Millennial-scale summer monsoon oscillations over the last 260 ka revealed by high-resolution elemental results of the Mangshan loess-palaeosol sequence from the southeastern Chinese Loess Plateau

摘要

Loess-based proxies have been widely used to infer glacial-interglacial to millennial-scale changes of the East Asian monsoon. However, the characteristic of millennial-scale variability is still unclear during glacial-interglacial cycles in loess-palaeosol sequence. Here, we present high-resolution (5-cm) elemental results of a 96.7-m thick Mangshan loess-palaeosol sequence on the southeastern Chinese Loess Plateau to emphasize millennial monsoon changes. We explore time series of loess proxies (magnetic susceptibility, CaCO3 content, Ca/K, Fe/K, and Rb/Sr ratios) and speleothem delta O-18 records and decompose these proxies into intrinsic components using the ensemble empirical mode decomposition method. Synthesized signals of lowand high-frequency components can track the monsoon variability at glacial-interglcial and millennial timescales, respectively. The proportions of millennial components of the loess proxies vary from 9.4%-13.4%, less than that in Chinese speleothem delta O-18 record (-24.4%). Among five loess proxies, Fe/K ratio is the most sensitive indicator of millennial-scale summer monsoon oscillations, exhibiting abrupt changes similar to that of the Chinese speleothem delta O-18 record. The amplitude of abrupt monsoon changes recorded in Mangshan is larger during interglacials than glacials, which is in line with Gulang records, implying the lower sensitivity of loess proxies to weak weathering during glacilals and an interglacial amplification of abrupt summer monsoon changes.