岁差驱动与中国黄土高原的次级气候旋回

以黄土高原普遍存在的次级古土壤为基础，结合粒度资料和磁化率资料，对黄土高原的次级气候阶段进行了划分与对比，初步建立了黄土高原L21以来的次级气候旋回序列。以北半球夏至日在近日点和远日点为界，将岁差旋回转变为北半球"理想岁差气候旋回"，并与黄土高原次级气候旋回逐一对比，发现L21以来的72个岁差旋回中，共发育了122个次级气候阶段，合61个次级气候旋回。除去岁差变化微弱的时段，黄土高原次级气候旋回与理想岁差旋回间几乎是一一对应的关系。从而认为，黄土高原的次级气候旋回主要由岁差旋回驱动。与反映全球变化的一级气候旋回相比，黄土高原的次级气候旋回凸显了具有半球效应的岁差旋回在黄土高原气候变化中的作用。黄土高原的次级气候旋回一定程度上受到冰期旋回的遮掩，需要在高原各地往复追索才能清楚揭示。黄土高原的次级气候旋回不仅可以作为地层划分与对比的基本单元，也由于岁差的约束而在一定程度上具有了绝对年代的意义，在地层划分和古气候研究中应引起足够的重视。

Second-order climatic cycles in the Chinese Loess Plateau and their bearing on precession driving

Sub-palaeosols are commonly observed in the Chinese Loess Plateau (CLP). Based on the grain size and magnetic susceptibility data, second-order climatic stages (SOCC) of the CLP are further divided and correlated, and the sequence of SOCC after L21 is preliminarily established in this paper. Taking the Northern Hemisphere summer solstice at perihelion and apohelion as boundaries, precession cycles are transformed into the “Ideal precession climatic cycle” (IPCC) for the Northern Hemisphere. Correlated with the SOCC established in the Loess Plateau, it is found that there are 122 second order climatic stages, corresponding to 61 secondary climatic cycles, could be identified in the 72 precession cycles since L21. Except for the stages which are too weak in precession variation, there is almost a one-to-one correspondent relationship between the SOCC and the IPCC. It is, therefore, concluded that the SOCC in the CLP are mainly driven by precession cycles. Compared with the first-order climatic cycle which reflect global climatic change, the SOCC of the CLP highlights the role of the precession cycle with hemispheric effect in the climatic change of the Loess Plateau. The SOCC have been partly obscured by the glacial-interglacial cycles. It is needed to trace back and forth across the plateau to reveal the pattern clearly. SOCC in the CLP not only serves as the basic unit for stratigraphic classification, but also has some absolute chronological significance to some extent due to the constraints of precession. Enough attention should be paid to its paleoclimatic implication in addition to stratigraphic significance.