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A detailed atmospheric carbon isotopic constraint on the causes of the deglacial CO2 increase

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Lourantou, A. , Lavric, J. V. , Köhler, P. , Barnola, J. M. , Michel, E. , Paillard, D. , Raynaud, D. and Chappellaz, J. (2008): A detailed atmospheric carbon isotopic constraint on the causes of the deglacial CO2 increase , Geophysical Research Abstracts, Vol. 10, 09056, 2008. European Geosciences Union, 5th General Assembly, 13-18 April 2008, Vienna, Austria.. .
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Abstract:

Paleo-environmental records and extensive modeling studies have demonstrated thatthe Sahara was largely covered by grass and steppe vegetation in the early to midHolocene. The orbitally controlled incoming summer insolation is the primary forcingfactor during the Holocene. It is well-documented that internal feedback-mechanismsbetween the vegetation and the atmosphere-ocean system caused a sudden shift fromthe vegetated humid Sahara state to a arid desert climate about 50004000 years ago.Proxy evidence suggests also an abrupt onset of the African Humid Period between14,000 and 11,000 yr BP. However, the attribution of the rapid onset to orbitally driveninsolation anomalies or to the Bølling-Allerød, Younger- Dryas transitions is non-trivial. Here we show in transient simulations with climate and vegetation modelsof different complexity that the abrupt change of the African Monsoon/vegetationsystem from dry/deserted glacial state to wet/green conditions is accelerated by thevegetation-albedo feedback. The non-linear response of the climate-vegetation sys-tem to precessional forcing leads to a rapid onset of the African Humid Period at∼11,000 yr BP.

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