ABRUPT HOLOCENE CHANGES IN THE ASIAN MONSOON RECORDED IN STALAGMITE CALCITE FROM DONGGE CAVE, CHINA

²³⁰Th ages and oxygen isotope ratios obtained from stalagmite D4 from Dongge Cave provide a continuous, detailed Asian monsoon history over the last 16,000 years. δ¹⁸O measurements, which provide information on shifts in monsoon precipitation and therefore Asian monsoon intensity, generally follow changes in insolation. However, changes in δ¹⁸O generally occur as abrupt shifts in contrast to smoothly varying insolation. δ¹⁸O values decreased dramatically (~3 ‰) at the start of the Holocene (~11.5 ka) and remained low for ~6 ka. Four positive δ¹⁸O events centered at 11225±97y BP (1.05‰), 10880±117y BP (1.15‰), 9165±75y BP (1.4‰), and a double event centered at 8260±64y BP (1.1‰) and 8080±74y BP (1.0‰) punctuated this period of high monsoon intensity. All four events correlate within error with climate changes in Greenland ice cores. Therefore, the relationship between the North Atlantic and the Asian monsoon, which was observed during the last glacial period (Wang et al., 2001, Science), appears to be maintained into the earliest millennia of the Holocene. In addition, three of the four events correlate within error with outburst events from Lake Agassiz (Teller and Leverington, 2004, GSA Bulletin). Other smaller events in the early Holocene could correlate with outburst events but dating uncertainties preclude making a precise correlation.

The Holocene is punctuated by numerous centennial- and multi-decadal-scale events (amplitudes 0.5 to 1‰) up to half the amplitude of the glacial interstadial events seen in the last glacial period. Thus, Holocene monsoon variability is significant, although not as large as glacial millennial-scale variability. Spectral analysis of the δ¹⁸O record shows significant peaks at solar periodicities of 208 y and 86 y suggesting variation is influenced by solar forcing. However, additional features must also affect the monsoon as there is significant spectral power at numerous sub-decadal- to multi-century-scale “non-solar frequencies” including peaks at El Niño frequencies (observed for high resolution portions of the record between 8110 and 8250 y). In addition, a distinctive biennial oscillation of the Asian monsoon is observed, which has been associated with the Tropospheric Biennial Oscillation (TBO; Meehl, 1997, Journal of Climate).