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.