A STALAGMITE RECORD OF CLIMATE VARIABILITY FROM THE LAST GLACIAL MAXIMUM THROUGH MIDDLE HOLOCENE FROM CAPE RANGE, WESTERN AUSTRALIA

Paleoclimate data from northwestern Australia can provide valuable information for investigating remote climate drivers during the last glacial period. Here we present an isotopic analysis of two stalagmites from cave C-126 in Cape Range Peninsula (21.2°S, 113.7°E), coastal Western Australia. The study area receives <300 mm of rainfall per year, and which is derived from a number of moisture sources including tropical cyclones during the summers, and winter precipitation from northwest cloud bands (NWCB) and storms generated by fronts associated with the southern westerlies. Stalagmite age models were constructed using polynomials fit through a suite of U/Th dates obtained at the University of New Mexico using a NEPTUNE MC-ICP-MS that allowed for precise measurements on these low U samples. The two stalagmites do not overlap in age but grew from approximately 26-15 ka and 11-6 ka, which enabled our comparison of the Last Glacial Maximum (LGM) with middle and early Holocene climate.

Stalagmite oxygen isotopic (δ¹⁸O) values during the LGM average -6.5‰, decreased to -8.0‰ at 16 ka and increased afterwards into the Holocene, also becoming 1.5‰ lighter coincident with Heinrich Stadial 1 (HS1). One possibility for this shift during HS1 is a southward shift of the Intertropical Convergence Zone introduced significant amounts of isotopically light Australian summer monsoon rain, an interpretation supported by stalagmite time series from Ball Gown Cave, tropical Western Australia (Denniston et al., 2013, QSR, 72, 159.). Alternatively, tropical cyclone activity may have changed during this time, or a southern source also could have accounted for the depleted δ¹⁸O values during HS1. South-central Australian megalake high stands occurred during deglaciation, including HS1, and have been tied to increased winter rainfall from the southern westerlies (Cohen et al., 2012, Palaeo3, 356, 89), which could as well explain the depleted δ¹⁸O values in our data . Changes in rainfall brought by NWCB could also have accounted for the decreased δ¹⁸O values in Cape Range stalagmites during HS1 although the behavior of this system in the last glacial period is not well constrained.