Toward a 530,000-year Hydroclimate History for the Southern Half of the Australasian Monsoon

Wednesday, 16 December 2015: 17:00
2012 (Moscone West)
Michael K Gagan1, Nicholas G. Scroxton1, Alena Kay Kimbrough1, Claire Krause1, Wahyoe S. Hantoro2, Linda K Ayliffe1, Gavin B Dunbar3, Hai Cheng4,5, R. Lawrence Edwards4, John Charles Hellstrom6, Chuan-Chou Shen7, Heather Scott-Gagan1, Bambang Widoyoko Suwargadi2 and Hamdi Rifai8, (1)Australian National University, Research School of Earth Sciences, Canberra, ACT 2601, Australia, (2)Indonesian Institute of Sciences, Research Center for Geotechnology, Bandung, 40135, Indonesia, (3)Victoria University of Wellington, Antarctic Research Centre, Wellington, New Zealand, (4)University of Minnesota Twin Cities, Dept. of Earth Sciences, Minneapolis, MN, United States, (5)Xi'an Jiaotong University, Institute of Global Environmental Change, Xian, China, (6)University of Melbourne, School of Earth Sciences, Parkville, VIC 3010, Australia, (7)Dept. of Geosciences, National Taiwan University, Taipei, 10617, Taiwan, (8)State University of Padang, Dept. of Physics, Padang, 25131, Indonesia
Speleothem 18O/16O records have revealed key aspects of past hydroclimates in the northern Australasian monsoon domain on orbital to millennial scales, but much less is known about the southern half of the monsoon system. We aim to develop a hydroclimate history for the southern Australasian monsoon based on speleothems from southwest Sulawesi and Flores, Indonesia (latitudes 5-9oS), which extend back to ~530 kyr BP and 90 kyr BP, respectively.

To date, the 18O/16O record for Sulawesi covers glacial terminations TIV (~340 kyr BP), TIII (~245 kyr BP) and TI (~18 kyr BP). The details of each termination are different, however two important hydroclimate patterns are emerging. First, the 18O/16O record shows sharp weakening of the monsoon immediately before each termination. This surprisingly robust pattern marks a southern extension of the northern ‘weak monsoon interval’, and reinforces the idea that southward monsoon displacement is a fundamental feature of terminations. Second, monsoon intensification around Sulawesi lags the rise in atmospheric CO2 and Antarctic temperature by several thousand years, but parallels the 18O/16O decrease in atmospheric O2. Our finding extends that of Wang et al. (2008) and Cheng et al. (2009) who noted the influence of the low-latitude hydrological cycle on the 18O/16O of tropical transpiration, and its potential for correlating ice core and paleomonsoon records.

Further south, the 90-kyr 18O/16O record for Flores shows clear precession-scale antiphasing with China, and southerly positioning of the summer monsoon rainfall belt during Heinrich stadials. Heinrich stadials 5, 4, 2 and 1 occur during wetter intervals in Flores that accompanied relatively high southern summer insolation. Intriguingly, these events are associated with abrupt atmospheric CH4 signals that may be due to increased Southern Hemisphere CH4 production related to intensification of monsoon rainfall over southern tropical land areas (Rhodes et al., 2014).