Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement

Aix-en-Provence, France

Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement

Aix-en-Provence, France
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Rebeix R.,University of Nimes | Rebeix R.,French National Center for Scientific Research | Le Gal La Salle C.,University of Nimes | Mayer A.,University of Avignon | And 4 more authors.
Applied Geochemistry | Year: 2014

The radioactive isotope 36Cl, with a half-life of 301ka, is a valuable chronometer for estimation of groundwater residence time up to 2 millions of years. Aerial thermonuclear fission bomb tests, performed during the late 1950s, injected a massive amount of this isotope into the atmosphere, which exceeded the natural fallout signal. Since this bomb pulse, atmospheric 36Cl deposition tends to return to natural fallout rate. The monitoring of this attenuation can provide a good opportunity to extend the use of this chronometer to shorter time spans. Venice's lagoon alimentation zone shows groundwaters with residence times distributed over last fifty years. This permits the estimation of a continuous 36Cl deposition curve, free from latitudinal and seasonal variations of the signal. Three old groundwater samples, with residence times comprised in the range -900 to -8000BP, allow the estimation of a mean natural deposition of 49atm-2s-1 and are in good agreement with 36Cl fallout observed for the last 40,000years by (Plummer et al., 1997). For the bomb pulse period, a fallout of 5300atm-2s-1 was calculated. This was followed by a strong attenuation period, taking place until the 1980s, during which the fallout reached values ranging between 167 and 354atm-2s-1. The attenuation reached then a plateau: it experienced a slower lowering until the actual deposition, with fallout values calculated between 124 and 252atm-2s-1. This persistence of high deposition rate was classically attributed to biological and atmospherical recycling processes or underestimation of the natural atmospheric production of the 36Cl. Additional source of 36Cl production has been envisaged through the activation of chlorine radicals from stratospherical CFCs, leading to a 36Cl production rate comparable with that of Ar spallation from the first approximation. Lastly, the latitudinal factor of the attenuation of the fallout rate is discussed and the impact of the jet streams is proposed as an explanation for the discrepancies in the attenuation rate. © 2014 Elsevier Ltd.

Avouac J.-P.,California Institute of Technology | Lallier-Verges E.,CNRS Earth Sciences Institute of Orléans | Bourles D.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Braucher R.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | And 5 more authors.
Earth and Planetary Science Letters | Year: 2011

Erosion is a fundamental player of the interactions existing between internal geodynamics and climate, in particular through its influence on the carbon dioxide budget. However, long term (>1Ma) erosion rates, estimated indirectly from sediment budget, remain poorly constrained. While some studies suggest that worldwide erosion rates increased at the Plio-Pleistocene climatic transition (~4-2Ma), the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins. In the present study, we estimate erosion rates over the last ~9Ma using in situ produced cosmogenic 10Be concentrations measured in magnetostratigraphically dated continental sediments. We focus on an intracontinental endorheic watershed draining the northern Tianshan in Central Asia, a key region regarding the ongoing debate. While erosion rates between 0.1 and 1mm.yr-1 are derived from most of our record, they reach values as high as ~2.5mm.yr-1 from 2.5 to 1.7Ma. Then, after 1.7Ma, recent and modern erosion rates fell below 1mm.yr-1. This temporary increase is correlated with the onset of Quaternary ice ages and suggests that global climate had a significant and transient impact on erosion. © 2011 Elsevier B.V.

Shroder J.F.,University of Nebraska at Omaha | Owen L.A.,University of Cincinnati | Seong Y.B.,Korea University | Bishop M.P.,University of Nebraska at Omaha | And 6 more authors.
Quaternary International | Year: 2011

Mass movement constitutes an important process in the evolution of landscapes in mountain regions. However, the role of massive slope failures in denudational unloading and landscape evolution has not been extensively studied. Large-scale mass movements in one of the greatest mountain ranges on Earth, the Central Karakoram in Pakistan, were therefore examined to help evaluate their role in landscape evolution in high mountains. Specifically, four major mass-movement complexes (Ghoro Choh rock avalanche, Busper sackung and slope failure, Gomboro slope failure, and Urdokas rockslide), each comprising 106 m3 of debris, were assessed and mapped in detail. Two of these mass-movement complexes, the Ghoro Choh rock avalanche and Gomboro slope failure, were dated using terrestrial cosmogenic nuclides. The ages of occurrence of the mass-movement complexes studied in the Central Karakoram date from the late Pleistocene to the Holocene. The four major mass-movement complexes all involved the removal of mass from the tops of mountain ridges and peaks that failed and were subsequently transported towards the bottom of their respective valleys. Such massive movement of mass is anomalous compared to other forms of mass movement and is generally spatially coincident with exposed deeply buried gneiss-dome structures. These large-scale movements appear to be part of a coupled system involving river incision and glacial debuttrussing, although earthquakes might have triggered these mass movements. This study illustrates the role of climate forcing, which is part of a coupled system of denudational unloading, but it is unclear whether high-magnitude, low-frequency events such as these initiate the isostatic and tectonic influx of mass, or if sustained high-magnitude denudation resulting from a coupled system is responsible for the exhumation of buried structures. © 2010 Elsevier Ltd and INQUA.

Stoffel M.,University of Geneva | Stoffel M.,University of Bern | Khodri M.,Paris-Sorbonne University | Corona C.,University Blaise Pascal | And 9 more authors.
Nature Geoscience | Year: 2015

Explosive volcanism can alter global climate, and hence trigger economic, political and demographic change. The climatic impact of the largest volcanic events has been assessed in numerous modelling studies and tree-ring-based hemispheric temperature reconstructions. However, volcanic surface cooling derived from climate model simulations is systematically much stronger than the cooling seen in tree-ring-based proxies, suggesting that the proxies underestimate cooling; and/or the modelled forcing is unrealistically high. Here, we present summer temperature reconstructions for the Northern Hemisphere from tree-ring width and maximum latewood density over the past 1,500 years. We also simulate the climate effects of two large eruptions, in AD 1257 and 1815, using a climate model that accounts explicitly for self-limiting aerosol microphysical processes. Our tree-ring reconstructions show greater cooling than reconstructions with lower spatial coverage and based on tree-ring width alone, whereas our simulations show less cooling than previous simulations relying on poorly constrained eruption seasons and excluding nonlinear aerosol microphysics. Our tree-ring reconstructions and climate simulations are in agreement, with a mean Northern Hemisphere extra-tropical summer cooling over land of 0.8 to 1.3 °C for these eruptions. This reconciliation of proxy and model evidence paves the way to improved assessment of the role of both past and future volcanism in climate forcing. © 2015 Macmillan Publishers Limited. All rights reserved.

Levard C.,Stanford University | Levard C.,Duke University | Levard C.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Mitra S.,Stanford University | And 8 more authors.
Environmental Science and Technology | Year: 2013

Pristine silver nanoparticles (AgNPs) are not chemically stable in the environment and react strongly with inorganic ligands such as sulfide and chloride once the silver is oxidized. Understanding the environmental transformations of AgNPs in the presence of specific inorganic ligands is crucial to determining their fate and toxicity in the environment. Chloride (Cl-) is a ubiquitous ligand with a strong affinity for oxidized silver and is often present in natural waters and in bacterial growth media. Though chloride can strongly affect toxicity results for AgNPs, their interaction is rarely considered and is challenging to study because of the numerous soluble and solid Ag-Cl species that can form depending on the Cl/Ag ratio. Consequently, little is known about the stability and dissolution kinetics of AgNPs in the presence of chloride ions. Our study focuses on the dissolution behavior of AgNPs in chloride-containing systems and also investigates the effect of chloride on the growth inhibition of E.coli (ATCC strain 33876) caused by Ag toxicity. Our results suggest that the kinetics of dissolution are strongly dependent on the Cl/Ag ratio and can be interpreted using the thermodynamically expected speciation of Ag in the presence of chloride. We also show that the toxicity of AgNPs to E.coli at various Cl - concentrations is governed by the amount of dissolved AgCl x (x-1)- species suggesting an ion effect rather than a nanoparticle effect. © 2013 American Chemical Society.

Yiou P.,CEA Saclay Nuclear Research Center | Bard E.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Dandin P.,Meteo - France | Legras B.,CNRS Dynamic Meteorology Laboratory | And 4 more authors.
Climate of the Past | Year: 2010

The relationship between solar activity and temperature variation is a frequently discussed issue in climatology. This relationships is usually hypothesized on the basis of statistical analyses of temperature time series and time series related to solar activity. Recent studies (Le Moul et al., 2008, 2009; Courtillot et al., 2010) focus on the variabilities of temperature and solar activity records to identify their relationships. We discuss the meaning of such analyses and propose a general framework to test the statistical significance for these variability-based analyses. This approach is illustrated using European temperature data sets and geomagnetic field variations. We show that tests for significant correlation between observed temperature variability and geomagnetic field variability is hindered by a low number of degrees of freedom introduced by excessively smoothing the variability-based statistics. © Author(s) 2010.

Parrenin F.,Laboratoire Chrono Environnement | Parrenin F.,CNRS Laboratory for Glaciology and Environmental Geophysics | Petit J.-R.,CNRS Laboratory for Glaciology and Environmental Geophysics | Masson-Delmotte V.,French Climate and Environment Sciences Laboratory | And 11 more authors.
Climate of the Past | Year: 2012

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0-145 kyr BP by using the volcanic signatures. 102 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0-45 kyr interval that provided 56 tie points to the ice core chronologies (Udisti et al., 2004). This synchronisation will serve to establish Antarctic Ice Core Chronology 2012, the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Lake Vostok, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. No significant phase difference is detected between the EDC and Vostok isotopic records, but depth shifts between the Vostok 3G and 5G ice cores prevent from looking at this problem accurately. Three possible candidates for the Toba volcanic super-eruption 73 kyr ago are suggested in the Vostok and EDC volcanic records. Neither the ECM, DEP nor the sulfate fingerprints for these 3 events are significantly larger than many others in the records. © 2012 Author(s).

Cossart E.,University of Paris Pantheon Sorbonne | Bourles D.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Braucher R.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Carcaillet J.,Laboratoire Of Geodynamique Des Chaines Alpines | And 2 more authors.
Geomorphologie: Relief, Processus, Environnement | Year: 2011

This paper aims to provide an overview of the investigations led in the Upper-Durance catchment (upstream Guillestre), focusing on the disappearance of glaciers after the Last Glacial Maximum. It is based on extensive fieldwork, describing and mapping the geomorphic remnants of past-glaciations, and 35 Cosmic Ray Exposure ages. A four-stage chronological sequence summarises glacial variations during the Late-Glacial/Holocene transition. The main results provide both chronological data (two generations of moraines identified as Younger Dryas and Preboreal) and spatial data (asymmetry of glaciers development in the Upper-Durance catchment during the Late-Glacial), providing new findings that may be useful for palaeo-climatologists.

Mesnage V.,University of Rouen | Lecoq N.,Jean Monnet University | Sakho I.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Vennin A.,University of Rouen
Comptes Rendus - Geoscience | Year: 2013

The dialysis porewater sampler, type Hesslein, allows sampling of sediment interstitial water according to a continuous gradient between sediment and the water column. Its equilibration time fluctuates according to the nature of sediment, so it has to be measured in each kind of sediment. The aim of this work is to develop a physical diffusion model in order to determine an equilibration time without using extensive field experiments. The model is validated by real nutrient concentration profiles obtained on two estuaries under different climates, moderate climate (estuary of the Seine) and tropical dry climate (estuary of Somone, Senegal). The results highlight that the equilibration of the dialysis porewater sampler is not homogeneous over the full sediment height investigated. Other sediment characteristics as compaction, rate of bioturbation or bacterial density must be taken into account in order to find a well-calculated value of the equilibration time. © 2013 Académie des sciences.

Owen L.A.,University of Cincinnati | Yi C.,CAS Institute of Tibetan Plateau Research | Finkel R.C.,University of California at Santa Cruz | Finkel R.C.,Center Europeen Of Recherche Et Denseignement Des Geosciences Of Lenvironnement | Davis N.K.,University of Cincinnati
Quaternary Science Reviews | Year: 2010

The Quaternary glaciation of Gurla Mandhata (Naimona'nyi), an impressive, isolated dome-shaped massif situated in a remote region of southern Tibet, was examined using glacial geomorphic methods and dated using 10Be terrestrial cosmogenic nuclides. The oldest moraines, representing an expanded ice cap that stretched ∼ 5km into the foreland of the Gurla Mandhata massif, likely formed during marine isotope stage (MIS) 10 or an earlier glacial cycle. Another glacial expansion of coalescing piedmont type occurred during the early part of the last glacial cycle or the penultimate glacial cycle, after which glaciers became restricted to entrenched valley types. Impressive latero-frontal moraines at the mouths of most valleys date to the early part of the last glacial cycle and MIS 3. A succession of six sets of moraines within the valleys and up to the contemporary glaciers show that glaciers advanced during the Lateglacial, Early Holocene, Neoglacial and possibly Little Ice Age. The change of style of glaciation throughout the latter part of the Quaternary, from expanded ice caps to deeply entrenched valley glaciers, might reflect: (1) climatic controls with reduced moisture supply to the region over time; and/or (2) tectonic controls reflecting increase basin subsidence due to detachment faulting and enhanced valley incision. © 2010 Elsevier Ltd.

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