10Be‐derived assessment of accelerated erosion in a glacially conditioned inner gorge,Entlebuch, Central Alps of Switzerland     

Fabien Van den Berg  Fritz Schlunegger  Naki Akçar  Peter Kubik 《地球表面变化过程与地形》2012,37(11):1176-1188

Inner gorges often result from the propagation of erosional waves related to glacial/interglacial climate shifts. However, only few studies have quantified the modern erosional response to this glacial conditioning. Here, we report in situ ¹⁰Be data from the 64 km² Entlen catchment (Swiss Alps). This basin hosts a 7 km long central inner gorge with two tributaries that are >100 m‐deeply incised into thick glacial till and bedrock. The ¹⁰Be concentrations measured at the downstream end of the gorge yield a catchment‐wide erosion rate of 0.42 ± 0.04 mm yr^‐1, while erosion rates are consistently lower upstream of the inner gorge, ranging from 0.14 ± 0.01 mm yr^‐1 to 0.23 ± 0.02 mm yr^‐1. However, ¹⁰Be‐based sediment budget calculations yield rates of ~1.3 mm yr^‐1 for the inner gorge of the trunk stream. Likewise, in the two incised tributary reaches, erosion rates are ~2.0 mm yr^‐1 and ~1.9 mm yr^‐1. Moreover, at the erosional front of the gorge, we measured bedrock incision rates ranging from ~2.5 mm yr^‐1 to ~3.8 mm yr^‐1. These rates, however, are too low to infer a post‐glacial age (15–20 ka) for the gorge initiation. This would require erosion rates that are between 2 and 6 times higher than present‐day estimates. However, the downcutting into unconsolidated glacial till favored high erosion rates through knickzone propagation immediately after the retreat of the LGM glaciers, and subsequent hillslope relaxation led to a progressive decrease in erosion rates. This hypothesis of a two‐ to sixfold decrease in erosion rates does not conflict with the ¹⁰Be‐based erosion rate budgets, because the modern erosional time scale recorded by ¹⁰Be cover the past 2–3 ka only. These results point to the acceleration of Holocene erosion in response to the glacial overprint of the landscape. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Numerical resolution of well-balanced shallow water equations with complex source terms   总被引：3，自引：0，他引：3  

Qiuhua Liang  Fabien Marche 《Advances in water resources》2009

This paper presents a well-balanced numerical scheme for simulating frictional shallow flows over complex domains involving wetting and drying. The proposed scheme solves, in a finite volume Godunov-type framework, a set of pre-balanced shallow water equations derived by considering pressure balancing. Non-negative reconstruction of Riemann states and compatible discretization of slope source term produce stable and well-balanced solutions to shallow flow hydrodynamics over complex topography. The friction source term is discretized using a splitting implicit scheme. Limiting value of the friction force is derived to ensure stability. This new numerical scheme is validated against four theoretical benchmark tests and then applied to reproduce a laboratory dam break over a domain with irregular bed profile.  相似文献   

Groundwater-driven temperature changes at thermal springs in response to recent glaciation: Bormio hydrothermal system,Central Italian Alps     

Giorgio Volpi  Fabien Magri  Paolo Frattini  Giovanni B. Crosta  Federico Riva 《Hydrogeology Journal》2017,25(7):1967-1984

Thermal springs are widespread in the European Alps, with hundreds of geothermal sites known and exploited. The thermal circulation and fluid outflows were examined in the area around Bormio (Central Italian Alps), where ten geothermal springs discharge from dolomite bodies located close to the regional Zebrù thrust. Water is heated in deep circulation systems and upwells vigorously at a temperature of about 40 °C. Heat and fluid transport is explored by steady and transient three-dimensional finite-element simulations taking into account the effect of the last glaciation, which in the study area was recognized to end around 11,000–12,000 years ago. The full regional model (ca. 700 km²) is discretized with a highly refined triangular finite-element planar grid. Numerical simulations suggest a reactivation of the system following the end of the Last Glacial Maximum. Results correctly simulate the observed discharge rate of ca. 2,400 L/min and the spring temperatures after ca. 13,000 years from deglaciation, and show a complete cooling of the aquifer within a period of approximately 50,000 years. Groundwater flow and temperature patterns suggest that thermal water flows through a deep system crossing both sedimentary and metamorphic lithotypes along a fracture network associated with the thrust system. This example gives insights into the influences of deep alpine structures and glaciations on groundwater circulation that control the development of many hydrothermal systems not necessarily associated with convective heat flow.  相似文献   

Response of estuarine meio- and macrofauna to in situ bioremediation of oil-contaminated sediment     

Schratzberger M  Daniel F  Wall CM  Kilbride R  Macnaughton SJ  Boyd SE  Rees HL  Lee K  Swannell RP 《Marine pollution bulletin》2003,46(4):430-443

Numerous studies have demonstrated the efficacy of bioremediation for enhancing oil removal but the ecological effect on shoreline biota is unclear. Therefore, a field experiment was designed at an intertidal sandflat in SW England to assess the effects of nutrient addition to oiled sediments on meio- and macrofauna for a period of up to 45 weeks. Natural assemblages were exposed to different types of experimental treatments (no oil, oil alone, oil treated with slow-release fertiliser or liquid fertiliser). Bioremediation stimulated the microbial population and increased oil biodegradation. This, however, did not result in faster recolonisation rates of fertilised versus non-fertilised oiled sediments. Mild effects of oil and bioremediation treatments on benthic fauna were observed, including short-term shifts in dominance patterns. Decreased abundance of dominant species in the oiled compared to unoiled sediments resulted in significantly higher evenness of benthic assemblages within the first 11 weeks of the experiment.  相似文献   

Stable Carbon and Nitrogen Isotopic     

Jennifer Lawson  Peter T Doran  Fabien Kenig  David J Des marais  John C Priscu 《Aquatic Geochemistry》2004,10(3-4):269-301

The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the lakes of Taylor Valley. The ¹³C compositions of seasonally ice-free edges of the lakes (moats) are enriched relative to under-ice organic matter. Thus, the organic carbon isotopic composition of buried sediments may be a proxy for sample position within the lake. In the moats, ¹³C values are governed by limited CO₂diffusion across benthic cyanobacterial cell membranes. During a high glacial melt (2001–2002) season, both ¹³C_POM and ¹³C_BOM in the moats were more depleted than during previous low melt years. We propose that this occurred in response to higher [CO₂]_(aq) and/or reduced growth rates resulting from turbidity-induced light limitation. Though moats and under-ice environments are usually poorly connected, during the 2001–2002 season, the enrichment of the ¹³C_POM values at 6 m depth in the stream-proximal sites relative to deep-profile sites implies enhanced connectivity between these environments. The ¹³C compositions of BOM and POM profiles in Lake Hoare and Lake Fryxell indicate that these lakes are dominated by benthic productivity. In contrast, in Lake Bonney, the similarity of the ¹³C values of BOM and POM indicates the pelagic component dominance in the carbon cycle.  相似文献   

Present Observational Status of Solar-type stars     

François Bouchy  Fabien Carrier 《Astrophysics and Space Science》2003,284(1):21-28

Observing stellar oscillations provides a powerful probe for studying stellarinteriors. The frequencies of these modes depend on the properties of the star and give strong constraints on stellar models and evolution theories. The five-minute oscillations in the Sun, induced by stochastic excitation of its convective zone, have provided a wealth of information about the solar interior and has led to significant revisions to solar models. Until recently, the Sun was the only star in which solar-like oscillations were clearly established and characterized. The most important difficulty lies in the extremely small amplitude of the acoustic modes. Thanks in great part to high precision ground based Doppler measurements, solar-like oscillations have been now clearly detected in a growing list of main sequence and subgiant stars (Procyon, Hyi, Her A, Cen A, Eri and Boo). In some of them, p-modes were identified and characterized. New results and prospects in this field are presented.  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   

Stochastic forecasts of seawater intrusion towards sustainable groundwater management: application to the Korba aquifer (Tunisia)     

Jaouher Kerrou  Philippe Renard  Fabien Cornaton  Pierre Perrochet 《Hydrogeology Journal》2013,21(2):425-440

A stochastic study of long-term forecasts of seawater intrusion with an application to the Korba aquifer (Tunisia) is presented. Firstly, a geostatistical model of the exploitation rates was constructed, based on a multi-linear regression model combining incomplete direct data and exhaustive secondary information. Then, a new method was designed and used to construct a geostatistical model of the hydraulic conductivity field by combining lithological information and data from hydraulic tests. Secondly, the effects of the uncertainties associated with the pumping rates and the hydraulic conductivity field on the 3D density-dependent transient model were analysed separately and then jointly. The forecasts of the impacts of two different management scenarios on seawater intrusion in the year 2048 were performed by means of Monte Carlo simulations, accounting for uncertainties in the input parameters as well as possible changes of the boundary conditions. Combining primary and secondary data allowed maps of pumping rates and the hydraulic conductivity field to be constructed, despite a lack of direct data. The results of the stochastic long-term forecasts showed that, most probably, the Korba aquifer will be subject to important losses in terms of regional groundwater resources.  相似文献   

Projecting future drought in Mediterranean forests: bias correction of climate models matters!   总被引：1，自引：0，他引：1  

Julien Ruffault  Nicolas K Martin-StPaul  Carole Duffet  Fabien Goge  Florent Mouillot 《Theoretical and Applied Climatology》2014,117(1-2):113-122

Global and regional climate models (GCM and RCM) are generally biased and cannot be used as forcing variables in ecological impact models without some form of prior bias correction. In this study, we investigated the influence of the bias correction method on drought projections in Mediterranean forests in southern France for the end of the twenty-first century (2071–2100). We used a water balance model with two different atmospheric climate forcings built from the same RCM simulations but using two different correction methods (quantile mapping or anomaly method). Drought, defined here as periods when vegetation functioning is affected by water deficit, was described in terms of intensity, duration and timing. Our results showed that the choice of the bias correction method had little effects on temperature and global radiation projections. However, although both methods led to similar predictions of precipitation amount, they induced strong differences in their temporal distribution, especially during summer. These differences were amplified when the climatic data were used to force the water balance model. On average, the choice of bias correction leads to 45 % uncertainty in the predicted anomalies in drought intensity along with discrepancies in the spatial pattern of the predicted changes and changes in the year-to-year variability in drought characteristics. We conclude that the choice of a bias correction method might have a significant impact on the projections of forest response to climate change.  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