Sahel megadrought during Heinrich Stadial 1: evidence for a three-phase evolution of the low- and mid-level West African wind system
Sahel megadrought during Heinrich Stadial 1: evidence for a three-phase evolution of the low- and mid-level West African wind system
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Heinrich Stadial 1 期间的萨赫勒特大干旱：西非低层和中层风系统三相演化的证据
DOI：
10.1016/j.quascirev.2012.10.015
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发表时间：
2012
影响因子：
4
通讯作者：
K. Zonneveld
中科院分区：
文献类型：
--
作者：
Bouimetarhan;M. Prange;E. Schefuß;L. Dupont;J. Lippold;S. Mulitza;K. Zonneveld
末次冰期北方半球季风区千年尺度的干旱事件通常归因于大西洋纬向翻转环流（AMOC）减弱期间热带辐合带（ITCZ）的南移以及东北（NE）信风系统的增强。通过使用高分辨率的末次冰消期花粉记录从塞内加尔大陆坡，我们的数据表明，在萨赫勒西部历史上最长和最极端的干旱之一，发生在北大西洋海因里希Stadial 1（HS 1），显示了三个主要阶段的继承。这些阶段的进展，从一个最大的花粉代表撒哈拉元素之间的间隔1019年和17.4 kyr BP指示干旱和加强东北信风的开始，其次是一个千年的插曲减少输入的撒哈拉花粉和增加输入的萨赫勒花粉，最后一个阶段之间的1016.2和15 kyr BP的特点是第二个最大的撒哈拉花粉丰度。花粉组合的这种变化表明，在两个不同的信风极大值之间发生的NE信风松弛的中期HS1插曲，沿着一个加强的对流层中部非洲东风急流（AEJ），表明西非大气过程发生了重大变化。因此，花粉数据表明，虽然东北贸易已经减弱，萨赫勒地区的干旱在这段时间内仍然严重。因此，仅仅是信风的加强和西非季风槽的南移不能完全解释在AMOC减弱期间萨赫勒地区发生的千年级干旱。相反，我们认为，需要加强AEJ来解释HS1期间干旱的持续性。共同体气候系统模式的模拟表明，在AMOC减少期间，AEJ的加强影响了北非的气候，通过加强西非地区的水分发散，从而延长萨赫勒干旱约4000年。
Millennial-scale dry events in the Northern Hemisphere monsoon regions during the last Glacial period are commonly attributed to southward shifts of the Intertropical Convergence Zone (ITCZ) associated with an intensification of the northeasterly (NE) trade wind system during intervals of reduced Atlantic meridional overturning circulation (AMOC). Through the use of high-resolution last deglaciation pollen records from the continental slope off Senegal, our data show that one of the longest and most extreme droughts in the western Sahel history, which occurred during the North Atlantic Heinrich Stadial 1 (HS1), displayed a succession of three major phases. These phases progressed from an interval of maximum pollen representation of Saharan elements between ∼19 and 17.4 kyr BP indicating the onset of aridity and intensified NE trade winds, followed by a millennial interlude of reduced input of Saharan pollen and increased input of Sahelian pollen, to a final phase between ∼16.2 and 15 kyr BP that was characterized by a second maximum of Saharan pollen abundances. This change in the pollen assemblage indicates a mid-HS1 interlude of NE trade wind relaxation, occurring between two distinct trade wind maxima, along with an intensified mid-tropospheric African Easterly Jet (AEJ) indicating a substantial change in West African atmospheric processes. The pollen data thus suggest that although the NE trades have weakened, the Sahel drought remained severe during this time interval. Therefore, a simple strengthening of trade winds and a southward shift of the West African monsoon trough alone cannot fully explain millennial-scale Sahel droughts during periods of AMOC weakening. Instead, we suggest that an intensification of the AEJ is needed to explain the persistence of the drought during HS1. Simulations with the Community Climate System Model indicate that an intensified AEJ during periods of reduced AMOC affected the North African climate by enhancing moisture divergence over the West African realm, thereby extending the Sahel drought for about 4000 years.
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发表时间：
1999
期刊：
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发表时间：
1995
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DOI：
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通讯作者：
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