B. Lemieux

University Joseph Fourier - Grenoble 1, Grenoble, Rhône-Alpes, France

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Publications (5)38.6 Total impact

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    ABSTRACT: The TALDICE project retrieved a new ice core from a peripheral dome of East Antarctica. Talos Dome (72° 49' S, 159° 11' E; 2315 m; mean accumulation rate 80 kg m-2 yr-1; mean annual temp. -41°C) is located in the Northern Victoria Land, close to the Ross Sea. Back-trajectory analyses suggest that the site is mostly fed by air masses arriving both from the Pacific (and Ross Sea) and Indian Ocean sectors. The drilling team reached the depth of 1619.2 m in December 2007, covering more than 300,000 years of climatic records according to a preliminary age scale. Up to 50,000 years before present, the ice core dating is based on the use of a glaciological model and an inverse method, constrained by numerous and reliable age markers. They are defined from the synchronization of CH4 records of Talos Dome and Greenland ice cores, using in particular the rapid CH4 changes associated with the last termination and the D/O events. Measurements of the CH4 mixing ratio have been performed by LGGE and Bern laboratories using slightly different techniques, with a depth resolution ranging between 0.5 to 4 m. The comparison of water isotopic profiles from Talos Dome, EDC, EDML (Antarctica) and North-GRIP (Greenland) ice cores, once put on a common time scale deduced from CH4 and the optimisation from the inverse method, reveals that during the last deglaciation and the last glacial period, climatic changes at Talos Dome were essentially in phase with the Antarctic plateau, extending the bipolar seesaw sequence to this coastal site. This comparison also highlights different climatic behaviors between sites situated in the Indo/Pacific sector and in the Atlantic sector of the Southern Ocean, the latter showing more abrupt swings toward relatively warm conditions of the Antarctic Isotope Maxima. We will discuss this feature with respect to the bipolar seesaw model of Stocker (2003) and with respect to other climatic proxies.
    05/2010;
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    ABSTRACT: This article was submitted without an abstract, please refer to the full-text PDF file.
    IOP Conference Series Earth and Environmental Science 02/2009; 6(28).
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    ABSTRACT: The international project IPICS of the International Polar Year 2007/09 aims in particular to use new coastal drillings in Antarctica to study the regional variability of Antarctic climate, and its relationship with climatic changes in other regions of the Earth. Here, we investigate a new drilling conducted by a consortium of five European nations led by Italy, on the coastal site of Talos Dome (Antarctica). It reached a depth of 1620 m during the field season 2007/2008. We measured the methane (CH4) mixing ratio in the Talos Dome ice core in the depth range from 73 (close-off) to 1620 m, at a depth resolution ranging from 0.5 to 4 m. Two laboratories (LGGE and Bern) were involved, using slightly different techniques. The well-known temporal evolution of this signal allows us to define tie points with respect to other ice cores from Greenland and Antarctica, using in particular the rapid CH4 changes associated with the last termination and the Dansgaard/Oeschger events. We also investigated the isotopic composition of molecular oxygen (making another dating tool in the gas phase of the ice core) in order to bring additional chronological constraints during periods where CH4 changes become more muted. It has been measured at the LSCE during MIS 2, 4, and the last glacial inception. Comparing these records with their counterpart in other ice cores, and using an ice flow model and an inverse method, we propose a preliminary age scale for the trapped gas and the surrounding ice at Talos Dome. It indicates that the Talos Dome stratigraphy is undisturbed down to 1560 m, corresponding to about 300 000 years BP. More importantly, the comparison of water isotopic profiles from the Talos Dome, EDC, and NGRIP ice cores, once put on a common time scale, reveals that during the last deglaciation, climatic changes at Talos Dome were essentially in phase with the Antarctic plateau, and that the bipolar seesaw with Greenland temperature is also valid for this coastal site, thus contradicting the neighbouring Taylor Dome ice core findings. We will also investigate if those conclusions can be extended to the last glacial period.
    01/2009;
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    ABSTRACT: Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between approximately 350 and approximately 800 parts per 10(9) by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of approximately 1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is approximately 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by approximately 100,000 yr glacial-interglacial cycles up to approximately 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.
    Nature 06/2008; 453(7193):383-6. · 38.60 Impact Factor
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    ABSTRACT: The deep ice core recovered from Dome Concordia in the framework of EPICA, the European Project for Ice Coring in Antarctica, has extended the record of Antarctic climate history back to 800,000 years [Jouzel et al., 2007]. We present the current status of measurements of CO2, CH4 and N2O on air trapped in the bubbles of the Dome C ice core. CO2 is measured in two laboratories using different techniques (laser absorption spectroscopy or gas chromatography on samples of 8 and 40 g of ice which are mechanically crushed or milled, respectively). CH4 and N2O are extracted using a melt-refreeze technique and then measured by gas chromatography (in two laboratories for CH4). The greenhouse gas concentrations have now been measured on the lowest 200 m of the Dome C core, going back to Marine Isotope Stage 20 (MIS 20) as verified by a consistent gas age/ice age difference determined at termination IX [Jouzel et al., 2007]. The atmospheric CO2 concentration mostly lagged the Antarctic temperature with a rather strong correlation throughout the eight and a half glacial cycles, but with significantly lower CO2 values between 650 and 750 kyr BP. Its lowest level ever measured in ice cores (172 ppmv) is observed during MIS 16 (minimum centered at 667 kyr BP according to the EDC3 chronology) redetermining the natural span of CO2 to 172-300 ppmv. With 2245 individual measurements, the CH4 concentration is now reconstructed over 800,000 years from a single core, with an average time resolution of 380 years. Spectral analyses of the CH4 signal show an increasing contribution of precession during the last four climatic cycles compared with the four older ones, suggesting an increasing impact of low latitudes sources/sinks. Millennial scale features in this very detailed signal allows us to compare their occurrence with ice volume reconstructions and the isotopic composition of precipitation over the East Antarctic plateau. N2O is still affected by glaciological artefacts involving dust content in the ice, and its exact temporal evolution remains to be deciphered. These measurements represent the basis of the so-called "EPICA Challenge" [Wolff et al., 2005]: they will put the climate and carbon cycle modelers under the challenge of fully understanding how orbital parameters and climate system configurations could have built such tight coupling between atmospheric composition and natural climate change during the late Quaternary. Jouzel et al., Science 317, 793-796, 10 August 2007 Wolff et al., EOS 86, N°38, 341-345, 20 September 2005
    AGU Fall Meeting Abstracts. 12/2007;