Palaeo-records from China demonstrate that the East Asian Summer Monsoon(EASM) is dominated by abrupt and large magnitude monsoon shifts onmillennial timescales, switching between periods of high and weak monsoonrains. It has been hypothesized that over these timescales, the EASMexhibits two stable states with bifurcation-type tipping points betweenthem. Here we test this hypothesis by looking for early warning signals ofpast bifurcations in speleothem δ18O records from Sanbao Caveand Hulu Cave, China, spanning the penultimate glacial cycle. We find thatalthough there are increases in both autocorrelation and variance precedingsome of the monsoon transitions during this period, it is only immediatelyprior to the abrupt monsoon shift at the penultimate deglaciation(Termination II) that statistically significant increases are detected. Tosupplement our data analysis, we produce and analyse multiple modelsimulations that we derive from these data. We find hysteresis behaviour inour model simulations with transitions directly forced by solar insolation.However, signals of critical slowing down, which occur on the approach to abifurcation, are only detectable in the model simulations when the change insystem stability is sufficiently slow to be detected by the samplingresolution of the data set. This raises the possibility that the earlywarning "alarms" were missed in the speleothem data over the period 224–150 kyr and it was only at the monsoon termination that the change in the systemstability was sufficiently slow to detect early warning signals.
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