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.