Variations of Asian summer monsoon and regional hydroclimate between the MIS 7.1 and 6.5

Abstract

Paleoclimatic evidence provides critical insights into the rhythm and mechanisms of the Asian summer monsoon (ASM). In this study, 1221 paired stalagmite δ¹⁸O and δ¹³C records, constrained by 20 U/Th dates, are used to reconstruct ASM and regional hydroclimate changes between MIS 7.1 and 6.5 (∼196.6 and ∼ 166.0 kyr BP). The major findings are as follows: 1) ASM changes did not consistently align with North Hemispher summer insolation (NHSI) variations, especially between ∼186.0 and ∼ 180.0 kyr BP. This asynchrony pattern likely occurred during higher precession and lower minima, suggesting that the NHSI may have reached to a threshold-like value and then triggered a collapse of the Atlantic meridional overturning circulation (AMOC) lasting for thousands of years, thus delaying the recovery of ASM via “high-low teleconnection” mechanism. 2) Within a single precession cycle, millennial-scale ASM failures occurred at an interval of ∼10.0 kyrs, this pattern corresponds to changes in the El Niño-Southern Oscillation, and climate proxy records in the warm pool regions, evidencing a fundamental role of prcesssion induced low-latitude processes in modulating the millennial-scale ASM failures. 3) Over the long-term, hydroclimate changes at the cave site are in line with an expansion of ice-volume and a strengthening winter monsoon.These broadly similar patterns suggest that regional hydroclimate variations are more strongly influenced by ice-volume and its feedback in oceanic-atmospheric anomalies than by precession induced insolation forcing.