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Abrupt monsoonal shifts over the precessional cycles documented in Yongxing Cave in China during the antepenultimate glacial period

Liang, Yijia, Chen, Shitao, Zhang, Zhenqiu, Yang, Shaohua, Li, Mingxia, Cheng, Hai, Wang, Yongjin
Environmental earth sciences 2018 v.77 no.6 pp. 228
carbon, climate, forests, karsts, land cover, latitude, methane, monsoon season, oxygen, solar radiation, stable isotopes, summer, China
Precession is the major orbital control of monsoon intensity, but the monsoonal response to the transition between precessional cycles has yet to be explored. Here, we present an Asian Summer Monsoon history that spans 327.7–280.5 ka BP based on a ²³⁰Th-dated and centennially resolved multi-proxy speleothem record from Yongxing Cave, central China. The δ¹⁸O profile, a proxy of monsoon intensity, follows the summer insolation changes, with three abrupt shifts occurring at precessional transitions. These shifts are supported by the stalagmite δ¹³C, grey-level and petrography analysis, indicating a coherent link between the karst processes and monsoon changes. Evidence from the coeval rapid changes in atmospheric CH₄ and forest evolution records within dating errors suggests a wider regional signal of monsoon changes. The weak monsoon intervals are temporally consistent with the ice-rafted debris layers in the North Atlantic, indicating a strong coupling of the high- and low-latitude climate systems. We speculate that the abrupt monsoonal shifts are initiated by the south–north shifts of the Intertropical Convergence Zone associated with the Atlantic Meridional Overturning Circulation and further amplified by land cover. In addition, the rates and magnitudes of insolation changes modify monsoon shifts, thus indicating the abrupt monsoonal shift as a result of an interaction of orbital and millennial forcing.