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Rapid Onset of the African Humid Period 14.5--11ka BP: External Forcing and Feedback Mechanisms

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Citation:
Timm, O. , Timmermann, A. , Köhler, P. and Menviel, L. (2008): Rapid Onset of the African Humid Period 14.5--11ka BP: External Forcing and Feedback Mechanisms , Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract PP23B-1477,15.-19.12.2008, San Francisco, USA.. .
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Abstract:

the onset of the African Humid Period (AHP) 14,500 to 11,000 years ago. Our analysis suggests that locally increased boreal summer solar radiation leads to a northward shift of the ITCZ. Vegetation in northern Africa adjusts to wetter conditions and provides a positive albedo-vegetation feedback that is further accelerating the northward migration of the ITCZ. Sensitivity experiments reveal that the albedo-vegetation feedback and its effect on the large-scale atmospheric circulation together with the CO2-fertilization effect provide a mechanism for generating multiple states of early to mid-Holocene vegetation over northern Africa. Our model simulations document that not only orbitally-driven insolation changes played a key role in controlling the onset of the AHP, but also the presence of the remnant ice-sheet over Europe, variations of the Atlantic Meridional Overturning circulation during the Younger Dryas and increasing levels atmospheric CO2. The model results presented here do not lend support to the notion that simple insolation thresholds govern the abrupt transitions of north African vegetation during the early to middle Holocene.

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