alps during the last millennium. Sedimentological (X-ray images, grain size distribution) and geochemical (major elements and organic matter) analyses show that Lake Vens sediments consist of a terrigenous, silty material (minerals and organic matter) sourced from the watershed and diatom frustules. A combination of X-ray images, grain-size distribution, major elements and magnetic properties shows the presence of six homogenite-type deposits interbedded in the sedimentary background. These sedimentological features are ascribed to sediment reworking and grain sorting caused by earthquake-generated seiches. The presence of microfaults that cross-cut the sediment supports the hypothesis of seismic deposits in this system. A preliminary sediment chronology is provided by ²¹⁰Pb measurement and AMS ¹⁴C ages. According to the chronology, the most recent homogenite events are attributable to damaging historic earthquakes in AD 1887 (Ligure) and 1564 (Roquebillière). Hence, the Lake Vens sediment recorded large-magnitude earthquakes in the region and permits a preliminary estimate of recurrence time for such events of ~400 years.  相似文献   

A 4D sedimentological approach to reconstructing the flood frequency and intensity of the Rhône River (Lake Bourget,NW European Alps)     

J.-P. Jenny  B. Wilhelm  F. Arnaud  P. Sabatier  C. Giguet Covex  A. Mélo  B. Fanget  E. Malet  E. Ployon  M. E. Perga 《Journal of Paleolimnology》2014,51(4):469-483

A high-resolution sedimentological study of Lake Bourget was conducted to reconstruct the flood frequency and intensity (or magnitude) in the area over the last 350 years. Particular emphasis was placed on investigating the spatio-temporal distribution of flood deposits in this large lake basin. The thicknesses of deposits resulting from 30 flood events of the Rhône River were collected over a set of 24 short sediment cores. Deposit thicknesses were compared with instrumental data for the Rhône River discharge for the period from 1853 to 2010. The results show that flood frequency and intensity cannot be reliably reconstructed from a single core because of the inhomogeneous flood-deposit geometry in such a large lake. From all documented flood-deposit thicknesses, volumes of sediment brought into the lake during each flood event were computed through a Kriging procedure and compared with the historical instrumental data. The results show, in this study, that reconstructed sediment volumes are well correlated to maximal flood discharges. This significant correlation suggests that the increase of embankment and dam settlements on the Rhône River during the last 150 years has not significantly affected the transport of the smallest sediment fraction during major flood events. Hence, assessment of the flood-sediment volumes deposited in the large Lake Bourget is the only way to reliably reconstruct the flood frequency and intensity.  相似文献