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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. Source


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. Source


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). Source


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. Source


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. Source

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