A SUB-DECADAL-RESOLUTION RECORD OF LATE HOLOCENE INDO-AUSTRALIAN SUMMER MONSOON VARIABILITY FROM TROPICAL AUSTRALIAN STALAGMITES

A high-resolution oxygen isotopic time series from aragonite speleothems from cave KNI-51 in the eastern Kimberly region of tropical Western Australia records Indonesian-Australian summer monsoon (IASM) variability spanning the last four millennia. Cave KNI-51 is located in the heart of the Australian summer monsoon system near the north Australian coast where δ¹⁸O values strongly reflect amount effects. Oxygen isotopic data from 12 stalagmites were assigned ages using growth models constructed from a total of 62 U-Th dates, with average errors of ±17 years. Excellent overlap of δ¹⁸O values of coeval portions of different stalagmites suggests equilibrium crystallization. Oxygen isotope trends track temperature reconstructions from the Northern Hemisphere (NH), with the Medieval Climate Anomaly (Little Ice Age) coinciding with increased (decreased) IASM rainfall. This rainfall response is similar to those reconstructed from speleothems from caves across southern Asia but given that northward (southward) displacement of the ITCZ is tied to NH warming (cooling), a north-south shift in the mean location of the ITCZ alone cannot readily explain this symmetric pattern of monsoon rainfall between Australia and southern Asia. These relations suggest an expansion/contraction of the tropical rainfall belt across the Indo-Pacific at multi-decadal time scales.