Natural attrition and growth frequency variations of stalagmites in southwest Sulawesi over the past 530,000 years

Previous studies have analysed the age distributions of stalagmites harvested from multiple caves and inferred important palaeoclimate changes that explain stalagmite growth phases. However, stalagmites may grow over tens of thousands of years; thus, they are irreplaceable. The value of speleothems to science must be weighed against their potential and current aesthetic and cultural value. In this study, we show that some palaeoclimate information can be extracted from a cave system without the removal of stalagmites. Our case study is based on basal U–Th dates for 77 individual stalagmites from thirteen caves located in and around BantimurungBulusaraung National Park, southwest Sulawesi, Indonesia. The stalagmites grew during discrete intervals within the last ~530,000 years, and an analysis of their age distribution shows a first-order exponential decrease in the number of older stalagmites surviving to the present day. Further, this exponential relationship is observed in stalagmite populations around the world and is therefore likely to be a general cave phenomenon. Superimposed on the first-order exponential age distribution in southwest Sulawesi are positive anomalies in stalagmite growth frequency at 425–400, 385–370, 345–335, 330–315, 160–155, 75–70 and 10–5 ka, which are typically coincident with wet periods on Borneo. To explain this distribution, we present a simple model of stalagmite growth and attrition. A first-order trend is controlled by processes intrinsic to karst systems that govern the natural attrition of stalagmites. These processes are nearly constant over time and result in the observed exponential relationship of stalagmite basal ages. Second-order variation is controlled by changes in the rate of stalagmite generation caused by fluctuating climates, which is a well-known concept in the speleothem literature. Removal of the exponential baseline allows for better assessment of relative peak heights and basic palaeoclimate information to be inferred. Importantly, the first- and second-order growth frequency variations can be characterised using basal stalagmite ages only, without the removal of stalagmites, thereby helping reduce the impact of scientific sampling on the cave environment