A review of orbital-scale monsoon variability and dynamics in East Asia during the Quaternary

Milankovitch theory and monsoon

“…Comparably, on the orbital scale, the insolation variations dominated by precession also appear to coordinate variations of monsoon changes as the major forcing, although the global ice volume and greenhouse gases also influence this as internal forcing/feedback to some extent, especially in the mean annual precipitation and temperature in the monsoon regime. 69 , 70 In terms of hydrological cycles, vapor-water transition constitutes the essence of the low-latitude monsoon regime, with a dominant precession cycle on orbital scale, in contrast to the liquid-solid transition prevailing in the high-latitude regime, with dominant ∼100-ka glacial-interglacial cycles in the Late Quaternary. 16 , 67 , 71 , 72 , 73 In fact, the monsoon has long been theoretically demonstrated to be primarily driven by tropical solar insolation 8 with dominated precession cycles.…”

“…Another longstanding issue regarding the monsoon hypothesis stems from the Chinese loess magnetic susceptibility (MS) records (as an AM precipitation proxy) from the central Chinese Loess Plateau, which show dominant ∼100-ka cycles (or glacial-interglacial cycles), 70 implying a major ice volume forcing of monsoon. This is in contradiction with the conventional insolation hypothesis 8 , 81 and Chinese speleothem records, 16 namely the “Chinese 100-ka problem.” 93 Cheng et al.…”

“… 69 On the other hand, some model simulations also show that the summer rainfall over the Chinese Loess Plateau is dominated by precession, whereas the annual temperature is more influenced by glacial conditions (CO 2 and ice sheets). 69 , 70 Therefore, it would be also possible that the loess MS was affected not only by summer precipitation but also by annual temperature and/or other factors/processes. 93 , 138 A recent study shows that the Tengger desert had also experienced large dry-wet fluctuations with strong 20-ka and 400-ka rhythms as well, probably suggesting East AM (EAM) variations forced dominantly by low-latitude insolation.…”

“… 69 Sun et al. 70 proposed that “insolation plays a leading role in affecting changes in temperature, precipitation, and southerly wind during the summer season. Changes in annual mean temperature and precipitation are affected to varying degrees by CO 2 and ice volume.” Overall, even with addition of ice volume/CO 2 forcing with ∼100-ka cycles to the transient simulations, the resultant summer monsoon variations remain predominant with precession cycles in most cases, in line with low-latitude insolation.…”

Coupled atmosphere-ice-ocean dynamics during Heinrich Stadial 2

“…Although there were different views in early studies regarding speleothem δ 18 O interpretation in the ASM domain (e.g., refs. 31 – 34 ), recent developments have shown a general consensus that speleothem δ 18 O variations on millennial-to-orbital timescales reflect the large-scale monsoonal circulation/rainfall, which is closely linked to the overall monsoon intensity, instead of local rainfall amount 7 , 35 – 37 (Supplementary Note 1.3 ). In sum, at millennial-to-orbital timescales, speleothem δ 18 O records from ASM and SASM regions are a first-order reflection of the intensity of large-scale monsoonal rainfall/circulation and the north-south shifts of the ITCZ 7 , 8 , 27 – 30 , 36 .…”