A multi-proxy approach to assessing multiscale monsoon variability over the past six glacial cycles

High-resolution proxies from Chinese loess deposits can document the East Asian monsoon changes at glacial-interglacial to millennial time scales. Unlike the absolutely dated speleothem δ¹⁸O records that exhibit persisitent millennial changes over the past 640 kyr, well resolved loess proxies can only reflect abrupt monsoon changes over the last two glacial cycles. Here we present grain-size and elemental records from a 180-m loess core retrieved from the western Chinese Loess Plateau, extending high-frequency variations of Asia monsoon back to the last six glacial-interglacial cycles. The mean grain-size records display significant glacial-interglacial timescales and match well with the marine δ¹⁸O record in terms of amplitude and periodicities. Because of varied sensitivity of grain-size and elemental ratios to grain-size sorting (winter monsoon) and chemical weathering (summer monsoon), precessional cyclicity are distinctive but with different intensities in these physical-chemical indicators. Moreover, large-amplitude and high-frequency oscillations were persistent during past glacial and interglacial intervals. Compared them with Chinese speleothem δ¹⁸O and North Atlantic ice-rafted debris (IRD) records, loess proxies display similar magnitudes of abrupt climate changes, however the timing and amplitude of these abrupt climatic events are not easily correlated. Our results indicate that integration of spleothem, loess, ice and marine record permits better understaning of the origin and dynamics of abrupt climatic changes, particularly regarding its links with glacial and astronomical forcings.