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Constraints on the causes of CO2 rise during deglaciations: atmospheric stable carbon isotope ratio of CO2 from Antarctic ice cores

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Lourantou, A. , Lavric, J. V. , Schaefer, H. , Köhler, P. , Barnola, J. M. , Michel, E. , Paillard, D. , Raynaud, D. and Chappellaz, J. (2008): Constraints on the causes of CO2 rise during deglaciations: atmospheric stable carbon isotope ratio of CO2 from Antarctic ice cores , Geophysical Research Abstracts, Vol. 10, 06938, 2008. European Geosciences Union, 5th General Assembly, 13-18 April 2008, Vienna, Austria.. .
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The analysis of air bubbles trapped in polar ice permits the reconstruction of the evo-lution of major greenhouse gases over various timescales. This study leans on thepast behaviour of the most important human-induced greenhouse gas, carbon dioxide(CO2). The past origin of CO2 is better comprehended when studying concomitantlythe evolution of its stable carbon isotope composition, as it is affected by various frac-tionation processes in and between carbon reservoirs.The LGGE dry extraction method of gases occluded in ice was used in combinationwith a new instrumental setup to investigate the CO2 mixing ratio and its stable car-bon isotope composition (delta13CO2) in air from the last deglaciation at the EPICADome Concordia site (Antarctica). The resolution of our results (250 years in average)allows us to divide Termination I (TI) into four sub-periods, each representing differ-ent climatic features at the Earth surface (Heinrich I, Bølling/Ållerød, Antarctic ColdReversal, Younger Dryas). We observe that CO2 and delta13CO2 are not correlated.Delta13CO2 shows positive and negative excursions associated with changes in thegrowth rate of atmospheric CO2. This illustrates the dynamic character of the carboncycle and its coupling to climate change during the deglaciation. The use of two car-bon cycle box models highlight oceanic mechanisms as the major contributors to theCO2 evolution during these periods of TI, and the terrestrial biosphere for the warmBølling/Ållerød event.We will also present pioneering delta13CO2 data obtained in the course of the penul-timate deglaciation (TII); this is expected to bring some more light in the carbon cyclequestion during glacial-interglacial transitions although the existing challenge on icephysics (clathrate ice for TII vs bubbly ice for TI) should not be neglected.

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