NOAA/WDS Paleoclimatology - Northwest Africa 120KYr Continental Humidity Index Reconstruction

The evolution of the northwest African hydrological balance throughout the Pleistocene epoch influenced the migration of prehistoric humans. The hydrological balance is also thought to be important to global teleconnection mechanisms during Dansgaard-Oeschger and Heinrich events. However, most high-resolution African climate records do not span the millennial-scale climate changes of the last glacial-interglacial cycle, or lack an accurate chronology. Here, we use grain-size analyses of siliciclastic marine sediments from off the coast of Mauritania to reconstruct changes in northwest African humidity over the past 120,000 years. We compare this reconstruction to simulations of palaeo-humidity from a coupled atmosphere-ocean-vegetation model. These records are in good agreement, and indicate the reoccurrence of precession-forced humid periods during the last interglacial period similar to the Holocene African Humid Period. We suggest that millennial-scale arid events are associated with a reduction of the North Atlantic meridional overturning circulation and that millennial-scale humid events are linked to a regional increase of winter rainfall over the coastal regions of northwest Africa.

更新世时期西北非水文平衡的演变，影响了史前人类的迁徙活动。同时，学界普遍认为，在丹斯果-奥什格尔（Dansgaard-Oeschger）事件与海因里希（Heinrich）事件期间，水文平衡对全球遥相关机制具有关键作用。然而，当前绝大多数高分辨率非洲气候记录要么未能覆盖末次冰期-间冰期旋回内的千年尺度气候变化，要么缺乏精确的年代序列。为此，本研究通过对毛里塔尼亚近岸硅质碎屑海洋沉积物的粒度分析，重建了过去12万年以来西北非的湿度变化。我们将该重建结果与耦合大气-海洋-植被模式的古湿度模拟结果进行对比，发现二者吻合度极佳，结果表明末次间冰期期间存在受岁差驱动的湿润期，其特征与全新世非洲湿润期高度相似。本研究提出，千年尺度的干旱事件与北大西洋经向翻转环流（North Atlantic meridional overturning circulation）的减弱存在关联，而千年尺度的湿润事件则与西北非沿岸地区冬季降水的区域性增加紧密相关。