Asian Monsoon Variations on Orbital-Millennial Scales and the `100 Thousand Year Problems'
Abstract
Speleothem oxygen isotope records from China characterize changes in the Asian monsoon and global climate. We have now extended our Chinese record to cover the full uranium/thorium dating range: the last 640,000 years. The record's length, temporal precision, and correlations with both ice core and marine records allow us to further probe the enduring `100 ka problem'—i.e., why do large-amplitude ice age cycles and changes in eccentricity share common spectral power although the latter generates negligible change in insolation? Based on our record's timing, the ice age terminations are separated by 4 or 5 precession cycles, supporting the idea that the 100 ka ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in precession and obliquity bands, and is nearly anti-phased with June 21 boreal insolation. These observations indicate that insolation, in part, paces the occurrence of millennial-scale events, including those associated with ice age terminations and `unfinished terminations'. In the East Asian summer monsoon (EASM) domain, Loess magnetic susceptibility records from the Chinese Loess Plateau (CLP) show that the EASM is dominated by 100 ka cycles, which is in contrast to the conventional notion that insolation changes caused by the 20 ka precession cycle are the primary driver of summer monsoon. These observations present another paradox, which we dub here as the `Chinese 100 ka problem'. The existing and new speleothem records from both China and India reinforce the idea that precession, rather than glacial-interglacial, cycles, is the dominant driver of both EASM and Indian summer monsoon variations. The lack of precession signals in the loess records from the CLP might stem partially from its unique climatological settings and complex nature of loess magnetic susceptibility proxy.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A21N..01C
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 3337 Global climate models;
- ATMOSPHERIC PROCESSESDE: 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHY