Over the Plio-Pleistocene interval a strong linkage exists between northern African climate changes and the supply of dust over the surrounding oceans and continental runoff towards the Mediterranean Sea. Both these signatures in the sedimentary record are determined by orbital cycles influencing glacial variability on the one hand and northern African monsoon intensity on the other hand. In this paper, we use the intermediate-complexity model CLIMBER-2 to simulate African climate during the Plio-Pleistocene between 3.2 and 2.3 million years ago (Ma) and compare our simulations with existing and new climate reconstructions. The CLIMBER-2 model is externally forced with atmospheric CO₂ concentrations, ice sheet topography, and orbital variations, all of which strongly influence climate during the Pliocene and Pleistocene. Our simulations indicate that the records of northern Africa climate oscillate in phase with climatic precession. For the Earth's obliquity cycle, the time lag between the 41 000-year component in insolation forcing and the climatic response increased after inception of Northern Hemisphere (NH) glaciation around 2.8 Ma. To test the outcome of our simulations, we have put emphasis on the comparison between the simulated runoff of grid boxes encompassing the Sahara desert and the Sahel region and the sedimentary records of marine sediment cores from ODP Site 659 (Atlantic Ocean) and ODP Site 967 (Mediterranean). In this study we will show for the first time an extended Ti∕Al record of Site 967 down to 3.2 Ma. This record strongly correlates with runoff in the Sahara and Sahel regions, whereas correlation with the dust record of Site 659 is moderate and slightly improves after NH ice sheet inception. We investigated the transient variability of the individual and combined contributions of the Sahel and Sahara regions and found significant transient behaviour overlapping the inception of NH ice sheets (2.8 Ma) and the Plio-Pleistocene transition (2.6 Ma). Prior to 2.8 Ma, a larger contribution from the Sahara region is required to explain the variability of Mediterranean dust input. After this transition, we found that a more equal contribution of the two regions is required, representing an increased influence of Sahel runoff and wet periods.

中文翻译：

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非洲季风对上新世地中海沉积物的短暂影响

在上新世之间，北非气候变化与周围海洋的粉尘供应以及通往地中海的大陆径流之间存在着很强的联系。沉积记录中的这两个特征均由一方面影响冰川变率的轨道周期决定，另一方面又受北非季风强度影响。在本文中，我们使用中间复杂度模型CLIMBER-2来模拟3.2-230万年前（Ma）上新世间的非洲气候，并将我们的模拟与现有和新的气候重建进行比较。CLIMBER-2模型受大气CO _2的外力作用浓度，冰盖地形和轨道变化，这些都强烈影响上新世和更新世期间的气候。我们的模拟表明，北非气候的记录与气候进动同步变化。对于地球的倾斜周期，在北半球（NH）形成冰层约2.8 Ma之后，日照强迫的41000年分量与气候响应之间的时间差增加了。为了测试模拟结果，我们重点比较了包括撒哈拉沙漠和萨赫勒地区的网格盒的径流与ODP 659号站点（大西洋）和ODP 967号站点的海洋沉积物芯的沉积记录（地中海）。在这项研究中，我们将首次显示扩展的Ti ∕ Al站点967的最低记录为3.2 Ma。该记录与撒哈拉和萨赫勒地区的径流密切相关，而与659号站点的尘埃记录的相关性中等，在NH冰盖开始后略有改善。我们调查了萨赫勒地区和撒哈拉地区的单个和组合贡献的瞬态变异性，发现与NH冰盖（2.8 Ma）的发源和上新世-上新世过渡（2.6 Ma）重叠的显着瞬变行为。在2.8 Ma之前，需要撒哈拉地区做出更大的贡献来解释地中海扬尘输入的变化性。过渡之后，我们发现需要两个地区的贡献更加相等，这代表了萨赫勒径流和湿润时期的影响增加。