Millennial-Scale Monsoon Variability Modulated by Low-Latitude Insolation During the Last Glaciation

Earth's climate system has experienced substantial millennial-scale oscillations characterized by abrupt changes superimposed on orbital-scale changes. However, the dynamic connection between millennial and orbital timescales remains elusive. Here, we provide a summer monsoon precipitation δ¹⁸O record spanning from ∼8 to ∼60.5 ka based on the oxygen isotopic composition of microcodium from loess deposits on the Chinese Loess Plateau. This record shows distinct precessional variations (23 ka) punctuated by prominent millennial-scale oscillations. It is generally consistent with speleothem δ¹⁸O and other loess-based records, reflecting the East Asian summer monsoon changes. More importantly, our result also shows that large increases in the magnitude of millennial-scale variability correspond to the Northern Hemisphere summer insolation minimum. We propose that precession-induced low-latitude summer insolation modulates the amplitudes of millennial-scale summer monsoon variability by changing the mean monsoon state during the last glaciation.