The time-transgressive termination of the African Humid Period
The time-transgressive termination of the African Humid Period
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DOI：
10.1038/ngeo2329
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发表时间：
2015-02
影响因子：
18.3
通讯作者：
T. Shanahan;N. McKay;K. Hughen;J. Overpeck;B. Otto‐Bliesner;C. Heil;J. King;C. Scholz;J. Peck
中科院分区：
文献类型：
--
作者：
T. Shanahan;N. McKay;K. Hughen;J. Overpeck;B. Otto‐Bliesner;C. Heil;J. King;C. Scholz;J. Peck
在大约14，800年至5，500年前的非洲湿润期，北方夏季太阳辐射的变化导致了非洲季风的大规模扩张和随后的崩溃。从干旱的北非水文重建显示非洲湿润期的突然开始和终止。这些突然的转变已被调用的参数，非洲季风迅速响应逐渐强迫非线性陆面反馈的结果。在这里，我们提出了一个重建的降水在潮湿的热带西非在过去的20,000年中使用的氢同位素组成的叶蜡保存在沉积物中，从博萨姆特维湖，加纳。我们发现，在大部分的热带和亚热带非洲的季风响应同步和可预测的冰川重组在大西洋翻转环流，但在非洲潮湿期的相对较弱的辐射强迫的响应在空间和时间上更加复杂。从非洲各地的水文重建的综合表明，非洲湿润期的终止是当地突然的，但在低纬度地区逐渐发生。我们建议，这种时间海侵终止非洲潮湿期反映了降雨强度下降直接引起的夏季日照减少，以及逐渐向南迁移的热带雨带，在此期间发生的。
During the African Humid Period about 14,800 to 5,500 years ago, changes in incoming solar radiation during Northern Hemisphere summers led to the large-scale expansion and subsequent collapse of the African monsoon. Hydrologic reconstructions from arid North Africa show an abrupt onset and termination of the African Humid Period. These abrupt transitions have been invoked in arguments that the African monsoon responds rapidly to gradual forcing as a result of nonlinear land surface feedbacks. Here we present a reconstruction of precipitation in humid tropical West Africa for the past 20,000 years using the hydrogen isotope composition of leaf waxes preserved in sediments from Lake Bosumtwi, Ghana. We show that over much of tropical and subtropical Africa the monsoon responded synchronously and predictably to glacial reorganizations of overturning circulation in the Atlantic Ocean, but the response to the relatively weaker radiative forcing during the African Humid Period was more spatially and temporally complex. A synthesis of hydrologic reconstructions from across Africa shows that the termination of the African Humid Period was locally abrupt, but occurred progressively later at lower latitudes. We propose that this time-transgressive termination of the African Humid Period reflects declining rainfall intensity induced directly by decreasing summer insolation as well as the gradual southward migration of the tropical rainbelt that occurred during this interval.