The Late Pliocene–Early Pleistocene is an important transitional period in the Cenozoic evolution of global climate and environment. Previously, we demonstrated the occurrence of distinct cycles in vegetation and climate in the Nihewan Basin, during 2.89–1.78 Ma. However, the specific cycles and their forcing mechanisms were not studied more in-depth. Here we present the results of wavelet and spectral analyses of pollen percentages (Picea, Pinus, xerophytic taxa and broadleaved trees), macro-charcoal concentration, clay % and sand %, and magnetic susceptibility of 340 samples from the NHA drill core in the Nihewan Basin, during 2.89–1.78 Ma. The results reveal dominant ∼20-kyr and ∼40-kyr cyclicities: the pollen percentages of Pinus and broadleaved trees, magnetic susceptibility, and clay %, indicating a warm and humid climate, are more significantly influenced by ∼20-kyr; in contrast, the percentages of Picea and xerophytic taxa, macro-charcoal concentration, and sand %, associated with a cold and dry climate, are mainly influenced by ∼40-kyr. The ∼20-kyr and ∼40-kyr cycles corresponding to the dominant cycles of the East Asian summer monsoon and winter monsoon, which are respectively driven by Earth orbital precession and tilt, indicating that vegetation and climate change in the Nihewan Basin during 2.89–1.78 Ma was forced by a combination of low- and high-latitude processes. Otherwise, most of the proxy indexes also show a pronounced ∼100-kyr cycle, which may be a response to changes in Northern Hemisphere ice sheets, emphasizing the importance of high-latitude forcing of vegetation and climate change in the Nihewan Basin.

晚上新世—早更新世是全球气候环境新生代演化的重要过渡时期。此前，我们证明了泥河湾盆地在 2.89-1.78 Ma 期间植被和气候的不同周期的发生。然而，具体的循环及其强迫机制没有更深入地研究。在这里，我们展示了来自泥河湾 NHA 钻芯的 340 个样品的花粉百分比（云杉、松属、旱生类群和阔叶树）、宏观木炭浓度、粘土百分比和沙子百分比以及磁化率的小波和光谱分析结果。盆地，在 2.89–1.78 Ma 期间。结果揭示了主要的~20-kyr 和~40-kyr 周期性：松树的花粉百分比阔叶树、磁化率和粘土百分比，表明气候温暖湿润，受~20-kyr的影响更显着；相比之下，云杉的百分比与寒冷干燥气候相关的旱生分类群、宏观木炭浓度和沙子百分比主要受~40-kyr的影响。～20-kyr和～40-kyr旋回对应东亚夏季风和冬季风的主导旋回，分别受地球轨道进动和倾斜驱动，表明泥河湾盆地2.89- 1.78 Ma 是由低纬度和高纬度过程共同推动的。另外，大多数代理指数也显示出明显的~100-kyr循环，这可能是对北半球冰盖变化的响应，强调了泥河湾盆地植被和气候变化的高纬度强迫的重要性。