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VARIABILITÉ CLIMATIQUE RAPIDE EN ATLANTIQUE NORD : L'APPORT DES ISOTOPES DE L'AIR PIÉGÉ DANS LA GLACE DU GROENLAND

Abstract : The water isotopes records from Greenland ice cores depict a succession of rapid warmings (Dansgaard-Oeschger) during the last glacial period. The records corresponding to the last interglacial and the glacial inception suggest as well a highly variable climate. We use here a recently developed method to perform isotopic measurements of the air trapped in the ice (N2, O2 and Ar) combined to firn modelling to (i) separate the true climatic variability from ice stratigraphic disturbance, (ii) quantify the temperature changes in Greenland during Dansgaard-Oeschger events and the glacial inception, and (iii) give a phasing between Greenland temperature evolution and other climatic parameters (Greenhouse gases concentration, ice sheet volume, vegetation, other latitude temperature). We first define the limits and precautions associated to the method. On the one hand, the isotopic composition of trapped oxygen can only be performed on ice conserved below -25°C to have a high precision. On the other hand, firn studies have enabled us to improve its description and modelling. However, even if we better understand the firn dynamic, uncertainties remain on the surface parameters (temperature, accumulation rate). The climatic interpretation of nitrogen and argon isotopes in Antarctica ice cores must consequently remains cautious as we show it on a deglaciation. We then essentially concentrate on Greenland (GRIP and NorthGRIP ice cores). The combination of air isotopes (nitrogen, argon, oxygen), water isotopes (oxygen, hydrogen) and a powerful firn model enables us to reconstruct the surface temperature evolution and to get rid of any bias due to the hydrological cycle in North Atlantic (the water isotopes can not be used as a quantitative paleothermometer). The amplitude of rapid warmings during the last glacial period is up to 16°C in ~100 years. The Greenland temperature over the Dansgaard-Oeschger events is less stable than initially suggested by the water isotopes hence highlighting the strong amplification of the thermohaline circulation variations by the atmosphere processes. Because of ice mixing, the GRIP ice core fails in giving a continuous record of the last interglacial period. The combination of oxygen isotopes and methane in the air trapped in the ice permits us to reconstruct a discontinuous sequence for the last interglacial in central Greenland. The temperature was 5°C warmer than today but ice was still there. The new NorthGRIP ice core contains ice from the last interglacial too. We show that NorthGRIP depicts the first Greenland continuous record for the glacial inception (the deepest part of the ice core can be dated to the middle of the last interglacial with ice volume minimum). The rapid climatic variability is first restricted to North Atlantic during a first Dansgaard-Oeschger event (DO event 25). When the ice volume is up to a certain threshold (~one third of the last glacial maximum/today difference), the second event depicts the classical signature of the Dansgaard-Oeschger events over the glacial period.
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https://tel.archives-ouvertes.fr/tel-00007403
Contributor : Amaelle Landais <>
Submitted on : Monday, November 15, 2004 - 1:13:55 PM
Last modification on : Tuesday, December 8, 2020 - 3:38:04 AM
Long-term archiving on: : Thursday, September 13, 2012 - 12:55:12 PM

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  • HAL Id : tel-00007403, version 1

Citation

Amaelle Landais. VARIABILITÉ CLIMATIQUE RAPIDE EN ATLANTIQUE NORD : L'APPORT DES ISOTOPES DE L'AIR PIÉGÉ DANS LA GLACE DU GROENLAND. Géochimie. Université Pierre et Marie Curie - Paris VI, 2004. Français. ⟨tel-00007403⟩

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