Skip Navigation | ANU Home | Search ANU | Directories
The Australian National University
Research School of Earth Sciences
Research Highlights
Printer Friendly Version of this Document

History in the making: A 90,000-year record of the Australasian monsoon

Mike Gagan1, Linda Ayliffe1, Nick Scroxton1, Wahyoe Hantoro2, John Hellstrom3, Hai Cheng4, Larry Edwards5, Jian-xin Zhao6, Russell Drysdale7, Heather Scott-Gagan1, Joan Cowley1, Hamdi Rifai8 and Bambang Suwargadi2

1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
2 Research Center for Geotechnology, Indonesian Institute of Sciences, Bandung 40135, Indonesia
3 School of Earth Sciences, University of Melbourne, Parkville, VIC 3010, Australia
4 Institute of Global Environmental Change, Xi’an Jiatong University, Xi’an 710049, China
5 Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA
6 Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, QLD 4072, Australia
7 School of Resource Management and Geography, University of Melbourne, Parkville, VIC 3010, Australia
8 Department of Physics, State University of Padang, Padang 25131, Indonesia

Stalagmite oxygen-isotope (18O/16O) records from China and Borneo have revealed changes in Asian monsoon rainfall over glacial-interglacial cycles (e.g. Wang et al. 2008, Cheng et al. 2010, Meckler et al. 2012), yet little is known about orbital- and millennial-scale climate change in the ‘southern half’ of the Australasian monsoon domain. To fill this gap, we aim to build stalagmite 18O/16O records for the seasonal monsoon rainfall belt of south-central Indonesia. We have completed four expeditions to Liang Luar cave on the island of Flores (Figure 1) and are currently analysing 18O/16O and carbon-isotope ratios (13C/12C) in stalagmites with U-series ages extending to ~90,000 yBP.

The new Flores 18O/16O records for ~90,000 to 35,000 yBP (analysed in 2012) serve to complete the first high-resolution, absolute-dated Late Pleistocene history of rainfall variability across the entire Australasian monsoon system.  There is clear (but non-linear) antiphasing of the Flores and China (Hulu/Sanbao caves) stalagmite 18O/16O records on precession time-scales over the last ~90,000 years (Figure 2).  A strong synchronous climate shift marks the onset of Marine Isotope Stage 3 ~60,000 yBP (drier Flores, wetter China) and heralds the driest 30,000-year interval on Flores.  A distinct monsoon rainfall maximum on Flores ~21,000 yBP suggests the intertropical convergence zone (ITCZ) moved southward during the Last Glacial Maximum in response to the southern hemisphere summer insolation maximum at that time (Ayliffe et al., submitted). 

Interestingly, the largest 13C/12C anomaly for the last ~90,000 years on Flores begins at ~70,000 yBP in the absence of any clear climate forcing (record not shown).  The ~4,000-year-long 13C/12C signal is under investigation, but probably reflects catastrophic vegetation collapse in the aftermath of a massive volcanic eruption (See Scroxton et al. 2012 RSES Research Highlight).

Targeted U-series dating of the new Flores stalagmite 18O/16O record is in progress, but it already shows that Australasian monsoon rainfall and climate change in the North Atlantic region are inextricably linked on millennial timescales (e.g. Griffiths et al. 2009, Lewis et al. 2011). For example, cooling in the North Atlantic region during Heinrich Event 1 (~16,000 yBP) and the Younger Dryas (~12,000 yBP) correlates with a southward shift of the Australasian ITCZ and increased rainfall in Flores.  There are still small gaps in the Flores record around Heinrich events 2 and 3, but a similar antiphased monsoon response is evident around Heinrich events 4, 5 and 6 (~38,000 yBP, ~48,000 yBP, ~61,000 yBP), and during other less distinctive intervals. 

Our findings indicate that millennial-scale changes in ITCZ positioning in tropical Australasia, through their influence on large-scale oceanic-atmospheric circulation, could have played a key role in the rise of atmospheric CO2 and global warming that ultimately led to the demise of the last ice age, as summarised by Denton et al. (2010) and others.

This research is supported by Australian Research Council Discovery grants DP0663274 to M.G., J.-x.,Z., R.D. and W.H. and DP1095673 to M.G., R.D., J.H., W.H., L.E. and H.C.

Cheng, H., Edwards, R.L., Broecker, W.S., Denton, G.H., Kong, X., Wang, Y., Zhang, R., Wang, X. (2009), Ice age terminations, Science 326: 248-252.

Denton, G.H., Anderson, R.F., Toggweiler, J.R., Edwards, R.L., Schaefer, J.M., Putnam, A.E. (2010), The last glacial termination, Science, 328: 1652-1656.

Griffiths, M.L., Drysdale, R.N., Gagan, M.K., Zhao, J.-x., Ayliffe, L.K., Hellstrom, J.C., Hantoro, W.S., Frisia, S., Feng, Y.-x., Cartwright, I., St Pierre, E., Fischer, M.J., Suwargadi, B.W. (2009), Increasing Australian-Indonesian monsoon rainfall linked to early Holocene sea-level rise, Nature Geoscience, 2: 636-639.

Lewis, S.C., Gagan, M.K., Ayliffe, L.K., Zhao, J.-x., Hantoro, W.S., Treble, P.C., Hellstrom, J.C., LeGrande A.N., Kelley, M., Schmidt, G.A., Suwargadi, B.W. (2011), High-resolution stalagmite reconstructions of Australian-Indonesian monsoon rainfall variability during Heinrich stadial 3 and Greenland interstadial 4. Earth and Planetary Science Letters, 303: 133-142.

Meckler, A.N., Clarkson, M.O., Cobb, K.M., Sodemann, H., Adkins, J.F. (2012), Interglacial hydroclimate in the tropical west Pacific through the Late Pleistocene, Science, 336: 1301-1304.

Wang, Y., Cheng, H., Edwards, R.L., Kong, X., Shao, X., Chen, S., Wu, J., Jiang, X., Wang, X., An, Z. (2008), Millennial- and orbital-scale changes in the East Asian monsoon over the past 224,000 years. Nature, 451: 1090-1093.

Figure 2. Comparison of stalagmite δ18O records for Liang Luar, Flores (blue) and Hulu / Sanbao, China from ~90,000 to 10,000 kyr BP (kyr BP, thousand years before the present).  The Liang Luar δ18O record is a composite of time-series produced by Lewis et al. (2010), Ayliffe et al. (submitted) and new data generated in 2012 for the ~90 to 35 kyr BP interval.  The U-series chronology is preliminary and will be refined with targeted dates.  Yellow bars show times of North Atlantic cold intervals (Younger Dryas and Heinrich Events 1 to 6), drier conditions in China, and wetter conditions in Flores.  Blue bars indicate the opposite.  The grey bar marks a ~4,000-year-long vegetation collapse in Flores related to a large volcanic eruption (See Scroxton et al. 2012 RSES Research Highlight).