Validation of glacial-interglacial rainfall variations in southwest Sulawesi using Mg/Ca and δ18O in speleothems

Speleothem δ18O is widely used as a proxy for rainfall amount in the tropics on glacial-interglacial to interannual scales. However, uncertainties in the interpretation of this renowned proxy pose a vexing problem in tropical paleoclimatology. Here, we present paired measurements of Mg/Ca and δ18O for multiple stalagmites from southwest Sulawesi, Indonesia, that that confirm changes in rainfall amount across ice age terminations. Collectively, the stalagmites span two glacial-interglacial transitions from 380 to 330 ky BP and 230 to 170 ky BP. Mg/Ca in our slow-growing stalagmites is affected by karst infiltration rates and prior calcite precipitation, making it a good proxy for changes in local rainfall. When paired, Mg/Ca and δ18O corroborate prominent shifts from drier glacials to wetter interglacials in the core of the Australasian monsoon domain. Deviations between the two proxies may reveal concurrent changes in rainfall amount and moisture-transport pathways indicative of regional monsoon circulation.