297 research outputs found
Terminations VI and VIII (∼ 530 and ∼ 720 kyr BP) tell us the importance of obliquity and precession in the triggering of deglaciations
No full textThe main variations of ice volume of the last million years can be explained from orbital parameters by assuming climate oscillates between two states: glaciations and deglaciations (Parrenin and Paillard, 2003; Imbrie et al., 2011) (or terminations). An additional combination of ice volume and orbital parameters seems to form the trigger of a deglaciation, while only orbital parameters seem to play a role in the triggering of glaciations. Here we present an optimized conceptual model which realistically reproduce ice volume variations during the past million years and in particular the timing of the 11 canonical terminations. We show that our model looses sensitivity to initial conditions only after ∼200 kyr at maximum: the ice volume observations form a strong attractor. Both obliquity and precession seem necessary to reproduce all 11 terminations and both seem to play approximately the same role. More precisely, obliquity plays a fundamental role in the triggering of termination VI (~530 kyr BP), while precession plays a fundamental role in the triggering of termination VIII (~720 kyr ago)
New modeling of the Vostok ice flow line and implication for the glaciological chronology of the Vostok ice core
Get PDFWe have used new spaceborne (elevation) and airborne (ice thickness) data to constrain a 2D1/2 model of snow accumulation and ice flow along the Ridge B-Vostok station ice flow line (East Antarctica). We show that new evaluations of the ice flow line geometry (from the surface elevation), ice thickness (from low-frequency radar data), and basal melting and sliding change significantly the chronology of the Vostok ice core. This new Vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the Dome Fuji glaciological timescale. At the same time, the new model shows significantly older ages than the previous GT4 timescale for the last glacial part, being thus in better agreement with the GRIP and GISP2 chronologies
© Author(s) 2012. CC Attribution 3.0 License. Climate of the Past
No full textTerminations VI and VIII ( ∼ 530 and ∼ 720 kyr BP) tell us the importance of obliquity and precession in the triggering of deglaciation
A study of different‑scale relationship between changes of the surface air temperature and the СО2 concentration in the atmosphere
Get PDFA concept of the anthropogenic origin of the current global climate warming assumes that growth of concentration of the atmospheric carbon dioxide and other greenhouse gases is of great concern in this process. However, all earlier performed analyses of the Antarctic ice cores, covering the time interval of several glacial cycles for about 1 000 000 years, have demonstrated that the carbon dioxide concentration changes had a certain lag relative to the air temperature changes by several hundred years during every beginning of the glacial terminations as well as at endings of interglacials. In contrast to these findings, a recently published careful analysis of Antarctic ice cores (Parrenin et al., 2013) had shown that both, the carbon dioxide concentration and global temperature, varied almost synchronously during the transition from the last glacial maximum to the Holocene. To resolve this dilemma, a special technique for analysis of the paleoclimatic time series, based on the wavelets, had been developed and applied to the same carbon dioxide concentration and temperature time series which were used in the above paper of Parrenin et al., 2013. Specifically, a stack of the Antarctic δ18O time series (designated as ATS) and the deuterium Dome C – EPICA ones (dD) were compared to one another in order to: firstly, to quantitatively estimate differences between time scales of these series; and, secondly, to clear up the lead–lag relationships between different scales variations within these time series. It was found that accuracy of the mutual ATS and dD time series dating lay within the range of 80–160 years. Perhaps, the mutual dating of the temperature and carbon dioxide concentration series was even worse due to the assumed displacement of air bubbles within the ice. It made us to limit our analysis by the time scales of approximately from 800 to 6000 years. But it should be taken into account that any air bubble movement changes the time scale of the carbon dioxide series as a whole. Therefore, if a difference between variations in any temperature and the carbon dioxide time series is found to be longer than 80–160 years, and if these variations are timescale‑dependent, it means that the bubble displacements are not essential, and so these advancing and delays are characteristic of the time series being compared. Our wavelet‑based comparative and different‑scale analysis confirms that the relationships between the carbon dioxide concentration and temperature variations were essentially timescale‑dependent during the transition from the last glacial maximum to the Holocene. The carbon dioxide concentration variations were ahead of the temperature ones during transition from the glacial maximum to the Boelling – Alleroud warming as well as from the Young Drias cooling to the Holocene optimum. However, the temperature variations were ahead during the transition from the Boelling – Alleroud warming to the Young Drias cooling and during the transition from the Holocene optimum to the present‑day climate
Age model of sediment core GeoB7920-2
No full textTie points to stck benthic isotope record of MD95 2042 on GRIP ss09sea timescale: Reference: Absolute calibration of the Greenland time scale: implications for Antarctic time scales and for D14C (N.J Shackleton, R.G Fairbanks, Tzu-chien Chiu, F. Parrenin, Quaternary Science Reviews 23 (2004) 1513-1522), Reference: Phase relationships between millennial scale events 64000 to 24000 years ago (N.J.Shackleton, M.A. Hall and E. Vincent, Paleoceanography, Vol. 15, no. 6, (2000), 565-569
Datation glaciologique des forages profonds en Antarctique et modélisation conceptuelle des paléoclimats : implications pour la théorie astronomique des paléoclimats.
No full textThe aim of this study is to bring new elements concerning the astronomical theory of paleoclimates using two tools : glaciological dating of polar ice cores using an inverse method and conceptual models of paleoclimate. We show how an inverse method applied to the glaciological dating model enables us to obtain an optimal chronology and to analyse its uncertainties. It is not possible to obtain a chronology for Vostok that satisfies all chronological constraints, probably because of our poor knowledge of the conditions along the ice flow line, upstream of Vostok. The chronologies for Dome C and Dome F are coherent with the constraints, meaning that the simple glaciological model used in the case of a dome is adequate. The Dome F case allows us to show that the Devils Hole record is probably biased by local conditions, and suggest that the phase relationship between insolation and Antarctic temperature is roughly constant. We also confirm that thinning is more important in the upper part of the ice sheet for a dome than for the rest of the flow line. Moreover, we suggest that estimates of the accumulation during glacial periods based on saturation vapour pressure and spatial isotope−surface temperature relationships are overestimated by ~30%. The conceptual model we developed yields a description of the sea level variations during the Quaternary as a response to the insolation forcing. We show that sea level variations can be explained with a conceptual model forced by insolation changes. In particular, we justify why the most important sea level transitions occurred when insolation changes were the weakest. Moreover, we show that small insolation−climate phase variations during deglaciations are compatibles with the astronomical theory of paleoclimate.L'objectif de cette thèse est d'apporter des éléments nouveaux concernant la théorie astronomique des paléoclimats au travers de deux outils : la datation glaciologique des forages polaires grâce à une méthode inverse et les modèles conceptuels de climat. Concernant la datation des forages polaires, nous montrons l'intérêt d'appliquer une méthode inverse au modèle de datation glaciologique pour obtenir une chronologie optimale et en analyser les incertitudes. Pour Vostok, il n'est pas possible d'obtenir une chronologie qui satisfasse toutes les informations chronologiques, probablement à cause d'une méconnaissance des conditions en amont de la ligne d'écoulement. Les chronologies pour Dôme C et Dôme F sont cohérentes avec les contraintes, ce qui signifie que le modèle glaciologique simple utilisé pour ces dômes est adéquate. Le cas de Dôme F nous permet de montrer que l'enregistrement de Devils Hole est probablement biaisé par des conditions locales et suggère que les déphasages entre insolation et température Antarctique sont grossièrement constants dans le temps. Nous confirmons par ailleurs que l'amincissement est plus fort dans le haut du glacier dans le cas d'un dôme que pour le reste de la ligne d'écoulement. Nous suggérons de plus que l'estimation de l'accumulation des périodes glaciaires par la relation de pression de vapeur saturante associée à la relation spatiale isotope−température de surface est surestimée d'environ 30%. Le modèle conceptuel que nous avons développé nous permet de décrire les variations de niveau des mers du Quaternaire en tant que réponse au forçage de l'insolation. En particulier, nous justifions pourquoi les transitions les plus importantes de niveau des mers ont eu lieu lorsque les changements d'insolation étaient les plus faibles. De plus, nous montrons que des variations faibles de déphasage insolation−climat lors des déglaciations sont compatibles avec la théorie astronomique
Bipolar and chronological consequences of methane measurements in the Talos Dome ice core
No full textBiodiversité et changement climatique : entre discours du spécialiste et discours vulgarisé
Get PDFCette contribution s’intéresse à la biodiversité et au changement climatique ainsi qu’à l’influence de l’un sur l’autre. Une première partie est consacrée au discours par les pairs et pour les pairs. L’analyse des rapports du Groupe d’experts intergouvernemental sur l’évolution du climat (désormais GIEC) montre la manière dont est traitée la problématique de la biodiversité dans le cadre du changement climatique et souligne la place qu’elle y occupe. Face à ces paroles d’experts, une seconde partie, relevant de l’analyse de discours, est consacrée au discours vulgarisateur. À partir de sites de vulgarisation, on analyse la manière dont il est parlé de la biodiversité en lien avec le changement climatique, en regard, entre autres, des paroles d’experts évoquées précédemment. L’accent est mis en particulier sur l’argumentation.This contribution deals with biodiversity and climate change, as well as about the influence of one over the other. The first part is devoted to the discourse produced by scientists in the context of IPCC reports (Intergovernmental Panel on Climate Change). The analysis of the IPCC assessment reports shows how the issue of biodiversity is addressed in the context of climate change and underlines its place. The second part, based on discourse analysis, is devoted to popular science writings. This part analyzes the way in which biodiversity is discussed in relation to climate change in popular science websites on internet. The focus is in particular on comparing and contrasting them with the comments of the IPCC scientific experts mentioned above, as well as on the argumentation structure
An extension of the TALDICE ice core age scale reaching back to MIS 10.1
Get PDFTALDICE (TALos Dome Ice CorE) is a 1620 m deep ice core drilled at Talos Dome, an ice dome located at the edge of the East Antarctic Plateau in the Ross Sea Sector. The Antarctic Ice Core Common Chronology (AICC2012) extended the age scale of the core until ∼150 ka (1438 m depth) (Bazin et al., 2013), while no age scale was available below 1438 m depth. In this work we present the new TALDICE-deep1 chronology using the new measurements of δ18Oatm, δD and 81Kr as well as the inverse model IceChrono1. The TALDICE-deep1 chronology stops at 1548 m, as the portion below this depth is probably affected by mixing processes. The new age scale extends the climate record for the Ross Sea Sector of the East Antarctic Ice Sheet back to MIS 10.1–343 ka (1548 m depth) and identifies both MIS 7 and 9 warm stages, which show specificities in the δD signal. However, it is not possible to recover the isotopic record beyond stage 10.1 as the signal shows a quasi-flat shape. Thereby, the new chronology TADICE-deep1 doubles the extension of the previous age scale as it covers the three past glacial/interglacial cycles
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