Asian summer monsoon variability across Termination II and implications for ice age terminations.

The detailed anatomy of Termination I (TI) is well depicted, but whether changes across Termination II (TII) resemble TI remains controversial. Here we present high-resolution Asian monsoon records covering TII using Shima Cave stalagmites from China. Correlating marine and ice-core records to our U/Th-dated records via millennial-scale variabilities, we find an initial CO rise from 139 ± 1 ka BP concordant with boreal summer insolation increase, which was followed by a major rise phase of CO between 135.7 ± 1 and 129 ± 1 ka BP. The major rise phases of CO were comparable during TI and TII, but the initial CO rise before TII was distinct from CO behavior before TI, likely forced by the Earth's internal variabilities, in particular an ice-sheet collapse event and a 50% reduction in southern hemisphere dust flux. Here, we show that ~4000-5000-year-long gradual changes in CO, along with insolation rise, preconditioned glacial terminations, supporting the "tipping point" theory.