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 delta O-18 record spanning from similar to 8 to similar 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 delta O-18 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. Plain Language Summary Understanding the dynamic connections between different timescales is crucial to predicting future climate variability. Here, we provide a summer monsoon precipitation delta O-18 record based on the oxygen isotopic composition of microcodium from loess deposits on the Chinese Loess Plateau, showing that large increases in the magnitude of millennial-scale variability correspond to Northern Hemisphere summer insolation minimum. We propose that low-latitude summer insolation modulates the amplitudes of millennial monsoon variability during the last glaciation. Our work provides clues for deciphering the dynamic connections between orbital and millennial timescales.