OXYGEN ISOTOPIC RATIOS AND MUD LAYERS FROM TROPICAL AUSTRALIAN STALAGMITES TIED TO EXTREME PRECIPITATION EVENTS OVER THE LAST 1000 YEARS

Ages of mud layers in rapidly growing aragonite stalagmites from cave KNI-51, located in near-coastal tropical Western Australia, are precisely constrained using high resolution U/Th dating of the surrounding stalagmite carbonate. The mud layers, which vary in thickness from <0.5-10 mm, are formed during cave flooding that results during extreme precipitation events. In the one stalagmite that grew during the 20^th century, this high precision chronology reveals that the mud layers track decadal-scale variability in tropical cyclone activity in the region as determined using the Australian Bureau of Meteorology’s online tropical cyclone tracking protocol. Overlapping stalagmites spanning most of the last millennium preserve mud layers that suggest that cave flooding events were highest from 1200-1400 yr AD, a period of elevated regional sea surface temperature. Oxygen isotopic ratios of stalagmite aragonite reflect monsoon rainfall via amount effect controls on precipitation oxygen isotopic ratios. Oxygen isotopic time series based on the same high precision U/Th dates reveal that Australian monsoon strength also varied in step with sea surface temperatures and cave flooding events during the past millennium.