High-resolution scanning XRF investigation of Chinese loess and its implications for millennial-scale monsoon variability

摘要

Millennial-scale monsoon variability has been investigated intensively using loess-based proxies; however, the amplitude and rhythms of millennial-scale signals have seldom been disentangled from the background glacial-interglacial changes. Here we present the results of high-resolution scanning X-ray fluorescence analysis of a 75-m-thick loess sequence from the north-western Chinese Loess Plateau to address glacial-interglacial to millennial monsoon variability over the last two climatic cycles. Variations of the Si/K, Fe/K and Ca/K ratios are separated spectrally into low-and high-frequency components corresponding to glacial-interglacial and millennial-scale monsoon variability, respectively. The results indicate that the three elemental ratios exhibit similar glacial-interglacial variability but with varying spectral densities at the 100-, 41- and 23-kyr periodicities. Millennial-scale variability is quite similar between the three elemental ratios, and comparable to those inferred from records of Chinese speleothem delta O-18, Greenland palaeotemperature and North Atlantic cooling events. Comparison of various proxies indicates the broad similar magnitudes of abrupt climate changes, at least during the last two glacial-interglacial cycles, whereas the timing and amplitude of abrupt climatic events are not well correlated. We suggest that refinement of loess chronology and intensive data-model integration in the future are critical to decipher the characteristics and dynamics of rapid monsoon changes. Copyright (c) 2016 John Wiley & Sons, Ltd.