Leaf-waxes hydrogen isotopic composition of sediment core GeoB4905-4

The rapidity and synchrony of the African Humid Period (AHP) termination at around 5.5 ka are debated, and it is unclear what caused a rapid hydroclimate response. Here we analyzed the hydrogen isotopic composition of sedimentary leaf-waxes (dDwax) from the Gulf of Guinea, a proxy for regional precipitation in Cameroon and the central Sahel-Sahara. Our record indicates high precipitation during the AHP followed by a rapid decrease at 5.8-4.7 ka. The similarity with a dDwax record from northern East Africa suggests a large-scale atmospheric mechanism. We show that northern high- and mid-latitude cooling weakened the Tropical Easterly Jet and, through feedbacks, strengthened the African Easterly Jet. The associated decrease in precipitation triggered the AHP termination and combined with biogeophysical feedbacks to result in aridification. Our findings suggest that extratropical temperature changes, albeit smaller than during the glacial and deglacial, were important in triggering rapid African aridification during the Holocene.

距今约5.5千年的非洲湿润期（African Humid Period, AHP）结束的快速性与同步性尚存争议，目前尚未明确引发此次快速水文气候响应的驱动因素。本研究对取自几内亚湾的沉积叶蜡氢同位素组成（dDwax）展开分析，该指标可作为喀麦隆及萨赫勒-撒哈拉中部区域降水的代用记录。本研究的同位素记录显示，非洲湿润期内区域降水充沛，随后在距今5.8至4.7千年间出现快速下降。该结果与东非北部的dDwax记录具有高度相似性，表明这一过程存在大尺度大气驱动机制。研究表明，北半球高纬度与中纬度的降温作用削弱了热带东风急流（Tropical Easterly Jet），并通过反馈机制增强了非洲东风急流（African Easterly Jet）。伴随的降水减少触发了非洲湿润期的结束，并与生物地球物理反馈共同作用，最终引发区域干旱化。本研究结果显示，尽管中高纬度温度变化的幅度小于冰期及冰消期，但其在全新世（Holocene）非洲快速干旱化的触发过程中扮演了关键角色。