Abstract:
Speleothem samples from Hulu (eastern China, 32[deg]30'N, 119[deg]10'E) and Dongge (southern China, 25[deg]17'N, 108[deg]5'E) Caves provide a nearly continuous record of the Asian monsoon over the last 160[no-break space]ka [Wang, Y.J., Cheng, H., Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.-C., Dorale, J.A., 2001. A high-resolution absolute-dated Late Pleistocene monsoon record from Hulu Cave, China. Science 294, 2345-2348; Yuan, D., Cheng, H., Edwards, R.L., Dykoski, C.A., Kelly, M.J., Zhang, M., Qing, J., Lin, Y., Wang, Y., Wu, J., Dorale, J.A., An, Z., Cai, Y., 2004. Timing, duration, and transitions of the last interglacial Asian Monsoon. Science 304, 575-578]. We have obtained higher resolution data in the interval between ~ 99 and 146[no-break space]ka B.P., providing a detailed account of [delta]18O variations over most of MIS 5 and the latter portion of MIS 6. Precise 230Th dating has replicated the chronology of the samples within error. The higher resolution data set confirms the timing of Asian Monsoon Termination II (the midpoint of the negative shift in [delta]18O marking the onset of the Last Interglacial Asian Monsoon), placing it at 129.0 0.9[no-break space]ka B.P. The bulk of this transition (~ 1.7[per mille sign]) took place within approximately 70[no-break space]years, with the total range of the transition being ~ 3[per mille sign]. The most abrupt portion of the shift in [delta]18O values (~ 1.1[per mille sign]) marking the end of the Last Interglacial Asian Monsoon occurred in ~ 120[no-break space]years, the midpoint of which is 120.7 1.0[no-break space]ka B.P. The Dongge Cave monsoon [delta]18O record over late MIS 6 exhibits a series of sub-orbital millennial-scale climate shifts that average 1.3[per mille sign] in magnitude and occur on average every 1.8[no-break space]ky. Abrupt shifts in [delta]18O of up to 1[per mille sign] also occurred throughout the Last Interglacial Asian Monsoon, with periods at multi-decadal to centennial timescales. Similar to the amplitude and periodicities of events found by Dykoski et al. [Dykoski, C.A., Edwards, R.L., Cheng, H., Yuan, D., Cai, Y., Zhang, M., Lin, Y., An, Z., Revenaugh, J., 2005. A high resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China. Earth and Planetary Science Letters 233, 71-86.] during the Holocene in the Dongge record, these shifts cover more than 1/2 of the amplitude of millennial-scale and multi-centennial-scale interstadial events during the Last Glacial Period [Wang, Y.J., Cheng, H., Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.-C., Dorale, J.A., 2001. A high-resolution absolute-dated Late Pleistocene monsoon record from Hulu Cave, China. Science 294, 2345-2348], and millennial-scale and multi-centennial-scale interstadial events during the Penultimate Glacial Period in China (this study). Abrupt decadal to millennial-scale climate events therefore appear to be a general feature of both glacial and interglacial climate. We demonstrate that monsoon intensity correlates well with atmospheric CH4 concentrations over the transition into the Bolling-Allerod, the Bolling-Allerod, and the Younger Dryas. In addition, we correlate an abrupt jump in CH4 concentration with Asian Monsoon Termination II. On the basis of this correlation, we conclude that the rise in atmospheric CO2, Antarctic warming, and the gradual portion of the rise in CH4 around Termination II occur within our 'Weak Monsoon Interval' (WMI), an extended interval of heavy [delta]18O between 135.5 1.0 and 129.0 1.0[no-break space]ka B.P., prior to Asian Monsoon Termination II and Northern Hemisphere warming. Antarctic warming over the millennia immediately preceding abrupt northern warming may result from the 'bipolar seesaw' mechanism. As such warming (albeit to a smaller extent) also preceded Asian Monsoon Termination I, the 'bipolar seesaw' mechanism may play a critical role in glacial terminations