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 CO₂ rise from 139 ± 1 ka BP concordant with boreal summer insolation increase, which was followed by a major rise phase of CO₂ between 135.7 ± 1 and 129 ± 1 ka BP. The major rise phases of CO₂ were comparable during TI and TII, but the initial CO₂ rise before TII was distinct from CO₂ 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 CO₂, along with insolation rise, preconditioned glacial terminations, supporting the “tipping point” theory.