Evidence for Shifts in Indo-Pacific Hydrology over the Last Two Millennia from Indonesian Speleothems
Abstract
A suite of climate proxy records from the tropical Pacific have provided detailed information on the behaviour of the El Niño-Southern Oscillation and associated Pacific Walker Circulation (PWC) over the past millennium. However, there is still disagreement as to the precise evolution of this phenomenon, because some records have indicated that the PWC was stronger during the Medieval Climate Anomaly (MCA; ~950-1250 A.D. as defined in northern midlatitudes) and weaker during the Little Ice Age (LIA; 1450-1750 A.D.), whilst other records have suggested quite the opposite. These conflicting hypotheses are partly due to the lack of well-dated and continuous reconstructions of tropical Pacific climate, with the resolution capable of resolving the interannual ENSO and related decadal variability. Here we address these shortcomings by constructing an annually resolved record of Indonesian monsoon (IM) variability over the past two millennia from 18O/16O in speleothems situated within the ascending branch of the PWC in south-central Indonesia. Our replicated 18O/16O record reveals that the IM was substantially weaker (relative to modern) between ~950 and 1350 A.D., and became stronger immediately thereafter between ~1350 and 1700 A.D. These patterns, which are synchronous with other proxy records from the Indo-Pacific, are anti-phased with records of Indian and East Asian summer monsoon variability, suggesting that the latitudinal migration of the Intertropical Convergence Zone may have been responsible for the observed phase relationships between the northern- and southern-hemisphere low latitude regions. However, comparison of our IM record with hydrological records from the central/eastern equatorial Pacific shows marked anti-phasing between these regions too. Hence, zonal changes in the PWC may also explain the observed hydrologic shifts in Indonesia. Evidence for a weaker PWC during the MCA is provided by a time-space wavelet transform of our 18O/16O profile which shows a significant increase in the variance at the decadal and multidecadal bands during this time. Moreover, the step-wise transition to a lower rainfall mean state in Flores at ca. 950 A.D. is synchronous with the construction of water temples in Bali (used to store water for irrigation of rice paddies), further support for the onset of a highly variable rainfall regime. These findings contribute to our understanding of the full spectrum of tropical Pacific behaviour in the past, and may thus present a possible analogue for what the Indonesian region could expect under a warming planet.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP51C..04G
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1616 GLOBAL CHANGE / Climate variability